7-B-i

APPENDIX 7-B. DETERMINATION OF BOILER ENERGY USE IN THE LIFECYCLE COST ANALYSIS

TABLE OF CONTENTS

7-B.1 INTRODUCTION ................................................................................................. 7-B-1

7-B.2 DETERMINATION OF SPACE HEATING ANNUAL FUEL ENERGY 

CONSUMPTION................................................................................................... 7-B-1

7-B.2.1 Thermal Efficiency Adjustments........................................................................... 7-B-2

7-B.2.1.1 Conversion Between Combustion Efficiency and Thermal 

Efficiency............................................................................................. 7-B-2

7-B.2.1.2 Adjustment to Rated Thermal Efficiency Based on Return Water 

Temperature Application, Part Load, and Cycling .............................. 7-B-3

7-B.2.1.3 Adjustment to Rated Thermal Efficiency Based on Part Load and 

Cycling................................................................................................. 7-B-7

7-B.2.2 Assigning Boiler Equipment Characteristics to Sampled Buildings ..................... 7-B-9

7-B.2.2.1 Input Capacity of Existing and New Equipment ............................... 7-B-13

7-B.2.3 Derivation of Existing Efficiencies...................................................................... 7-B-13

7-B.3 DETERMINATION OF ANNUAL ELECTRICAL ENERGY 

CONSUMPTION................................................................................................. 7-B-16

7-B.3.1 Boiler Electrical Components.............................................................................. 7-B-16

7-B.3.2 Standby Energy.................................................................................................... 7-B-17

LIST OF TABLES

Table 7-B.2.1 Linear Fit Parameters for Converting Combustion Efficiency to 

Thermal Efficiency .............................................................................. 7-B-3

Table 7-B.2.2 Return Water Temperatures at Each Outside Air Temperature Bin .... 7-B-4

Table 7-B.2.3 Adjustment to Thermal Efficiency Based on RWT Application and 

Part Load or Cycling Operation for Commercial Packaged Boilers.... 7-B-7

Table 7-B.2.4 Part Load and Cycling at Each Outside Air Temperature Bin............. 7-B-8

Table 7-B.2.5 Adjustment to Thermal Efficiency Based on Part-Load and 

Cycling Operation................................................................................ 7-B-9

Table 7-B.2.6 Range of Existing Heating Energy Use Based on CBECS 2003 and 

RECS 2009 Data for Each Boiler Equipment Class, MMBtu/year ... 7-B-10

Table 7-B.2.7 Range of Adjusted Heating Load for Each Boiler Equipment Class, 

MMBtu/year....................................................................................... 7-B-11

Table 7-B.2.8 Range of Baseline Boiler Heating Annual Operating Hours for 

Each Boiler Equipment Class, hours ................................................. 7-B-12

Table 7-B.2.9 Historical Efficiencies by Equipment Class, Natural Draft Boilers .. 7-B-14

Table 7-B.2.10 Historical Efficiencies by Equipment Class, Mechanical Draft 

Boilers................................................................................................ 7-B-14

Table 7-B.3.1 Electrical Component Power ............................................................. 7-B-17
7-B-ii

LIST OF FIGURES

Figure 7-B.2.1 Efficiency vs. Return Water Temperature, Condensing Boilers.......... 7-B-5

Figure 7-B.2.2 Average Curve for Condensing Boilers............................................... 7-B-5

Figure 7-B.2.3 Efficiency vs. Return Water Temperature, Non-Condensing 

Boilers.................................................................................................. 7-B-6

Figure 7-B.2.4 Fulton Caliber Condensing Boiler Relationship between Burner 

Input and Thermal Efficiency .............................................................. 7-B-8
7-B-1

APPENDIX 7-B. DETERMINATION OF BOILER ENERGY USE IN THE LIFECYCLE COST ANALYSIS

7-B.1 INTRODUCTION

For calculating the energy consumed by commercial packaged boilers, the U.S. 

Department of Energy (DOE) considers the energy use associated with providing space heating 

and domestic water heating. DOE develops a methodology for estimating the space heating and 

water heating energy use provided by boilers. The calculation to determine the total energy use 

per unit is as follows:

EEEEEE UU TTTTT = FF F SS + FF F W + E EE ETTTTT

Eq. 7-B.1

Where:

FF F SS = fuel used for space heating,

FF F W = fuel used for water heating, and

E EE ETTTTT = electrical energy use

Refer to Chapter 7 for the space heating and water heating energy use calculation 

methodology. This appendix provides details on some of the inputs used in the calculations.

