CHAPTER 4. SCREENING ANALYSIS

TABLE OF CONTENTS

4.1 INTRODUCTION ..................................................... 4-1

4.2 DISCUSSION OF DESIGN OPTIONS .................................... 4-1

4.2.1 Design Options that Passed Screening ................................ 4-2

4.2.1.1 Improved Heat Exchanger Effectiveness ...................... 4-2

4.2.1.2 Modulating Operation .................................... 4-4

4.2.1.3 Increased or Improved Insulation 4-6

4.2.1.4 Condensing Secondary Heat Exchanger ...................... 4-7

4.2.1.5 Electronic Ignition ....................................... 4-8

4.2.1.6 Induced and Forced-Draft Combustion Systems ................ 4-9

4.2.1.7 Infrared Burner ........................................ 4-10

4.2.1.8 Direct Vent ............................................ 4-10

4.2.1.9 Fuel Filtration ......................................... 4-11

4.2.1.10 Pulse Combustion ...................................... 4-12

4.2.1.11 Dampers .............................................. 4-12

4.2.1.12 Air-atomized Burner with Modulation ...................... 4-13

4.2.1.13 Delayed-Action Oil-Pump Solenoid Valve ................... 4-13

4.2.1.14 Increased Motor Efficiency ............................... 4-14

4.2.1.15 Increased Blower Impeller Efficiency ....................... 4-14

4.2.2 Design Options Eliminated from Further Consideration ................. 4-15

4.2.2.1 Self-Generation of Electric Power .......................... 4-15

4.2.2.2 Fuel-Driven Heat Pumps ................................. 4-16

4.2.2.3 Flue-Gas Recirculation .................................. 4-16

4.2.2.4 Smart Valve ........................................... 4-17

4.2.2.5 Design Options Yielding 82 Percent and Higher

AFUE for Non-condensing Non-weatherized Gas Furnaces ...... 4-17

4.3 SUMMARY OF SCREENING .......................................... 4-18

LIST OF TABLES

Table 4.3.1 Screening Results for Design Options by Product Class ................. 4-19

 EE-RM/STD-01-350 COMMENT 164

CHAPTER 4. SCREENING ANALYSIS 

TABLE OF CONTENTS 

4.1 INTRODUCTION ..................................................... 4-1 

4.2 DISCUSSION OF DESIGN OPTIONS .................................... 4-1 

4.2.1 Design Options that Passed Screening ................................ 4-2 

4.2.1.1 Improved Heat Exchanger Effectiveness. . . . . . . . . . . . . . . . . . . . .. 4-2 

4.2.1.2 Modulating Operation .................................... 4-4 

4.2.1.3 Increased or Improved Insulation ........................... 4-6 

4.2.1.4 Condensing Secondary Heat Exchanger ...................... 4-7 

4.2.1.5 Electronic Ignition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4-8 

4.2.1.6 Induced and Forced-Draft Combustion Systems. . . . . . . . . . . . . . .. 4-9 

4.2.1.7 Infrared Burner ........................................ 4-10 

4.2.1.8 Direct Vent ........................................... , 4-10 

4.2.1.9 FuelFiltration ......................................... 4-11 

4.2.1.10 Pulse Combustion ...................................... 4-12 

4.2.1.11 Dampers .............................................. 4-12 

4.2.1.12 Air-atomized Burner with Modulation ...................... 4-13 

4.2.1.13 Delayed-Action Oil-Pump Solenoid Valve .................. , 4-13 

4.2.1.14 Increased Motor Efficiency .............................. , 4-14 

4.2.1.15 Increased BlowerImpeller Efficiency ...................... , 4-14 

4.2.2 Design Options Eliminated from Further Consideration ................. 4-15 

4.2.2.1 Self-Generation of Electric Power ......................... , 4-15 

4.2.2.2 Fuel-Driven Heat Pumps ................................. 4-16 

4.2.2.3 Flue-Gas Recirculation .................................. 4-16 

4.2.2.4 Smart Valve .......................................... , 4-17 

4.2.2.5 Design Options Yielding 82 Percent and Higher 

AFUE for Non-condensing Non-weatherized Gas Furnaces ...... 4-17 

4.3 SUMMARY OF SCREENING .......................................... 4-18 

LIST OF TABLES 

Table 4.3.1 Screening Results for Design Options by Product Class ................. 4-19 

4-i 
CHAPTER 4. SCREENING ANALYSIS

4.1 INTRODUCTION

The purpose of the screening analysis is to identify those design options that the

Department will consider for the engineering analysis and to screen out those design options that

the Department will not consider further. The Department consulted with industry, technical

experts, and other interested parties to develop a list of design options for consideration. The

Department then applied a set of screening criteria to determine which design options were

unsuitable for further consideration in the rulemaking. These screening criteria are based on the

Process Rule, 61 FR 36974 (July 15, 1996). The criteria are summarized here:

® Technological feasibility: Design options used in commercial products or in working

prototypes are considered feasible.

® Practicability to manufacture, install, and service: Design options should be able to be

mass-produced and be reliable to install and service on the scale necessary to serve the

relevant market at the time of the effective date of the standard.

® Adverse impacts on utility or availability to consumers: Design options should not create

adverse impacts on product utility, or result in the unavailability of any covered product

type with performance characteristics (including reliability), features, sizes, capacities,

and volumes that are substantially the same as products generally available in the U.S.

® Adverse impacts on health or safety: Design options must not adversely affect health or

safety aspects of the regulated product.

Based on past analysis, and on public comments on the September 8, 1993, Advance

Notice of Proposed Rulemaking (ANOPR), the Department prepared a draft screening analysis

and presented it for review and comment at the Furnaces and Boilers Standards Framework

Rulemaking Workshop, held in Washington, D.C. on July 17, 2001.' This chapter presents the

screening analysis of design options that DOE carried out in response to comments received

during and after the Framework Workshop. The subsequent analyses do not consider or

incorporate technologies that do not pass these tests.

4.2 DISCUSSION OF DESIGN OPTIONS

This chapter presents the design options in two categories. The first category is design

options that met the screening criteria and that DOE used in the subsequent analyses for at least

some product classes. The second category is design options that DOE eliminated from further

4-1

 EE-RM/STD-01-350 COMMENT 164

CHAPTER 4. SCREENING ANALYSIS 

4.1 INTRODUCTION 

The purpose of the screening analysis is to identify those design options that the 

Department will consider for the engineering analysis and to screen out those design options that 

the Department will not consider further. The Department consulted with industry, technical 

experts, and other interested parties to develop a list of design options for consideration. The 

Department then applied a set of screening criteria to determine which design options were 

unsuitable for further consideration in the rulemaking. These screening criteria are based on the 

Process Rule, 61 FR 36974 (July 15, 1996). The criteria are summarized here: 

.. Technological feasibility: Design options used in commercial products or in working 

prototypes are considered feasible. 

.. Practicability to manufacture, install, and service: Design options should be able to be 

mass-produced and be reliable to install and service on the scale necessary to serve the 

relevant market at the time of the effective date of the standard. 

.. Adverse impacts on utility or availability to consumers: Design options should not create 

adverse impacts on product utility, or result in the unavailability of any covered product 

type with performance characteristics (including reliability), features, sizes, capacities, 

and volumes that are substantially the same as products generally available in the U.S. 

• Adverse impacts on health or safety: Design options must not adversely affect health or 

safety aspects of the regulated product. 

Based on past analysis, and on public comments on the September 8, 1993, Advance 

Notice of Proposed Rulemaking (ANOPR), the Department prepared a draft screening analysis 

and presented it for review and comment at the Furnaces and Boilers Standards Framework 

Rulemaking Workshop, held in Washington, D.C. on July 17,2001. 1 This chapter presents the 

screening analysis of design options that DOE carried out in response to comments received 

during and after the Framework Workshop. The subsequent analyses do not consider or 

incorporate technologies that do not pass these tests. 

4.2 DISCUSSION OF DESIGN OPTIONS 

This chapter presents the design options in two categories. The first category is design 

options that met the screening criteria and that DOE used in the subsequent analyses for at least 

some product classes. The second category is design options that DOE eliminated from further 

4-1 
consideration for all product classes. The discussions under both categories respond to the

screening criteria described in the Process Rule.

4.2.1 Design Options that Passed Screening

4.2.1.1 Improved Heat Exchanger Effectiveness

Heat exchanger effectiveness can be improved in many ways.2 To accomplish this,

furnace manufacturers optimize the heat exchanger size and geometry , gas input rate,

combustion air delivery system, heat transfer coefficient, and heat exchanger mass, and may

apply electrohydrodynamic enhancements to provide the greatest comfort, reliability , and safety.

By adjusting the heat exchanger effectiveness , a gas furnace can be designed with an annual fuel

utilization efficiency (AFUE) rating ranging from 75 percent to 98 percent.

Between roughly 83 percent and 89 percent AFUE, condensate problems can occur and,

because of the high temperature of the flue at these efficiencies, stainless steel is needed to vent

wet flue gases to the outdoors. Above 89 percent AFUE, flue-gas temperatures drop below

155°F, and polyvinyl chloride (PVC) pipe can be used for venting.'

Heat Exchanger Area. Heat exchanger effectiveness can be improved by increasing the

heat exchanger area for a given burner input rate. This is a common way to improve the oncycle efficiency of the furnace. Increasing the size of the heat exchanger improves the steadystate efficiency and the AFUE of the furnace. However, it also can increase the pressure drop on

the flue side and/or air side of the heat exchanger, so the blower system must be rebalanced to

deliver the same flows. A general rule is that doubling the heat exchanger area will increase

efficiency by half the difference between the current efficiency and 100 percent AFUE.4 For

example, going from 80 percent to 90 percent AFUE requires doubling the heat exchanger area.

Derating. Derating, which usually refers to reducing the burner input of the furnace

while keeping the heat exchanger area constant , is a direct way to improve furnace performance

because it does not involve design changes. Decreasing the gas input rate to a furnace improves

the steady-state efficiency and AFUE.

A small derate of up to 10-15 percent will not impair the heat exchanger function, but a

larger reduction will have a negative impact on the performance characteristics of the heat

exchanger. A similar impact on efficiency may be achieved by increasing the heat exchanger

area and keeping the burner input rate constant.

Combustion Air Delivery System . Reducing the excess air fraction improves efficiency

because it changes the flue gas temperature and flow rates in the heat exchanger. A reduction in

excess air from 50 percent to 40 percent should improve AFUE by about 1 percent. Factors to

consider when reducing the excess air to the burners include size and alignment variations in the

drilled gas orifices, pressure and temperature variations within the gas manifold, and pilot gas

feed into only one heat exchanger tube.

4-2

 EE-RM/STD-01-350 COMMENT 164

consideration for all product classes. The discussions under both categories respond to the 

screening criteria described in the Process Rule. 

4.2.1 Design Options that Passed Screening 

4.2.1.1 Improved Heat Exchanger Effectiveness 

Heat exchanger effectiveness can be improved in many ways.2 To accomplish this, 

furnace manufacturers optimize the heat exchanger size and geometry, gas input rate, 

combustion air delivery system, heat transfer coefficient, and heat exchanger mass, and may 

apply electrohydrodynamic enhancements to provide the greatest comfort, reliability, and safety. 

By adjusting the heat exchanger effectiveness, a gas furnace can be designed with an annual fuel 

utilization efficiency (AFUE) rating ranging from 75 percent to 98 percent. 

Between roughly 83 percent and 89 percent AFUE, condensate problems can occur and, 

because of the high temperature of the flue at these efficiencies, stainless steel is needed to vent 

wet flue gases to the outdoors. Above 89 percent AFUE, flue-gas temperatures drop below 

155°F, and polyvinyl chloride (PVC) pipe can be used for venting. 3 

Heat Exchanger Area. Heat exchanger effectiveness can be improved by increasing the 

heat exchanger area for a given burner input rate. This is a common way to improve the oncycle efficiency of the furnace. Increasing the size of the heat exchanger improves the steadystate efficiency and the AFUE of the furnace. However, it also can increase the pressure drop on 

the flue side and/or air side of the heat exchanger, so the blower system must be rebalanced to 

deliver the same flows. A general rule is that doubling the heat exchanger area will increase 

efficiency by half the difference between the current efficiency and 100 percent AFUE.4 For 

example, going from 80 percent to 90 percent AFUE requires doubling the heat exchanger area. 

