(Effective July 1, 2023)

PDFWAC 51-11C-403325

Table C403.3.2(5)Minimum efficiency requirementsWarm air furnaces and unit heaters.

Table C403.3.2(5)
Warm Air Furnaces and Combination Warm Air Furnaces/Air-Conditioning Units, Warm Air Duct Furnaces and Unit HeatersMinimum Efficiency Requirements
Equipment Type
Size Category (Input)
Subcategory or Rating Condition
Minimum Efficiencyd,c
Test Procedurea
Warm-air furnace, gas fired for application outside the U.S.
< 225,000 Btu/h
Maximum capacityc
80% AFUE (nonweatherized) or
1% AFUE (weatherized) or 80% Etb,d
DOE 10 C.F.R. 430 Appendix N or Section 2.39, Thermal Efficiency, ANSI Z21.47
Warm-air furnace, gas fired
< 225,000 Btu/h
Maximum capacityc
80% Etb,d before 1/1/2023
81% Etd after 1/1/2023
Section 2.39, Thermal Efficiency, ANSI Z21.47
Warm-air furnace, oil fired
< 225,000 Btu/h
Maximum capacityc
83% AFUE (nonweatherized) or
78% AFUE (weatherized) or 80% Etb,d
DOE 10 C.F.R. 430 Appendix N or Section 42, Combustion UL 727
Warm-air furnace, oil fired
< 225,000 Btu/h
Maximum capacityc
80% Et before 1/1/2023
82% Etd after 1/1/2023
Section 42, Combustion UL 727
Electric furnaces for applications outside the U.S.
< 225,000 Btu/h
All
96% AFUE
DOE 10 C.F.R. 430 Appendix N
Warm air duct furnaces, gas fired
All capacities
Maximum capacityc
80% Ece
Section 2.10, Efficiency, ANSI Z83.8
Warm air unit heaters, gas fired
All capacities
Maximum capacityc
80% Ece,f
Section 2.10, Efficiency, ANSI Z83.8
Warm air unit heaters, oil fired
All capacities
Maximum capacityc
80% Ece,f
Section 40, Combustion, UL 731
For SI: 1 British thermal unit per hour = 0.2931 W.
 
a
Chapter 6 contains a complete specification of the referenced standards, which include test procedures, including the referenced year version of the test procedure.
 
b
Combination units (i.e., furnaces contained within the same cabinet as an air conditioner) not covered by DOE 10 C.F.R. 430 (i.e., 3-phase power or with cooling capacity greater than or equal to 65,000 Btu/h) may comply with either rating. All other units greater than 225,000 Btu/h sold in the U.S. must meet the AFUE standards for consumer products and testing using U.S. DOE's AFUE test procedure at DOE 10 C.F.R. 430 Subpart B, Appendix N.
 
c
Compliance of multiple firing rate units shall be at the maximum firing rate.
 
d
Et
=
Thermal efficiency. Units must also include an interrupted or intermittent ignition device (IID), have jacket losses not exceeding 0.75 percent of the input rating, and have either power venting or a flue damper. A vent damper is an acceptable alternative to a flue damper for those furnaces where combustion air is drawn from the conditioned space.
 
e
Ec
=
Combustion efficiency (100% less flue losses). See test procedure for detailed discussion.
 
f
Units must also include an interrupted or intermittent ignition device (IID) and have either power venting or an automatic flue damper.
 
g
This table is a replica of ASHRAE 90.1 Table 6.8.1-5 Warm-Air Furnaces and Combination Warm-Air Furnaces/Air-Conditioning Units, Warm-Air Duct Furnaces, and Unit HeatersMinimum Efficiency Requirements.
[Statutory Authority: RCW 19.27A.020, 19.27A.025, 19.27A.160 and chapters 19.27A and 19.27 RCW. WSR 22-14-091, § 51-11C-403325, filed 7/1/22, effective 7/1/23.]