7-B.2 DETERMINATION OF SPACE HEATING ANNUAL FUEL ENERGY 

CONSUMPTION

DOE calculates the annual fuel consumption (FuelUse) for each boiler using the 

following formula:

FF F SS = BBBSS × Qii

Eq. 7-B.2

Where:

BOHSH = space heating burner full-load operating hours (hr/yr), and

Qin = input capacity of existing boiler (kBtu/hr).

DOE derives space heating burner operating hours (BOH) from the building heating load 

served by a single boiler. Building heating load is determined from annual fuel consumption for 

heating reported in the U.S. Energy Information Administration (EIA) Commercial Buildings 
7-B-2

Energy Consumption Survey (CBECS) and Residential Energy Consumption Survey (RECS),

and is based on the efficiency of the existing boiler.a

7-B.2.1 Thermal Efficiency Adjustments

In the determination of the annual fuel energy consumption, DOE adjusts the rated 

thermal efficiency (TE) to account for the conversion between combustion efficiency and 

thermal efficiency when applicable, part-load operation (in the case of multi-stage equipment) 

and cycling losses (for single-stage equipment), as well as return water temperature (RWT).

7-B.2.1.1 Conversion Between Combustion Efficiency and Thermal Efficiency

DOE uses the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) database to 

determine the relationship between combustion efficiency and thermal efficiency for the four 

equipment classes with combustion efficiency as the efficiency metric.

1

, DOE develops a linear 

relationship between the two efficiency metrics from boiler models where both combustion 

efficiency and thermal efficiency are listed. The parameters are determined separately for gasfired and oil-fired boilers. The following formula illustrates the relationship between the two 

efficiency metrics:

T = a × C + b

Eq. 7-B.3

The linear fit parameters are in Table 7-B.2.1:

 

a CBECS is a national sample survey that collects information on the stock of U.S. commercial buildings, including 

their energy-related building characteristics and energy usage data (consumption and expenditures). See 

http://www.eia.gov/consumption/commercial/about.cfm. RECS is a nationally representative data sample of 

information about the energy characteristics of housing units, including usage patterns, and household 

demographics. This information is combined with data from energy suppliers to the homes to estimate energy costs 

and usage for heating, cooling, appliances and other end uses. See 

http://www.eia.gov/consumption/residential/index.cfm
7-B-3

Table 7-B.2.1 Linear Fit Parameters for Converting Combustion Efficiency to Thermal 

Efficiency

Oil Gas

a 0.9804 1.0867

b 0.4721 -8.0927

7-B.2.1.2 Adjustment to Rated Thermal Efficiency Based on Return Water 

Temperature Application, Part Load, and Cycling

Rated thermal efficiency and combustion efficiency for commercial packaged boilers are 

determined during laboratory testing under subpart E of Title 10 of the Code of Federal 

Regulations, Part 431 (10 CFR Part 431), section 431.86.b The DOE website for commercial 

packaged boilers provides additional information about the test procedure.

2 The test procedure 

prescribes a supply water temperature of 180°F. The test procedure allows a range of boiler inlet

water temperatures at which the boiler may be tested. DOE assumes that all boilers are rated at a

return water temperature of 80°F. The boiler return water temperature in typical installations 

varies by heating load and by heating application. DOE assumes that all boilers operate with 

supply water temperature reset. That is, at the peak heating load the supply water temperature is 

at its design temperature, or the highest temperature. At lower heating loads, the supply water 

temperature resets down to lower temperatures. In typical non-condensing boiler installations the 

design supply water temperature is 180°F and can reset down to 155°F. In typical condensing 

boiler installations the design supply water temperature is 160°F and can reset down to 104°F. 

Some condensing boilers are installed in high temperature applications, in which the supply 

water temperatures are higher, with a design of 180°F and resetting down to 130°F. DOE 

assumes an average temperature drop between the supply water temperature and the return water 

temperature of 20°F. See Table 7-B.2.2 for the assumed return water temperature as it varies 

with outside air temperature.

 

b See http://www.ecfr.gov/cgi-bin/textidx?type=simple;c=ecfr;cc=ecfr;sid=26fa9f9a78e320d5d603e37c3675a135;idno=10;region=DIV1;q1=431;rgn=div5

;view=text;node=10%3A3.0.1.4.19
7-B-4

Table 7-B.2.2 Return Water Temperatures at Each Outside Air Temperature Bin

Temperature 

Bin

Condensing 

Units - Low 

RWT (°F)

Condensing 

Units –

High RWT

(°F)

NonCondensing 

Units –

High RWT

(°F)

Over 68°F - - -

50 - 68°F 84 110 135

41 - 50°F 112 132 150

28 - 41°F 116 136 155

14 - 28°F 129 149 160

At or below 

14°F 140 160 160

The relationship between RWT and efficiency for both condensing and non-condensing 

commercial packaged boilers is described below.

