Using both AIRXCEL propane furnace and Coleman heat pump to heat in freezing weather

[Dave Schapansky]

We are newbies and are just 8 weeks into fulltime RVing here in BC, Canada in our 2021 Solitude 310GK.And loving it. With the weather getting colder, I had the thermostat setting on HEAT and ELECTRIC and the hot air is coming just fine from the ceiling ducts from the AC/heat pump. But I did notice when I initially turn on the thermostat in cooler mornings (52F), then the propane furnace kicks on as well and I can feel the hot air coming from floor ducts and also in the water bay and storage in the belly.
Later in the day, when the weather warms up, the heat just comes from the ceiling units.

We have free electricity so I like to use the AC/heat pump, but as weather dips below freezing we still need to have heat in the water bay and belly to protect the pipes from freezing. My question is- can I leave the thermostat setting on HEAT ELECTRIC in freezing weather and rely that the propane furnace will automatically kick on and supplement heat to protect the pipes in the belly from freezing? Or should I just leave the thermostat setting on HEAT GAS? Thanks for the help.
Dave

[howson]

Dave Schapansky -- FYI I removed the duplicate post, Dave, in the Appliances channel. I see you're new, so don't worry. No big deal. Sorry i can't address your specific question as I don't have a heat pump nor any experience with them. I'm sure someone will chime in soon.

Welcome to the forum!

Howard

[Country Campers]

Dave Schapansky

I am not sure how the gas furnace and the heat pump in the AC is wired but I would not count on the furnace coming on when needed. Keeping the pass thru storage heated is a must in freezing temps. The furnace also heats the underbelly where the tanks are, there are water lines running thru this area as well. There may be information in the owners manual that will help you with how the heating system works. Second Chance Rob has a Solitude 310 maybe he will help you with how the system works.

Brian

[Second Chance]

Dave Schapansky

I am not sure how the gas furnace and the heat pump in the AC is wired but I would not count on the furnace coming on when needed. Keeping the pass thru storage heated is a must in freezing temps. The furnace also heats the underbelly where the tanks are, there are water lines running thru this area as well. There may be information in the owners manual that will help you with how the heating system works. Second Chance Rob has a Solitude 310 maybe he will help you with how the system works.

Brian

We do not have the heat pump option, but your description of how your system is operating coincides with how the system is designed to operate. As long as the LP furnace cycles when the temps are below freezing, you're OK. I would not depend on space heaters in the basement storage area alone. That would not circulate the heat toward the rear where the kitchen water lines are. Just keep an eye on things until you're sure the system is operating as it should and you're comfortable. The Solitudes are insulated well enough that I don't worry about things until the temps get into the mid-20s or below and/or the winds are really blowing (sucks more heat out of everything faster!). Finally, waste and fresh water tanks won't typically freeze in the 20s even without the tank heaters on. They are enclosed, heated, and have mass to them which takes longer to loose heat and freeze. We wintered at the top of the Chesapeake Bay in Maryland last winter with several ice and snow storms, temps in the teens, and some high winds. We ran the furnace and had no issues (not even sure I turned the tank heaters on...).

Rob

[Dave Schapansky]

Thanks for the advice here (and thanks for the help deleting my duplicate post)...we are expecting our coldest weather to be in the teens or 20's so your experience in this brings us a degree of comfort that we should be good for the winter. Thanks again, Dave.

[Jlawles2]

Dave Schapansky Dave, There is a point where heat pumps actually stop working. Think of a heat pump as a backwards AC. When there is not enough heat outside to draw from, the heat pump becomes inefficient or non functional. Most AC systems only produce pressures that will draw heat out of about 30F temps. IIRC the heat pump installed in my parents house back in the 90's actually changed to gas mode when outside temps reached 32-36F. If you are experiencing temps in the 20's then the Heat pump may not work.

[steve&renee]

Dave Schapansky Dave, There is a point where heat pumps actually stop working. Think of a heat pump as a backwards AC. When there is not enough heat outside to draw from, the heat pump becomes inefficient or non functional. Most AC systems only produce pressures that will draw heat out of about 30F temps. ...

We're building a new house and temporarily living full-time in the RV. It's getting colder here in Wisconsin, so we've had some recent experience with the heat pump and gas furnace interaction.

In our unit, the heat pump puts out heat until the outside temp gets down to around 30 degrees F, then the gas furnace automatically kicks in and takes over. As the temperature comes back up the next day, the heat pump takes over and the gas furnace doesn't operate. All this automaticity comes for free when we set the thermostat to "Heat Electric".

We're using the tank heaters proactively whenever the temp is predicted to be below freezing at night. I added a tank heater under my lithium battery bank because the lithium's won't charge below 35-40 degrees F -- and the furnace and refrigerator controls require 12 volt power. With the tank heater, my battery bank temps have been running at 58-60 degrees F even when the outside temp is below freezing.

I'm planning to install some incandescent lights in the Nautilus back panel area for plumbing-line heat pretty soon.

