Colder weather with a 2 AC unit-HP with furnace backup

[Piggy Bank]

I've been reading a lot of questions lately about how to set the thermostat and how to keep a trailer heated during cold weather.

So I wanted to share what we do when we are on shore power, and expect a cold night.

This is not for extreme winter weather, but more for camping when it drops to about freezing overnight.

Note: our unit is a 2019 unit. We have a regular furnace, not the Alde heating system.

We have a 50 amp unit with the 2 rooftop AC/HP units. There are 2 zones, zone 1 and zone 2.

Only one of your zones will have FURNACE as one of the settings. For your rig, scroll through the thermostat settings and see which this is.

Assume these things:
1-you want to run on heat pump as long as possible so that you are using the electricity included in your campsite fee to heat vs the propane you had to pay for, as long as that makes sense.

2-if it's going to dip into a temperature below 40 outside, then the heat pump will not work well enough to keep the rig warm and toasty

3-if it's going to dip into a temperature below 40 outside, you want to run the furnace so it will heat the spaces below the floor and warm the plumbing to prevent any issues.

This is what we do:

Set thermostat 1 (assume this is the one with the furnace, to Furnace, and an indoor temperature setting like 61)

Set thermostat 2 (assume this is the one without the furnace, to Heat Pump, and an indoor temperature like 65)

The idea is you have a 3-4 degree "dead band" between the settings for the 2 kinds of heat.

What happens is the heat pump is the Primary, and will run and keep things toasty at 65.

As it gets colder outside, your heat pump won't be able to work as efficiently and eventually it won't be able to keep up, and the temperature will start to drop below 65 inside.

Once the temperature inside gets below 61 the furnace will kick on, and stay on until your temperature goes back up to 61.

You don't have to worry about the rig getting too cold, and you don't have to wake up and change anything in the middle of the night.

[DCPAS]

We have the same model year with 2 A/C's with the OEM Dometic thermostat. If you just use HP, it will switch over to furnace by itself when it gets too cold for the HP's. This works, but the HP's go through a defrost cycle as it gets near being too cold to work. This creates noise and vibration and will wake me up. I've gone to just turning on the furnace. I wish I could set the switch to furnace parameters, but I don't think it is possible.

[Piggy Bank]

Reducing the defrost cycle is one of the major benefits of my method.

By engaging the furnace once the heat pump can't keep up.

[DCPAS]

Originally Posted by Piggy Bank

Reducing the defrost cycle is one of the major benefits of my method.

By engaging the furnace once the heat pump can't keep up.

Good point. Thanks, I will try it.

[ModernVista]

My wife thinks the heat pump is too loud, so we got a little Vornado fan/heater that sits on the stove. It has a temperature so I just set it to what we like- has to be low heat or it blows the breaker. I put propane furnace on a few degrees cooler just in case, but usually the Vornado keeps up. That’s when we camp with power, of course.

[coasttocoast]

I have a Vornado with 3 heat settings and an electric blanket. If I’m not plugged in, it’s propane and the blanket.

[PAntonia]

What happens when your heat is on and all of a sudden white smoke starts coming out of the vents? We turned it off.
Could that be a freon issue? Even when the thermostat was set at heat?

[805Vet]

We seem to RV a lot in cold weather lately. The thermostat is set fairly low, 55-58 to limit propane use. We run a either a small space heater or the desiccating dehumidifier to keep the chill off. A desiccating dehumidifier discharges warm air. I have marked the space heater for 62 degrees (ish). About 30 minutes before the dogs wake us up the thermostat switches up to 65 and the heater, heat pump attend to whatever happens next.