Several manufacturers publish a relationship between boiler TE and RWT for certain 

boiler series.3, 4, 5, 6, 7 DOE uses the information to develop an average TE versus RWT 

relationship representative of boiler performance for a range of return water temperatures. The 

analysis assumes that the efficiencies scale according to the relationship reported for the TE. 

Figure 7-B.2.1 presents the information from these sources and the derived average efficiency 

curve for condensing boilers.

c

 

c The average efficiency curve represents the mean efficiency at each return water temperature reported in the 

manufacturers’ information. 
7-B-5

Figure 7-B.2.1 Efficiency vs. Return Water Temperature, Condensing Boilers

For condensing boilers, the analysis uses the average relationship shown in Figure 7-

B.2.2 to establish the magnitude of the efficiency adjustment required for the high and low 

temperature condensing boiler applications. As shown in Figure 7-B.2.2, the relationship 

indicates an approximate reduction of 8 percent thermal efficiency for an average return water 

temperature of 140°F and approximate reduction of 4.5 percent thermal efficiency for an average 

return water temperature of 115°F. 

Figure 7-B.2.2 Average Curve for Condensing Boilers

80

85

90

95

100

60 80 100 120 140 160 180

Thermal Efficiency (%)

Return Water Temperature

Boiler Efficiency vs Return Water Temperature

(Condensing)

Hydrotherm

Hydrotherm 2

Aerco

Burderus

ASHRAE

Deppman

Crest

Average Curve
7-B-6

For non-condensing boilers, the analysis uses the average efficiency/RWT relationship at 

the 140-180°F temperature range to establish the efficiency adjustment required for the high 

temperature applications. The data for temperatures between 140°F and 180°F is used to 

extrapolate the efficiency at 80°F using linear regression. As shown in Figure 7-B.2.3, the 

relationship resulted in an approximate reduction of 4.2 percent thermal efficiency for an average 

return water temperature of 155°F.

Figure 7-B.2.3 Efficiency vs. Return Water Temperature, Non-Condensing Boilers

As described above, DOE addresses three different water temperature scenarios: high 

temperature non-condensing (RWT 135°F to 160°F), high temperature condensing (RWT 110°F

to 160°F), and low temperature condensing (RWT 84°F to 140°F). DOE analyzes each of these 

three scenarios in each of the American Society of Heating, Refrigerating and Air Conditioning 

Engineers (ASHRAE) 16 climate zones. For each scenario, the annual average return water 

temperature is determined in each climate zone. For each average return water temperature, a 

thermal efficiency adjustment is determined per the figures above. The thermal efficiency 

adjustments in the analysis are shown in Table 7-B.2.3.
7-B-7

Table 7-B.2.3 Adjustment to Thermal Efficiency Based on RWT Application and Part 

Load or Cycling Operation for Commercial Packaged Boilers

ASHRAE 

Climate

ASHRAE 

Climate Condensing Non-Cond

Zone # Zone Code Low Temp High Temp High Temp

Operation Operation Operation

1 1A -4.07 -7.14 -4.03

2 2A -4.60 -7.55 -4.12

3 2B -4.18 -7.23 -4.05

4 3A -5.11 -7.89 -4.16

5 3B-CA -4.03 -7.10 -4.02

6 3B-other -4.45 -7.44 -4.11

7 3C -4.14 -7.19 -4.04

8 4A -5.52 -8.13 -4.19

9 4B -5.03 -7.84 -4.16

10 4C -4.49 -7.47 -4.11

11 5A -6.07 -8.38 -4.22

12 5B -5.79 -8.26 -4.20

13 6A -6.35 -8.48 -4.23

14 6B -6.14 -8.41 -4.22

15 7 -6.68 -8.58 -4.24

16 8 -7.10 -8.64 -4.26

7-B.2.1.3 Adjustment to Rated Thermal Efficiency Based on Part Load and 

Cycling

Typical non-condensing boilers may be single stage or two-stage, but do not often 

modulate beyond that. DOE assumes that all non-condensing boilers are single-stage. In a singlestage boiler when the load is low, the boiler cycles on and off to meet the load. The cycling 

produces losses as heat is lost to the mechanical room when the boiler cycles off. In view of 

information from consultants, DOE understands that the cycling losses increase as the heating 

load decreases. See Table 7-B.2.4 for the assumed cycling losses at different outside air 

temperatures.

