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[woodman]

Just to avoid any confusion, I am talking about the furnace blower in my basement. My current setup is a water to air hx in forced air furnace. I use a separate programmable thermostat to  turn the blower fan on and off. If I changed the single speed blower to a ECM variable rate blower would it be possible to make it operate like a 2 stage furnace? Here is what I would like, set point would be the slowest speed. If it was cold and could not keep up and temp fell more than 1 degree below set point it would go to medium speed. A difference of 3 or more would put the motor in high speed. Is this possible to do with just a thermostat or does the blower need to communicate with the furnace burner?

[mlappin]

The low and medium might work pretty well, running it on high depending of the CFM of your furnace fan could actually make the air coming out of the vents feel cold. This is just based off my furnace though.

[slimjim]

You are right there mlappin and I think the diff should be further apart as any forced air unit that I have ever dealt with will blow cool air for the first minute or so just to purge the cool air out of the ductwork, this will usually cool the home 1-5 degrees before warming it back up again.

[RSI]

That would be pretty easy to do with a multi speed blower. Controlling a variable speed blower would probably be much more complicated.

If you have a newer furnace it probably has a multi speed blower already in it..