Air Conditioner Heating / Propane Heating

[UK-RV]

Hi Guys

The last few nights it has been a little cold.

When this happens, we will set the Gas (propane) heating to come on in the bedroom at 60F or thereabouts.

For some reason last night I flicked the switch on the control panel to Electric (Air Con heat) instead of Gas.

That is fine as the heater in the Air Con will come on if the temp gets below 60F just like the propane.

However, is it correct that if the Electric (air con) cannot get the heat upto 60F the Gas (propane) automatically switches in ?

In effect, you can have a night when both the Air Con and Propane will alternate trying to get the heat to temp.

We've noticed this before but just never thought of it until today (as we nearly always set it to Gas).

Is that what's happening ?

Thanks
Paul

[Ned]

The heat pump isn't very efficient at outside temps below about 40F so the system will automatically switch to the propane furnace when that happens.  It has nothing to do with the thermostat setting, just the outside air temperature.

[Tom]

Paul,

I may have misunderstood your question, but on our coach we can only have heat pumps or furnace (LPG heater) or A/C. No option to have heat pumps and furnace on at the same time.

[Ned]

Tom, if you have the Dometic system, it will work as I described and will automatically switch to furnace even when set to heat pump if the outside temp is too low.  Next time you decide to camp in the snow, you can check it out

[Tom]

Well I'll be darned, another day when Ned can say "I was right again". I just checked my owners manual and here's what it says (paraphrased):

When in heat pump mode and ambient temperatures are approx 30F, the heat pump will stop and the furnace takes over. The furnace becomes the primary heat source until ambient temperatures rise above 42F. Between 30F and 42F the defrost cycle kicks in every 40 minutes and heat pump operation resumes after 5 minutes.

I learn something new every day.

[Ned]

The defrost cycle sounds exactly like a stalled compressor.  The first time I heard it I was got a bit excited until I looked at the thermostat and it said it was defrosting.

Now you know why I read manuals

[UK-RV]

Tom

Isn't it great how us confused non-technical people (that's a reference to me not Ned  ) can help educate you old-timers with our lack of knowledge.

Oh yes, I guess Ned can claim some credit too.

Paul

[John From Detroit]

Two of the differences between heat pump (Air Conditioning) and furnace heating are

1: Heat pumps do not work well when tempertures drop below a set point, above freezing, (I thiknk 40 degrees)
In fact heat pumps can be damaged if they are started below a cut off temp (around freezing, I do not know the exact temp)

2: Heat pumps do not heat the basement on the Motor home.   The Furnace may heat the basement, or parts of it, specifically the parts with water tanks and/or hoses in them.  I recall when I was in the desert there were a couple of times I took a shower, it was rather chilly out so the furnace was running and the cold water you usually get when you first turn on the flow... .Was quite warm.

[Tom]

LOL Paul. As I say, I learn something new every day.

[Karl]

Home a/c's and heat pumps have a built-in crankcase heater to prevent cold weather startup damage. Don't know if RV types do also, or if they simply lock out when below a set temp. That would be my guess.

[Ned]

if they simply lock out when below a set temp.

That's exactly what we have been discussing.  Below about 30F the system automatically switches to the furnace even if heat pump is selected.

[John From Detroit]

Home a/c's and heat pumps have a built-in crankcase heater to prevent cold weather startup damage. Don't know if RV types do also, or if they simply lock out when below a set temp. That would be my guess.

While this SHOULD be true, I'd not wish to test the theory on my budget.  Bit like my power awning  It is supposed to retract in 20mph sustained winds (7 seconds)   Not in 0.20 mph winds. but depending on other factors it either retracts or not, the other factors have nothing to do with wind speed though, it ignores that completly.

[UK-RV]

depending on other factors it either retracts or not

How right you are John - like when they forget to install the actual wind sensor in your awning - been there 

Paul

[BernieD]

While this SHOULD be true, I'd not wish to test the theory on my budget.  Bit like my power awning  It is supposed to retract in 20mph sustained winds (7 seconds)   Not in 0.20 mph winds. but depending on other factors it either retracts or not, the other factors have nothing to do with wind speed though, it ignores that completly.

John

Trust me, it works   Learned our lesson the hard way, waking up during the nite with interior temperatures around 40°. Had only the rear heat pump running when we went to bed and it shut down when the outside temps got into the low 30s. Were instructed to use the front heat pump since that is the one with the auto transfer to the furnace and haven't had the problem since   I do hear the defrost cycle switching in and out when the outside temperature gets down to around 40°.

Since the heat pump switches over to the furnace in the low 30s, there shouldn't be any issue of lack of heat to the bays.

[Ned]

Thanks, Bernie, I forgot to mention that it only works on the front zone.