Condensing boilers on the other hand typically modulate to meet the heating load. That 

is, if the heating load is low, then the firing rate will reduce in order to meet the load. Thermal 

efficiency increases as the boiler firing rate decreases. A typical relationship between burner 

input ratio and thermal efficiency is shown for one manufacturer in Figure 7-B.2.4. See Table 7-

B.2.4 for the fraction of boiler input capacity required at different outside air temperatures.
7-B-8

Figure 7-B.2.4 Fulton Caliber Condensing Boiler Relationship between Burner Input 

and Thermal Efficiencyd

Table 7-B.2.4 Part Load and Cycling at Each Outside Air Temperature Bin

Temperature 

Bin

Condensing 

Fraction of 

Boiler 

Capacity

NonCondensing 

Adjustment 

for Cycling

Over 68°F - -

50 - 68°F 20% -10%

41 - 50°F 40% -2%

28 - 41°F 60% -1%

14 - 28°F 80% 0%

At or below 

14°F 100% 0%

For each of the 16 ASHRAE Climate Zones, the average percentage that the boiler is 

loaded compared to its full capacity is calculated based on outside air temperature. In view of the 

average load percentage, a cycling-load adjustment and a part-load adjustment can be calculated

for non-condensing boilers and condensing boilers, respectively. These adjustments are given in 

Table 7-B.2.5.

 d Fulton Caliber Condensing Boiler, http://www.fulton.com/product-profile.php?ptc=hw&uid=40
7-B-9

Table 7-B.2.5 Adjustment to Thermal Efficiency Based on Part-Load and Cycling 

Operation

ASHRAE 

Climate 

ASHRAE 

Climate 

Condensing

Part Load

Non-Cond

Cycling

Zone # Zone Code Adj. Adj.

1 1A 2.15 -0.10

2 2A 1.65 -0.07

3 2B 2.03 -0.08

4 3A 1.41 -0.06

5 3B-CA 2.20 -0.10

6 3B-other 1.73 -0.06

7 3C 2.07 -0.09

8 4A 1.10 -0.05

9 4B 1.41 -0.05

10 4C 1.70 -0.06

11 5A 0.80 -0.04

12 5B 0.95 -0.04

13 6A 0.66 -0.04

14 6B 0.76 -0.04

15 7 0.51 -0.04

16 8 0.33 -0.04

7-B.2.2 Assigning Boiler Equipment Characteristics to Sampled Buildings

To estimate the heating load of each sample building, DOE represents the existing boiler 

by assigning an input capacity and efficiencies to the boiler in the CBECS and RECS sample 

building units. 

Table 7-B.2.6 shows the original CBECS 2003 and RECS 2009 heating energy use. 
7-B-10

Table 7-B.2.6 Range of Existing Heating Energy Use Based on CBECS 2003 and RECS 

2009 Data for Each Boiler Equipment Class, MMBtu/year

Equipment Class Min Max Average Percentiles

5% 25% 50% 75% 95%

Natural Draft Gas-Fired Hot Water 

Commercial Packaged Boiler ≥300,000 Btu/hr 

and ≤2,500,000 Btu/hr

0.0 17132.1 996.9 78.7 343.8 727.1 1202.3 2647.4

Natural Draft Gas-Fired Hot Water 

Commercial Packaged Boiler >2,500,000 

Btu/hr

0.0 39381.5 4016.3 172.4 1360.0 2881.9 5300.9 11697.8

Natural Draft Oil-Fired Hot Water Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

0.1 4641.0 773.9 6.6 62.4 601.6 1223.3 2163.9

Natural Draft Oil-Fired Hot Water Commercial 

Packaged Boiler >2,500,000 Btu/hr

0.0 24518.8 2863.6 16.9 443.8 2482.4 5122.5 7469.6

Natural Draft Gas-Fired Steam Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

3.5 17132.1 901.1 80.0 343.8 746.0 1194.1 2096.6

Natural Draft Gas-Fired Steam Commercial 

Packaged Boiler >2,500,000 Btu/hr

0.0 39381.5 4451.2 331.4 1729.6 3669.5 5811.4 12349.3

Natural Draft Oil-Fired Steam Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

