humidifier install

The unit goes on the hot plenum, because that's where the heat is. Only humidifier I recommend is Aprilaire, which is an excellent design and trouble free. I also recommend getting one that is powered by a small fan and not bypass type.

Since there are different designs for furnaces and humidifiers and different situations, I suggest looking in the install instructions that should have come with the humidifier.

Do you have the humidifier yet? How much access do you have to the furnace and ducts? Access to water supply and drain?/

Read the installation manual. Better yet, have a HVAC company install it for you.

I've installed a bunch of Aprilaire, and that's not what the manual says.

Is there a specific reason you are adding a humidifier? Keep in mind that if your house is very tight, adding extra humidity can hurt more than it can help.