When it’s time to replace your old furnace with a new one, one of your first choices will be whether to stick with an old-school single-stage furnace, or ramp up to a two-stage or three-stage model. You’ll also likely have to decide whether to select a variable-speed blower motor. Your decision will come down to whether you’d like a relatively cheap purchase and installation, but are willing to cope with high energy bills for the life of your furnace, or vice-versa. Here in our cold Upper Midwest climate, you should probably go with “vice-versa,” meaning a two-stage furnace or three-stage model, with a variable-speed blower motor.
So What’s the Difference?
- In this context, “stage” refers to the furnace gas valve. A single-stage furnace only has two settings for the gas
valve, off and on. And the “on” setting has the valve fully open, for maximum heat production. The problem is that you don’t always need your furnace operating at full blast for a few minutes, and then cycling off. This wastes energy and stresses parts, while not providing even air distribution. - The two-stage furnace operates in two different valve settings when “on,” and the setting it runs in most of the time is at roughly 65 percent of full capacity. When colder weather dictates that more heat is needed, the gas valve opens wide, and that extra 35 percent of heating capability kicks in. With a three-stage or multi-stage furnace, even more settings are available. Overall, the two-stage approach is very efficient, and it runs more quietly since the furnace is not often running at capacity.
- A furnace with a variable-speed blower motor can adjust fan speed as needed to disperse heat throughout the home. Technically, the furnace itself doesn’t even have to be on for the blower to be operating, which even without heat output, will continue to filter the air and provide air movement. Variable-speed blowers usually operate a lower, more continuous speed than one-speed blowers, and as a result, provide more even heating, less stress on parts, and lower energy use. A variable-speed blower is usually combined with a two-stage furnace or multi-stage model.
Contact Us
For any expert advice on home comfort issues, please contact us at Marsh Heating & Air Conditioning. We are a family-owned and operated business serving the Greater Twin Cities area.
Our goal is to help educate our customers in Minneapolis-St. Paul, Minnesota about energy and home comfort issues (specific to HVAC systems). For more information about furnaces and other HVAC topics, download our free Home Comfort Resource guide.
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