Humidifier in return

[Big Unit]

I have a resi. remodel where we are taking a single zone system and making it into three zones. With the limited room in the plenum and basement we do not have room in the supply now to add a humidifier. I was told that I could put it in the return if needed but I always thought that it was not good to do that. Any thoughts?

[Some Dude]

I have never liked the bypass or power humidifier in the return,
True steam makes an adaptor that will allow remote installation.

[hivacer]

I prefer the bypass mounted in the return, I always mount it in the return if I can, hot air comes in the bypass line and is pulled across the pad into the duct and then goes into the airstream via return air duct. Either way the humid air goes into the return, the only difference of where you mount it is which direction the hot air goes across the pad.

A power humidifier should always go on the supply because it brings air in from the same duct that it blows the humid air right back into, so if you mount it on the return you arent introducing any hot air into it, if I had to mount a power humidifier on the return I would try to use hot water to it.

[Frogbone]

I have a similar problem but I don't seem to really understand how the airflow works in a bypass system.
I am installing an Aprilaire 224 that I got from a remodel. My return duct is inaccessible to mount the unit.
If I mount the unit above the furnace (supply side) and run the 6" round duct that comes out of the humidifier back to the return duct, how do I make sure that the airflow goes from return duct to the humidifier and into the supply duct ?
What prevents it from operating in reverse? e.g. the blower pushes air into the supply duct then the air flows through the unit across the pad and flows back though the bypass to the return where it then would go through the burner and, well, dry up again ?

[docholiday]

It makes no difference, warm air from the supply goes through the pad either way.

[Frogbone]

It makes no difference, warm air from the supply goes through the pad either way.

Yes, but in one instance humidified air goes directly into the supply and in the other it would pass through the furnace and gets dehumidified by the gas flames?
big difference IMHO

[beenthere]

Yes, but in one instance humidified air goes directly into the supply and in the other it would pass through the furnace and gets dehumidified by the gas flames?
big difference IMHO

Don't take this the wrong way.

But, your confused on what your talking about.

Residential furnaces. The return air never goes through the burners.
The return air can not be forced into the supply side by a bypass humidifier.

The supply is a positive pressure. The return is a negative pressure.

Contact your local HVAC company. And they can either install that used humidifier. Or sell and install a new one for you.