Derating. Derating, which usually refers to reducing the burner input of the furnace 

while keeping the heat exchanger area constant, is a direct way to improve furnace performance 

because it does not involve design changes. Decreasing the gas input rate to a furnace improves 

the steady-state efficiency and AFUE. 

A small derate of up to 1 0-15 percent will not impair the heat exchanger function, but a 

larger reduction will have a negative impact on the performance characteristics of the heat 

exchanger. A similar impact on efficiency may be achieved by increasing the heat exchanger 

area and keeping the burner input rate constant. 

Combustion Air Delivery System. Reducing the excess air fraction improves efficiency 

because it changes the flue gas temperature and flow rates in the heat exchanger. A reduction in 

excess air from 50 percent to 40 percent should improve AFUE by about 1 percent. Factors to 

consider when reducing the excess air to the burners include size and alignment variations in the 

drilled gas orifices, pressure and temperature variations within the gas manifold, and pilot gas 

feed into only one heat exchanger tube. 

4-2 
Heat Transfer Coefficient. Increasing the heat transfer coefficient (on either the air side

or the gas side of the heat exchanger) can improve heat exchanger efficiency . This can be

achieved through special surface treatments, the addition of fins or dimples, or otherwise

modifying the air- or gas-flow characteristics . Increasing the heat transfer coefficient can

increase the pressure drop, which may result in increased electrical power demand.

The industry achieved a major improvement in the gas -side heat transfer coefficient when

it shifted from natural-draft heat exchangers to induced-draft combustion. This allowed

manufacturers to substantially reduce the size of the flue gas passageway , thus increasing the gas

velocities. The heat transfer coefficient and pressure drop both increase exponentially with

velocity.

The heat transfer on the internal surface of the heat exchanger offers an area for

improvement. As flue gases pass through the heat exchanger of a furnace , they cool from about

2000°F to less than 400°F. With this large drop in temperature, the specific volume of the gas

changes by a factor of three. Thus, the combustion gas passageway of the heat exchanger can be

reduced in size by the same factor of three at the outlet, while maintaining approximately

constant gas velocity.

Air-side heat exchanger coefficients also can be improved by increasing the air velocity

over the heat exchanger . This can be accomplished by making the air passages smaller or by

increasing the total air flow. Increasing the air flow also will reduce the change in the air

temperature as it crosses over the heat exchanger.

There are several other ways to improve the heat transfer coefficient . In the case of the

serpentine clamshell heat exchanger, this can be accomplished by decreasing the channel area

and perimeter in the direction of the gas flow, and creating dimples in the latter passes of the

channel. Each dimple consists of two half-spherical indentations that reduce the local crosssectional area of the internal passage. ' Gas-side performance also may be enhanced by adding

external fins to the heat exchanger tubes. These are frequently used in the condensing heatexchanger section of condensing furnaces.

Heat Exchanger Mass. Lower heat-exchanger mass allows the furnace to heat up and

cool down faster during each heating cycle . This effect is due to the reduced thermal storage

capacity of the heat exchanger. The overall impact is a reduction of off-cycle energy losses.

Because of the advantages of low heat-exchanger mass in terms of AFUE as well as

manufacturing costs, the forced-air furnaces of today have much lighter heat exchangers than did

the natural draft furnaces common 20 years ago . The blower-on time delays of today's furnaces

run about 30 seconds, whereas, with natural draft furnaces, blower-on time delays of two

minutes or more were common.' Computer simulation studies found that the flue-gas-side heat

transfer in higher-mass heat exchangers could be improved by 24 percent before reaching a

steady-state efficiency where condensation problems may arise.'

4-3

 EE-RM/STD-01-350 COMMENT 164

Heat Transfer Coefficient. Increasing the heat transfer coefficient (on either the air side 

or the gas side of the heat exchanger) can improve heat exchanger efficiency. This can be 

achieved through special surface treatments, the addition of fins or dimples, or otherwise 

modifying the air- or gas-flow characteristics. Increasing the heat transfer coefficient can 

increase the pressure drop, which may result in increased electrical power demand. 

The industry achieved a major improvement in the gas-side heat transfer coefficient when 

it shifted from natural-draft heat exchangers to induced-draft combustion. This allowed 

manufacturers to substantially reduce the size of the flue gas passageway, thus increasing the gas 

velocities. The heat transfer coefficient and pressure drop both increase exponentially with 

velocity. 

The heat transfer on the internal surface of the heat exchanger offers an area for 

improvement. As flue gases pass through the heat exchanger of a furnace, they cool from about 

2000°F to less than 400°F. With this large drop in temperature, the specific volume of the gas 

changes by a factor of three. Thus, the combustion gas passageway of the heat exchanger can be 

reduced in size by the same factor of three at the outlet, while maintaining approximately 

constant gas velocity. 

Air-side heat exchanger coefficients also can be improved by increasing the air velocity 

over the heat exchanger. This can be accomplished by making the air passages smaller or by 

increasing the total air flow. Increasing the air flow also will reduce the change in the air 

temperature as it crosses over the heat exchanger. 

There are several other ways to improve the heat transfer coefficient. In the case of the 

serpentine clamshell heat exchanger, this can be accomplished by decreasing the channel area 

and perimeter in the direction of the gas flow, and creating dimples in the latter passes of the 

channel. Each dimple consists of two half-spherical indentations that reduce the local crosssectional area of the internal passage. 5 Gas-side performance also may be enhanced by adding 

external fins to the heat exchanger tubes. These are frequently used in the condensing heatexchanger section of condensing furnaces. 

Heat Exchanger Mass. Lower heat-exchanger mass allows the furnace to heat up and 

cool down faster during each heating cycle. This effect is due to the reduced thermal storage 

capacity of the heat exchanger. The overall impact is a reduction of off-cycle energy losses. 

Because of the advantages of low heat-exchanger mass in terms of AFUE as well as 

manufacturing costs, the forced-air furnaces of today have much lighter heat exchangers than did 

the natural draft furnaces common 20 years ago. The blower-on time delays oftoday's furnaces 

run about 30 seconds, whereas, with natural draft furnaces, blower-on time delays of two 

minutes or more were common.4 Computer simulation studies found that the flue-gas-side heat 

transfer in higher-mass heat exchangers could be improved by 24 percent before reaching a 

steady-state efficiency where condensation problems may arise.6 

4-3 
Electrohydrodynamic Enhancement. Electrohydrodynamic enhancement is a technique

for increasing heat transfer in heat exchangers for single-phase or phase-change processes. A

high-voltage, low-current wire or plate electrode mixes fluid (or air, in the case of furnaces) of

different temperatures by increasing turbulence and destabilizing the thermal boundary layer

near the heat transfer wall. The effect, a "corona wind," is caused by accelerated ionized

particles colliding with gas molecules, generating a flow that can quickly reach a speed of a few

meters per second.' A corona wind interacting with the main gas flow intensifies mixing of the

gas, increasing heat transfer rates.

Electrical power consumed by this operation is a few watts or less, additional

manufacturing costs are minimal, and installation and maintenance are no more difficult than for

other active heat-transfer techniques.' The principal cost is the high-voltage power supply.

Enhancements to heat transfer can be as high as 300 percent. Safety concerns are minimal. The

electrical hazard is low due to the small current and, given no moving parts, the mechanical

hazard is non-existent.

Summary. All of the above technologies to increase heat exchanger effectiveness have

been demonstrated and incorporated in residential or commercial products and are therefore

technologically feasible. There are no known barriers to manufacturing, installing, or servicing

products with these technologies. Since heat exchanger technology today is mature, there is no

reason to expect adverse impacts on product utility or availability. There are, however, practical

limitations to the heat exchanger technologies discussed above. For example, for a given furnace

output capacity, it is mainly the heat exchanger's material properties that dictate a minimum heat

exchanger size and mass. The known health and safety risks associated with heat exchangers

include carbon monoxide (CO) exposure and fire danger. However, these problems are not

related to a specific heat exchanger technology or attribute. Rather, they arise for several

reasons, including poor design and/or fabrication, and improper furnace set-up, installation, and

maintenance. In summary, improved heat exchanger effectiveness passes all of the screening

criteria.

4.2.1.2 Modulating Operation

A modulating control is any control that uses either gradual or step-wise adjustment of

the furnace input rate in response to changes in the heating load. Two different types of

modulating controls that can be applied to furnaces and boilers-two-stage and step

control-could increase AFUE and reduce electricity consumption.

Two-stage control refers to a modulating control that cycles a burner between a reduced

heat-input rate and off, or between the maximum heat-input rate and off. Two-stage controls are

limited to these two operations. They are not capable of operating from reduced heat input to

maximum heat input, nor of operating from maximum heat input to reduced heat input.

Two-stage control can be achieved by a variety of means. Use of two-stage gas valve

modulation by itself is rarely considered in practice because, if gas flow is reduced without

4-4

 EE-RM/STD-01-350 COMMENT 164

Electrohydrodynamic Enhancement. Electrohydrodynamic enhancement is a technique 

for increasing heat transfer in heat exchangers for single-phase or phase-change processes. A 

high-voltage, low-current wire or plate electrode mixes fluid (or air, in the case of furnaces) of 

different temperatures by increasing turbulence and destabilizing the thermal boundary layer 

near the heat transfer wall. The effect, a "corona wind," is caused by accelerated ionized 

particles colliding with gas molecules, generating a flow that can quickly reach a speed of a few 

meters per second.7 A corona wind interacting with the main gas flow intensifies mixing of the 

gas, increasing heat transfer rates. 

Electrical power consumed by this operation is a few watts or less, additional 

manufacturing costs are minimal, and installation and maintenance are no more difficult than for 

other active heat-transfer techniques. 8 The principal cost is the high-voltage power supply. 

Enhancements to heat transfer can be as high as 300 percent. Safety concerns are minimal. The 

electrical hazard is low due to the small current and, given no moving parts, the mechanical 

hazard is non-existent. 

Summary. All of the above technologies to increase heat exchanger effectiveness have 

been demonstrated and incorporated in residential or commercial products and are therefore 

technologically feasible. There are no known barriers to manufacturing, installing, or servicing 

products with these technologies. Since heat exchanger technology today is mature, there is no 

reason to expect adverse impacts on product utility or availability. There are, however, practical 

limitations to the heat exchanger technologies discussed above. For example, for a given furnace 

output capacity, it is mainly the heat exchanger's material properties that dictate a minimum heat 

exchanger size and mass. The known health and safety risks associated with heat exchangers 

include carbon monoxide (CO) exposure and fire danger. However, these problems are not 

related to a specific heat exchanger technology or attribute. Rather, they arise for several 

reasons, including poor design and/or fabrication, and improper furnace set-up, installation, and 

maintenance. In summary, improved heat exchanger effectiveness passes all of the screening 

criteria. 

4.2.1.2 Modulating Operation 

A modulating control is any control that uses either gradual or step-wise adjustment of 

the furnace input rate in response to changes in the heating load. Two different types of 

modulating controls that can be applied to furnaces and boilers-two-stage and step 

control-could increase AFUE and reduce electricity consumption. 

Two-stage control refers to a modulating control that cycles a burner between a reduced 

heat-input rate and off, or between the maximum heat-input rate and off. Two-stage controls are 

limited to these two operations. They are not capable of operating from reduced heat input to 

maximum heat input, nor of operating from maximum heat input to reduced heat input. 

Two-stage control can be achieved by a variety of means. Use of two-stage gas valve 

modulation by itself is rarely considered in practice because, if gas flow is reduced without 

4-4 
reducing combustion air flow, the excess air increases and the steady-state operating efficiency

of the furnace decreases. By reducing the firing rate for longer periods, off-cycle losses are

diminished and off-period efficiency can increase.' A two-speed circulation fan control is also

rarely considered without modulating the gas input, because increasing circulating air flow

beyond a certain point reduces comfort, increases noise, and increases electrical operating cost.

The heating speed of the blower should be selected to provide optimum comfort and minimum

operating cost.

Another control configuration, the two-stage gas valve with two-stage combustion fan

control, requires appropriate design considerations to ensure that the flue products do not

condense in the primary heat exchanger. The AFUE of such a system may improve, but the

furnace would run for a longer time.' The two-stage gas valve and two-stage circulating blower

design, on the other hand, is similar to two-stage gas valve modulation, except that using an

electronically commutated motor (ECM) would result in reductions in the electrical operating

cost that would more than compensate for the increased cost of gas, and the AFUE rating would

be lower.