6.1 4641.0 1086.6 116.0 598.3 950.3 1404.4 2238.3

Natural Draft Oil-Fired Steam Commercial 

Packaged Boiler >2,500,000 Btu/hr

0.0 13464.8 3598.2 37.0 761.4 4419.5 5227.4 8182.9

Mechanical Draft Gas-Fired Hot Water 

Commercial Packaged Boiler ≥300,000 Btu/hr

and ≤2,500,000 Btu/hr

0.0 17132.1 1022.1 78.7 350.6 740.5 1319.0 3017.6

Mechanical Draft Gas-Fired Hot Water 

Commercial Packaged Boiler >2,500,000 

Btu/hr

0.0 39381.5 3691.7 16.1 1137.1 2437.7 4928.4 10304.5

Mechanical Draft Oil-Fired Hot Water 

Commercial Packaged Boiler ≥300,000 Btu/hr 

and ≤2,500,000 Btu/hr

0.1 4641.0 855.9 44.6 259.6 639.7 1265.4 2238.3

Mechanical Draft Oil-Fired Hot Water 

Commercial Packaged Boiler >2,500,000 

Btu/hr

0.0 24518.8 2732.5 16.9 432.5 1802.8 5122.5 7144.8

Mechanical Draft Gas-Fired Steam 

Commercial Packaged Boiler ≥300,000 Btu/hr 

and ≤2,500,000 Btu/hr

3.5 17132.1 910.7 80.0 341.4 740.5 1194.1 2096.6

Mechanical Draft Gas-Fired Steam 

Commercial Packaged Boiler >2,500,000 

Btu/hr

0.0 39381.5 4358.7 294.1 1729.6 3657.8 5507.4 12098.5

Mechanical Draft Oil-Fired Steam Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

6.1 4641.0 1067.8 116.0 580.1 938.3 1404.4 2235.9

Mechanical Draft Oil-Fired Steam Commercial 

Packaged Boiler >2,500,000 Btu/hr

0.0 13464.8 3600.2 37.0 761.4 4419.5 5227.4 8182.9

Table 7-B.2.7 shows the results for the range in adjusted heating load among sample 

buildings and households.
7-B-11

Table 7-B.2.7 Range of Adjusted Heating Load for Each Boiler Equipment Class, 

MMBtu/year

Equipment Class Min Max Average Percentiles

5% 25% 50% 75% 95%

Natural Draft Gas-Fired Hot Water 

Commercial Packaged Boiler ≥300,000 Btu/hr 

and ≤2,500,000 Btu/hr

0.0 10507.2 587.7 45.9 208.3 430.7 708.5 1575.0

Natural Draft Gas-Fired Hot Water 

Commercial Packaged Boiler >2,500,000 

Btu/hr

0.0 22755.8 2400.7 106.8 808.6 1709.2 3161.1 6790.7

Natural Draft Oil-Fired Hot Water Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

0.1 2832.7 460.7 4.0 37.0 363.1 719.1 1307.8

Natural Draft Oil-Fired Hot Water Commercial 

Packaged Boiler >2,500,000 Btu/hr

0.0 15125.7 1697.5 10.3 270.0 1487.4 3010.0 4189.1

Natural Draft Gas-Fired Steam Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

2.3 10084.6 508.7 44.3 203.9 413.3 668.9 1198.6

Natural Draft Gas-Fired Steam Commercial 

Packaged Boiler >2,500,000 Btu/hr

0.0 22089.4 2522.5 184.1 975.3 2099.5 3260.4 6899.3

Natural Draft Oil-Fired Steam Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

3.7 2785.6 635.1 69.4 346.9 575.5 810.5 1332.4

Natural Draft Oil-Fired Steam Commercial 

Packaged Boiler >2,500,000 Btu/hr

0.0 7915.3 2093.4 22.1 451.9 2522.4 3022.4 4725.0

Mechanical Draft Gas-Fired Hot Water 

Commercial Packaged Boiler ≥300,000 Btu/hr 

and ≤2,500,000 Btu/hr

0.0 11502.6 662.4 50.3 228.7 477.7 850.1 1924.6

Mechanical Draft Gas-Fired Hot Water 

Commercial Packaged Boiler >2,500,000 

Btu/hr

0.0 23818.0 2273.4 10.1 689.9 1517.8 2991.1 6281.9

Mechanical Draft Oil-Fired Hot Water 

Commercial Packaged Boiler ≥300,000 Btu/hr

and ≤2,500,000 Btu/hr

0.1 2915.1 523.7 27.3 160.7 419.7 779.4 1388.0

Mechanical Draft Oil-Fired Hot Water 

Commercial Packaged Boiler >2,500,000 

Btu/hr

0.0 15544.2 1661.2 10.6 272.0 1118.4 3052.4 4253.5

Mechanical Draft Gas-Fired Steam 

Commercial Packaged Boiler ≥300,000 Btu/hr 

and ≤2,500,000 Btu/hr

2.4 10301.3 526.5 45.3 189.3 424.2 684.2 1224.8

Mechanical Draft Gas-Fired Steam 

Commercial Packaged Boiler >2,500,000 

Btu/hr

0.0 22427.7 2510.3 166.2 975.6 2119.6 3224.7 6860.2

Mechanical Draft Oil-Fired Steam Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

3.7 2806.6 629.4 70.0 341.5 553.2 811.7 1335.7

Mechanical Draft Oil-Fired Steam Commercial 

Packaged Boiler >2,500,000 Btu/hr

0.0 7895.2 2090.0 22.1 450.7 2516.3 3014.7 4712.6
7-B-12

Table 7-B.2.8 shows the results for the baseline heating boiler operating hours among 

sample buildings and households.

