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Old 02-20-2021, 04:48 PM   #1
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Furnace in cold weather

I live in South Texas. Last Monday, we lost electric at home where I keep my camper. It was 17 degrees Tuesday and below freezing for several days. I winterized a month ago. A question regarding using the furnace in cold weather. To startup, does it use battery or does it need 110V to start furnace? Does the furnace blower use 110V or battery to run? If it uses battery how long would furnace last in freezing weather without 110V? At below freezing will the LP work?
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Old 02-20-2021, 05:23 PM   #2
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Without knowing more specifics on your furnace,it should be fine on your batteries, but not for too many days. It is a large load for you battery system.
You should be good on propane down to about -35 before it will start liquifying.
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Old 02-20-2021, 05:30 PM   #3
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Originally Posted by txredfish View Post
I live in South Texas. Last Monday, we lost electric at home where I keep my camper. It was 17 degrees Tuesday and below freezing for several days. I winterized a month ago. A question regarding using the furnace in cold weather. To startup, does it use battery or does it need 110V to start furnace? Does the furnace blower use 110V or battery to run? If it uses battery how long would furnace last in freezing weather without 110V? At below freezing will the LP work?

Most furnaces are 12V only. They don’t use a lot of battery as they are just using the battery to run a fan and some electronics once lit.
However - is the battery out in the cold? If so it may not work. Propane also has a freezing point or at least a point below which it won’t work as it cannot turn into gas.
Remember also not to discharge the battery too far - not below 50% capacity or it may be ruined. BTW: 50% is not a voltage amount.
More accurate info can be found by google searches. Good luck.
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Old 02-20-2021, 05:50 PM   #4
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The furnace is a power hog using approx 6-8 amps (depending on the BTU's) when running. At below freezing temps you would be lucky to run 12-14 hrs on a 100 AH battery.
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Old 02-20-2021, 06:25 PM   #5
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You should be good on propane down to about -35 before it will start liquifying.
Propane...LP...Liquid Propane is already “liquified”.

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Old 02-20-2021, 07:02 PM   #6
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As boondocking said above the furnace is a battery hog. Once the battery runs below a certain voltage the sail switch will shut off the furnace. A lot depends on how cold it is outside and how high you're trying to raise the temperature inside the RV. My rule of thumb is: One battery, one night of furnace operation; two batteries, two nights of heat.
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Old 02-20-2021, 07:44 PM   #7
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Most furnaces are 12V only. They don’t use a lot of battery as they are just using the battery to run a fan and some electronics once lit.
However - is the battery out in the cold? If so it may not work. Propane also has a freezing point or at least a point below which it won’t work as it cannot turn into gas.
Remember also not to discharge the battery too far - not below 50% capacity or it may be ruined. BTW: 50% is not a voltage amount.
More accurate info can be found by google searches. Good luck.
At 14 degrees and there is a risk of freezing to death, I don't think worrying about damaging a battery is going to be high on one's list of worries.

I would try to only heat the RV to a minimum temperature rather than the normal "comfy warm". Wear warm clothes and heat to 55 degrees or so in order to save propane and battery if possible.
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Old 02-21-2021, 08:20 PM   #8
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Originally Posted by RiderBloke View Post
Most furnaces are 12V only. They don’t use a lot of battery as they are just using the battery to run a fan and some electronics once lit.
However - is the battery out in the cold? If so it may not work. Propane also has a freezing point or at least a point below which it won’t work as it cannot turn into gas.
Remember also not to discharge the battery too far - not below 50% capacity or it may be ruined. BTW: 50% is not a voltage amount.
More accurate info can be found by google searches. Good luck.
If there's a 12 volt item in your RV that uses more power than your furnace fan, I sure can't think of what it is, and the colder it gets outside the more it's going to use. Running on a single 12 volt battery on a night in the 30's with the thermostat set at 64 in a 25 foot Class C, I've had it pull my battery from 100% to below 50% well before sunrise. Obviously results will vary with temperatures, condition of the battery, volume of heated area and other factors, but they are not insignificant in terms of battery drain.
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Old 02-21-2021, 10:58 PM   #9
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Hopefully you have a generator to charge that battery daily to provide 12v power to the furnace fan at night to keep warm, that’s been my experience in cold wether.
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Old 02-21-2021, 11:02 PM   #10
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Hopefully you have a generator to charge that battery daily to provide 12v power to the furnace fan at night to keep warm, that’s been my experience in cold wether.
Generators are probably in short supply in Texas right about now.
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Old 02-22-2021, 07:45 AM   #11
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Furnace in cold weather

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If there's a 12 volt item in your RV that uses more power than your furnace fan, I sure can't think of what it is, and the colder it gets outside the more it's going to use. Running on a single 12 volt battery on a night in the 30's with the thermostat set at 64 in a 25 foot Class C, I've had it pull my battery from 100% to below 50% well before sunrise. Obviously results will vary with temperatures, condition of the battery, volume of heated area and other factors, but they are not insignificant in terms of battery drain.

