Top-rated gas furnaces share common characteristics such as modular operation, increased efficiency and comfort and lower energy bills, according to a WebHVAC comparison. Brands that share these attributes include the Carrier Infinity Series, Lennox Signature Collection SLP98V, Heil QuietComfort EC97, Armstrong A97MV and Bryant 987M Evolution.
Modulating furnaces are equipped with gas valves that operate at variable capacity of 40 to 100 percent, depending on the moment's precise heating requirements. In contrast, older furnaces operate at either a high or low setting, either to increase heating temperature or to maintain heating comfort. Modulating furnaces achieve highly balanced temperatures, resulting in better indoor comfort, higher efficiency and heating cycles.
The annual fuel utilization efficiencies of top-rated modulating furnaces range from 97 percent for the Heil QuietComfort EC97 to 98.5 percent for the Carrier Infinity 98. At such efficiencies, only 1.5 to 3 percent of the heat generated is wasted. A secondary heat exchanger traps any heat that is not transferred by the primary heat exchanger, resulting in lower energy bills.