Table 7-B.2.8 Range of Baseline Boiler Heating Annual Operating Hours for Each 

Boiler Equipment Class, hours

Equipment Class Min Max Average Percentiles

5% 25% 50% 75% 95%

Natural Draft Gas-Fired Hot Water Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

0.0 8760.0 1035.0 88.8 415.7 803.1 1329.9 2766.2

Natural Draft Gas-Fired Hot Water Commercial 

Packaged Boiler >2,500,000 Btu/hr 0.0 6956.7 757.0 42.5 271.6 607.1 978.9 2081.1

Natural Draft Oil-Fired Hot Water Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

0.1 4688.1 936.2 4.3 87.1 864.0 1412.4 2272.3

Natural Draft Oil-Fired Hot Water Commercial 

Packaged Boiler >2,500,000 Btu/hr 0.0 3907.6 585.6 3.8 78.8 494.5 939.6 1494.3

Natural Draft Gas-Fired Steam Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

6.3 8760.0 1000.0 100.4 490.8 885.7 1283.1 2375.7

Natural Draft Gas-Fired Steam Commercial 

Packaged Boiler >2,500,000 Btu/hr 0.0 7125.8 861.5 87.3 388.7 883.3 1110.5 1890.1

Natural Draft Oil-Fired Steam Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

2.2 4666.9 1197.2 112.7 735.8 1280.5 1524.6 2119.1

Natural Draft Oil-Fired Steam Commercial 

Packaged Boiler >2,500,000 Btu/hr 0.0 3905.9 734.9 5.6 189.6 833.6 1099.5 1655.6

Mechanical Draft Gas-Fired Hot Water 

Commercial Packaged Boiler ≥300,000 Btu/hr 

and ≤2,500,000 Btu/hr

0.0 8760.0 1121.5 95.8 435.2 901.9 1446.9 2589.6

Mechanical Draft Gas-Fired Hot Water 

Commercial Packaged Boiler >2,500,000 Btu/hr 0.0 7281.4 714.4 4.1 267.6 595.8 963.7 1749.2

Mechanical Draft Oil-Fired Hot Water 

Commercial Packaged Boiler ≥300,000 Btu/hr

and ≤2,500,000 Btu/hr

0.1 4830.2 1024.0 51.9 197.3 1024.0 1472.5 2298.1

Mechanical Draft Oil-Fired Hot Water 

Commercial Packaged Boiler >2,500,000 Btu/hr 0.0 4015.2 574.6 3.9 78.5 457.5 917.0 1448.2

Mechanical Draft Gas-Fired Steam Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

6.3 8760.0 1003.7 98.4 485.1 875.7 1285.4 2364.8

Mechanical Draft Gas-Fired Steam Commercial 

Packaged Boiler >2,500,000 Btu/hr 0.0 7041.3 838.1 76.3 381.4 854.6 1089.6 1863.9

Mechanical Draft Oil-Fired Steam Commercial 

Packaged Boiler ≥300,000 Btu/hr and 

≤2,500,000 Btu/hr

2.2 4703.5 1184.1 113.0 722.8 1288.4 1519.4 2081.4

Mechanical Draft Oil-Fired Steam Commercial 

Packaged Boiler >2,500,000 Btu/hr 0.0 3896.0 730.1 5.6 189.0 831.4 1096.7 1651.4
7-B-13

7-B.2.2.1 Input Capacity of Existing and New Equipment

The determination of the input capacity of the boiler accounts for the adjusted heating

load of the building (adjusted with the considerations described above), the efficiency of the 

existing boiler, and the oversize factor. The boiler input capacity is assumed to be the same for 

the existing boiler and the boiler being considered under the standard.

Qii = AAA A A AAA A

T ee e e

× O OO F

Eq. 7.1

Where:

AdjustedHeatLoad = estimated building heat loss adjusted for building weather location

(kBtu/h), 

TEexisting = TE of the existing boiler for each equipment class, and,

OversizeFactor = 1.1, based on input from consultants on typical sizing practices.

DOE calculates the adjusted heating load for each sample building based on the 

applicable building characteristics and outdoor conditions derived from the CBECS and RECS 

data. DOE assumed a nominal heating load of 30 btu/h/sqft based on industry standard.

8 DOE 

determined the heated building area by multiplying the reported building area by the reported 

percentage of area heated. DOE then adjusted this load by the design outdoor air temperature of 

the climate region.

