Nate Nagel wrote:

Hi all,

I have an old Aprilaire powered humidifier connected to my furnace,
which is an old Ruud 90+ gas unit. Currently the humidifier is enabled
whenever the fan is running. I assume that there is a terminal on the
board that goes hot when the fan runs, intended for this connection.
Here's the issue - it's cold enough here and the insulation in my house
is uneven enough, that currently I have the fan manually turned on low
speed all the time to provide circulation. Otherwise my bedroom gets as
cold as 62 degrees when the downstairs, where the thermostat is located,
is 67 degrees. This allows the humidifier to operate when there is no
heat call. What would be the best approach to change things around so
that the humidifier operates only when the furnace is actually firing?
I bet I could come up with something that works by looking at it myself,
but I figured I'd throw this out there in case there were any "gotchas"
that I might overlook.


While you could simply reconnect it so that the burner firing enables
it, I'd suggest connecting it to a humidistat, so that when the fan is
running *and* the humidity is low it will run, and of course not run
when the humidity is high.