Furnace and single battery

So i took it out this weekend and one of you were right, it was doable without the furnace. it dropped into the high 30's at night, however, once bundled up, we slept thought the night with all 3 kids no heater. in the morning, i turned the heater on and got some warmth. So we did not need to run it at night, good thing because it was loud and the smoke alarm went off the first morning from the new furnace being burned the first time, that would of been annoying the first night. The poor battery did not have enough juice to lower the pop up evenly one of the front sides would not go down, i started freaking out, however, once i hooked the generator up and got it going, all went down fine, so it must have been not enough power or the right kind of power

teejaywhy wrote:

Jollero wrote:

The Jayco pop up manual shows 12 amps is what the furnace uses...

I question the 12A number if indeed you have a Jayco popup. Can you tell us the make and model of the furnace to double check that figure?

Maybe you have a big highwall unit with a bigger furnace? My Baja uses the Atwood 7916-II (very typical popup furnace) which is rated at 3.5A. Basically the DC draw is from the fan motor.

Agreed, I use 4A to estimate. A healthy group 24 has ~80 ah (20 hr rate) to ~100 ah (1A rate). I divide 80 by 2 and get 40 ah usable.

40 / 4 = 10 hrs of furnace run time to use. That could be 1 day if it is cold and windy or many days if the furnace doesn't run much.

Never got over 3 nights with my Jayco 10X battery in California's Mountains.

Replacing the mechanical thermostat with a digital programmable one is worth it! I replaced mine and it has kept the temperatures very stable. I also like that it turns way down at night to reduce battery & propane use (we have good sleeping bags), then comes back up in the morning BEFORE I need to get up. Here's a link to how I did my replacement: Thermostat Replacement.

One thing I haven't seen mentioned yet is that the furnace blower needs to run at a fairly high speed (i.e. needs higher voltage) before the safety interlocks allow the gas to turn on and ignite. The furnace not igniting is usually the first sign of a weak battery. It will blow cold air for a little while then shut off. My experience is that it does this a littel before the battery hits 50% SOC. So when the furnace doesn't light, it's time to recharge; unless it's 3AM AND we're in a campground. If boondocking, the generator fires up whenever I need it to!

I will have to look at the furnace when i pull it out. I got that number out of the owners manual i downloaded from the internet. We will find out this weekend, what i don't want is the middle of the night the battery to run low and the dumb LP detector starts beeping. Then i wake up the whole family going outside to unplug a battery!!!!!

Jollero wrote:

The Jayco pop up manual shows 12 amps is what the furnace uses...

I question the 12A number if indeed you have a Jayco popup. Can you tell us the make and model of the furnace to double check that figure?

Maybe you have a big highwall unit with a bigger furnace? My Baja uses the Atwood 7916-II (very typical popup furnace) which is rated at 3.5A. Basically the DC draw is from the fan motor.

How long the battery will last depends on:
- Battery capacity and health
- How cold it is outside
- How warm you want it inside.

Best case scenerio:
- Get the largest capacity true deep cycle battery and maintain it rigorously.
- Use reflectix window inserts and PUG bunk end covers
- Use the furnace conservatively - warm it up at bedtime then cut the thermostat back to 55 or so. Use warm sleeping bags or blankets. A digital thermostat will help with more precise temp control.

For a real world example, we spent four nights at 9000' in the mountains of Colorado. Overnight lows were in the low 40's / upper 30's. We used the furnace conservatively as described above (no reflectix or PUGs) and still had >50% state of charge on departure day. Battery was a Trojan SCS225 (130Ah).

If you have a way to recharge your battery in the morning you should be fine. Make sure you have a deep cycle battery, they are designed to be discharged over and over. They can be drawn down by as much as 70-80%, then recharged. Hence the term deep cycle.

Try running the furnace while at home and monitor the battery. That way you will have a good idea before you go camping.

I suspect that, unless your children have a medical condition that requires they sleep in a warm environment, they will be very content as long as you are happy. I suggest forgetting about the furnace other than maybe to take the chill off in the morning before the kids get up...for you. Just have a campfire at night (I am generally not a campfire person)and then go to bed with lots of covers.

Just my thoughts....having snow camped (in tents and snow caves) since a child.

Winter camping is great. Have fun.
Steve

Ouch, i did not want to go back the route of 6 volt batteries again, they cost me a big chunk of change before. Half the time we have hookups, the other half, we are in yosemite and normally don't use a heater in the summer and really have no use for a battery since my kids go to bed at sunset. But dry camping for a weekend at the beach in the winter like next weekend, might not work well. Weather is supposed to be 40 degrees at night plus wind, i will need that furnace for the little guys, one battery is not going to cut it, in fact two 12volt deep cycles might not even cut it, i do have a generator i could recharge each day though.

Jollero,

Take the amp-hr rating of your battery (for easy math, lets just say it's 100 Amp-hrs.
Divide by your power usage .... 12 Amps (you can ignore the CO detector for now because it represents so little of your total usage).
This yields a result of 8.3 hours.
This means that if you run your furnace constantly, a new, fully charged 100 Amp-Hr battery will be completely depleted in 8.3 hours.
Fortunately, it is likely that your finance doesn't run constantly, and perhaps is only on about 20% of the time. So dividing 8.3 hours by 20% (0.25) you get 41.5 hours.
While this initially sounds great, something to keep in mind is that your battery will last much longer before it needs to be replaced if you don't use more than about 1/2 of it's total capacity before recharging.
Hence, multiplying 41.5 hours by 50% (0.5) gives you 20.8 hours.
So, with a single 100 Amp-Hr battery running only your 12 amp furnace, you are likely to have to recharge at least once every ~24 hours to maintain good battery health. This seems to agree with the rule of thumb of "one battery per day".

I hope you or someone else finds this useful,
Steve

After posting, I see others are able to type faster than I and have also answered your question. O-well. :)