My bad - you are right. The heater fan is the biggest single draw on a 12v system. It made me think - it would be helpful if there were a table of what draws what on 12v. Maybe there is but I haven’t seen it.
I know the list would vary according to how each RV is set up. LEDs dropped my draw by a measurable amount. Anything that uses electricity to heat will draw a lot; there are numerous little “hidden” draws by circuit boards, radios, TV aerial amplifiers and USB chargers and so on. It is hard to turn many of these off.
My main point in my original reply is that the temperature of the battery and how much total draw on it is going to be the big killer. 50% state is the low point for battery survival and if that happens in just one night and one doesn’t have any way to charge the next day then there is no way survive past that point.
I guess it may be all moot now but it is worth thinking about.
I have friends who have just bought an all electric no propane A Class but to make that sustainable they have a generator built in. Most TTs do not. Most do not have solar. Winter is the enemy of such rigs.
Sorry if I misled a bit about the heater fan. If anyone knows what wattage a fan is or what it draws it would help the conversation.
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Old 02-22-2021, 08:46 AM   #12
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My bad - you are right. The heater fan is the biggest single draw on a 12v system. It made me think - it would be helpful if there were a table of what draws what on 12v. Maybe there is but I haven’t seen it.
I know the list would vary according to how each RV is set up. LEDs dropped my draw by a measurable amount. Anything that uses electricity to heat will draw a lot; there are numerous little “hidden” draws by circuit boards, radios, TV aerial amplifiers and USB chargers and so on. It is hard to turn many of these off.
My main point in my original reply is that the temperature of the battery and how much total draw on it is going to be the big killer. 50% state is the low point for battery survival and if that happens in just one night and one doesn’t have any way to charge the next day then there is no way survive past that point.
I guess it may be all moot now but it is worth thinking about.
I have friends who have just bought an all electric no propane A Class but to make that sustainable they have a generator built in. Most TTs do not. Most do not have solar. Winter is the enemy of such rigs.
Sorry if I misled a bit about the heater fan. If anyone knows what wattage a fan is or what it draws it would help the conversation.
after a quick google search for RV amp draws i found this...

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Old 02-22-2021, 09:12 AM   #13
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after a quick google search for RV amp draws i found this...

This list is for what they call 115vAC. The request was for a chart for 12vDC.
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Old 02-22-2021, 09:29 AM   #14
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This list is for what they call 115vAC. The request was for a chart for 12vDC.
so it is...LOL thats what i get for rushing....

heres 12v....

Appliance or Accessory Estimated Amps
Aisle Light 1 Amp
CO Detector 1 Amp
Fluorescent Light 1-2 Amps
Furnace 10-12 Amps
LP Gas Leak Detector 1 Amp
Overhead lights (Per Bulb) 1 Amp
Porch Light 1 Amp
Power Roof Vent 1.5 Amps
Radio/Stereo 4 Amps
Range Hood (Fan & Light) 2-3 Amps
Refrigerator (LP Gas Mode) 1.5- 2 Amps
Security System 1 Amp
Television (12 volt) 4-5 Amps
TV Antenna Booster <1 Amp
TV Antenna Booster 12 Volt outlet Up to 8 Amps
Variable Speed Ceiling / Vent Fan 4 Amps
VCR Recorder / Player 2 Amps
Water Pump 4 Amps
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Old 02-22-2021, 01:14 PM   #15
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That list is far from being accurate.

Furnace 10-12 Amps, CO Detector 1 Amp, LP Gas Leak Detector 1 Amp ................

The CO detector and LP detector alone would drain the average RV battery by 50% in 24 hrs.
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Old 02-22-2021, 01:28 PM   #16
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Furnace in cold weather

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Originally Posted by boondocking View Post
That list is far from being accurate.



Furnace 10-12 Amps, CO Detector 1 Amp, LP Gas Leak Detector 1 Amp ................



The CO detector and LP detector alone would drain the average RV battery by 50% in 24 hrs.


Someone needs to upgrade their detectors. My CO detector runs on a 9 volt battery for over a year.

The current drain of the LP leak detector on mine is also far less than one amp because my motorhome does not have the electric shutoff valve at the tank, unlike older units. If the OP has that valve then 1 amp is very possible.

So as one of the first people to respond said, more specifics are needed, including how many house batteries the OP has, their capacity, and their type. 6 volt golf cart batteries versus 12 volt marine batteries is a big difference.

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Old 02-22-2021, 03:25 PM   #17
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I have a standard rv trailer furnace that came when purchased. My battery is just a single marine 12 volt. As others have said battery probably would not last long. I was thinking about purchasing a generator. But in South TX this was like a 100 year event. It would be like purchasing an AC to run in Alaska for 100 degree days. But on the other hand since being down here (15 years) we have lost power over extended period 3 times. Each time I have had to throw food from refrig and freezer. Plus either freezing or trying to keep cool.
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Old 02-22-2021, 03:52 PM   #18
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I have a standard rv trailer furnace that came when purchased. My battery is just a single marine 12 volt. As others have said battery probably would not last long. I was thinking about purchasing a generator. But in South TX this was like a 100 year event. It would be like purchasing an AC to run in Alaska for 100 degree days. But on the other hand since being down here (15 years) we have lost power over extended period 3 times. Each time I have had to throw food from refrig and freezer. Plus either freezing or trying to keep cool.
One idea you might consider is adding another battery and 200W of solar panels. The extra battery (for storage) and that amount of solar would keep your batteries charged while still running the furnace.
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Old 02-22-2021, 04:01 PM   #19
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But in South TX this was like a 100 year event.
Hopefully. We've had a few "100 year" flood events in the last five years where we live. Fortunately we're on higher ground but some of the neighbors on our street had their basements and lower levels flooded.

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Old 02-22-2021, 04:59 PM   #20
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That list is far from being accurate.

Furnace 10-12 Amps, CO Detector 1 Amp, LP Gas Leak Detector 1 Amp ................

The CO detector and LP detector alone would drain the average RV battery by 50% in 24 hrs.
i would rather err on the high side for amperage....LOL i also did not put that together, just snagged it from another site...
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