The primary measure of efficiency for gas furnaces is the Annual Fuel Utilization Efficiency (AFUE), which is a measure of the percentage of heat produced for every unit volume of fuel consumed per year. Energy efficiencies for gas furnaces can be gained through:
- Condensing (multiple heat exchangers) to capture waste heat
- Heat exchanger improvements
- Two-stage and modulating combustion (to reduce cycling)
- Low nitrogen oxide premix burners
- Insulation improvements
- Direct and/or concentric venting
- Off-cycle dampers
- More efficient blower motors
The RTF's measure applies to ENERGY STAR or CEE Tier 2 furnaces with an AFUE of 0.95+ or CEE Tier 3 furnaces with an AFUE of 0.97+. Applicable furnaces are in existing single family or manufactured homes with a heating output of less than 225,000 BTU per hour.
The savings analysis uses SEEM runs of RBSA homes with gas furnaces to estimate gas heating consumption for homes by type and heating zone. These values are then adjusted to target AFUEs of interest for the measure (Current Practice baseline AFUE by heating zone and AFUE for each efficiency tier) using the ratio of target AFUE to average AFUE.