RV Furnace/Thermostat: Does it need 12v power????

[Muskieguy]

I just purchased a 1978 travel trailer. It has an actual Thermostat(just a temp dial, no on/off or fan) that runs the Funace. (pilot light kind)

My question is, will I need 12 volt power to run the thermostat. I thought I read somewhere that the pilot light will not start if there is no 12v power(some safety thing).

Any RV'ers out there that can help?

Thanks,

Muskieguy.....

[ChuckN]

This is going to sound stupid because I can't think of the terms of these furnaces, but I will try to explain what I have dealt with.

Is it a forced air furnace?

On my forced air unit you do not need 12V to the thermostat itself, only to the furnace.

12V is necessary to run the fan and the gas valve, without the 12V and enough juice it won't open the valve and burn the gas inside the heating element. The fan will turn on and run, but blow cold air unless the gas valve kicks open and ignites the fire.

I've had problems with my furnace, too much draw on other accessories = no heat. It's a wiring glitch somewhere.

The pilot light should run regardless of power to the unit (at least mine).

[Muskieguy]

Yeah, makes sense to me....I guess I don't know if there is power directly to the Thermostat or just to the furnace unit itself, all I know is that we didn't have the 12v battery hooked up. I have 2 vents(registers some call them) in the floor. One in the front one in the rear, so I would assume that it is Forced Air. So once I hook up the 12v battery and turn up the thermostat, I would assume, at least the fan would work. Once I light the pilot light hopefully there is enough juice to allow the gas valve to open and fire up some heat for the fan to blow out.

Am I on the right track?

Muskieguy......

[ChuckN]

You are on track.

If you have the option for AC power I would go that route and avoid a battery. There should be a location outside the camper to plug into an outlet.

With both AC/DC power, there should be a transformer box, and panel on the wall, that allows you to plug into AC power, or use a battery if no electricity is available. Switch to the appropriate power source on that panel.

[Muskieguy]

I do have 110 power plug, however, I do not remember seeing a switch to go to electric or 12v power. I will look more...it is possible that in 1978 they didn't have this switch? Meaning furnace must run off of 12v even if 110 is available?

Question: If the Thermostat is 12v and the blower is 12v like you state in your first reply, wouldn't I need a power inverter to turn 110 into 12v? If that is the case I am pretty sure that my camper doesn't have that inverter...

This camper is going to used deer hunting and no 110 hookup is available so running off of 110 power is not an option anyway...that being said, I am looking at amp draw for these force air heaters....I found a HSOforum that says forced air heaters draw 7amps per hour, and I think most deep cycles are about 100 amp hour batteries, which means I can run the furnace for 100/7 = 14 hours non stop before the battery would drain...

Thoughts?

Muskieguy....

[hawkeye43]

If there is no fan in the funace and the thermostat has no switchs you need no power. The thermostat works off of a coil spring and mercury switch. as the air cools the coil spring opens and the mercury makes contact and the furace fires up. the pilot light must be burning for this to happen.

[upnorth]

Ok I am no real expert here but most of the items such as lights, furnace and blower etc. run off of 12 volt, you either have to have a battery or a transformer available for them to run. What makes convenient to have power is that you are always charging the battery so it don't drain when plugged in. I am not sure if you can run that stuff without a battery in place, I am guessing you can since we had a dead batttery last year and went to a campground that had power and everything worked fine.

Unless a device on the older RVs has switch like you see on the 3 way fridges to switch to AC it needs DC/12 volt to work.

[DANR]

Most RV's of that era have a convertor that runs those items on 12 volts and, as you said, charges the battery. The battery takes over when there is no 110 to the convertor. The forced air furnaces in the RV's that I have had would drain the battery overnite on a cold night. We would run the furnace right before bedtime, then pile in the sleeping bags for the night. Never tried that on a below zero night though

[Surface Tension]

I know someone with the same furnace and relying on a battery to power the furnace is a joke. The blower drains the battery to fast and it gets to the point where it won't turn the gas valve on but the blower will still kick in and blow cold air continuously, draining the battery down even more. You can't use the calculation of a 7 amp motor and a 115 amp hr battery because the gas vavle won't open after a certain draw done on the battery.

You'll need 2 good deep cycle batteries for that furnace and a way to charge them up every day. Something else we're looking into is a newer blower that won't draw so many amps or disconnecting the blower all together. Depending on your furnace you may quite possibly be able to do that because the blower doesn't cool the furnace nor are they power vented.

[luckey]

I have a 1978 trailer. It can hook to 12vdc or 110ac. You should look into a small generator to run during the evening to charge the battery and provide light etc. If you don't you better have jumper cables ready to go. lol

[ChuckN]

I agree with all these posts. It really takes a lot of battery power to run that furnace and sufficient power to open the gas valve. If you are at deer camp, your trip might be in jeapordy running batteries.

I quit depending on the furnace. If I have electricity, I run a portable baseboard heater. If I am in the boon docks my Mr. Buddy heater and a CO detector works well along with the furnace if needed.

If you have a large camper, maybe a fishhouse ventless heater will work.

Get a CO detector regardless if you are running any gas heaters in that camper. My camper furnace omits some strange gases with the pilot light on.

[IFallsRon]

I've been able to run the tent camper furnace off a new battery for a couple nights. That's stretching it and keeping the thermostat low. Best thing I did was buy an electric heater with built-in thermostat. It sure cuts down on propane use. But the best thing is that you don't have condensation like with the furnace.

[Muskieguy]

Wow, thanks for all of the posts....I guess the only way to surely tell how long the battery will last running the furnace is to try it out...my original post was to figure out if in needs a battery in the first place..I see that it does. Thank you ChuckN and all.

Again thanks for all the posts, we will make sure to bring a few batteries and a charger. Maybe the local bar will allow us to charge up our batteries while we sip a cold one with dinner.

Muskieguy.....