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Beginner's Guide To Two Stage Furnaces

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Many people erroneously assume that all furnaces operate on basically the same set of principles. While this may once have been true, massive changes have been brought about by a relative newcomer to the HVAC world: two stage furnaces. If you are considering investing in a new furnace for your home, and would like to learn more about two stage furnaces, read on. This article will provide a helpful overview to this exciting technology.


The difference between a single stage and a two stage furnace has everything to do with the burner section. In fact, the distinction can be narrowed even further to the valve that is responsible for controlling the furnace's fuel valve. A single stage furnace only has two valve settings: open and closed. That means that when the furnace is on, it is on all the way.

A two stage furnace, on the other hand, has three fuel valve settings: partially open, all the way open, and closed. During periods of extreme cold, the furnace will utilize the fully open position. This will provide the maximum amount of heating power. Yet, unlike a regular furnace, in mild weather a two stage will automatically switch to the partially open setting. This reduces the amount of fuel used, while still keeping your home at the desired temperature. 

How A Two Stage Furnace Works

In order to determine which valve setting it should operate with, a two stage furnace receives electrical information from your thermostat. The most important piece of information is, of course, the difference between the thermostat's temperature setting and the actual temperature inside of your home. When the difference between the two is minimal, the furnace will operate in the low heat stage, thus saving energy.

Your thermostat will also provide information about how often the furnace is being turned on and off. This helps to minimize the occurrence of short cycle times. You see, a single stage furnace is often too powerful for its own good. That means that when the temperature differential inside your home is relatively small, it won't run for as long as it should before turning off.

Short Cycling

Short cycling leads to two principal problems: uneven heating and poor air filtration. Uneven heating is often the result of a furnace that turns off too quickly. Once the room where the temperature gauge is located comes up to heat, the furnace shuts down. Unfortunately, this often happens too quickly for the blower to have distributed the heat to rooms farther away. Such rooms thus tend to remain much chillier.

Short cycle times lead to poorer air quality for much the same reason. Here the furnace doesn't remain on long enough for your home's air to have properly circulated through the system. That prevents your HVAC system from performing a vital secondary task: filtering unwanted impurities from the air. As a result, the air inside of your home may contain an elevated percentage of such potential irritants as dust, mildew, and mold spores. Select a two stage furnace to ensure that you breathe only clean air--all year round! For more information, contact companies like Chappel's Heating & Cooling.