The two-stage gas valve, two-speed combustion fan, and two-speed supply fan

configuration is a standard way to design a modulating gas furnace. Combustion efficiency is

maintained because the burners operate at high and low input rates with equal excess air rates. A

considerable amount of electrical energy is saved if an ECM motor is used.

Step modulation can provide a number of performance improvements. Furnaces that

operate at substantially reduced output over longer periods of time can provide more uniform

space temperatures, quieter operation, greater efficiency, and reduced emissions. Achieving

these objectives, however, requires that the combustion stoichiometry (the proper fuel/air

mixture to assure clean combustion) be carefully controlled at all firing rates to ensure safe

operation and minimum emissions.

The primary difference between two-stage and step-modulating control is that the twostage control must operate between either the low firing rate and off, or the high firing rate and

off, whereas the continuous modulating control can operate between multiple firing rates (e.g.,

off to low-fire to high-fire to low-fire to off). According to manufacturer literature, 10'" a

continuously modulating furnace contains several specific components: modulated output

thermostat, modulating gas valve, integrated furnace control, two-speed or variable-speed

blower, two-speed induced draft blower, supply-air temperature sensor, and return-air

temperature sensor.

Step modulation can be achieved by the same variety of means described for two-stage

modulation. This system would have all the advantages of the modulating gas valve, modulating

combustion fan, and modulating supply fan configuration, with the further advantage of slightly

better efficiency and less electrical consumption.

4-5

 EE-RM/STD-01-350 COMMENT 164

reducing combustion air flow, the excess air increases and the steady-state operating efficiency 

of the furnace decreases. By reducing the firing rate for longer periods, off-cycle losses are 

diminished and off-period efficiency can increase.9 A two-speed circulation fan control is also 

rarely considered without modulating the gas input, because increasing circulating air flow 

beyond a certain point reduces comfort, increases noise, and increases electrical operating cost. 

The heating speed of the blower should be selected to provide optimum comfort and minimum 

operating cost. 

Another control configuration, the two-stage gas valve with two-stage combustion fan 

control, requires appropriate design considerations to ensure that the flue products do not 

condense in the primary heat exchanger. The AFUE of such a system may improve, but the 

furnace would run for a longer time.4 The two-stage gas valve and two-stage circulating blower 

design, on the other hand, is similar to two-stage gas valve modulation, except that using an 

electronically commutated motor (ECM) would result in reductions in the electrical operating 

cost that would more than compensate for the increased cost of gas, and the AFUE rating would 

be lower. 

The two-stage gas valve, two-speed combustion fan, and two-speed supply fan 

configuration is a standard way to design a modulating gas furnace. Combustion efficiency is 

maintained because the burners operate at high and low input rates with equal excess air rates. A 

considerable amount of electrical energy is saved if an ECM motor is used. 

Step modulation can provide a number of performance improvements. Furnaces that 

operate at substantially reduced output over longer periods of time can provide more uniform 

space temperatures, quieter operation, greater efficiency, and reduced emissions. Achieving 

these objectives, however, requires that the combustion stoichiometry (the proper fuel/air 

mixture to assure clean combustion) be carefully controlled at all firing rates to ensure safe 

operation and minimum emissions. 

The primary difference between two-stage and step-modulating control is that the twostage control must operate between either the low firing rate and off, or the high firing rate and 

off, whereas the continuous modulating control can operate between multiple firing rates (e.g., 

off to low-fire to high-fire to low-fire to off). According to manufacturer literature, 10, II a 

continuously modulating furnace contains several specific components: modulated output 

thermostat, modulating gas valve, integrated furnace control, two-speed or variable-speed 

blower, two-speed induced draft blower, supply-air temperature sensor, and return-air 

temperature sensor. 

Step modulation can be achieved by the same variety of means described for two-stage 

modulation. This system would have all the advantages of the modulating gas valve, modulating 

combustion fan, and modulating supply fan configuration, with the further advantage of slightly 

better efficiency and less electrical consumption. 

4-5 
According to manufacturers, step modulation requires a fully modulating gas valve, a

variable-output induced draft fan, a variable-output circulating air fan, and a combustion

controller, to maintain proper control of a modulating gas-fired appliance." This is the key to a

fully modulating appliance, which interfaces with all of the furnace controls, including the

thermostat, the ignition and flame-proving devices, the two motors, the gas valve, and all of the

safety controls.

Based on current information, modulating technologies do not pose any known safety

hazards. The manufacturer installation manuals12 state that the venting system for modulating

gas furnaces (at 80 percent and 81 percent AFUE levels) should use double-wall vent

connectors, which are widely used in venting heating equipment. The double-wall vent

connector ensures that condensation does not occur in the vent connector, which is the most

likely point in the vent system for condensation to occur. 13

Brookhaven National Laboratory is currently testing prototypical air-atomizing oil

burners (fan-atomizing burners) for potential two-stage firing rates. However, the conventional

pressure-atomizing burners used in residential applications operate with firing rates that are

typically too high to be effective in a staged-firing application."

Summary. Modulating gas furnaces and boilers, both two-stage and step, are currently

on the market, which demonstrates the technological feasibility and the practicability to

manufacture, install, and service them. There are no known published discussions on adverse

impacts on product utility. In fact, one of the advantages of modulating furnaces and boilers is

that they provide additional utility to consumers (e.g., quieter operation, less variation in air

temperatures). Based on the fact that most major furnace manufacturers currently market

modulating models, which use standard technologies and production processes, there are no

adverse impacts on product availability. This technology appears to have no adverse impacts on

health or safety. Thus, two-stage modulating and continuous modulating technologies, as

applied to gas-fired equipment, pass all the screening criteria.

4.2.1.3 Increased or Improved Insulation

Many furnaces and boilers are equipped with a layer of insulation designed to reduce the

amount of heat transferred to the appliance's environment through the jacket. Increasing the

thickness of the insulation layer reduces the jacket losses in isolated combustion systems (ICS)

(outdoor installations). For indoor installations, jacket losses are considered useful heat and do

not affect the product's efficiency. Fiberglass is the most commonly used insulation material.

Using materials with a higher R-value (i.e., thermal resistance, the measure of how quickly heat

can be lost through the insulation) would further reduce the jacket losses.

An increase in insulation affects the width but not the height of the furnace. Whereas an

increase in height can present a problem in some installations, the increase in width considered

for this design option does not pose any problems with respect to product utility.

4-6

 EE-RM/STD-01-350 COMMENT 164

According to manufacturers, step modulation requires a fully modulating gas valve, a 

variable-output induced draft fan, a variable-output circulating air fan, and a combustion 

controller, to maintain proper control of a modulating gas-fired appliance. II This is the key to a 

fully modulating appliance, which interfaces with all of the furnace controls, including the 

thermostat, the ignition and flame-proving devices, the two motors, the gas valve, and all of the 

safety controls. 

Based on current information, modulating technologies do not pose any known safety 

hazards. The manufacturer installation manualsl2 state that the venting system for modulating 

gas furnaces (at 80 percent and 81 percent AFUE levels) should use double-wall vent 

connectors, which are widely used in venting heating equipment. The double-wall vent 

connector ensures that condensation does not occur in the vent connector, which is the most 

likely point in the vent system for condensation to occur. 13 

Brookhaven National Laboratory is currently testing prototypical air-atomizing oil 

burners (fan-atomizing burners) for potential two-stage firing rates. However, the conventional 

pressure-atomizing burners used in residential applications operate with firing rates that are 

typically too high to be effective in a staged-firing application. 14 

Summary. Modulating gas furnaces and boilers, both two-stage and step, are currently 

on the market, which demonstrates the technological feasibility and the practicability to 

manufacture, install, and service them. There are no known published discussions on adverse 

impacts on product utility. In fact, one of the advantages of modulating furnaces and boilers is 

that they provide additional utility to consumers (e.g., quieter operation, less variation in air 

temperatures). Based on the fact that most major furnace manufacturers currently market 

modulating models, which use standard technologies and production processes, there are no 

adverse impacts on product availability. This technology appears to have no adverse impacts on 

health or safety. Thus, two-stage modulating and continuous modulating technologies, as 

applied to gas-fired equipment, pass all the screening criteria. 

4.2.1.3 Increased or Improved Insulation 

Many furnaces and boilers are equipped with a layer of insulation designed to reduce the 

amount of heat transferred to the appliance's environment through the jacket. Increasing the 

thickness of the insulation layer reduces the jacket losses in isolated combustion systems (ICS) 

(outdoor installations). For indoor installations,jacket losses are considered useful heat and do 

not affect the product's efficiency. Fiberglass is the most commonly used insulation material. 

Using materials with a higher R-value (i.e., thermal resistance, the measure of how quickly heat 

can be lost through the insulation) would further reduce the jacket losses. 

An increase in insulation affects the width but not the height of the furnace. Whereas an 

increase in height can present a problem in some installations, the increase in width considered 

for this design option does not pose any problems with respect to product utility. 

4-6 
Many ICS and weatherized furnaces (and outdoor boilers) already include the jacket

insulation design option, so adding or improving jacket insulation is technologically feasible.

Similarly, the capability to manufacture, install, and service equipment with increased or

improved jacket insulation is practical using today's processes . Jacket insulation is already used

in existing products and it is therefore a technologically feasible design option. Jacket insulation

poses no health or safety risks. Increasing or improving jacket insulation would not have any

adverse impacts on health or safety. Therefore, the jacket insulation design option passes all the

criteria.

4.2.1.4 Condensing Secondary Heat Exchanger

While a primary heat exchanger captures most of the heat available in the combustion

process, a secondary heat exchanger is designed to condense the water vapor in the flue gas, thus

harnessing the latent heat associated with the phase change of the water . The heat of

vaporization of water in the combustion products of natural gas represents about 9 percent of the

total energy in the gas.

This analysis focuses on the most common way to condense water vapor in the flue

gases, by adding a secondary condensing heat exchanger to the dry primary heat exchanger.

Because sulfur, chlorine, and other impurities can combine with water vapor to create acids and

may be present in the gas and combustion air, it is essential that the condensing heat exchanger

materials be highly corrosion-resistant. Most designs that meet this criterion use stainless steel.

Another solution is to use low-cost carbon steel with a plastic coating that is impervious to

condensate and to the flue gas.

The water vapor in the flue gases condenses if the temperature of the heat exchanger is

sufficiently low. The heat exchanger area of a condensing furnace must be about double that of

the heat exchanger of an 80 percent AFUE furnace having equivalent heating capacity. Most

condensing furnaces operate with higher inducer pressure than non-condensing furnaces,

because of the higher density of the low-temperature flue products going through the inducer fan

and the greater pressure drop across the larger heat exchanger.

Another way to condense flue gases is to increase the heat-transfer coefficient in the heat

exchanger. In a condensing heat exchanger , mass transfer (condensing water vapor) takes place

simultaneously with heat transfer, which improves the heat-transfer coefficient.

Operating in a condensing mode is not a practical near-term option for oil-fired furnaces.

The use of low-sulfur fuel oil may make this a more attractive option in the future, but

considerable research that includes evaluation of safety concerns is needed.

Condensing gas furnaces account for nearly one quarter of annual gas furnace shipments.

Condensing hot-water boilers are also available from several manufacturers . The high volume of

shipments demonstrates the technological feasibility of condensing secondary heat exchangers.

Likewise, the ready availability of models of condensing non-weatherized gas furnaces and hot4-7

 EE-RM/STD-01-350 COMMENT 164

Many ICS and weatherized furnaces (and outdoor boilers) already include the jacket 

insulation design option, so adding or improving jacket insulation is technologically feasible. 

Similarly, the capability to manufacture, install, and service equipment with increased or 

improved jacket insulation is practical using today's processes. Jacket insulation is already used 

in existing products and it is therefore a technologically feasible design option. Jacket insulation 

poses no health or safety risks. Increasing or improving jacket insulation would not have any 

adverse impacts on health or safety. Therefore, the jacket insulation design option passes all the 

criteria. 

4.2.1.4 Condensing Secondary Heat Exchanger 

While a primary heat exchanger captures most of the heat available in the combustion 

process, a secondary heat exchanger is designed to condense the water vapor in the flue gas, thus 

harnessing the latent heat associated with the phase change of the water. The heat of 

vaporization of water in the combustion products of natural gas represents about 9 percent of the 

total energy in the gas. 

This analysis focuses on the most cornmon way to condense water vapor in the flue 

gases, by adding a secondary condensing heat exchanger to the dry primary heat exchanger. 

Because sulfur, chlorine, and other impurities can combine with water vapor to create acids and 

may be present in the gas and combustion air, it is essential that the condensing heat exchanger 

materials be highly corrosion-resistant. Most designs that meet this criterion use stainless steel. 

