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CHAPTER 4. SCREENING ANALYSIS

TABLE OF CONTENTS

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

4.2 SCREENED-OUT TECHNOLOGIES............................................................................ 4-2

4.2.1 Furnace Energy Efficiency Standards.................................................................. 4-2

4.2.2 Central Air Conditioner and Heat Pump Energy Efficiency Standards............... 4-4

4.2.3 Standby Mode and Off Mode Power Consumption Standards............................ 4-4

4.3 REMAINING TECHNOLOGIES ................................................................................... 4-6

4.3.1 Furnace Energy Efficiency Standards.................................................................. 4-6

4.3.2 Central Air Conditioner and Heat Pump Energy Efficiency Standards............... 4-6

4.3.3 Standby Mode and Off Mode Power Consumption Standards............................ 4-7
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4.1 INTRODUCTION

This chapter details the screening analysis that the U.S. Department of Energy 

(DOE) conducted in support of the direct final rule for energy conservation standards for 

residential furnaces and central air conditioners and heat pumps.

In the market and technology assessment (MTA; chapter 3), DOE presents an 

initial list of technologies that manufacturers can use to improve the energy efficiency of 

residential furnaces, central air conditioners and heat pumps, or their standby and off 

mode electrical power consumption. The purpose of the screening analysis is to evaluate 

the technologies that improve product energy efficiency or reduce standby and off mode 

energy consumption to determine which technologies DOE should consider further in the 

rulemaking analyses. DOE consulted a range of parties, including industry and technical 

experts and others, to develop a list of technologies for consideration in the market 

assessment (see chapter 3 of the TSD). Some of these technologies can reduce annual 

energy consumption of products in actual applications but may not improve the annual 

fuel utilization efficiency (AFUE), seasonal energy efficiency ratio (SEER), heating 

seasonal performance factor (HSPF), or reduce standby and off mode electrical power 

consumption. These rating metrics are measured according to DOE regulations at 10 CFR 

430 Subpart B, Appendices M and N, which incorporate by reference various industry 

test procedures. DOE removed from consideration those technologies that do not increase 

AFUE, SEER, or HSPF or reduce standby and off mode electrical power consumption 

per the DOE test procedures. DOE evaluated the remaining technologies pursuant to the 

criteria in the Energy Policy and Conservation Act (EPCA), as amended. (42 U.S.C.

6311-6317)

Section 325(o) of EPCA establishes criteria for prescribing new or amended 

standards designed to achieve the maximum improvement in energy efficiency. 

Furthermore, EPCA directs the Secretary of Energy to determine whether a standard is 

technologically feasible and economically justified. (42 U.S.C. 6295(o)(2)(A)(B)) In 

view of this requirement, 10 CFR Part 430 Subpart C, Appendix A, Procedures, 

Interpretations and Policies for Consideration of New or Revised Energy Conservation

Standards for Consumer Products (the Process Rule), guides DOE in its consideration 

and promulgation of new or revised product efficiency standards. These procedures 

elaborate on the statutory criteria provided in 42 U.S.C. 6295(o) and, in part, eliminate 

problematic technologies early in the process of prescribing or amending an energy 

efficiency standard. In particular, DOE determines whether to eliminate from 

consideration any technology that presents unacceptable problems with respect to the 

following criteria:

Technological feasibility. Technologies that are not incorporated in commercial 

products or in working prototypes will not be considered further.

Practicability to manufacture, install, and service. If it is determined that mass 

production of a technology in commercial products and reliable installation and servicing 
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of the technology could not be achieved on the scale necessary to serve the relevant 

market at the time of the effective date of the standard, then that technology will not be 

considered further.

Impacts on product utility to consumers. If a technology is determined to have 

significant adverse impact on the utility of the product to significant subgroups of 

consumers or results 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. at the time, it will not 

be considered further.

Safety of technologies. If it is determined that a technology will have significant 

adverse impacts on health or safety, it will not be considered further. In sum, if DOE

determines that a technology, or a combination of technologies, has unacceptable impacts 

on the policies stated in section 5(b) of the Process Rule, it will be eliminated from 

consideration. If a particular technology fails to meet one or more of the four criteria, it 

will be screened out from further consideration in the engineering analysis. 61 FR 36974-

36987; 10 CFR part 430, subpart C, appendix A, section (5)(b). The reasons for 

eliminating any technology are documented in section 4.2.

4.2 SCREENED-OUT TECHNOLOGIES

This section describes the technologies that DOE eliminated based on 

consideration of the following four factors: 1) technological feasibility; 2) practicability 

to manufacture, install, and service; 3) adverse impacts on product utility or product 

availability; and 4) adverse impacts on health or safety.

