A couple days ago we had to replace the air conditioning condenser and evaporator units in our home’s central air system.  The unit was 21 years old and was leaking coolant slowly throughout the last summer.  It was just time.  The new unit is much more efficient, handles more air, and should be quieter even though it’s physically larger.

We had been talking about another item in our furnace and that was replacing the A/C motor with a D/C motor.  The A/C motor is called a PSC or permanent split capacitor motor and they are largely inefficient over time.  The Nest Thermostat allows you to schedule your fan to be on for time periods in the day.  We’ve been running our fan for 15 minutes every hour during the daytime to keep air circulating to reduce warm/cool spots and to help reduce dust.  Running the fan that much with a standard PSC blower is expensive and taxing on the motor itself.


The D/C motor is called an ECM – or electronically commutated motor.  It has a built-in transformer to convert to DC, uses less energy and can change its speed variably without suffering on efficiency.  The motors are also built with better ball bearings and are meant to be on 24×7 for the life of the unit.  The ECM motor is set to run at the lowest & quietest speed for circulation and then speeds up when the heat or A/C turns on.  We can leave the fan on 24×7 for the same (maybe even less) energy cost that the old A/C fan for 15 minutes every hour between 6am and 10pm.

If you have an energy efficient furnace (which we don’t right now) then you may be eligible for a rebate from your State.  The State of Wisconsin gives homeowners a $125 check for replacing their PSC motors with an ECM if you have a furnace that is efficient at 90% or greater.

More about ECMs