Simply put, a multi-stage furnace is one that has more than one speed so they can produce heat at different rates.
By contrast, most of us grew up in a home with a single-stage furnace that has two settings: on and off. When the temperature in the house dropped below the desired setting on the thermostat, the furnace turned on at maximum capacity until the right temperature was reached and then it would turn off. This process would continue all day and night throughout the cold months.
How does a multi-stage furnace work?
Sometimes called a “variable-capacity” or “modulating” furnace, the multi-stage furnace works together with a manufacturer’s specific communicating thermostat to adjust on-the-fly to changes in temperature in your home. If the temperature drops by only a little bit, the furnace produces a small amount of heat to compensate. If the drop is significant, more heat will be produced. A multi-stage furnace can adjust its heat output in small increments as needed throughout the day. The furnace will stay on longer at low capacities to increase the likelihood of quieter operation and consistent temperatures throughout the house.
How efficient are they?
Typically, multi-stage furnaces have a AFUE rating of 94% or higher. Many units can achieve as high as a 98% rating. To put that into practical terms, it means that for every $1 you spend on energy fuel costs, 98 cents is turned into heat for your home. By contrast, it wasn’t so long ago that the typical furnace ran at 70-80% efficiency.
Are there different types of multi-stage furnaces?
Yes! The next evolution after single-stage furnaces were two- and three-stage furnaces. They have low/high or low/medium/high settings to be more efficient than earlier single-stage models. The most efficient furnace on the market is a true variable-speed model where each incremental change in temperature is met with an equal-size adjustment that keeps a constant level of comfort throughout the home. It’s worth taking a minute to review the difference types of furnaces available.
Make sure your new furnace comes equipped with an electronically commutated motor (ECM) motor. According to Natural Resources Canada, ECM motors can use up to 70% less energy than standard motors. This is the motor that blows the the heating and cooling around as well as circulate the air in your home. There is a bit more expense up front but remember that you’re buying a 16-20 year investment so the long-term savings are well worth it.
PRO TIP: Pair a multi-stage furnace with a multi-stage air conditioner. Both work together in the same capacity for an ultimate comfort system.