Furnace/Thermostat Help

[davidhalljr1@yahoo.com]

We have a 2021 Montana High Country. When have have the thermostat set to electric & gas cold air blows out of the ceiling vents. But when I turn it on gas only heat blows out of the floor vent. Why would be causing this? Thanks for any help and guidance.

Jerry

[Lee-CI]

Originally Posted by davidhalljr1@yahoo.com

We have a 2021 Montana High Country. When have have the thermostat set to electric & gas cold air blows out of the ceiling vents. But when I turn it on gas only heat blows out of the floor vent. Why would be causing this? Thanks for any help and guidance.

Jerry

The "electric" portion of the thermostat selection is for the heat pump function of your rear A/C unit. If the outdoor temperature is below 40º, then the heat pump won't work well at all. Even when above 40º, the heat pump only supplies mildly warm air. If the temperature outdoors is cold, then best to just utilize the "gas" portion of the thermostat for furnace operation. I'm assuming you have the electric fireplace as well, if so that helps to know off the chill as well. Good luck! Snowed here in Southwest Arkansas yesterday and we stayed toasty warm.

[M&M]

Also if you want furnace only to come on, you set fan to off.

[Bourbon County]

In all likelihood, your Monty is working as designed. The fact that you have a thermostat that has an "electric & gas" option, means you likely have at least 1 AC that's actually a heat pump instead of AC only. The only difference is that a heat pump has a reversing valve for the refrigerant and a little difference in the controls. The heat pump(s) are mounted on the roof and ducted through the ceiling while the furnace is a totally different and separate piece of equipment located and ducted under the floor, but controlled by the same thermostat.

If you aren't used to a heat pump in your home they do feel colder than other types of heat. A heat pump is dependent on outdoor air temp and the colder it is and the more you need it, the less efficient it is. Coleman and Dometic don't post their performance data (that I can find) like residential HVAC manufacturers do but most heat pumps can only raise discharge air temps about 50-55 degrees above outdoor temp. You will only get discharge air temps in the 85-92 degree range. This is warmer than the set point on your thermostat but since it's lower than body temperature it will feel cold to the touch. A gas furnace is not dependent on outdoor temperature and will produce discharge air temps in the 120-140 degree range. Obviously this is higher than body temperature and will feel warm to the touch.

The advantages to heat pumps is you are using the electricity that's included in the rent you pay for the campsite and aren't using your LP gas which you carry a finite amount of. Heat pumps are very efficient in maintaining indoor temps once it's raised to set point with favorable outdoor temps. The disadvantages to heat pumps is they are very inefficient in raising the indoor temp by more than a couple of degrees and as mentioned dependent on outdoor temps.

A good way to warm up a cold RV is to switch to "furnace" or "gas" mode on the thermostat and let the furnace warm the RV up initially, once you get to set point then switch to the "electric & gas" mode. If the thermostat is set up like I think it is, it will default to the heat pump and has an outdoor temp sensor and will turn the gas furnace on at a pre determined outdoor temperature or if there's a indoor temp drop of maybe 2 degrees or so.

There is still a possibility you have straight AC units rather than heat pumps or they installed the wrong thermostat, and a possibility one or the other isn't working right. A quick and easy test is to take a thermometer, even a BBQ thermometer and stick it into a supply vent while the heat pump is running. If you are reading temps in the 85-92 degree range, it's working properly. If you are just reading the ambient temperature inside the RV you might have issues.

[wed]

It’s the heat pump kicking on and not the heater

[twindman]

I had a house with a heat pump back in 1977 in Iowa. Early, ineffecient versions. When the outdoor temp was around 35-40, the air out the vents was 65. I had a blanket on from Oct 1 to Apr 1!!!!!