Heat pump working at 28 degrees ambient

Why a heat pump? COP - coefficient of performance. For a heat pump it's about 3.0. What this means is the heat pump uses electricity to move heat from the outside to the inside at a rate of 3 to 1. You use 1000 btu's of electricity to move 3000 btu's of heat to the interior of your unit. You could use heat strips instead (this is the backup to the heat pump normally anyway) but you use 3000 btu's of electricity to generate 3000 btu's of heat.

Daboo wrote:
does any manufacturer of RVs make an "electric" heater...why screw with a heat pump when they could have put a heating element in the unit and made a true heater..I don't like our heat pump (in Winnebago) just seemed like it didn't work from the git go...

They do make "Heat Strips" and have for over 40 years that are installed by the evaporator. BUT, they only have about 5600 btu's of heat energy. That is NOT enough heat when it is freezing outside. The Heat Pump will have the same BTU AS ITS AC RATING (13.5 or 15k). The PLAIN fact is simple, there is NOT enough heat energy to extract heat when it is below 32 degrees and it makes the HP work hard to heat. Home (residential) systems have a 240 volt heat coil emergency override system to heat when the outside temps drop below 26 to 32 degrees, as the HP CANNOT do a efficient job of heating a house in sub 32 degree temps. Heat pumps are designed for the 35 degree plus temps, not for freezing temps, which is why they have the Furnace system override. Doug

One of the parks I stay at has heat pumps designed for low temp operation, they work well even when it's several degrees below freezing. No reason an RV heat pump can not also be designed that way. In fact I am amazed when they are not.

Also. Some heat pumps have sensors to shut them down when it is too cold out, some do not.

The danger is this... If it's too cold out and you fire it up you damage the compressor. This often happens when people in the north buy a new house in the winter. They turn on the A/C and fry the compressor.

does any manufacturer of RVs make an "electric" heater...why screw with a heat pump when they could have put a heating element in the unit and made a true heater..I don't like our heat pump (in Winnebago) just seemed like it didn't work from the git go...

I'm in Camp Verde. Night before last I forgot to switch from heat pump to furnace before going to bed. During the night I could hear the heat pump going through its defrost cycles but could tell it was warming the MH. I got up and the temp said 24 outside. Never had it work that low before. Weather was dry and dead calm. Ran it last night all night with low this am of 27.

The Ambient Temp Thermister for a Dometic is in the 34 to 38 degree range. BUT, the Thermister is NOT completely exposed to the outside. It is on the inner case frame under the plastic shroud, and IF the HP is running and producing heat, THAT small amount of heat will affect the Ambient sensor. So, it is possible for a HP to run in ambient temps lower than that 34 to 38 degree setting. The Wall tstat has a 5 degree up or down margin of error according to Dometic, so it is possible the Ambient sensor also has that margin up or down. Doug

My Dometic roof top heat pump worked fine to upper 20's in Maryland recently. We also have a portable heat pump/AC unit that sets in the front of our coach, and has a single hose vented to the outside. Since this unit is inside the coach, it works at any temperature and puts out 9500btu's of heat while drawing only a little over 8 amps. This means we are good down into the teens without needing our furnace to remain comfortable.

I'm not impressed as contrary to what most post on here, heat pumps will work into the 20's. Even then they are more efficient than anything else other than geothermal.

RayChez wrote:
What I can not figure out on the OP is that he states it is 42F degrees inside the motorhome. That is pretty darn cold inside his motorhome if he is using heat pumps. .

Yes, I was wondering that myself. If it was 42 inside I would be switching to the furnace no matter what the heatpump was doing :)

Maybe the '42' is a typo?????

What I can not figure out on the OP is that he states it is 42F degrees inside the motorhome. That is pretty darn cold inside his motorhome if he is using heat pumps. It seems to me like he has a problem with the switch to furnace.

We just got back from Las Vegas where the temperatures were dipping down around 38F degrees at night. We would leave only the front heat pump on all night with the thermostat set at 70 degrees. And it maintained that temperature all night long.
Heat pumps work really good on our coach.