Minimum furnace run time?

[MN Renovator]

Originally Posted by Servicetech

Blower is single speed, one of my previous mods was replacing the OEM 3 speed 1075PRM motor with a single speed 825RPM. PSC motors have awful efficiency on low speed, old motor used 355W, new uses 150W. Temp rise did go up about 7 degrees when I changed motors. Furnace is rated 25-55f, 45f is on the high side, but still 10f from max.

I did do the mod you are talkind about on my old furnace. It had to be on HIGH speed to stay off limit, and the giant blower produced a cold draft when it 1st kicked on. A sequencer was my "time delay" of choice, had a fixed 30 second delay. Long enough to let the blower clear the cold air out of the ductwork while still on low speed.

Dumping the oversized beast and installign a furance 1/2 the size fixed a lot of comfort issues. No need for a low speed anymore since the blower isn't overpowering to begin with.

Is the 44k an 80% unit?
44000*.8=35200
35200/(45*1.08)= 724 CFM
You are getting 724CFM from 150 watts? Is this 825RPM motor a PSC motor?

The reason I ask is I replaced my old shaded pole furnace motor with a PSC motor and I thought I was impressed by going from 804 watts down to 320 watts on the highest speed tap. I'm a little under 800CFM based on my own output capacity and temp rise.