Can the humidifier be mounted on the returm plenum?

After 32 years, I decided it's not worth repairing and maintaining my Autoflo 200P. I'll probably replace it with an Aprilaire 500. There's no easy room to mount the Aprilaire on the hot plenum where the Autoflo was. I'll have to mount it on the return plenum, which would be easy. I was told the humidifier won't work as efficiently as it would mounted on the hot plenum. Is this true? The ranch home is 1350 sq ft with a full basement.

Second question.... If I buy the Aprilaire, could I carry over only the two electrical wires that are feeding the Autoflo motor? The humidistat is still working, and it would simplify dealing with all the wiring I see in the installation guide. I measured 30VAC to the running Autoflo motor.

 

Yes.... you can install the humidifier on the return plenum. Since the air at that point is not heated.... the water to air transfer will be lower. I'm thinking it may be a good idea to tap into the hot water line. This would be effective if the hot water heater was fairly close by.

Yes.... you can extend the two wires from your old unit to the new one. The voltage and the function is the same.

 

Wouldn't the pressure differential draw heated air past the humidifier toward the return plenum?

 

The pressure of the supply side will force the air thru the bypass line thru the humidifier and into the return air.

 

I bought the Aprilaire 600M. It was only $2 more than the 500M model. I installed it on the return plenum and everything works fine. I used the old humidistat. The new one will be kept as a spare. Thanks for the help.