Note:

On and after May 28, 2024, any representations made with respect to the energy use or efficiency of commercial warm air furnaces must be made in accordance with the results of testing pursuant to this section. At that time, manufacturers must use the relevant procedures specified in this appendix, which reference ANSI Z21.47-2021, ASHRAE 103-2022, UL 727-2018, or AHRI 1500-2015. On and after July 3, 2023 and prior to May 28, 2024, manufacturers must test commercial warm air furnaces in accordance with this appendix or 10 CFR 431.76 as it appeared on January 1, 2023. DOE notes that, because testing under this section is required as of May 28, 2024, manufacturers may wish to begin using this amended test procedure as soon as possible. Any representations made with respect to the energy use or efficiency of such commercial warm air furnaces must be made in accordance with whichever version is selected.

Manufacturers must use the results of testing under appendix B to this subpart to determine compliance with any standards for commercial warm air furnaces that use the thermal efficiency 2 (TE2) metric.

0. Incorporation by reference.

In § 431.75, DOE incorporated by reference the entire standard for AHRI 1500-2015, ANSI Z21.47-2021, ASHRAE 103-2022, ASME PTC 19.3-1974 (R2004), ASTM D240-09, ASTM D396-14a, ASTM D4809-09a, ASTM D5291-10, ASTM E230/E230M-17, NFPA 97-2003, and UL 727-2018. However, for standards AHRI 1500-2015, ANSI Z21.47-2021, ASHRAE 103-2022, and UL 727-2018, only the enumerated provisions of those documents apply to this appendix, as follows:

0.1 ANSI Z21.47-2021

(a) Sections 5.1, 5.1.4, 5.2, 5.3, 5.4, 5.5, 5.5.1, 5.6, and 7.2.1 as specified in section 1.1 of this appendix;

(b) Section 5.40 as specified in sections 1.1 and 3.1 of this appendix;

(c) Section 5.2.8 as specified in section 4.1 of this appendix;

(d) Annex I as specified in section 3.1 of this appendix.

0.2 ASHRAE 103-2022

(a) Sections 7.2.2.4, 7.8, and 9.2 as specified in section 2.2 of this appendix;

(b) Sections 11.3.7.1 and 11.3.7.2 as specified in section 4.1 of this appendix.

0.3 UL 727-2018

(a) Sections 2, 3, 37, 38 and 39, 40, 40.6, 41, 42, 43.2, 44, 45, and 46 as specified in section 1.2 of this appendix;

(b) Figure 40.3 as specified in section 2.1 of this appendix.

0.4 AHRI 1500-2015

(a) Section C3.2.1.1 as specified in section 1.2 of this appendix;

(b) Sections C7.2.4, C7.2.5, and C7.2.6.2 as specified in section 3.2 of this appendix.

1. Test setup and Testing. Where this section prescribes use of ANSI Z21.47-2021 or UL 727-2018, perform only the procedures pertinent to the measurement of the steady-state efficiency, as specified in this section.

1.1 Gas-fired commercial warm air furnaces. The test setup, including flue requirement, instrumentation, test conditions, and measurements for determining thermal efficiency are as specified in section 1.3 of this appendix, and the following sections of ANSI Z21.47-2021: 5.1 (General, including ASME PTC 19.3-1974 (R2004) as referenced in Section 5.1.4), 5.2 (Basic test arrangements), 5.3 (Test ducts and plenums), 5.4 (Test gases), 5.5 (Test pressures and burner adjustments), 5.6 (Static pressure and air flow adjustments), 5.40 (Thermal efficiency), and 7.2.1 (Basic test arrangements for direct vent central furnaces). If section 1.3 of this appendix and ANSI Z21.47-2021 have conflicting provisions (e.g., the number of thermocouples that should be used when testing units with flue outlets that have a cross-sectional area of 3.14 square inches or less), follow the provisions in section 1.3 of this appendix. The thermal efficiency test must be conducted only at the normal inlet test pressure, as specified in section 5.5.1 of ANSI Z21.47-2021, and at the maximum hourly Btu input rating specified by the manufacturer for the product being tested.

1.2 Oil-fired commercial warm air furnaces. The test setup, including flue requirement, instrumentation, test conditions, and measurement for measuring thermal efficiency is as specified in section 1.3 of this appendix and the following sections of UL 727-2018: 2 (Units of Measurement), 3 (Glossary, except that the definitions for “combustible” and “non-combustible” in sections 3.11 and 3.27 shall be as referenced in NFPA 97-2003), 37 (General), 38 and 39 (Test Installation), 40 (Instrumentation, except 40.4 and 40.6.2 through 40.6.7 which are not required for the thermal efficiency test, and including ASTM E230/E230M-17 as referenced in Sections 40.6), 41 (Initial Test Conditions), 42 (Combustion Test—Burner and Furnace), 43.2 (Operation Tests), 44 (Limit Control Cutout Test), 45 (Continuity of Operation Test), and 46 (Air Flow, Downflow or Horizontal Furnace Test). If section 1.3 of this appendix and UL 727-2018 have conflicting provisions (e.g., the number of thermocouples that should be used when testing units with flue outlets that have a cross-sectional area of 3.14 inches or less), follow the provisions in section 1.3 of this appendix. Conduct a fuel oil analysis for heating value, hydrogen content, carbon content, pounds per gallon, and American Petroleum Institute (API) gravity as specified in section C3.2.1.1 of AHRI 1500-2015, including the applicable provisions of ASTM D240-09, ASTM D4809-09a, ASTM D5291-10, and ASTM D396-14a, as referenced. The steady-state combustion conditions, specified in section 42.1 of UL 727-2018, are attained when variations of not more than 5 °F in the measured flue gas temperature occur for three consecutive readings taken 15 minutes apart.