The derivation of the existing boiler efficiency is described in Section 7-B.2.3. The boiler 

input capacity is assumed to be the same for the existing boiler and the boiler being considered 

under the standard.

7-B.2.3 Derivation of Existing Efficiencies

As described in Chapter 7, the efficiency of existing equipment already installed is 

required to calculate the building heating load. DOE develops the historical distributions of 

efficiencies by equipment class for existing boilers based on the AHRI database from 2007 to 

2009. DOE calculates the average efficiency of all boilers in each equipment class from the 2009 

AHRI database to determine the existing efficiency for the year 2009. This calculated average is 

assumed to be the representative efficiency for that equipment class in 2009. The same process 

was used to determine the existing efficiencies in 2007 and 2008. DOE assumes that in 2005 and 

2006 the existing efficiencies were equal to those in 2007. From 1973 to 2004 DOE has assumed 

that the existing efficiency reduced by 1 percent every 5 years. For all years prior to 1973 DOE 

has assumed that the efficiency was equal to that in 1973. See the historical efficiencies by 

equipment class in Table 7-B.2.15 and Table 7-B.2.16.
7-B-14

Table 7-B.2.9 Historical Efficiencies by Equipment Class, Natural Draft Boilers

SGNDHW LGNDHW SONDHW LONDHW SGNDST LGNDST SONDST LONDST

TE CE TE CE TE TE TE TE

1973 75 75 76 78 71 72 74 75

1974 75 75 76 78 71 72 74 75

1975 76 76 77 79 72 73 75 76

1976 76 76 77 79 72 73 75 76

1977 76 76 77 79 72 73 75 76

1978 76 76 77 79 72 73 75 76

1979 76 76 77 79 72 73 75 76

1980 77 77 78 80 73 74 76 77

1981 77 77 78 80 73 74 76 77

1982 77 77 78 80 73 74 76 77

1983 77 77 78 80 73 74 76 77

1984 77 77 78 80 73 74 76 77

1985 78 78 79 81 74 75 77 78

1986 78 78 79 81 74 75 77 78

1987 78 78 79 81 74 75 77 78

1988 78 78 79 81 74 75 77 78

1989 78 78 79 81 74 75 77 78

1990 79 79 80 82 75 76 78 79

1991 79 79 80 82 75 76 78 79

1992 79 79 80 82 75 76 78 79

1993 79 79 80 82 75 76 78 79

1994 79 79 80 82 75 76 78 79

1995 80 80 81 83 76 77 79 80

1996 80 80 81 83 76 77 79 80

1997 80 80 81 83 76 77 79 80

1998 80 80 81 83 76 77 79 80

1999 80 80 81 83 76 77 79 80

2000 81 81 82 84 77 78 80 81

2001 81 81 82 84 77 78 80 81

2002 81 81 82 84 77 78 80 81

2003 81 81 82 84 77 78 80 81

2004 81 81 82 84 77 78 80 81

2005 82 82 83 85 78 79 81 82

2006 82 82 83 85 78 79 81 82

2007 82 82 83 85 78 79 81 82

2008 82 82 83 85 78 79 81 82

2009 82 82 83 85 78 79 81 82

Table 7-B.2.10 Historical Efficiencies by Equipment Class, Mechanical Draft Boilers
7-B-15

