Furnace Power Drain

[chaseav]

We’re heading north for Turkey day and will likely need to catch some Zzzzz’s in a rest area along the way. No hookups available.

Does anyone know what kind of electrical draw the gas furnace uses? I’d think it would be pretty light but with all the gadgetry and sensors, maybe not. Thoughts appreciated!

By the way, equipment is a 2015 Intl Sig 25FB if it helps or matters.

[chaseav]

Oh, the fan unit... that’s probably a huge drain.

[OTRA15]

Bingo, the fan which moves the hot air out of the furnace draws quite a bit. If your tow vehicle is keeping the batteries charged while on the road, however, you should be fine running the furnace for 8 hours or so, at a minimum, before healthy batteries get down to 50% [12.2 volts +/-]. Lots of other variables, but you can keep checking the voltage as you nap/sleep. [Wait an hour after towing/charging, and remove all 12-volt loads before you check the voltage.]

Where will you be, and what will the outside temp be?

Have fun!

Peter

[Adventure.AS]

Have you checked your furnace manual? Our manual for the Atwood AFMD25 furnace shows It uses about 7.5 amps per hour at 12 volts. Thus,for 8 hours at 100% duty your battery drain will be about 60 amps (although the furnace may not run full time.) If you are using a pair of group 24 batteries the capacity will be about 150 amp hours and you can safely use about 50%. I would recommend that you run the furnace while travelling as the trailer will be much more comfortable when you do stop for the night. The TV will be able to keep up with the power usage of the furnace.

Propane consumption is input of 25,000 BTUs with a nominal output of 19,000 BTUs.

One pound of propane has about 21,600 BTUs. Therefore your 60 pounds of propane is about 648,000 BTUs. If your furnace were the only consumer of the propane (which it is not) you would have about 25 hours of runtime.

[Paprika]

Chaseav is correct: the blower is a major power user. The furnace in my 2017 International 27FB--probably similar to yours--is rated at 7.5 amps per the spec sheet, but actually draws 6 amps when running (as measured by my solar charging controller's amp counter). Either way, that's a lot. Assuming you use it all night and into the morning, and assuming it runs 50% of the time, that would be about 30 to 40 amp-hours. If you have the standard (minimal) Airstream battery setup, that's a fair-sized dent in your batteries' capacity.

Of course, much depends on how cold it is outside and where you set your thermostat. Your situation could be better or worse than the scenario I just mentioned. But in general, you can count on your batteries taking a big hit when you use that furnace.

If you plan to do much cold-weather camping, you may want to consider adding less power-hungry supplemental heat sources, such as a Wave 3 or Wave 6 catalytic heater (zero current drain) or a Dickinson P9000 or P12000 wall-mounted fireplace/heater (half an amp or less). These units won't replace your furnace--they put out much less heat--but in many situations you can warm up the interior in the morning by running the furnace for a short period, then maintain a comfortable temperature with the auxiliary heater.

[chaseav]

Thanks all for the help. I haven't checked the manual... honestly, that thing may as well be in another language for me. I was playing with it this evening and for as loud as my fan unit is and as much air as it's pushing, I couldn't imagine the battery would last for all that long. Currently it's only looking like overnight temps will be in the 40's so not too bad. The wife and kid will just have to sleep in jackets.

Great thought though to turn the furnace on while driving and have the alternator take the load. Probably wouldn't drive that way the whole time but maybe the last hour. We could even use the remote start on the truck if we needed to warm up for a bit. (I hate to do that but it's possible!)

[Trailbob]

I had this same question (can I run the furnace all night on our batteries?) when we took our 25FC on a hunting trip in October this year, near Stanley, ID. The temp got down to 15 deg (F) at night. We used about 20% of our battery capacity each night (measured with a Trimetric 2030RV) keeping the trailer heated to 50 deg with the furnace. We have two 6V Lifeline batteries that give about 220 ah capacity. My goal was to start each night at 90%+ battery level, then I knew we would be fine in the morning. I kept the trailer at 50 deg so the plumbing would not freeze.

As was suggested in a earlier post, we also used a catalytic heater while we were awake to supplement the furnace and save battery power. We did not sleep with it on.

[chaseav]

So, we found a really good solution: Rather than stop and run off battery power, we found a great overnight with 30amp hookup, problem solved! Ironically, the spot we were initially assigned had a bad breaker and, after doing every single other thing to prep for the night, had to disconnect and do it all over again one site over. Learned much though, that's to everyone for the replies.

[Boxite]

We camped/boondocked in freezing temps for three days and ran our furnace all nite/most of the day keeping temps around 67F for the wife. We sleep cool..around 60 or so, however.

After three days... things were still doing just fine... no problems whatsoever, on our single, group 27 deep-cycle WalMart flooded cell battery.

We'd been warned by every "expert" owner that it'd never work and we'd kill our battery and that simply isn't so. (We did run our portable generator on the third day for about 3 hours before going to sleep because I wanted to watch a game on TV.) Our flooded cell Walmart battery was not hurt that I can tell, as we've used the trailer several times since and no capacity shortcomings have been noticed.

I've come to disregard sky-is-falling warnings on battery useage over the last year or so because our experience simply hasn't been supportive of the worrysomeness of them. The battery has a 2-yr warranty and then a $90 replacement is all the worst it can do anyway.

[Fred L]

I spent a week in late October in the UP of Michigan on near Lake Superior boondocking and ran the furnace each night. Cant say exactly where it was set, but I adjusted it to where it was good sweater temps (58-60?)
One night I forgot and left the ceiling fan cover open, furnace ran quite often that night as I thought for sure the outside temps had dropped dramatically...
Anyway, not a single issue. Ran the Honda 2000 for a couple hours each afternoon and provided more than enough re-charge.
BTW, I also used only the reading lights front and back, as well as the stove vent light. All were converted to LED before the trip. Still has the basic 12V AS battery set-up too.

[Gearheart]

Deer hunting 3 weeks ago I used the trailer as base camp. Couldn't use shore power as I have a ground fault somewhere. I went 2 days before needing to charge the batteries( 2 X group 24). Temps were in the low 20's overnight and low 30's in the day. The furnace ran 50% 8 minutes burn, 2 minutes cool down 10 minutes rest. If you are only concerned with 1 night sleep and travelling again the next day. I see no problem.