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wsrb · 11-05-2018, 05:10 PM

We have a 2018 25FB International Serenity. When the Dometic thermostat is set to HP (Heat Pump) mode will it automatically switch over to the Furnace mode when it's too cold outside for the heat pump to work?

mpsgolf · 11-05-2018, 05:19 PM

My Dometic thermostat does NOT automatically switch to furnace. HP and Furn are separate modes.

GMFL · 11-05-2018, 06:06 PM

Mine does. If the heat pump runs for a certain amount of time and does not satisfy the thermostat the furnace comes on.

OriginalMrT · 11-05-2018, 06:21 PM

I think the mode needs to be set to auto for that to happen.

uraljohn · 11-05-2018, 06:22 PM

The furnace in our 2017 23D kicks in if HP can't keep up. We experienced this last November in Columbus, Ohio. We got caught in a cold snap (20 degree nights for 5 nights). I now try to set thermostat to furnace ahead of time if it is going to be really cold.

robertstaley · 11-05-2018, 06:28 PM

Yeah! when you set to Hp and after running the heat pump it automatically switches over to the Furnace mode.

Tomfeury · 11-06-2018, 10:47 AM

wow never knew this! Great question.
I now will feel more comfortable using the HP, and campsites electric instead of my propane, when I leave the AS there for a period of time unattended.

Mollysdad · 11-06-2018, 10:58 AM

Quote:

Originally Posted by wsrb

We have a 2018 25FB International Serenity. When the Dometic thermostat is set to HP (Heat Pump) mode will it automatically switch over to the Furnace mode when it's too cold outside for the heat pump to work?

Mine did.
About 30 degrees. However, I never set up the programming. I can only assume the dealer put a program in or a miracle happened.

guskmg · 11-06-2018, 11:26 AM

Don't feel ignorant. I had mine for 10 years before a tech at Airstream Service
informed me.
guskmg

billrector · 11-06-2018, 05:15 PM

Really? We have a 2017 FC and just returned from a camping trip to Utah. We had the HP running one night and it got down in the 30's. The HP seemed to run non-stop, but it did not switch over to the furnace.

Do you have to have Auto set for this to happen? I can't imaging setting it to HP and having it change automatically???

Al and Missy · 11-06-2018, 07:25 PM

On my older Dometic 5-button CCC thermostat, auto mode is for fan control. The heat pump has a temperature sensor in the outside unit and the thermostat switches to furnace when it reaches 30 degrees. With the heat from the compressor, 30 degrees in the unit is probably several degrees above the ambient.

Al

Mollysdad · 11-06-2018, 11:36 PM

Quote:

Originally Posted by billrector

Do you have to have Auto set for this to happen? I can't imaging setting it to HP and having it change automatically???

I couldn't either, but it happened. If you look into the manual for the climate control unit, (CCC 2) it mentions a "auto changeover". I never did anything, but at around 30 degrees, the furnace kicked on.
I got up the next morning and felt warm air at my feet.
Nice feature.

Quote:

Auto Change Over Heating: If the room temperature goes below the temperature set-point by 2 °F / °C, the available heat source will be cycled ON until the room temperature reaches the temperature set point at which time it will cycle OFF.
If more than one heat source is available on this zone, the priority for selecting the heat source will be heat pump (first), furnace (second), and heat strip (third).

Quote:

F. Auxiliary Heat (Heat Pump Models Only)
Auxiliary heat operation will be activated when the measured temperature of the outdoor temperature sensor is less than 30 °F (-1 °C). If the system is equipped with a furnace, the control will select FURN heating mode for the auxiliary heat source. Auxiliary heat operation, once initiated, will have priority over a heat pump defrost cycle. Auxiliary heat operation will be de-activated and the heat pump operation will resume when the temperature of the outdoor temperature sensor is higher than 35 °F (2 °C).

wsrb · 11-07-2018, 07:34 PM

Reporting back as we’re in cold enough temps to try this out. Outside temp is 30F. The heat pump was working but instead of automatically switching over to furnace it froze up. So, I just switched the thermostat to furnace. Seems that answers my question for this 2018 25FB international serenity.

ChuckZ · 11-09-2018, 09:19 AM

Thanks for the thread WSRB. It's good information since we'll be picking up a 2012 FC 28 with a heat pump in 2 weeks. Never had one in our '66. It'll be great.

Chuck

SpinWhite · 11-09-2018, 12:37 PM

We set the heat a few degrees warmer then the AC cool. I have had the inside temp warm up to set temp. Then heat shut off and then the AC cool come on to lower inside temp to Auto AC temp set. So changed the mode to furnace to stop the temp chasing.

Bigventure · 11-09-2018, 08:11 PM

The auto change over happens when the stat is set to auto.

Tomfeury · 11-10-2018, 06:42 AM

I went to bed when it was 40 degrees last night. I had the thermostat set to HP at 70. I just woke up to 30 degrees and snowing at Penn State University.
The HP did indeed switch to FURN overnight and my 2017 27FB is a toasty 70!
The thermostat now floahes "HP.....FURN"

wsrb · 11-10-2018, 06:54 AM

Quote:

Originally Posted by ChuckZ

Thanks for the thread WSRB. It's good information since we'll be picking up a 2012 FC 28 with a heat pump in 2 weeks. Never had one in our '66. It'll be great.

Chuck

You're going to love that 2012 FC 28. We have close friends picking up a 2012 FC 28 then too.

wsrb · 11-10-2018, 07:03 AM

Reviewing the installation instructions for the HP, it appears it can automatically switch over to the furnace if installed accordingly. Specifically, part of the wiring needs to include a wire from the HP to the furnace. Second, there are a series of dip switches on the HP itself. One of those needs to be switched to on to control the auto changeover to the furnace. Given we just woke up to 12 degrees outside, I don't plan on checking that out anytime soon. By the way, at these temps the furnace burns through a 30lb LP tank about every two days.