4.2.1 Furnace Energy Efficiency (i.e., AFUE) Standards

DOE eliminated the following technology options for residential furnaces from 

further consideration: condensing and near-condensing technologies for weatherized 

furnaces; pulse combustion; low NOX

4.2.1.1 Condensing and Near-Condensing Technologies for Weatherized Gas 

Furnaces

premix burners; derating; advanced forms of 

insulation; and low-pressure, air-atomized oil burners.

Non-weatherized gas furnaces can yield efficiencies of up to 98 percent AFUE by 

utilizing condensing technology. However, although weatherized gas furnaces are nearly 

identical to their non-weatherized counterparts, they cannot reliably achieve the same 

efficiency levels because they are installed outdoors and are often exposed to harsh

weather conditions. Installing a condensing furnace in below freezing outdoor 

temperatures can lead to frozen condensate, which can disrupt proper operation of the 

furnace, rendering it unreliable and decreasing consumer utility. Weatherized gas 

furnaces are limited by their inability to prevent condensate from freezing when the 

outdoor temperature drops below freezing.
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To the best of DOE’s knowledge, manufacturers and others have not succeeded in 

developing a weatherized gas furnace that can prevent condensate from freezing. DOE 

notes, however, that a U.S. patent has been granted for a condensate drainage system for 

condensing, weatherized furnaces.1

4.2.1.2 Pulse Combustion

However, the grant of a patent does not necessarily 

indicate a proof of concept. In this case, DOE was unable find evidence that the patented 

design had been demonstrated in a working prototype. As a result, because DOE could 

not identify this technology in commercial products or in working prototypes, DOE did

not consider condensing or near-condensing weatherized gas furnaces to be 

technologically feasible. Furthermore, as noted above, DOE believes that frozen 

condensate has the potential to disrupt proper operation of the furnace, which will 

ultimately decrease consumer utility. For these reasons, DOE excluded this technology 

option from further consideration in these rulemaking analyses.

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). Pulse combustion systems are capable direct venting without the assistance 

of mechanical draft. Because the pulse combustion process is very efficient, pulse 

combustion is generally used in condensing appliances.

In contrast to natural draft and induced draft furnaces, pulse combustion furnaces 

generate positive pressure in the heat exchanger. This creates a potential safety problem

because combustion products can contaminate the circulation-air stream if the heat 

exchanger breeches. 

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

two decades. However, they were withdrawn from the market because manufacturers 

found that competing technologies, such as condensing, secondary heat exchangers, cost 

significantly less to manufacture and operate. In light of the ability of furnace 

manufacturers to cost-effectively achieve high efficiencies without the use of pulse

combustion, DOE believes that the technology’s risks to health and safety do not 

outweigh its benefits. DOE did not further analyze this technology option as part of this 

rulemaking.

4.2.1.3 Low NOX Premix Burners

Premix burners work by completely mixing primary air and fuel prior to 

combustion, eliminating the need for secondary air. However, atmospheric burners 

cannot entrain sufficient primary air to completely premix the air and gas. Therefore, to 

ensure sufficient and complete mixing, the burner incorporates a fan to deliver 

combustion air at positive pressure. To the extent of DOE’s knowledge, low NOX premix 

burners have not yet been successfully incorporated into a residential furnace design; and 

technological feasibility in a furnace has not been proven. For this reason, DOE did not 

consider this technology option further in the rulemaking analyses.
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4.2.1.4 Burner Derating 

Decreasing the burner size to increase the ratio of heat transfer area to fuel input, 

or burner derating, can increase the AFUE rating of gas and oil-fired furnaces. However, 

because heat output rate is directly related to burner size, derating also reduces the 

amount of heated air available to the consumer. This reduction in heat output adversely 

affects the utility to consumers. Therefore, DOE did not consider this technology option.

4.2.1.5 Advanced Forms of Insulation

Insulating furnaces with foam, a vacuum, inert gases, aerogel, or evacuated panels 

is an alternative to increasing the thickness of the insulation to decrease jacket heat loss. 

Manufacturers may elect to use alternative types of insulation because increasing the 

thickness of insulation may create shipping and installation problems if the footprint

exceeds typical dimensions. However, DOE notes that none of these technologies has 

been applied to residential furnaces in the past or present, and as a result, DOE has 

insufficient information to judge the merits and practicability of incorporating advanced 

forms of insulation into residential furnaces. DOE eliminated this technology option from 

further consideration.

4.2.1.6 Low-Pressure, Air-Atomized Oil Burner 

To overcome the low input limitations of conventional oil burners, Brookhaven 

National Laboratory developed a low-pressure, air-atomized oil burner that can operate at 

firing rates as low as 0.25 gallons of oil per hour (10 kW). In addition, it can operate with 

low levels of excess combustion air (less than 10 percent) for lean-burning, ultra-clean 

combustion. A lower level of excess air generally improves AFUE rating. This burner 

design is also capable of firing fuel at a high or low input rate, which is manually 

actuated by a switch, allowing the burner to closely match the smaller heating loads of 

well-insulated modern homes. 