Another solution is to use low-cost carbon steel with a plastic coating that is impervious to 

condensate and to the flue gas. 

The water vapor in the flue gases condenses if the temperature of the heat exchanger is 

sufficiently low. The heat exchanger area of a condensing furnace must be about double that of 

the heat exchanger of an 80 percent AFUE furnace having equivalent heating capacity. Most 

condensing furnaces operate with higher inducer pressure than non-condensing furnaces, 

because of the higher density of the low-temperature flue products going through the inducer fan 

and the greater pressure drop across the larger heat exchanger. 

Another way to condense flue gases is to increase the heat-transfer coefficient in the heat 

exchanger. In a condensing heat exchanger, mass transfer (condensing water vapor) takes place 

simultaneously with heat transfer, which improves the heat-transfer coefficient. 

Operating in a condensing mode is not a practical near-term option for oil-fired furnaces. 

The use of low-sulfur fuel oil may make this a more attractive option in the future, but 

considerable research that includes evaluation of safety concerns is needed. 

Condensing gas furnaces account for nearly one quarter of annual gas furnace shipments. 

Condensing hot-water boilers are also available from several manufacturers. The high volume of 

shipments demonstrates the technological feasibility of condensing secondary heat exchangers. 

Likewise, the ready availability of models of condensing non-weatherized gas furnaces and hot4-7 
water boilers confirms the practicability to manufacture , install, and service this design option,

and indicates no adverse impact on product availability from an increased reliance on this

technology. Condensing technology seems to pose no adverse impacts on product utility or on

health and/or safety. Therefore, the Department determined that this technology option meets all

screening criteria for the non-weatherized gas furnace and hot-water boiler product classes.

4.2.1.5 Electronic Ignition

The baseline model ignition system used in hot-water gas boilers and mobile home

furnaces (MHFs) is a standing pilot. A type of electronic ignition system, the hot-surface ignitor

(HSI), is also available for these products . Unlike standing-pilot ignition systems that consume

gas continuously, HSI devices operate only at the beginning of each "on" period. Although

electronic ignition devices do not increase the steady -state efficiency, burner on-time may

increase slightly to make up for the heat the standing pilot would have supplied during standby

periods. HSIs use a hot surface to ignite the main burners. This type of igniter uses 400 Watts

(w) for 37 seconds during startup and 2.5 W continuously during on-cycle. This design does not

require maintenance. However, because the igniter itself does not last indefinitely, igniter

replacement is occasionally necessary.

A design option that DOE considered, the "hot-surface pilot," is a modification of the

HSI system. It is a small, hot-surface igniter that lights a pilot, which in turn lights the main

burner. It uses much less electrical power than the typical HSI and is much more reliable (i.e.,

less likely to burn out).

Residential oil burners are currently ignited using an intermittent-duty ignition.

Underwriters Laboratories, Inc. (UL) defines intermittent-duty ignition as "ignition by an energy

source that is continuously maintained throughout the time the burner is firing."" This design

has been the standard of the industry for many years . Reductions in electric consumption are

possible through "interrupted ignition," which is available for residential oil burners.'4 The UL

defines interrupted-duty ignition as an "ignition system that is energized each time the main

burner is to be fired and de-energized at the end of a timed trial period or after the main burner is

proven to be established." In other words, the ignitor comes on to light the flame , and then, after

the flame is established, the ignitor is turned off and the flame keeps burning.

The burner industry promotes the interrupted -duty ignition strategy . The industry is

currently transitioning away from electromechanical controls and iron core transformers, and

toward solid-state controls with interrupted-duty capability and electronic igniters. So far, the

reaction from installers and consumers has been positive, since these devices are smaller, weigh

less, offer improved performance with cold-oil or delayed-spark conditions, are less sensitive to

line voltage fluctuations, and extend the life of the igniter and the electrodes.16°"

Since this design option is already being used, it is clearly technologically feasible and

practical to manufacture , install, and service. There is no reason to expect that widespread

adoption of this design option would have an adverse impact on product availability. No adverse

4-8

 EE-RM/STD-01-350 COMMENT 164

water boilers confirms the practicability to manufacture, install, and service this design option, 

and indicates no adverse impact on product availability from an increased reliance on this 

technology. Condensing technology seems to pose no adverse impacts on product utility or on 

health andlor safety. Therefore, the Department determined that this technology option meets all 

screening criteria for the non-weatherized gas furnace and hot-water boiler product classes. 

4.2.1.5 Electronic Ignition 

The baseline model ignition system used in hot-water gas boilers and mobile horne 

furnaces (MHFs) is a standing pilot. A type of electronic ignition system, the hot-surface ignitor 

(HSI), is also available for these products. Unlike standing-pilot ignition systems that consume 

gas continuously, HSI devices operate only at the beginning of each "on" period. Although 

electronic ignition devices do not increase the steady-state efficiency, burner on-time may 

increase slightly to make up for the heat the standing pilot would have supplied during standby 

periods. HSIs use a hot surface to ignite the main burners. This type of igniter uses 400 Watts 

(w) for 37 seconds during startup and 2.5 W continuously during on-cycle. This design does not 

require maintenance. However, because the igniter itself does not last indefinitely, igniter 

replacement is occasionally necessary. 

A design option that DOE considered, the "hot-surface pilot," is a modification of the 

HSI system. It is a small, hot-surface igniter that lights a pilot, which in tum lights the main 

burner. It uses much less electrical power than the typical HSI and is much more reliable (i.e., 

less likely to bum out). 

Residential oil burners are currently ignited using an intermittent-duty ignition. 

Underwriters Laboratories, Inc. (UL) defines intermittent-duty ignition as "ignition by an energy 

source that is continuously maintained throughout the time the burner is firing."Is This design 

has been the standard of the industry for many years. Reductions in electric consumption are 

possible through "interrupted ignition," which is available for residential oil burners. 14 The UL 

defines interrupted-duty ignition as an "ignition system that is energized each time the main 

burner is to be fired and de-energized at the end of a timed trial period or after the main burner is 

proven to be established. IS In other words, the ignitor comes on to light the flame, and then, after 

the flame is established, the ignitor is turned off and the flame keeps burning. 

The burner industry promotes the interrupted-duty ignition strategy. The industry is 

currently transitioning away from electromechanical controls and iron core transformers, and 

toward solid-state controls with interrupted-duty capability and electronic igniters. So far, the 

reaction from installers and consumers has been positive, since these devices are smaller, weigh 

less, offer improved performance with cold-oil or delayed-spark conditions, are less sensitive to 

line voltage fluctuations, and extend the life of the igniter and the electrodes. 16, 17 

Since this design option is already being used, it is clearly technologically feasible and 

practical to manufacture, install, and service. There is no reason to expect that widespread 

adoption of this design option would have an adverse impact on product availability. No adverse 

4-8 
impacts on product utility or on health and/or safety have been reported. This design option

passes all the screening criteria.

4.2.1.6 Induced and Forced-Draft Combustion Systems

Induced-draft and forced-draft combustion systems are two alternatives to natural-draft

systems. Induced- and forced-draft systems use a fan to provide the air flow necessary for

combustion, without the need for a draft hood or draft diverter.

The combustion-air blower in an induced-draft system is located downstream from the

burner and heat exchanger. This is the safest way to obtain the advantages of a power-draft

furnace. An induced-draft system maintains negative pressures throughout the flue gas stream

within the appliance, thus ensuring that any leakages will be directed into the flue gas stream and

away from the surroundings. This provides an added measure of safety, because a negative

pressure is established in the heat exchanger as well, preventing the combustion gases inside the

heat exchanger from contaminating the conditioned air, should the heat exchanger develop a

crack or opening during its lifetime.

The forced-draft combustion system provides almost the same efficiency advantages as

an induced-draft furnace. The difference is that the combustion -air blower in a forced-draft

system is located upstream of the burner. This difference may affect heat loss from the collector

box assembly because the combustion-air blower is not located in the flue-gas stream in forceddraft systems. Although once more common, forced-draft systems are not widely used today, as

they cannot maintain negative pressures in the flue-gas stream.

The induced-draft technology is commonly used for non-weatherized and weatherized

gas furnaces. Oil-fired furnaces and oil-fired boilers typically use forced -draft combustion.

Mobile home furnaces and gas hot water boilers typically use natural draft systems. Therefore,

the Department considers induced-draft combustion as a design option for mobile home furnaces

and gas hot-water boilers.

In the case of gas-fired furnaces, both the induced and forced-draft combustion

technology have a significant efficiency advantage compared to the natural draft combustion

system. A Gas Research Institute (GRI) study6 points out that using an induced draft system

increases efficiency by 6.6 AFUE points compared to the natural draft system . Electricity

consumption increases slightly, but the total site energy consumption decreases considerably.

In the case of gas-fired boilers, the induced -draft combustion technology also has an

efficiency advantage compared to the natural draft combustion system. The GRI study6 points

out that using the natural draft system instead of induced draft system would increase the

efficiency by 2.3 AFUE points. Electricity consumption increases, but the total site energy

consumption decreases considerably.

4-9

 EE-RM/STD-01-350 COMMENT 164

impacts on product utility or on health and/or safety have been reported. This design option 

passes all the screening criteria. 

4.2.1.6 Indu.ced and Forced-Draft Combu.stion Systems 

Induced-draft and forced-draft combustion systems are two alternatives to natural-draft 

systems. Induced- and forced-draft systems use a fan to provide the air flow necessary for 

combustion, without the need for a draft hood or draft diverter. 

The combustion-air blower in an induced-draft system is located downstream from the 

burner and heat exchanger. This is the safest way to obtain the advantages of a power-draft 

furnace. An induced-draft system maintains negative pressures throughout the flue gas stream 

within the appliance, thus ensuring that any leakages will be directed into the flue gas stream and 

away from the surroundings. This provides an added measure of safety, because a negative 

pressure is established in the heat exchanger as well, preventing the combustion gases inside the 

heat exchanger from contaminating the conditioned air, should the heat exchanger develop a 

crack or opening during its lifetime. 

The forced-draft combustion system provides almost the same efficiency advantages as 

an induced-draft furnace. The difference is that the combustion-air blower in a forced-draft 

system is located upstream of the burner. This difference may affect heat loss from the collector 

box assembly because the combustion-air blower is not located in the flue-gas stream in forceddraft systems. Although once more common, forced-draft systems are not widely used today, as 

they cannot maintain negative pressures in the flue-gas stream. 

The induced-draft technology is commonly used for non-weatherized and weatherized 

gas furnaces. Oil-fired furnaces and oil-fired boilers typically use forced-draft combustion. 

Mobile home furnaces and gas hot water boilers typically use natural draft systems. Therefore, 

the Department considers induced-draft combustion as a design option for mobile home furnaces 

and gas hot-water boilers. 

In the case of gas-fired furnaces, both the induced and forced-draft combustion 

technology have a significant efficiency advantage compared to the natural draft combustion 

system. A Gas Research Institute (GRI) study6 points out that using an induced draft system 

increases efficiency by 6.6 AFUE points compared to the natural draft system. Electricity 

consumption increases slightly, but the total site energy consumption decreases considerably. 

In the case of gas-fired boilers, the induced-draft combustion technology also has an 

efficiency advantage compared to the natural draft combustion system. The GRI study6 points 

out that using the natural draft system instead of induced draft system would increase the 

efficiency by 2.3 AFUE points. Electricity consumption increases, but the total site energy 

consumption decreases considerably. 

4-9 
Induced-draft combustion systems are used in most gas furnaces currently sold in the

U.S., and forced-draft systems were once common, demonstrating that this technology is feasible

and practical to manufacture, install, and service. The Department is aware of no reports of

adverse impacts on product utility or product availability , or of adverse impacts on health and/or

safety, that are attributable to the use of these technologies. This design option passes all of the

screening criteria.

4.2.1.7 Infrared Burner

Infrared burners are a design option for gas-powered burners in furnaces and boilers.

Infrared burners are typically premix burners that produce a high radiant-heat flux with low

emissions. Infrared burners have a small efficiency advantage over blue-flame burners because

they can operate at lower levels of excess air. However, because these burners use 100 percent

primary air, they are susceptible to uneven operation (flashback). To prevent this from

becoming a safety problem, flashback-sensing devices must be added to each burner, thus

increasing the cost. Low nitrogen oxides (NOX) production is a strong advantage of all infrared

burners.'

