Heat Pump Operation and Furnace Fan

[danhannah]

I would like the furnace fan to run anytime the heat pump is on to distribute the heat to the bays to keep them from freezing. The problem with an electric space heater to save propane is that the bays don't get any of the heat.

2 cents worth...

[Morich]

Originally Posted by danhannah

I would like the furnace fan to run anytime the heat pump is on to distribute the heat to the bays to keep them from freezing. The problem with an electric space heater to save propane is that the bays don't get any of the heat.

2 cents worth...

Dan makes a really good point here and it is always important to give some thought to why you want heat and where you want to put it. Just heating the space where you are doesn't always mean it gets to the wet bay and the hose sticking out the side!

[danhannah]

Originally Posted by powercat_ras

> why does the furnace fan always run when the heat pump runs, even when the furnace is not being called upon for heat, and is that normal?

No, it's not normal. The furnace only has 12 volt power and on/off from the thermostat input connections. So, unless modified by someone, if the furnace fan is running then the furnace is going to be trying to put out heat. There is no input connection on the furnace to ask it to run fan only without heating.

So, I don't know why.

I almost never disagree, Randy, but check the picture of the thermostat posted above in comment #6 - this is the same one I have. The FAN switch says "Auto or On". So in the "On" position, the propane furnace fan runs constantly, regardless of a call for heat. It would be relatively easy to activate that wire with the overhead heat pump.

[jerichorick]

Originally Posted by danhannah

I would like the furnace fan to run anytime the heat pump is on to distribute the heat to the bays to keep them from freezing. The problem with an electric space heater to save propane is that the bays don't get any of the heat.

2 cents worth...

You're absolutely correct. Your 2 cents is worth gold in this case.

My space heater is outside, under the protection of the slide, pointed at the tank.
When things get above freezing I rely upon a space heater and the electric fireplace to heat the main area. The bedroom door is closed and heated by the gas furnace to about 55*. I don't get the heater outside to heat the bedroom. Usually warms up enough during the day to run the heat pumps.

[powercat_ras]

Originally Posted by danhannah

I almost never disagree, Randy, but check the picture of the thermostat posted above in comment #6 - this is the same one I have. The FAN switch says "Auto or On". So in the "On" position, the propane furnace fan runs constantly, regardless of a call for heat. It would be relatively easy to activate that wire with the overhead heat pump.

I agree that the thermostat has the separate FAN and GAS HEAT outputs, that each are either open or have +12 volts on them as determined by the thermostat.

However, all sizes of the standard Atwood propane furnace that Winnebago uses DOES NOT have a fan input connection. ONLY a heat input connection.

Could you modify it to have a fan on only mode? Yes. I have considered doing it myself to mine.

It would involve:

--- 12 volt coil 10 amp SPDT contact relay wired to switch the fan motor +12 lead between the control board output and direct 12 volts, added inside the furnace somewhere near the control board.

--- A new wire between the thermostat and the furnace to provide the switched fan signal wire to the coil of the relay added to the furnace.

--- two SPST switches at the thermostat, both would wire to the FAN output wire of the thermostat, switch 1 would connect to the roof unit FAN input, switch 2 would connect to the modified furnace FAN input. So one can control if one, other, or both of the fans run when the thermostat fan switch is turned on.

Here's the un-modified furnace wiring diagram ...