While tests performed at the Brookhaven National Laboratory seem to have 

successfully demonstrated enhanced oil boiler AFUE performance per the DOE test 

procedure for furnaces and boilers, the prototype was never tested on a furnace.2

4.2.2 Central Air Conditioner and Heat Pump Energy Efficiency Standards

Therefore, the technological feasibility of the burner prototype for incorporation into a 

residential oil-fired furnace remains unknown, and DOE does not consider low-pressure, 

air-atomized oil burners to be a viable technology for efficiency improvement at this 

time. 

DOE did not eliminate any technology options from consideration in its SEER 

and HSPF standards rulemaking analysis for central air conditioners and heat pumps.

4.2.3 Standby Mode and Off Mode Power Consumption Standards

DOE screened out from consideration electronically commutated motor (ECM)

control relays in its residential furnaces standby power consumption standards analysis
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and its central air conditioner and heat pump off mode power consumption standards 

analysis. 

4.2.3.1 ECM Control Relay

While PSC blower motors do not draw any power when off, ECM blower motors

and their associated controls consume an average of 3 watts in order to provide power to

an integral control board for modulating the fan speed. To reduce standby power 

consumption of a furnace and off mode consumption of a central air conditioner or heat 

pump equipped with an ECM blower, DOE considered adding a relay to the circuit to 

disconnect the blower motor’s control circuit when not in use. A typical relay activates a 

switch when current runs through it, and a spring holds the switch open when there is no 

current flow. Manufacturer feedback provided during the interview process (see chapter 

12 of this TSD) indicated that ECMs are subject to an inrush of current upon startup. The 

power supply on the ECM’s control board, which is typically a switching mode power 

supply, cannot withstand the repeated surge of current that occurs at ECM startup and,

therefore, completely depowering and reactivating the motor by use of a control relay

would shorten the motor’s lifetime significantly. DOE considers a premature failure of 

the blower to be a reliability issue that has an adverse impact on product utility to the 

consumer. Therefore, DOE believes that disconnection of an ECM fan motor when the 

blower is not in use should not be considered in the engineering analysis. In addition,

DOE has not found any HVAC products that utilize a control relay or other mechanism to 

disconnect the ECM fan when the product in standby or off mode. Therefore, DOE did 

not consider this technology option for this rulemaking.
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4.3 REMAINING TECHNOLOGIES

After eliminating those technologies that have no effect or do not increase energy 

efficiency and screening out those technologies that that do not meet the requirements of 

sections 4(a)(4) and 5(b) of the Process Rule, DOE considered the technologies in the 

following sections.

4.3.1 Furnace Energy Efficiency Standards

For its AFUE standards rulemaking analysis, DOE considered the following 

technology options:

• Condensing secondary heat exchanger for non-weatherized furnaces

• Heat exchanger improvements for non-weatherized furnaces

o Increased heat exchanger surface area

o Heat exchanger surface features

o Heat exchanger baffles and turbulators

• Two-stage and modulating combustion

• Insulation improvements

o Increased jacket insulation

• Off-cycle dampers

o Electro-mechanical flue damper

o Electro-mechanical burner inlet damper

• Concentric venting

• High-static oil burner

• Delayed-action oil pump solenoid valve

4.3.2 Central Air Conditioner and Heat Pump Energy Efficiency Standards

For its SEER and HSPF standards rulemaking analysis, DOE considered the 

following technology options:

• Higher efficiency fan motors

• Higher efficiency fan blades

• Higher efficiency expansion valves

• Improved evaporator coils

• Improved condenser coils

• Higher efficiency compressors

• Microchannel heat exchangers

• Flat-tube heat exchangers

• Inverter technology

• Heat pump defrost cycle controls
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4.3.3 Standby Mode and Off Mode Power Consumption Standards

Because DOE is required by EPCA, as amended by EISA 2007, to include a 

descriptor for standby mode and off mode energy consumption for residential furnaces 

and a descriptor for off mode energy consumption for central air conditioners and heat 

pumps, a separate screening analysis was conducted for standby and off mode design 

options. (42 U.S.C. 6295(gg)(2)(A))

DOE identified the following design options that are capable of reducing the 

standby and off mode electrical power consumption of furnaces and central air 

conditioners and heat pumps, respectively:

Table 4.3.1 Screened-In Standby Mode and Off Mode Design Options

Design Option Residential 

Furnaces

Central Air 

Conditioners and 

Heat Pumps

Toroidal transformer X X

Switching mode power supply X

Thermostatically controlled crankcase 

heater X

Self-regulating (i.e., variable resistance) 

crankcase heater X

Compressor cover X
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REFERENCES

1 United States Patent US6684878, http://www.freepatentsonline.com/6684878.pdf

2 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.