1.3 Additional test setup requirements for gas-fired and oil-fired commercial warm air furnaces

1.3.1 Thermocouple setup for gas-fired and oil-fired commercial warm air furnaces with flue outlets that have a cross-sectional area of 3.14 square inches or less. For units with flue outlets having a cross-sectional area of 3.14 square inches or less, the flue gas temperatures may optionally be measured using five individual thermocouples, instead of nine thermocouples.

1.3.2 Procedure for flue gas measurements when testing units with multiple flue outlets. For units that have multiple flue outlets, record flue gas measurements (e.g., flue gas temperature, CO2 in the flue gasses) separately for each individual flue outlet and calculate a weighted-average value based on the readings of all flue outlets. To determine the weighted average for each measurement, first determine the input rating of the furnace module associated with each flue outlet. Then multiply the ratio of the input rating for the furnace module associated with each individual flue outlet to the total nameplate input rating of the furnace (i.e., the input rating associated with each individual flue outlet divided by the total nameplate input rating) by that flue outlet's respective component measurement and the sum of all of the products of the calculations for all of the flue outlets to determine the weighted-average values. Use the weighted-average values to determine flue loss, and whether equilibrium conditions are met before the official test period.

2. Additional test measurements

2.1 Determination of flue CO2 (carbon dioxide) or O2 (oxygen) for oil-fired commercial warm air furnaces. In addition to the flue temperature measurement specified in section 40.6.8 of UL 727-2018, locate one or two sampling tubes within six inches downstream from the flue temperature probe (as indicated on Figure 40.3 of UL 727-2018). If an open end tube is used, it must project into the flue one-third of the chimney connector diameter. If other methods of sampling the flue gas are used, place the sampling tube so as to obtain an average sample. There must be no air leak between the temperature probe and the sampling tube location. Collect the flue gas sample at the same time the flue gas temperature is recorded. The CO2 or O2 concentration of the flue gas must be as specified by the manufacturer for the product being tested, with a tolerance of ±0.1 percent. Determine the flue CO2 or O2 using an instrument with a reading error no greater than ±0.1 percent.

2.2 Procedure for the measurement of condensate for a gas-fired condensing commercial warm air furnace. The test procedure for the measurement of the condensate from the flue gas under steady-state operation must be conducted as specified in sections 7.2.2.4, 7.8, and 9.2 of ASHRAE 103-2022 under the maximum rated input conditions. This condensate measurement must be conducted for an additional 30 minutes of steady-state operation after completion of the steady-state thermal efficiency test specified in section 1.1 of this appendix.

3. Calculation of thermal efficiency

3.1 Gas-fired commercial warm air furnaces. Use the calculation procedure specified in Section 5.40, Thermal efficiency, of ANSI Z21.47-2021. When determining the flue loss that is used in the calculation of thermal efficiency, the calculation method specified in Annex I of ANSI Z21.47-2021 shall be used.

3.2 Oil-fired commercial warm air furnaces. Calculate the percent flue loss (in percent of heat input rate) by following the procedure specified in sections C7.2.4, C7.2.5, and C7.2.6.2 of the AHRI 1500-2015. The thermal efficiency must be calculated as: Thermal Efficiency (percent) = 100 percent − flue loss (in percent).

4. Procedure for the calculation of the additional heat gain and heat loss, and adjustment to the thermal efficiency, for a condensing commercial warm air furnace.

4.1 Calculate the latent heat gain from the condensation of the water vapor in the flue gas, and calculate heat loss due to the flue condensate down the drain, as specified in sections 11.3.7.1 and 11.3.7.2 of ASHRAE 103-2022, with the exception that in the equation for the heat loss due to hot condensate flowing down the drain in section 11.3.7.2, the assumed indoor temperature of 70 °F and the temperature term TOA must be replaced by the measured room temperature as specified in section 5.2.8 of ANSI Z21.47.

4.2 Adjustment to the thermal efficiency for condensing commercial warm air furnaces. Adjust the thermal efficiency as calculated in section 3.1 of this appendix by adding the latent gain, expressed in percent, from the condensation of the water vapor in the flue gas, and subtracting the heat loss (due to the flue condensate down the drain), also expressed in percent, both as calculated in section 4.1 of this appendix, to obtain the thermal efficiency of a condensing furnace.

[88 FR 36234, June 2, 2203]