Several infrared burner materials have been developed, including ceramic, stainless steel,

and glass fiber . Most ceramic burners are flat plates and have not been used in gas furnaces,

although they have been used in boilers. Recently, a ceramic burner design that consists of

ceramic fibers formed into a mat structure has been reported . " This design satisfies the heating

load requirements for residential furnaces , has very low NOX emissions, and is capable of

operating within a very wide turndown ratio (the ratio of the maximum to minimum output).

Perforated high-temperature stainless steel and woven high-temperature wire are formable and

adaptable to various configurations. However, metal gets brittle with time, creeps out of shape,

and cracks. Glass fiber is the most successful material , since it can be formed and it reliably

maintains its shape.

Infrared burners are currently used in many applications, demonstrating technological

feasibility and practicability to manufacture, install, and service. Experience shows no adverse

impacts on product utility. The existence of several technological options to produce infrared

burners (as described above) indicates that there are no adverse impacts on product availability.

No reports have been found indicating adverse impacts on health and/or safety attributable to

infrared burners. None of the criteria would screen out this design option.

The infrared burner design option is not currently applicable to oil burners , because the

oil fuel requires fuel atomization and vaporization prior to combustion . Ongoing research on

alternative fuel-oil atomization and combustion methods may someday permit the development

of radiant oil burners. However, due to the lack of current technological feasibility, this is not a

viable option for oil-burning appliances at this time."

4-10

 EE-RM/STD-01-350 COMMENT 164

Induced-draft combustion systems are used in most gas furnaces currently sold in the 

U.S., and forced-draft systems were once common, demonstrating that this technology is feasible 

and practical to manufacture, install, and service. The Department is aware of no reports of 

adverse impacts on product utility or product availability, or of adverse impacts on health and/or 

safety, that are attributable to the use of these technologies. This design option passes all of the 

screening criteria. 

4.2.1.7 Infrared Burner 

Infrared burners are a design option for gas-powered burners in furnaces and boilers. 

Infrared burners are typically premix burners that produce a high radiant-heat flux with low 

emissions. Infrared burners have a small efficiency advantage over blue-flame burners because 

they can operate at lower levels of excess air. However, because these burners use 100 percent 

primary air, they are susceptible to uneven operation (flashback). To prevent this from 

becoming a safety problem, flashback-sensing devices must be added to each burner, thus 

increasing the cost. Low nitrogen oxides (NOJ production is a strong advantage of all infrared 

burners.4 

Several infrared burner materials have been developed, including ceramic, stainless steel, 

and glass fiber. Most ceramic burners are flat plates and have not been used in gas furnaces, 

although they have been used in boilers. Recently, a ceramic burner design that consists of 

ceramic fibers formed into a mat structure has been reported. 18 This design satisfies the heating 

load requirements for residential furnaces, has very low NOx emissions, and is capable of 

operating within a very wide turndown ratio (the ratio of the maximum to minimum output). 

Perforated high-temperature stainless steel and woven high-temperature wire are formable and 

adaptable to various configurations. However, metal gets brittle with time, creeps out of shape, 

and cracks. Glass fiber is the most successful material, since it can be formed and it reliably 

maintains its shape. 

Infrared burners are currently used in many applications, demonstrating technological 

feasibility and practicability to manufacture, install, and service. Experience shows no adverse 

impacts on product utility. The existence of several technological options to produce infrared 

burners (as described above) indicates that there are no adverse impacts on product availability. 

No reports have been found indicating adverse impacts on health and/or safety attributable to 

infrared burners. None of the criteria would screen out this design option. 

The infrared burner design option is not currently applicable to oil burners, because the 

oil fuel requires fuel atomization and vaporization prior to combustion. Ongoing research on 

alternative fuel-oil atomization and combustion methods may someday permit the development 

of radiant oil burners. However, due to the lack of current technological feasibility, this is not a 

viable option for oil-burning appliances at this time. 14 

4-10 
4.2.1.8 Direct Vent

Direct-vent appliances use ducts to provide outdoor air for combustion. Non-direct-vent

appliances typically use air from the appliance's environment for combustion. Direct-vent

systems may use a combustion-air preheat system that passes the outdoor combustion air through

a heat exchanger in contact with the flue gases. The combustion air does not mix with the flue

gases. The so-called direct-vent with preheat design uses a concentric vent/combustion air

system in which the flue gases pass through a central-vent pipe and the combustion air passes

through a concentric duct surrounding it. This arrangement creates a counter-flow heat

exchanger that recovers some heat from the flue gases to preheat the combustion air.

The direct vent with preheat technology provides an efficiency advantage compared to

non-direct vent systems. The GRI study6 points out that using the combustion air preheat

technology instead of non-direct vent system would increase the AFUE by 3.4 AFUE points.'

The direct-vent-without-preheat design is the same as the direct-vent-with-preheat

design, except that the combustion air is not preheated by the flue gases. There are separate vent

and combustion air systems and the combustion air is not preheated. The current test procedure

does not differentiate between the performance of direct-vent with and without preheat

technology; both are evaluated as ICS installations.

The fact that direct-vent designs are currently available for many models of furnaces and

boilers shows that this design option is technologically feasible and practical to manufacture,

service, and install. Long experience with direct-vent systems has shown no adverse impacts on

product utility, product availability, or health or safety. Thus, this design option meets all of the

screening criteria.

4.2.1.9 Fuel Filtration

An option for oil-fired equipment is the use of modern fuel-filtration technology to

improve system efficiency by maintaining clean flames and reducing the rate of fouling in the

heat exchanger. 14

Fuel filtration is currently available for some models of oil-fired furnaces and boilers, and

therefore this design option is technologically feasible and practical to manufacture. The

Department is aware of no reports of adverse impacts on product utility, on product availability,

a These results are obtained under the current DOE test procedure conditions, which specify relatively short vent runs

(five-foot venting section). These conditions reflect the installations of mobile home furnaces and do not require the

concentric vent to be made of special stainless material. However, relatively longer venting sections are required in most

homes, which may cause condensate problems in a concentric vent system in the colder parts of the country. Therefore,

corrosion-resistant vent materials should be considered with this design option for applications other than mobile homes.

4-11

 EE-RM/STD-01-350 COMMENT 164

4.2.1.8 Direct Vent 

Direct-vent appliances use ducts to provide outdoor air for combustion. Non-direct-vent 

appliances typically use air from the appliance's environment for combustion. Direct-vent 

systems may use a combustion-air preheat system that passes the outdoor combustion air through 

a heat exchanger in contact with the flue gases. The combustion air does not mix with the flue 

gases. The so-called direct-vent with preheat design uses a concentric vent/combustion air 

system in which the flue gases pass through a central-vent pipe and the combustion air passes 

through a concentric duct surrounding it. This arrangement creates a counter-flow heat 

exchanger that recovers some heat from the flue gases to preheat the combustion air. 

The direct vent with preheat technology provides an efficiency advantage compared to 

non-direct vent systems. The GRI study6 points out that using the combustion air preheat 

technology instead of non-direct vent system would increase the AFUE by 3.4 AFUE points: 

The direct-vent-without-preheat design is the same as the direct-vent-with-preheat 

design, except that the combustion air is not preheated by the flue gases. There are separate vent 

and combustion air systems and the combustion air is not preheated. The current test procedure 

does not differentiate between the performance of direct-vent with and without preheat 

technology; both are evaluated as Ies installations. 

The fact that direct-vent designs are currently available for many models of furnaces and 

boilers shows that this design option is technologically feasible and practical to manufacture, 

service, and install. Long experience with direct-vent systems has shown no adverse impacts on 

product utility, product availability, or health or safety. Thus, this design option meets all of the 

screening criteria. 

4.2.1.9 Fuel Filtration 

An option for oil-fired equipment is the use of modern fuel-filtration technology to 

improve system efficiency by maintaining clean flames and reducing the rate of fouling in the 

heat exchanger. 14 

Fuel filtration is currently available for some models of oil-fired furnaces and boilers, and 

therefore this design option is technologically feasible and practical to manufacture. The 

Department is aware of no reports of adverse impacts on product utility, on product availability, 

a These results are obtained under the current DOE test procedure conditions, which specify relatively short vent mns 

(five-foot venting section). These conditions reflect the installations of mobile home furnaces and do not require the 

concentric vent to be made of special stainless material. However, relatively longer venting sections are required in most 

homes, which may cause condensate problems in a concentric vent system in the colder parts of the country. Therefore, 

corrosion-resistant vent materials should be considered with this design option for applications other than mobile homes. 

4-11 
or on health or safety that are attributable to the use of fuel filtration technology. This design

option meets the screening criteria.

4.2.1.10 Pulse Combustion

Pulse-combustion burners operate on self-sustaining resonating pressure waves that

alternately rarefy the combustion chamber (drawing a fresh fuel/air mixture into the chamber)

and pressurize it (causing ignition by compression heating of the mixture to its flash point). This

process is initiated by a blower supplying an initial fuel-and-air mixture to the combustion

chamber. The mixture is ignited with a spark. Once resonance is initiated, the process becomes

self-sustaining." Pulse frequencies are on the order of 100 cycles per second. Pulse combustion

systems feature high heat-transfer rates, are capable of self-venting, and can draw outside air for

combustion even when installed indoors. The CO emissions from pulse combustion burners are

50-66 percent lower than those of a conventional burner.19 Because the pulse combustion

process is highly efficient, the burners generally are used with condensing appliances.

In contrast to other forced-air furnaces utilizing natural draft and induced draft

technologies, pulse-combustion furnaces generate positive pressure on the flue side of the heat

exchanger. This creates a potential safety problem, because any leak in the heat exchanger

results in the potential for combustion products contaminating the circulation-air stream.

Pulse-combustion gas furnaces were available in the United States for more than two

decades, but they were withdrawn from the market because the manufacturers found that

competing technologies such as condensing flue gases using a secondary heat exchanger cost

significantly less to manufacture and operate. Regarding oil-fired pulse combustion of boilers

and furnaces, at least one prototype version has been developed, but no commercially available

units have been introduced for residential applications in the United States.

The length of time this technology was available demonstrates the technological

feasibility and the practicability to manufacture, install, and service products with this design

option. The Department is not aware of any adverse impacts on product utility or health or

safety that are attributable to the use of pulse combustion technology. Given the long years of

production of this design option, there is enough experience available to assure product

availability. For gas furnaces, this design option passes all the screening criteria.

4.2.1.11 Dampers

Burner-box dampers and flue dampers restrict the exhaust gas flow on the flue-gas side

of the heat exchanger during the off cycle, thereby trapping residual heat in the heat exchanger.

Burner-box dampers are installed at the combustion-air inlet to the appliance and flue dampers

are installed in the flue, where the flue gases leave the appliance. Stack dampers may be used

with appliances equipped with draft hoods; they are installed downstream of the draft hood. The

stack damper closes during the off cycle to restrict the flow of dilution air through the vent

4-12

 EE-RM/STD-01-350 COMMENT 164

or on health or safety that are attributable to the use of fuel filtration technology. This design 

option meets the screening criteria. 

4.2.1.10 Pu.lse Combu.stion 

Pulse-combustion burners operate on self-sustaining resonating pressure waves that 

alternately rarefy the combustion chamber (drawing a fresh fuel/air mixture into the chamber) 

and pressurize it (causing ignition by compression heating of the mixture to its flash point). This 

process is initiated by a blower supplying an initial fuel-and-air mixture to the combustion 

chamber. The mixture is ignited with a spark. Once resonance is initiated, the process becomes 

self-sustaining. 19 Pulse frequencies are on the order of 100 cycles per second. Pulse combustion 

systems feature high heat-transfer rates, are capable of self-venting, and can draw outside air for 

combustion even when installed indoors. The CO emissions from pulse combustion burners are 

50-66 percent lower than those of a conventional burner. 19 Because the pulse combustion 

process is highly efficient, the burners generally are used with condensing appliances. 

In contrast to other forced-air furnaces utilizing natural draft and induced draft 

technologies, pulse-combustion furnaces generate positive pressure on the flue side of the heat 

exchanger. This creates a potential safety problem, because any leak in the heat exchanger 

results in the potential for combustion products contaminating the circulation-air stream. 

Pulse-combustion gas furnaces were available in the United States for more than two 

decades, but they were withdrawn from the market because the manufacturers found that 

competing technologies such as condensing flue gases using a secondary heat exchanger cost 

significantly less to manufacture and operate. Regarding oil-fired pulse combustion of boilers 

and furnaces, at least one prototype version has been developed, but no commercially available 

units have been introduced for residential applications in the United States. 

