What Does It Mean That a Furnace is “Two Stage” or “Modulating”?

Did you ever notice that when your furnace reaches the temperature set by the thermostat it will shut off, often leaving areas of the home that are still cool? Then, when the temperature gets low again and tells the furnace to turn back on there are blasts of hot air out of the registers creating another period of discomfort. Two stage and modulating furnaces are designed to counter that effect and stabilize the comfort in your home all while reducing your energy bills.

nahb_logoThe National Association of Home builders likens a standard furnace to stop and go traffic, with its inefficient use of energy for your car and frustration for you. Two stage and modulating furnaces are designed to allow the system to run at lower, more efficient levels providing more consistent comfort. Two stage furnaces are just that…2 stages. These models have two settings allowing the system to run at 50% and 100% capacities when needed. The modulating furnaces will adjust automatically between 35% and 100% in small .50 – .65% increments, continuously regulating the amount of fuel burned according to the thermostat setting.

2_Stage_ChartTypically, both of these types of gas furnaces, such as York’s High Efficiency Two Stage Gas Furnaces and Modulating Furnaces, combine the multi-position gas valve with a variable speed blower. These features working together provide the benefits of quiet operation and less energy use with annual fuel utilization efficiency (AFUE) of 95-98%. Comfort can be significantly enhanced with two stage and modulating furnaces by keeping a more even temperature compared to a 4-6 degree swing in temperature often seen in St. Louis which is typical with standard, single stage furnaces.

High efficiency two stage and modulating furnaces are Energy Star rated and qualify for the highest level of rebates offered through Laclede Gas’ rebate program.