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Talking Furnaces

Oct 11, 2011

What is the difference between a single stage furnace, a two stage furnace and a two stage variable furnace?

Let’s start with the single stage furnace. Pretend for a moment you have a 100K furnace.

Single stage furnace

Picture a thermostat on the wall. You walk over and turn it on. Let’s say you have it set at 78. Once the heat in the room warms to 78 degrees, the furnace shuts off. That’s it…single stage…turns on…turns off.

Two stage furnace

Now let’s take that same furnace and make it a two stage furnace. It’s like getting two furnaces in one. One stage is at 100K and the second stage is about 70 K. When you turn on the furnace it comes on at the lower stage first. On mild days it may never kick into the high stage. However when conditions call for it…on colder days your furnace will have the capacity to heat the home quickly by kicking into the higher stage. The two stage furnace runs for a longer period of time, but the longer a furnace runs the more evenly it will distribute the air in the home.

Two Stage variable speed furnace

Another step up from the two stage furnace is the two stage variable. To start with the variable speed furnace has two stages just like the above furnace. So you get the same two stage benefits mentioned above. In addition, you get the benefits of an ECM motor. An ECM motor uses about 1/3 the electrical of a regular furnace. The blower motor on a variable speed does not have a set speed. It senses the pressure in your duct system and adjusts itself so that you have the correct amount of airflow.

There are two other important benefits of a variable speed furnace; they are some of the quietest furnaces that you can buy and they raise the seer rating of most air conditioners by approximately one SEER. (a measurement of air conditioning efficiency)

There is also a $50 tax credit available when you install a furnace with an ECM motor.

If you would like us to analyze your home and give you recommendations on what furnace would work best for you, please give us a call.

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