The length of time this technology was available demonstrates the technological 

feasibility and the practicability to manufacture, install, and service products with this design 

option. The Department is not aware of any adverse impacts on product utility or health or 

safety that are attributable to the use of pulse combustion technology. Given the long years of 

production of this design option, there is enough experience available to assure product 

availability. For gas furnaces, this design option passes all the screening criteria. 

4.2.1.11 Dampers 

Burner-box dampers and flue dampers restrict the exhaust gas flow on the flue-gas side 

of the heat exchanger during the off cycle, thereby trapping residual heat in the heat exchanger. 

Burner-box dampers are installed at the combustion-air inlet to the appliance and flue dampers 

are installed in the flue, where the flue gases leave the appliance. Stack dampers may be used 

with appliances equipped with draft hoods; they are installed downstream of the draft hood. The 

stack damper closes during the off cycle to restrict the flow of dilution air through the vent 

4-12 
system when the appliance is off. The dampers are most useful with natural-draft combustion

systems.6

A high-quality flue damper may be used in lieu of a fan-assisted design.6 In order for

such a furnace to achieve performance which matches or exceeds the current minimum

efficiency requirements, the damper closure ratio must be close to 100 percent.

Dampers currently are installed on many models of gas boilers, which demonstrates the

technological feasibility of this design option and its practicability to manufacture, install, and

service. Since the design option is not a complicated technology and has been produced for at

least two decades, there is no reason to expect adverse impact on product availability. The

Department is not aware of any adverse impacts on product utility, or on health or safety, from

damper designs. This design option meets all the criteria.

4.2.1.12 Air-atomized Burner with Modulation

The residential oil burner market is currently dominated by the pressure-atomized

retention head burner . At low firing rates, pressure-atomizing nozzles suffer rapid fouling of the

small internal passages, leading to bad spray patterns and poor combustion performance.

To overcome the low input limitations of conventional burners, a low-pressure

air-atomized burner has been developed that can operate at firing rates as low as 0.25 gallons of

oil per hour (10 kW). In addition, the burner can be operated in a high/low-firing rate mode.

This burner is currently being commercialized. It can operate with almost no excess combustion

air (less than 10 percent) with lean-burning, ultra-clean combustion. This burner design is

capable of firing fuel at low input rates to closely match the smaller heating loads of wellinsulated modern homes. Tests performed at the Brookhaven National Laboratory have

demonstrated that the use of this technology produces significant reductions in emission of

nitrogen oxides (NOX) and particulates.20

This burner design has been available for more than a decade. The results from longterm tests at Brookhaven National Laboratory indicate that there are no problems with

technological feasibility or practicability to manufacture, install, or service this technology.

There are no reasons to expect adverse impacts on product utility, and no indications of adverse

impacts on health or safety. This design option passes all the screening criteria.

4.2.1.13 Delayed-Action Oil-Pump Solenoid Valve

Delayed-action oil-pump solenoid valves can improve overall efficiency and lower

particulate emissions during burner on-off cycling. This device is installed to supplement the

fuel pump regulator; by delaying the fuel release by several seconds, it allows the pressure to

build to the required level and to be fully discharged in the combustion chamber without

dripping. Testing at Brookhaven National Laboratory indicates that the typical efficiency benefit

of delayed-action solenoid valves is expected to be less than 1 percent.

4-13

 EE-RM/STD-01-350 COMMENT 164

system when the appliance is off. The dampers are most useful with natural-draft combustion 

systems. 6 

A high-quality flue damper may be used in lieu of a fan-assisted design. 6 In order for 

such a furnace to achieve performance which matches or exceeds the current minimum 

efficiency requirements, the damper closure ratio must be close to 100 percent. 

Dampers currently are installed on many models of gas boilers, which demonstrates the 

technological feasibility of this design option and its practicability to manufacture, install, and 

service. Since the design option is not a complicated technology and has been produced for at 

least two decades, there is no reason to expect adverse impact on product availability. The 

Department is not aware of any adverse impacts on product utility, or on health or safety, from 

damper designs. This design option meets all the criteria. 

4.2.1.12 Air-atomized Burner with Modulation 

The residential oil burner market is currently dominated by the pressure-atomized 

retention head burner. At low firing rates, pressure-atomizing nozzles suffer rapid fouling of the 

small internal passages, leading to bad spray patterns and poor combustion performance. 

To overcome the low input limitations of conventional burners, a low-pressure 

air-atomized burner has been developed that can operate at firing rates as low as 0.25 gallons of 

oil per hour (10 kW). In addition, the burner can be operated in a high/low-firing rate mode. 

This burner is currently being commercialized. It can operate with almost no excess combustion 

air (less than 10 percent) with lean-burning, ultra-clean combustion. This burner design is 

capable of firing fuel at low input rates to closely match the smaller heating loads of wellinsulated modem homes. Tests performed at the Brookhaven National Laboratory have 

demonstrated that the use of this technology produces significant reductions in emission of 

nitrogen oxides (NOx) and particulates.2o 

This burner design has been available for more than a decade. The results from longterm tests at Brookhaven National Laboratory indicate that there are no problems with 

technological feasibility or practicability to manufacture, install, or service this technology. 

There are no reasons to expect adverse impacts on product utility, and no indications of adverse 

impacts on health or safety. This design option passes all the screening criteria. 

4.2.1.13 Delayed-Action Oil-Pump Solenoid Valve 

Delayed-action oil-pump solenoid valves can improve overall efficiency and lower 

particulate emissions during burner on-off cycling. This device is installed to supplement the 

fuel pump regulator; by delaying the fuel release by several seconds, it allows the pressure to 

build to the required level and to be fully discharged in the combustion chamber without 

dripping. Testing at Brookhaven National Laboratory indicates that the typical efficiency benefit 

of delayed-action solenoid valves is expected to be less than 1 percent. 

4-13 
Delayed-action oil-pump solenoid valves for oil-fired equipment are already offered in at

least two fuel-pump models (Valcor Scientific and Taisan), which indicates the technical

feasibility of this design option. It also indicates the practicability to manufacture , install, and

service products incorporating this design option. The Department is aware of no reports of

adverse impacts on product utility or adverse impacts on health or safety caused by this design

option. Therefore, this design option passes all the screening criteria.

4.2.1.14 Increased Motor Efficiency

More-efficient electric motors could be used in furnace blowers, hot-water boiler pumps,

and draft inducers.

Most furnace-blower motors and hot-water boiler pumps use a permanent split capacitor

(PSC) design. PSC motors are reasonably efficient (above 70 percent) when operating at high

speed. However, when these motors are operated at low speed, their efficiencies may drop into

the 20 percent range. The circulating blower for most gas furnaces is also used to circulate the

supply air when the air conditioner is operating. The air-conditioner evaporator coil needs a

higher airflow than the furnace heat exchanger ; therefore, the blower motors operate at low

speed, and thus inefficiently, for the furnace operation.

Technologies that use power electronics offer dramatic improvements in efficiency at low

speeds. In the ECM-also known as the brushless, permanent-magnet motor -the rotor is a

permanent magnet. A rotating magnetic field is created in the armature by switching current in a

coordinated manner among six coils. This creates a three-phase motor with essentially no losses

in the rotor. The speed and torque of the motor can be accurately varied by controlling the

frequency and voltage applied to the armature coils. ECMs can operate at efficiencies above 80

percent across a very wide range of speeds. A similar, slightly-the-less-efficient motor

technology, the switched-reluctance motor, has a solid-steel rotor instead of a permanent magnet.

The power electronics are more complicated than for the ECM.

Designs to increase PSC motor efficiency are currently available; about 5 percent of

furnace shipments currently use ECMs, so there is apparently no issue with technological

feasibility or practicability to manufacture, install, and service. There have been no reports of

adverse impacts on product utility or availability . In fact, the electronic controls on ECMs allow

manufacturers to offer additional features such as continuous ventilation, reduced noise, and

better control of air flow , which improve the utility of furnaces. There have been no reports of

adverse impacts on health or safety . In fact, improvements that become possible with electronic

controls may lead to a healthier indoor environment due to the lower temperature variations, and

also reduce noise. Increased motor efficiency passes the screening criteria.

4-14

 EE-RM/STD-01-350 COMMENT 164

Delayed-action oil-pump solenoid valves for oil-fired equipment are already offered in at 

least two fuel-pump models (Valcor Scientific and Taisan), which indicates the technical 

feasibility of this design option. It also indicates the practicability to manufacture, install, and 

service products incorporating this design option. The Department is aware of no reports of 

adverse impacts on product utility or adverse impacts on health or safety caused by this design 

option. Therefore, this design option passes all the screening criteria. 

4.2.1.14 Increased Motor Efficiency 

More-efficient electric motors could be used in furnace blowers, hot-water boiler pumps, 

and draft inducers. 

Most furnace-blower motors and hot-water boiler pumps use a permanent split capacitor 

(PSC) design. PSC motors are reasonably efficient (above 70 percent) when operating at high 

speed. However, when these motors are operated at low speed, their efficiencies may drop into 

the 20 percent range. The circulating blower for most gas furnaces is also used to circulate the 

supply air when the air conditioner is operating. The air-conditioner evaporator coil needs a 

higher airflow than the furnace heat exchanger; therefore, the blower motors operate at low 

speed, and thus inefficiently, for the furnace operation. 

Technologies that use power electronics offer dramatic improvements in efficiency at low 

speeds. In the ECM-also known as the brushless, permanent-magnet motor-the rotor is a 

permanent magnet. A rotating magnetic field is created in the armature by switching current in a 

coordinated manner among six coils. This creates a three-phase motor with essentially no losses 

in the rotor. The speed and torque of the motor can be accurately varied by controlling the 

frequency and voltage applied to the armature coils. ECMs can operate at efficiencies above 80 

percent across a very wide range of speeds. A similar, slightly-the-Iess-efficient motor 

technology, the switched-reluctance motor, has a solid-steel rotor instead of a permanent magnet. 

The power electronics are more complicated than for the ECM. 

Designs to increase PSC motor efficiency are currently available; about 5 percent of 

furnace shipments currently use ECMs, so there is apparently no issue with technological 

feasibility or practicability to manufacture, install, and service. There have been no reports of 

adverse impacts on product utility or availability. In fact, the electronic controls on ECMs allow 

manufacturers to offer additional features such as continuous ventilation, reduced noise, and 

better control of air flow, which improve the utility of furnaces. There have been no reports of 

adverse impacts on health or safety. In fact, improvements that become possible with electronic 

controls may lead to a healthier indoor environment due to the lower temperature variations, and 

also reduce noise. Increased motor efficiency passes the screening criteria. 

4-14 
4.2.1.15 Increased Blower Impeller Efficiency

This technology discussion applies to furnaces only, since boilers do not have blowers.

Improving the efficiency of the blower impeller (wheel) lowers the power requirements of the

motor. The maximum efficiency of the commonly used forward-curved fan impellers is 65

percent, although efficiency in operation may be much lower. A viable alternative design is a

backward-curved impeller, which has a maximum efficiency of 78 percent. It has been available

in larger blowers for decades.

Impellers with improved efficiency are technologically feasible and practical to

manufacture, install, and service. As long as the blower moves the same amount of air as current

designs, there will be no impact on product utility, health, or safety. The improved designs are

not expected to be appreciably different to manufacture, so product availability will not be a

problem. This design option passes all the screening criteria.

4.2.2 Design Options Eliminated from Further Consideration

The Department eliminated the following design options from. further consideration

because they do not meet the screening criteria as described in section 4.1.

4.2.2.1 Self-Generation of Electric Power

It may be possible to use the heat generated by a furnace's combustion system to generate

the electricity needed to operate the various electrical components.21, 22 Known methods include

thermophotovoltaic (TPV) generators, thermoelectric generators, and thermionic conversion.

Other techniques use engines based on the Rankine cycle, Brayton cycle, Stirling cycle, or Otto

cycle, where the engine drives an electrical generator or provides direct mechanical power and

the waste heat from the engine is used for space heating. Several references provide detailed

discussion of the self-powered heating appliance technologies.21' 22

TPV devices convert radiant heat directly into electrical power by using a semiconductor

cell situated inside of the combustion zone. Currently, TPV systems are not available for oil- or

gas-fired equipment. Preliminary testing at Brookhaven National Laboratory has not yet

produced an effective prototype. Future advances in TPV technology may allow incorporation

of this new technology into control systems and power generation for residential equipment.

