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# Understanding Varible Speed / 2 Stage Blowers

## Understanding Varible Speed / 2 Stage Blowers

#1
09-25-08, 12:04 PM
Member
Join Date: Sep 2008
Location: USA
Posts: 108
Understanding Varible Speed / 2 Stage Blowers

Howdy.

I am trying to understand the differences between varible speed and 2 Stage Furnance blowers?

Some have 2 stage only, some have 2 stage AND variable speed. Are there furnaces with only variable speed motors and no x stage speeds?

The little I know is that 2 stage is used for heating where the gas furnace opens 1/2 way and the blower blows 1/2 speed for a gentel heat startup and later kicks in full speed if needed.

For variable speed systems, is the variable speed motor used only for cooling? Or is it also used for heating?

#2
09-25-08, 06:40 PM
Member
Join Date: Jan 2008
Location: Tennessee
Posts: 438
apples and oranges

You are talking about 2 different things the 2 stage they are referring to is concerning steps of heating either a multi stage gas valve or multiple stages of electric.
The variable speed is concerning blower motor operation only.

#3
09-26-08, 02:12 PM
Member
Join Date: Sep 2008
Location: USA
Posts: 108
So on a unit like this one that has two stage and variable speed.

Is the variable speed for A/C only, or it is also used for heating or both?

#4
09-26-08, 05:16 PM
Member
Join Date: Sep 2001
Location: Rochester, Minnesota
Posts: 16,984
Variable speed is used in both heating and cooling.. The cooling side of it ramps up and down more than heating.

An example, on call of cool, the blower will run 50% speed for about a minute, then ramps up to about 80% speed for 9 minutes, then ramps up to full speed. If the blower is hooked up to a humidistat, and say the house is humid, the blower will stay at 80% speed to help remove the humidity, and when it goes down to set point, then the blower ramps up to full speed.

On heating, the blower starts up soft to 1st stage heating speed, and if 2nd stage is called for the blower ramps up to 2nd stage heating speed. When heat is not needed anymore, the it ramps down slowly to off.

On fan "ON" mode, the blower runs about 50% speed.. Just enough to move air around and provide comfort, and not a loud cold drafts.

If the furnace only says 2-stage heating, the the blower is a fixed speed.

If it says 2-stage with variable speed, then will be what I said above.

I have ours now for 4 years, and I will never go back to a standard blower. I love the quiet speed since the furnace is only 10' away from me.