SGMDHW LGMDHW SOMDHW LOMDHW SGMDST LGMDST SOMDST LOMDST

TE CE TE CE TE TE TE TE

1973 78 77 76 78 73 73 75 75

1974 78 77 76 78 73 73 75 75

1975 79 78 77 79 74 74 76 76

1976 79 78 77 79 74 74 76 76

1977 79 78 77 79 74 74 76 76

1978 79 78 77 79 74 74 76 76

1979 79 78 77 79 74 74 76 76

1980 80 79 78 80 75 75 77 77

1981 80 79 78 80 75 75 77 77

1982 80 79 78 80 75 75 77 77

1983 80 79 78 80 75 75 77 77

1984 80 79 78 80 75 75 77 77

1985 81 80 79 81 76 76 78 78

1986 81 80 79 81 76 76 78 78

1987 81 80 79 81 76 76 78 78

1988 81 80 79 81 76 76 78 78

1989 81 80 79 81 76 76 78 78

1990 82 81 80 82 77 77 79 79

1991 82 81 80 82 77 77 79 79

1992 82 81 80 82 77 77 79 79

1993 82 81 80 82 77 77 79 79

1994 82 81 80 82 77 77 79 79

1995 83 82 81 83 78 78 80 80

1996 83 82 81 83 78 78 80 80

1997 83 82 81 83 78 78 80 80

1998 83 82 81 83 78 78 80 80

1999 83 82 81 83 78 78 80 80

2000 84 83 82 84 79 79 81 81

2001 84 83 82 84 79 79 81 81

2002 84 83 82 84 79 79 81 81

2003 84 83 82 84 79 79 81 81

2004 84 83 82 84 79 79 81 81

2005 85 84 83 85 80 80 82 82

2006 85 84 83 85 80 80 82 82

2007 85 84 83 85 80 80 82 82

2008 87 85 84 85 80 81 82 82

2009 87 85 84 86 80 81 82 82
7-B-16

7-B.3 DETERMINATION OF ANNUAL ELECTRICAL ENERGY 

CONSUMPTION 

DOE calculates the electricity consumption as:

E EE E = BBBSS × AAABB × E EEE EEE + E EE W × E EEE EEE

+S × S

Eq. 7-B.4

Where:

BOHSH = as defined previously,

AdjBOH = adjustment factor that takes into account part-load operation (for condensing units 

only),

ElecPower = power of multiple electrical components required during boiler operation, (kW),

ElecBOHWH = assumed to be 20 percent of BOHSH adjusted for part-load operation,

StdbyPower = total standby power of the equipment, and

StdbyHrs = standby hours, takes into account water heating times in the summer

7-B.3.1 Boiler Electrical Components

DOE assumes that all hot water boilers have a circulating water pump. DOE assumes that 

small boilers have the same size pump and, likewise, large boilers have the same size pump. 

Table 7-B.3.1 depicts the applicable input power in watts for the circulating water pump and the 

draft inducer.
7-B-17

Table 7-B.3.1 Electrical Component Power

Water 

Pump 

Electrical 

Power

(watts)

Draft 

Inducer 

Electrical 

Power

(watts)

SGNDHW 250 0

LGNDHW 950 0

SONDHW 250 0

LONDHW 950 0

SGNDST 250 0

LGNDST 950 0

SONDST 250 0

LONDST 950 0

SGMDHW 250 250

LGMDHW 950 500

SOMDHW 250 250

LOMDHW 950 500

SGMDST 250 250

LGMDST 950 500

SOMDST 250 250

LOMDST 950 500

7-B.3.2 Standby Energy

DOE assumes that mechanical draft boilers have a standby power of 10.5 watts, based on 

the engineering analysis done for the Residential Boilers rulemaking. 9 Also, DOE assumes that 

natural draft boiler does not use any power while in standby mode.
7-B-18

REFERENCES

1. Air Conditioning Heating and Refrigeration Institute, Directory of Certified Product 

Performance for Commercial Boilers, 2014. (Last accessed 5/26/2014, 2014.) 

<http://www.ahridirectory.org/ahridirectory/pages/home.aspx>

2. U.S. Department of Energy-Office of Energy Efficiency and Renewable Energy, Energy 

Efficiency Program for Certain Commercial and Industrial Equipment: Test Procedures 

and Efficiency Standards for Commercial Packaged Boilers, October 21, 2004. 

Washington, DC. 

3. Lochinvar, Crest Condensing Boiler, 2013. Lochinvar. (Last accessed October 11, 

2013.) <http://www.lochinvar.com/_linefiles/FBN-04.pdf>

4. Buderus, SB Series Commercial Condensing Boilers, 2008. Bosch Thermotechnology 

Corp. (Last accessed October 11, 2013.) 

<http://www.buderus.us/files/201001151453140.sb_series12-08V21.pdf>

5. HydroTherm, HydroTherm KN Series, (Last accessed October 11, 2013.) 

<http://mesteksa.com/fileuploads/Literature/Hydrotherm%20Boilers/KN%20Series%20B

oiler/KN%20Series%20Catalog%20%28KNAP-3%291.pdf>

6. Hall, N., The Importance of Turndown Ratio in Condensing Boilers & Water Heaters, 

2009. R.L. Deppmann Co. (Last accessed October 11, 2013.) 

<http://www.deppmann.com/2009/10/19th/>

7. Benchmark 2.0 Low NOx Boiler, 2013. AERCO. (Last accessed October 11, 2013.) 

<http://www.aerco.com/Products/Boilers/Benchmark-Boilers/Benchmark-2-0-Low-NOxBoiler>

8. Jr., A. A. B., Part 7: Heating Load Rules of Thumb. In HVAC Equations, Data, and Rules 

of Thumb. 2000. McGraw-Hill: San Francisco

9. U.S. Department of Energy - Energy Efficiency & Renewable Energy, Energy 

Conservation Program for Consumer Products: Technical Support Document: Energy 

Efficiency Standards for Consumer Products: Residential Boilers, 2014. Washington, 

DC.