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Old 11-21-2021, 05:12 PM   #1
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Boondocking and Using Furnace

We are newbies……please be kind

We have a 2021 FR3 30DS which has a 35000 btu Suburban furnace. We will be traveling some during the cooler/cold days and would like to utilize some boon docking to save money

My questions

1. Am I correct that as long as we have propane and charged batteries, we can run the furnace without shore power or running the generator?

2. What is the amperage draw per hour ?

3. Does the amperage draw include the blower motor on the furnace?

Thank you
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Old 11-21-2021, 05:20 PM   #2
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You will need to look up the amp draw for your specific model furnace. And then you have to allow for light usage and the controls on the fridge.

You will need a minimum of two deep cycle batteries, and you may make it through the night. A lot will depend on how cold it is, how warm you keep the RV and how often the furnace cycles.

Manufacturers are not known to install e lot of battery capacity on these trailers. You might want to see about one of the small quiet inverter generators to have on hand for when the batteries get low.


There is no firm answer for your questions. You
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Old 11-21-2021, 05:36 PM   #3
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RV furnace is DC & AC needed to run

35,000 btu rated NEW Suburban furnace
8.5A DC Draw and consume 34,000 btu of propane/hour run time

*Gallon of propane has 91,500 btu

Biggest issue will be the Battery Voltage
1 battery...ONE night of furnace/need battery recharged
*Low battery voltage and Furnace Fan can not run fast enough to supply proper combustion air & room airflow
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Old 11-21-2021, 05:39 PM   #4
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Furnace and Boondocking

Thank you for the response

We have 2 deep cycle batteries and 115w solar panel. I believe the amp draw to be around 9 but checking to be sure
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Old 11-21-2021, 06:24 PM   #5
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I have a 30,000 btu/hr furnace on our 2021 Thor Axis. I have measured its current draw at about 6 amps. This includes the blower and the burner solenoid valve. On my 25.5' Axis it heats the living area up very quickly. When we wake up and it is 50 degrees inside, we turn on the furnace and within 30 minutes it is at 70. Then we usually turn it off as when the sun hits the coach it will stay warm. On a cold, cloudy morning we will usually have to keep it running (not continuously though) for another hour or so until the outside temp warms up enough.

On a 12 day trip last April down to NC we used about 5 gallons of propane. That represents about 15 hours of furnace run time.

As others have noted above, all you need to run your furnace when dry camping is decently charged batteries and enough propane.

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Old 11-21-2021, 06:55 PM   #6
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We have a 2017 Axis, 25 ft RV. We have run the heat overnight many times while dry camping.

The heat draws 7 amps but that's only when it's running. Even if it ran 50% of the time, that's only 3.5 amp hours ( AHs ).

It would have to be really cold to need more furnace time then that.

We have two 100 AH 12 volt batteries for a total of 200 AHs. The heater would only use 40ish AH over a 12 hour night at 50% run time.
We have plenty of battery power left in the AM to use our inverter powered electric coffee maker.
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Old 11-21-2021, 07:41 PM   #7
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I owned an older Class C, initially it only had one battery which normally would do OK but if we needed the furnace it would drain the battery overnight.

I decided to install a 2nd battery with an a disconnect that I could use 1, 2 or both batteries. So if we needed the furnace at night I'd isolate to one battery and in the AM switch over to the second battery, start the generator and charge the first one back up. My engine had a separate battery so we could always run that to charge the batteries enough to start the generator.

How will you be able to charge your batteries, that will be the trick. You'll need more solar then you have to be able to charge efficiently.
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Old 11-21-2021, 09:11 PM   #8
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Depends on many things including

- amount of insulation
- outside temp
- wind speed
/ humidity
- single or double pane glass
- how warm you want inside temp
- how many other 12 volt loads overnight
- capacity of battery bank

In boondocks mode we use an propane Butty heater while we’re awake. Never after bedtime. That decreases the load of the furnace on the power system. In our MH with temps in mid 30 s we got only two nights on the lead acid batteries. Converted to three heated Battlrborn batteries and can get 4+ nights. No solar on this RV yet.
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Old 11-21-2021, 11:16 PM   #9
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We have dry camped and boondocked in temps as low as 28 degrees.

We have two 6V deep cycle batteries currently, and the will keep the furnace running as we sleep. We set the temperature for 55 degrees. We also cover the windows with tight felt blankets, using velcro. We engage the generator for breakfast. The Progressive Dynamics smart charger does the rest.

We are planning on adding Lithium and solar soon. We love to boondock.
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Old 11-22-2021, 09:55 AM   #10
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We've used our 30' class A regularly during spring and fall and have a good feel for how it works in cooler temps. Even around freezing out, and 68F inside the average runtime of the furnace is only 20 minutes or so every hour. 50% on-time would be on the high side of that estimate, and lowering the thermostat only reduces runtime further. So at a nominal 4Ah per hour that'd be about 32Ah for an 8 hour overnight, about 15% of a pair of GC-2's. When factoring other house power used we can easily make it 2 full days and nights before having to fire up the generator. As far as propane, with no effort to economize I average 1.5 gallons a day. Discovered on one trip how poorly insulated my RV is, left the heat off one night and by morning the temp inside was just a few degrees warmer inside than outside.

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Old 11-28-2021, 09:44 PM   #11
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I would add if your just running the "RV" genny to charge batteries ,a single plug in heater, AC heat strip or heat pump probably won't burn much extra fuel .
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Old 11-28-2021, 10:05 PM   #12
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90% of my camping has been dry camping and I always use the heater. My bride cant stand to be cold. I use it as my gauge as to when to replace the batteries lol
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Old 11-28-2021, 11:16 PM   #13
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Might be worth some basic tests about what run time required vs heat loss. It may be more efficient to run heater to a higher interior temp as the RV may heat faster than it cools in some conditions

That would reduce overall LP and battery consumption of you can heat faster than it cools off.

Of course this is dependent on you manually controlling the furnace. Doesn't work as well overnight when the t-stat only allows for 1-2 degree delta
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Old 11-29-2021, 08:21 AM   #14
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I would recommend turning the generator on early enough so the batteries are fully charged by 8:00 pm or so. Then run your heater. The next morning, check your batteries to see how much power they have left. Do that three or four nights, and you will know what the power usage is in your rig the way you use it. You do have a battery monitor installed, don’t you? It is the very first thing I recommend a boondocker install. You need to learn your battery usage, and a real battery monitor is the way to do it. BTW, I don’t mean a 3 button idiot light.
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ace, furnace

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