However, this technology is not yet available for residential use, and considerable research is

needed before its potential savings and costs can be evaluated.

Thermoelectric generators are thermocouples made from semiconducting alloys with

power conversion efficiencies capable of small-scale power generation. A thermocouple is a

circuit formed by two wires of dissimilar metals, where the junctions are kept at different

temperatures, producing an electromotive force in the circuit, also known as the Seebeck effect.

For furnace designs, the thermoelectric generator would form a cylinder around a firing flame.

A rechargeable battery would start the thermoelectric generator but, once hot, the thermoelectric

4-15

 EE-RM/STD-01-350 COMMENT 164

4.2.1.15 Increased Blower Impeller Efficiency 

This technology discussion applies to furnaces only, since boilers do not have blowers. 

Improving the efficiency of the blower impeller (wheel) lowers the power requirements of the 

motor. The maximum efficiency of the commonly used forward-curved fan impellers is 65 

percent, although efficiency in operation may be much lower. A viable alternative design is a 

backward-curved impeller, which has a maximum efficiency of 78 percent. It has been available 

in larger blowers for decades. 

Impellers with improved efficiency are technologically feasible and practical to 

manufacture, install, and service. As long as the blower moves the same amount of air as current 

designs, there will be no impact on product utility, health, or safety. The improved designs are 

not expected to be appreciably different to manufacture, so product availability will not be a 

problem. This design option passes all the screening criteria. 

4.2.2 Design Options Eliminated from Further Consideration 

The Department eliminated the following design options from further consideration 

because they do not meet the screening criteria as described in section 4.1. 

4.2.2.1 Self-Generation of Electric Power 

It may be possible to use the heat generated by a furnace's combustion system to generate 

the electricity needed to operate the various electrical components. 21,22 Known methods include 

thermophotovoltaic (TPV) generators, thermoelectric generators, and thermionic conversion. 

Other techniques use engines based on the Rankine cycle, Brayton cycle, Stirling cycle, or Otto 

cycle, where the engine drives an electrical generator or provides direct mechanical power and 

the waste heat from the engine is used for space heating. Several references provide detailed 

discussion of the self-powered heating appliance technologies. 21,22 

TPV devices convert radiant heat directly into electrical power by using a semiconductor 

cell situated inside of the combustion zone. Currently, TPV systems are not available for oil- or 

gas-fired equipment. Preliminary testing at Brookhaven National Laboratory has not yet 

produced an effective prototype. Future advances in TPV technology may allow incorporation 

of this new technology into control systems and power generation for residential equipment. 

However, this technology is not yet available for residential use, and considerable research is 

needed before its potential savings and costs can be evaluated. 

Thermoelectric generators are thermocouples made from semiconducting alloys with 

power conversion efficiencies capable of small-scale power generation. A thermocouple is a 

circuit formed by two wires of dissimilar metals, where the junctions are kept at different 

temperatures, producing an electromotive force in the circuit, also known as the Seebeck effect. 

For furnace designs, the thermoelectric generator would form a cylinder around a firing flame. 

A rechargeable battery would start the thermoelectric generator but, once hot, the thermoelectric 

4-15 
generator would provide sufficient excess capacity to recharge the battery.23 With no moving

parts, a thermoelectric generator is maintenance-free and can last the life of the furnace.

No self-powered furnaces or boilers are currently on the market. While there has been

research and development work that looks promising, at this point the Department is not

convinced that this design option is technologically feasible. There are no data to indicate the

practicability to manufacture, install, and service products incorporating this design option. The

Department is aware of no reports assessing the impacts on product utility or impacts on health

or safety resulting from this design option. Therefore, the Department excluded this design

option from further consideration for the purposes of this rulemaking.

4.2.2.2 Fuel-Driven Heat Pumps

Heat pumps extract heat from outdoor air or the ground and thus offer the potential for

greater heating output than energy input. This technology takes advantage of the thermodynamic

principle that energy can be extracted from the appliance's environment and delivered to the

conditioned space.

It is possible to manufacture fuel-fired heat pumps that use engine-driven vapor

compression cycles. The fact that, in the past, several manufacturers marketed this type of

equipment shows that this design is technologically feasible. Other designs use absorption

cycles and adsorption cycles. (Several manufacturers sold air conditioners utilizing an aquaammonia-based absorption cycle from the late 1960s up to the 1990s, but the reliability problems

and related service costs were prohibitive, and the manufacturers took these models off the

market.) This option uses a fundamentally different thermodynamic phenomenon from the

process of convective and conductive heat exchange that occurs in furnaces and boilers, and

would require a complete redesign of the appliance.

Fuel-driven heat pump technology appears to be technologically feasible and has no

adverse impact on product utility or on health and safety. During the 1990s, one manufacturer

marketed, in limited localities, a design for a fuel-driven heat pump, but withdrew it after a few

years. Based on the past experience with fuel-driven technology," the Department found that

residential fuel-driven heat pumps would not be able to be mass-produced and be reliable to

install and service on the scale necessary to serve the relevant market at the time of the effective

date of the standard. Therefore, the Department excluded this option from further consideration.

4.2.2.3 Flue-Gas Recirculation

Flue-gas recirculation (FGR) design allows a fraction of the flue gas to be recirculated to

the inlet and mixed with the combustion air so that some of the products of combustion pass

through the burner more than once. This process reduces NOR, but potentially increases CO

production. The flame temperature and the temperature of the flue products are also reduced.

This technology has been implemented for pollution control in automobiles and large

commercial boilers.

4-16

 EE-RM/STD-01-350 COMMENT 164

generator would provide sufficient excess capacity to recharge the battery.23 With no moving 

parts, a thermoelectric generator is maintenance-free and can last the life of the furnace. 

No self-powered furnaces or boilers are currently on the market. While there has been 

research and development work that looks promising, at this point the Department is not 

convinced that this design option is technologically feasible. There are no data to indicate the 

practicability to manufacture, install, and service products incorporating this design option. The 

Department is aware of no reports assessing the impacts on product utility or impacts on health 

or safety resulting from this design option. Therefore, the Department excluded this design 

option from further consideration for the purposes of this rulemaking. 

4.2.2.2 Fuel-Driven Heat Pumps 

Heat pumps extract heat from outdoor air or the ground and thus offer the potential for 

greater heating output than energy input. This technology takes advantage of the thermodynamic 

principle that energy can be extracted from the appliance's environment and delivered to the 

conditioned space. 

It is possible to manufacture fuel-fired heat pumps that use engine-driven vapor 

compression cycles. The fact that, in the past, several manufacturers marketed this type of 

equipment shows that this design is technologically feasible. Other designs use absorption 

cycles and adsorption cycles. (Several manufacturers sold air conditioners utilizing an aquaammonia-based absorption cycle from the late 1960s up to the 1990s, but the reliability problems 

and related service costs were prohibitive, and the manufacturers took these models off the 

market.) This option uses a fundamentally different thermodynamic phenomenon from the 

process of convective and conductive heat exchange that occurs in furnaces and boilers, and 

would require a complete redesign of the appliance. 

Fuel-driven heat pump technology appears to be technologically feasible and has no 

adverse impact on product utility or on health and safety. During the 1990s, one manufacturer 

marketed, in limited localities, a design for a fuel-driven heat pump, but withdrew it after a few 

years. Based on the past experience with fuel-driven technology,24 the Department found that 

residential fuel-driven heat pumps would not be able to be mass-produced and be reliable to 

install and service on the scale necessary to serve the relevant market at the time of the effective 

date of the standard. Therefore, the Department excluded this option from further consideration. 

4.2.2.3 Flue-Gas Recirculation 

Flue-gas recirculation (FGR) design allows a fraction of the flue gas to be recirculated to 

the inlet and mixed with the combustion air so that some of the products of combustion pass 

through the burner more than once. This process reduces NOx , but potentially increases co 

production. The flame temperature and the temperature of the flue products are also reduced. 

This technology has been implemented for pollution control in automobiles and large 

commercial boilers. 

4-16 
Computer simulations of furnace performance show that FGR with the current furnace

design improves the AFUE by 0.3 percent, due to the reduction of the excess air. However, the

combustion fan would consume 10 percent more electricity in order to overcome the pressure

drop associated with the flue-gas recirculation.'

In the case of boilers, a study showed that the addition of NON-control systems, such as

FGR and low NON burners, can reduce combustion efficiency (due to lower combustion

temperatures), resulting in higher CO and organic emissions relative to uncontrolled boilers.

The FGR process reduces the peak flame temperature because the flue gas that is reintroduced

into the furnace's combustion and flame zones is at a lower temperature and has a lower oxygen

concentration.25 This process reduces excess air (free oxygen) fractions, potentially

compromising the furnace's ability to meet the requirements of the American National Standards

Institute (ANSI) Z21.47 overfire test, which stipulates that the carbon monoxide level in the flue

products must remain below 0.04 percent when the furnace is fired at 12 percent over its rated

input. Incorporating the FGR process would make it more difficult for furnace (and boiler)

manufacturers, who currently design their equipment to operate with excess air fractions that are

sufficiently high enough to account for the practical aspects of field operations and maintain safe

operation, to meet the ANSI CO limit.6, 26

Furnaces with FGR design are technologically feasible and practical to manufacture,

install, and service. This design is used extensively in commercial-sized equipment and,

therefore, the product availability is not a problem. There are no known negative impacts on the

product utility. However, this design may result in higher CO production, and therefore, given

the potential negative impact on health and safety due to an increased potential for CO

production, the Department excluded this technology from further consideration.

4.2.2.4 Smart Valve

One option for oil-fired furnaces and boilers is a "smart valve" or positive shut-off valve

on the fuel nozzle, which reduces smoke and soot production during burner start-up and shutdown. This valve is generally installed directly in the nozzle tip and prevents oil from dripping

into the combustion chamber. This option can also be retrofitted on existing burners. Smartvalve design for oil-fired equipment does not affect the efficiency of the appliance, but plays a

role as an emission-control device.

Smart valve design has no known adverse impact on product utility or on health and

safety. Although this technology has been offered by at least one oil-burner manufacturer for

commercial-sized equipment, the Department is not aware of any prototypes for use in

residential-sized equipment. Since there is no proof that smart valve design would be able to be

mass-produced and be reliable to install and service on the scale necessary to serve the relevant

market at the time of the effective date of the standard, the Department excluded it from further

consideration.

4-17

 EE-RM/STD-01-350 COMMENT 164

Computer simulations of furnace performance show that FGR with the current furnace 

design improves the AFUE by 0.3 percent, due to the reduction of the excess air. However, the 

combustion fan would consume 10 percent more electricity in order to overcome the pressure 

drop associated with the flue-gas recirculation. 6 

In the case of boilers, a study showed that the addition of NO x-control systems, such as 

FGR and low NOx burners, can reduce combustion efficiency (due to lower combustion 

temperatures), resulting in higher CO and organic emissions relative to uncontrolled boilers. 

The FGR process reduces the peak flame temperature because the flue gas that is reintroduced 

into the furnace's combustion and flame zones is at a lower temperature and has a lower oxygen 

concentration.25 This process reduces excess air (free oxygen) fractions, potentially 

compromising the furnace's ability to meet the requirements of the American National Standards 

Institute (ANSI) Z21.4 7 overfire test, which stipulates that the carbon monoxide level in the flue 

products must remain below 0.04 percent when the furnace is fired at 12 percent over its rated 

input. Incorporating the FGR process would make it more difficult for furnace (and boiler) 

manufacturers, who currently design their equipment to operate with excess air fractions that are 

sufficiently high enough to account for the practical aspects of field operations and maintain safe 

operation, to meet the ANSI CO limit. 6,26 

Furnaces with FGR design are technologically feasible and practical to manufacture, 

install, and service. This design is used extensively in commercial-sized equipment and, 

therefore, the product availability is not a problem. There are no known negative impacts on the 

product utility. However, this design may result in higher CO production, and therefore, given 

the potential negative impact on health and safety due to an increased potential for CO 

production, the Department excluded this technology from further consideration. 

4.2.2.4 Smart Valve 

One option for oil-fired furnaces and boilers is a "smart valve" or positive shut-off valve 

on the fuel nozzle, which reduces smoke and soot production during burner start-up and shutdown. This valve is generally installed directly in the nozzle tip and prevents oil from dripping 

into the combustion chamber. This option can also be retrofitted on existing burners. Smartvalve design for oil-fired equipment does not affect the efficiency of the appliance, but plays a 

role as an emission-control device. 

