Humidifiers and Dehumidifiers - Humidifier Efficiency and Connections

I have an older Aprilaire model 110 humidified installed on the cold air return due to limited space on the hot air side of the furnace. The installers hooked it up to a cold water line which I changed to a hot water line after reading several forum entries. We run our fan 24 hours a day by using the fan switch on the Honeywell thermostat in our living room. Because we always intended to run the fan continuously, the installers didn’t connect the humidifier into the limit switch so it also runs 24 hours a day unless the house reaches the manually set % humidity. Our house is fairly tight and we heat it to 68-69 degrees during the day. At night between midnight and 8 AM we set the thermostat back and the burner never comes on. If it’s cold the temperature within the house might drop to 60 during the night. Is it still effective to let the humidifier run 24 hours a day even when the house is cooler at night?

Is there a way to use the limit switch to turn the humidifier on and off with the heat cycle even though we have the fan running continuously? The furnace is a Thermo Pride OH5-85.

If I understand what you are saying, is that the humidifier won't come on if you have the fan switched to ON? How is it wired/controled?

I as well run my fan 24/7, and did try running the humidifier with the fan only, and it kept up, but ran awful lot.(due to lack of heat to help eveperate the water). So this year, I switch back to only run with call of heat, and it keeps up just fine.

Thanks for your reply Jay.

The humidifier does run. The problem is that it is not currently tied into the furnaces 24 volt system so the humidistat is the only control that turns the humidifier off and on.

Like you, I feel that it is running more than it needs to and would prefer that it turns on and off with the call for heat, or preferably with the limit switch which would allow it to run a bit longer. I couldn’t visualize how to connect to the limit switch since we run the fan 24 hours a day so I was wondering if anyone knew a way to do that.

As a second choice I would wire it into the call for heat as you did. When you tied yours in did you tie directly into the red wire from the thermostat or did you isolate the humidifier with a relay?

I have a newer furnace, so I am able to set it up in the menu in the t-stat control to tell it to run in heat only, or fan/heat, or force fan on.

What is the make and model of your furnace, you may have something on the board that we can wire it up to.

Its a Thermo Pride oil furnance , model OH5-85. It was installed in 1993. No air conditioning at this time. The thermostat that we use is a Honeywell, model T8602C. It has a manual switch that we use to run the fan continuously.

Its a Thermo Pride oil furnance , model OH5-85.

What are the letters after 85?

There are no letters following the 85. I doubled checked the nameplate on the furnace but didn't find any.

Here is the address of the furnace manual on Thermo Prides website if that helps. The wiring diagram is at the top of page 27: http://www.thermopride.com/manuals/Mo100G.pdf

Currently only the red, white, and green wires are connected to the thermostat. There is also a installer added relay that isolates the "T" terminals on the burner circuit from the thermostat circuit. The "R" terminal goes directly from the Fan Center Relay to the thermostat. The installer added relay is connected in line on the white terminal side between the Fan Relay Center and the thermostat. When the thermostat calls for heat it closes the installer added relay and completes the circuit between the two "T" terminals.

Where is the humidifier getting power from now?

Sorry for the delay, today was our 12th wedding aniversary, we just returned from dinner and I had a monent to respond while she is off changing...

The Aprilaire model 110 has its own 120 volt power supply (it plugs into a separate outlet at the furnace, and I suspect its own internal 24 volt transformer. Aprilaire seems pretty protective of its wiring diagrams so I haven't found one on line to verify the configuration and the user manual doesn't have one either.

I certainly appreciate your help on this!

Ok, so what you'll have to use is the A50 or Sail switch to turn the humidifier on and off.

You'll have to order them on line since most places don't have these in stock.

Thanks for your help Jay. I will look into getting the switch.