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The Difference Between Single-Stage and Two-Stage Furnaces

The heating season is here, and some Chicago-area residents may find that they want more performance out of their home furnaces. But with the range of different furnace models on the market and the variety of specifications available, it's difficult to understand how any given furnace model will perform in your home. In this article, we'll help you understand what it means when a furnace is single-stage or two-stage.

Furnace Operation

A furnace produces heat by combustion. The heat produced is used to warm the air that circulates through your home and the fumes are vented outside.

Furnaces burn natural gas or oil; these fuels produce a fixed amount of heat per volume burned. In general, managing heat levels within the home is not handled by changing the amount of fuel provided to the furnace, but rather by managing when the furnace is in operation: the furnace will continually supply heat at a steady rate until the target temperature is reached, then cease supplying warm air until the temperature drops low enough to trigger the heat supply again.

Single-Stage Furnaces

A single-stage furnace is designed to meet the heating needs of the coldest part of the heating season – the absolute coldest weather in your geographic area. So, in Chicago, a single-stage heater might be rated to keep your home warm down to temperatures of -40 degrees. However, because the heat a single-stage furnace produces is constant, that means that the furnace will be supplying heat as though the temperature was at the bottom of its range, even when the temperature is more cool than frigid – say, at 50 degrees in the autumn months. (A furnace designed to operate at -40 degrees can still heat your home when the temperature is 50 degrees, but a furnace designed to operate in more mild weather will fail to heat your home when the temperature drops to freezing or below.)

During cool weather, because more heat is produced than is needed to keep your home warm, a single-stage furnace will operate intermittently, as discussed above. This can lead to air fluctuations, intermittent noise as the furnace's fan engages and disengages, and some subtle temperature variations, depending on how the sensors are calibrated. This also reduces the frequency with which air passes through the furnace's built-in filter, in turn reducing the degree to which airborne particles are filtered out of the air.

Because single-stage furnaces run at their fullest capacity throughout the heating season, they often consume more energy than is needed to heat your home.

Two-Stage Furnaces

Two-stage furnaces are designed to operate at two different capacities: a low and a high. The low capacity is capable of heating your home through much of the heating season, when outdoor temperatures are chilly but not at the lowest extremes of the year. When temperatures drop to the point where the low stage of a two-stage furnace can no longer keep your home at a comfortable temperature, the furnace switches to its high-stage operational mode automatically, producing and circulating additional heat.

Because a two-stage furnace doesn't produce excess heat during cool weather, it avoids the air fluctuations that come of a furnace switching on and off frequently as it manages temperature. And because a two-stage furnace will generally only operate in its high stage for about 25 percent of the heating season, it offers energy savings over a single-stage furnace while still retaining the ability to meet heating needs throughout the year.

Two-stage furnaces are often preferred for home comfort because they can offer steady streams of warm air in both mildly cool and very cold weather. And because air is continually circulating through the furnace system, it's passing through the furnace's air filters more regularly, leading to improved air filtration and quality.

Thinking of an Upgrade?

If you're thinking of upgrading an existing HVAC system or installing a new one, or if you want to learn more about two-stage furnaces and other HVAC upgrades, don't hesitate to find a dealer near you at Comfort24-7.com. Our HVAC contractors are proud to serve the heating and cooling needs of our customers in the Chicagoland area, Northwest Indiana and Southwest Michigan.

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