Smart valve design has no known adverse impact on product utility or on health and 

safety. Although this technology has been offered by at least one oil-burner manufacturer for 

commercial-sized equipment, the Department is not aware of any prototypes for use in 

residential-sized equipment. Since there is no proof that smart valve design would be able to be 

mass-produced and be reliable to install and service on the scale necessary to serve the relevant 

market at the time of the effective date of the standard, the Department excluded it from further 

consideration. 

4-17 
4.2.2.5 Design Options Yielding 82 Percent and Higher AFUE for Non-condensing

Non-weatherized Gas Furnaces

Technologies for producing non-condensing non-weatherized gas furnaces can yield

efficiency of up to 89 percent AFUE. At levels of 82 percent AFUE and above, however, there

are concerns regarding corrosion in vents and condensation that could pose risk to the consumer.

According to the National Fuel Gas Code, condensation occurs at 83 percent steady-state

efficiency, which is close to 82 percent AFUE.4 Based on comments received at and after the

ANOPR public meeting, the Department believes that non-condensing non-weatherized furnaces

with necessary venting systems at AFUE levels of 82 percent and higher would not be able to be

mass-produced and be reliable to install and service on the scale necessary to serve the relevant

market at the time of the effective date of the standard. Further, there are safety issues related to

venting at these AFUE levels. Therefore, DOE discontinued consideration of non-condensing

non-weatherized gas furnaces at 82 percent AFUE and higher.

4.3 SUMMARY OF SCREENING

Table 4.3.1 presents the results of the screening of design options by product class. The

design options showing a "Y" (for "yes") pass all of the screening criteria. Some options are not

applicable (n/a) for certain product classes. For example, improved or increased insulation is not

applicable for boilers because boilers are tested as indoor appliances according to the DOE test

procedure.

 EE-RM/STD-01-350 COMMENT 164

4.2.2.5 Design Options Yielding 82 Percent and Higher AFUE for Non-condensing 

Non-weatherized Gas Furnaces 

Technologies for producing non-condensing non-weatherized gas furnaces can yield 

efficiency of up to 89 percent AFUE. At levels of 82 percent AFUE and above, however, there 

are concerns regarding corrosion in vents and condensation that could pose risk to the consumer. 

According to the National Fuel Gas Code, condensation occurs at 83 percent steady-state 

efficiency, which is close to 82 percent AFUE.4 Based on comments received at and after the 

ANOPR public meeting, the Department believes that non-condensing non-weatherized furnaces 

with necessary venting systems at AFUE levels of 82 percent and higher would not be. able to be 

mass-produced and be reliable to install and service on the scale necessary to serve the relevant 

market at the time of the effective date of the standard. Further, there are safety issues related to 

venting at these AFUE levels. Therefore, DOE discontinued consideration of non-condensing 

non-weatherized gas furnaces at 82 percent AFUE and higher. 

4.3 SUMMARY OF SCREENING 

Table 4.3.1 presents the results of the screening of design options by product class. The 

design options showing a "Y" (for "yes") pass all of the screening criteria. Some options are not 

applicable (n/a) for certain product classes. For example, improved or increased insulation is not 

applicable for boilers because boilers are tested as indoor appliances according to the DOE test 

procedure. 

4-18 
Table 4.3.1 Screening Results for Design Options by Product Class

Gas Furnaces

Oil fi d M bil H

Hot

Nonweatherized Weatherized

- re

furnaces

o e- ome

Gas Furnaces Water

Boilers

Design Option Gas Oil

Improved Heat Exchanger Effectiveness Y Y Y Y Y Y

Modulating Operation Y Y Y Y Y Y

Increased or Improved Insulation Y Y Y Y n/a n/a

Condensing Secondary Heat Exchanger Y N N Y Y Y

Electronic Ignition b b b Y Y b

Induced or Forced Draft b b b Y Y b

Infrared Burner Y Y Y Y Y Y

Direct Vent Y Y Y Y Y Y

Fuel Filtration n/a n/a Y n/a n/a Y

Pulse Combustion Y Y N Y Y N

Dampers n/a b n/a Y Y n/a

Air-Atomized Burner with Modulation n/a n/a Y n/a n/a Y

Delayed Action Oil Pump Solenoid Valve n/a n/a Y n/a n/a Y

Increased Motor Efficiency Y Y Y Y Y Y

Increased Blower Impeller Efficiency Y Y Y Y n/a n/a

Self-Generation of Electricity N N N N N N

Fuel-Driven Heat Pumps N N N N N N

Flue Gas Recirculation N N N N N N

Smart Valve n/a n/a N n/a n/a N

Y = The design option is applicable to this product class and passes screening.

N = The Department screened out this design option from further analysis for this product class.

b = The design option is already in the baseline model of this product class.

n/a = The design option is not applicable to this product class.

 EE-RM/STD-01-350 COMMENT 164

T a e bi 431 .. s creenmg R eSli It S f or D eSlgn Of 'pllOns b Iy Pdt ro lie CI ass 

Gas Furnaces Hot Oil-fired Mobile- Home 

Non- Water furnaces Gas Furnaces 

weatherized Weatherized Boilers 

Design Option Gas Oil 

Improved Heat Exchanger Effectiveness Y Y Y Y Y Y 

Modulating Operation Y Y Y Y Y Y 

Increased or Improved Insulation Y Y Y Y nla nla 

Condensing Secondary Heat Exchanger Y N N Y Y Y 

Electronic Ignition b b b Y Y b 

Induced or Forced Draft b b b Y Y b 

Infrared Burner Y Y Y Y Y Y 

Direct Vent Y Y Y Y Y Y 

Fuel Filtration nla nla Y nla nla Y 

Pulse Combustion Y Y N Y Y N 

Dampers nla b nla Y Y nla 

Air-Atomized Burner with Modulation nla nla Y nla nla Y 

Delayed Action Oil Pump Solenoid Valve nla nla Y nla nla Y 

Increased Motor Efficiency Y Y Y Y Y Y 

Increased Blower Impeller Efficiency Y Y Y Y nla nla 

Self-Generation of Electricity N N N N N N 

Fuel-Driven Heat Pumps N N N N N N 

Flue Gas Recirculation N N N N N N 

Smart Valve nla nla N nla nla N 

Y = The design option IS applicable to this product class and passes screening. 

N = The Department screened out this design option from further analysis for this product class. 

b = The design option is already in the baseline model of this product class. 

nla The design option is not applicable to this product class. 

4-19 
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and Boilers, 2001. (Posted November 5, 2001)

<http://www.eere.energy.gov/buildings/appliance-standards/>

2. Bergles, A. E., M. K. Jensen, E. F. C. Sommerscales, and R. M. Manglik, Literature

Review of Heat Transfer Enhancement Technology for Heat Exchangers in Gas-Fired

Applications, 1991. Gas Research Institute. Chicago, IL. Report No. GRI-91/0146.

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4-20

 EE-RM/STD-01-350 COMMENT 164

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and Boilers, 2001. (Posted November 5,2001) 

<http://www. eere. energy. gov Ibuildingsl appliance _ standards/> 

2. Bergles, A. E., M. K. Jensen, E. F. C. Sommerscales, and R. M. Manglik, Literature 

Review of Heat Transfer Enhancement Technology for Heat Exchangers in Gas-Fired 

Applications, 1991. Gas Research Institute. Chicago, IL. Report No. GRI-9110146. 

3. National Fire Protection Association, National Fuel Gas Code -2002 Edition, 2002. 1 

Batterymarch Park, P.O. Box 9101, Quincy MA. 

4. Gable, G. K., Detailed Discussion of Design Options, January 2, 2002. Carmel, IN. 

Consultant to LBNL. 

5. Fang, L., J. Abraham, and V. W. Goldsmchmidt, A Thermal Model of Clamshell Heat 

Exchangers in Residential Gas Furnaces. HVAC&R Research, 2001. 7(3): pp. 289-308 

6. Jakob, F. E., 1. 1. Crisafulli, J. R. Menkedick, R. D. Fischer, D. B. Philips, R. L. Osbone, 

1. C. Cross, G. R. Whitacre, J. G. Murray, W. 1. Sheppard, D. W. DeWirth, and W. H. 

Thrasher, Assessment of Technology for Improving the Efficiency of Residential Gas 

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Institute. AGA Laboratories, Chicago, IL. Report No. GRI-94/0175. 

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December 

9. Turiel, 1., Design Options for Energy Efficiency Improvements of Residential Appliances, 

October, 1986. Lawrence Berkeley Laboratory. Berkeley, CA. Report No. LBL-22372. 

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AL. 

11. Bassett, B. and 1. Krueger, Modulating Combustion, 2001. Appliance Manufacturer. 

(Posted 09/27/2001) (Last accessed January 9, 2002.) 

<http://www.ammagazine.com!aml cdal articleinformationlfeatures/bnp_features_iteml 

0,2606,64194,00.html> 

4-20 
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13. Paul, D. D., G. R. Whitacre, R. D. Fischer, A. L. Rutz, J. J. Crisafulli, S. G. Talbert, R.

W. DeWerth, and V. Kam, Venting Guidelines for Category I Gas Appliances With FanAssisted Combustion Systems, July, 1992. Gas Research Institute. Report No. GRI89/0016. Prepared by Batelle and A.G.A. Laboratories.

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Consumer Products: Standards for Furnaces & Boilers, DOE Docket Number EERM/STD-01-350, Comment No. 20, August 16, 2001. Oilheat Manufacturers Association.

15. Underwriters Laboratories Inc., Standardfor Safety For Oil Burners, UL 296. 9th ed.

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16. R.W. Beckett Corporation, Getting Acquainted with Electronic Ignitors: Technical

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19. Vishwanath, P. S., Design Recommendations for Pulse Combustion Burners. ASHRAE

Transactions, 1987. 93(2): pp. 1606-1618

20. Butcher, T. A., R. Krajewski, L. R., Y. Celebi, F. L., and B. Kamath, Residential Oil

Burners with Low Input and Two-Stage Firing. ASHRAE Transactions, 1997. 103 Pt. 1:

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21. Weller, A. E., An Assessment of Technology for Self-Powered Gas Appliances, 1989.

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22. McFadden, D. and A. D. Little, Opportunitiesfor Self-Powered Heating Appliances,

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4-21

 EE-RM/STD-01-350 COMMENT 164

12. Carrier Corporation, 58CVAI58CVX Installation, Start-up, Operating, and Service and 

Maintenance Instructions, December, 2002. Carrier Cop oration. Report No. Catalog No: 

535-80103. 

13. Paul, D. D., G. R. Whitacre, R. D. Fischer, A. L. Rutz, 1. 1. Crisafulli, S. G. Talbert, R. 

W. DeWerth, and V. Kam, Venting Guidelinesfor Category I Gas Appliances With FanAssisted Combustion Systems, July, 1992. Gas Research Institute. Report No. GRI89/0016. Prepared by Batelle and A.G.A. Laboratories. 

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Consumer Products: Standards for Furnaces & Boilers, DOE Docket Number EERMISTD-Ol-350, Comment No. 20, August 16, 2001. Oilheat Manufacturers Association. 

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June 30, 1994. par.4.22. 

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Information Bulletin, May, 1999. Elyria, OR. 

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Intermittent Duty, 2002. (Last accessed October 29,2002.) 

<http://www.carlincombustion.comlTechLib/tech _speaking l.html> 

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Manufacturer, 2000. 

19. Vishwanath, P. S., Design Recommendations for Pulse Combustion Burners. ASHRAE 

Transactions, 1987.93(2): pp. 1606-1618 

20. Butcher, T. A., R. Krajewski, L. R., Y. Celebi, F. L., and B. Kamath, Residential Oil 

Burners with Low Input and Two-Stage Firing. ASHRAE Transactions, 1997. 103 Pt. 1: 

pp.928-935.PH-97-13-4. 

21. Weller, A. E., An Assessment of Technology for Self-Powered Gas Appliances, 1989. 

Report No. GRI-89/0093. 

22. McFadden, D. and A. D. Little, Opportunities for Self-Powered Heating Appliances, 

May, 1994. Report No. GRI/GATC Task Report 42943-11. 

23. Babyak, R. 1., Gas Furnace Unplugged. Appliance Manufacturer, 1993(May): pp. 76 

24. Cler, G., The York Triathlon: Natural Gas-Fred, Engine-Driven Heat Pump, November 

1995. E. Source, Inc. Report No. PP-95-4. 

4-21 
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4-22