Biggest headache I'm handling is fresh water and holding tank discharge. Now that freezing temps have come at night, the fresh water line freezes by morning. We typically have to switch over to pump and holding tank to take a shower in the morning.

I'm using a macerator pump to dump the holding tanks into a sewer clean-out that's about 120' away from the trailer. That line freezes at night, too. After next week, the temps will go below freezing night and day, so I'm gonna have to roll up the water and sewer hoses every time I use them and keep the someplace warm. That should be a pain. . .

I think we can pull this off, but I'm nervous.

-Steve

[DarnDave]

Dave Schapansky In our unit, the furnace supplements the heat pump whenever the requested temp is more than 5 degrees higher than indoor ambient temp. Once it recovers that differential, the "override" stops. It will repeat whenever that 5 degree differential exists. Jlawles2 is correct; however our cutoff is closer to 40 degrees outside.

Dave

[JBill9694]

steve&renee If you have reliable power available, you might want to look at heat tape and insulation for the exterior water supply hose, hose spigot, and discharge line.

An alternative is to not necessarily roll up and unroll the hose and discharge line each day, but just drain the line. The hose/line may get cold but if there is no water in them there is nothing to expand and burst. I haven't had to worry about my sewer hose (short runs with good negative slope) but I do disconnect the water supply hose at the spigot and then loosen the connection at the trailer to allow air to enter the hose as I walk the hose, lifting it to drain. Works well for me, I just have to remember to tighten the connection at the trailer before I hook up the water to refill my tanks.

The same principal could be applied to the pump discharge. I assuming that the pump discharge is higher than the sewer intake, even if there is some higher ground between the two.

[steve&renee]

steve&renee If you have reliable power available, you might want to look at heat tape and insulation for the exterior water supply hose, hose spigot, and discharge line.

An alternative is to not necessarily roll up and unroll the hose and discharge line each day, but just drain the line. The hose/line may get cold but if there is no water in them there is nothing to expand and burst. I haven't had to worry about my sewer hose (short runs with good negative slope) but I do disconnect the water supply hose at the spigot and then loosen the connection at the trailer to allow air to enter the hose as I walk the hose, lifting it to drain. Works well for me, I just have to remember to tighten the connection at the trailer before I hook up the water to refill my tanks.

The same principal could be applied to the pump discharge. I assuming that the pump discharge is higher than the sewer intake, even if there is some higher ground between the two.

I guess I'm not so much worried about expanding and bursting as I am about developing a frozen clog that wouldn't thaw until April or May.

My biggest problem is the length of the hoses. Both water and sewer are more than 100' -- slightly uphill from the RV to both the spigot and the sewer cleanout. Definitely wouldn't want to try and drain the sewer line away from the cleanout toward the trailer. And I doubt 100 plus feet of heat tape is do-able.

-Steve

[pengle]

My question is- can I leave the thermostat setting on HEAT ELECTRIC in freezing weather and rely that the propane furnace will automatically kick on and supplement heat to protect the pipes in the belly from freezing? Or should I just leave the thermostat setting on HEAT GAS? Thanks for the help.
Dave

If you leave it on HEAT ELECTRIC and it is below 40 degrees (or 36 or 37 - at some point the heat pump can't replace the heat you are losing in the trailer) outside here is what will happen. Let's say you set the thermostat to 75 (arbitrary number). When the room gets down to 74 the heat pump will turn on. The furnace will not. There isn't an outside thermostat that turns the furnace on when you set the thermostat to HEAT ELECTRIC. As the heat pump tries to get the room to 76 degrees, when it would normally shut off, it just can't produce enough heat to replace what you are losing.

So now the temperature in the room starts to fall. When the temperature hits 70 degrees (5 degrees below your thermostat setting of 75) the furnace will kick on. It will continue to heat the room until the room reaches 76 degrees. Now you'll hear the heat pump turn off, the furnace heat will turn off and the furnace fan will continue to run for 90 seconds or so.

There are times when it's 37/38/39 degrees outside that I'll let the heat pump run and run "because I'm not paying for the electricity". Below that temp the runtime gets annoying and I get tired of hearing it. Below 37 I'll set the thermostat to HEAT GAS and just let the furnace cycle on and off. The added benefit is that the underbelly, the wet bay, and the main storage are all being heated by individual 1 1/2" ducts.

The main point of all this is that when the thermo is set to HEAT ELECTRIC the gas furnace will not kick on until your room temp falls 5 degrees below what you set the thermostat at. Who wants that?

[Guest]

As outside temps approach 40F, a heat pumps efficiency approaches zero. This is due to the heat pumps inability to efficiently extract and transfer heat from the outside air where supplemental heat via electric strip or gas furnace must be used to heat the living space.

Jim

[JBill9694]

steve&renee , you probably know better than I do that the real problem isn't the freezing of the water or other stuff as much as the pressure increase in the system caused by the expansion of the frozen material. If heat tape is not a possibility I would still be looking at draining my water supply line, even if I have to drain it towards the trailer. For the sewage discharge I'm wondering if there is any way to fill the hose with antifreeze?