Warm-air furnace, reducing excess capacity

abogart · 01-22-12, 04:44 PM

Back to the subject of derating furnaces...

If modulating furnaces only change the inducer blower speed and the gas manifold pressure, I don't see why I couldn't wire a dimmer switch inline with the inducer motor and adjust the manifold pressure on the regulator. The inducer motor seems to be a shaded-pole AC motor, so a dimmer switch should be sufficient to control the motor speed. I would want to use a more sturdy dimmer, not just an off-the-shelf cheapo. I have used those before for this purpose and they don't maintain motor speed very well.

The fuel-air mixture could be adjusted with reference to the exhaust temperature and temperature rise over the heat exchanger.

01-22-12, 04:44 PM	#36
abogart Efficiency Afficionado Join Date: Jan 2012 Location: Michigan, US Posts: 68 Thanks: 21 Thanked 6 Times in 4 Posts	Back to the subject of derating furnaces... If modulating furnaces only change the inducer blower speed and the gas manifold pressure, I don't see why I couldn't wire a dimmer switch inline with the inducer motor and adjust the manifold pressure on the regulator. The inducer motor seems to be a shaded-pole AC motor, so a dimmer switch should be sufficient to control the motor speed. I would want to use a more sturdy dimmer, not just an off-the-shelf cheapo. I have used those before for this purpose and they don't maintain motor speed very well. The fuel-air mixture could be adjusted with reference to the exhaust temperature and temperature rise over the heat exchanger.