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Old 12-10-2013, 04:08 PM   #1
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2000 34' Limited S/O
Aubrey , Texas
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Furnace Help - Gas Consumption

Hello All:

I'm having a bit of trouble with propane usage in the furnace and am looking for ideas to narrow down the possibilities.

The rig is parked onsite near where I work in East Texas, about 2 1/2 hours from home. I stay in it during the week and go home on the weekends. Twice now, I have come back to the RV park Monday morning with both bottles drained. The thermostat was set at 55 degrees, and the temps dipped into the high 20's over a 4-night period. The week previous, I had used 1/4 tank of propane under similar conditions over 4 nights. Also, last January I was averaging about 9 days per tank, so obviously something is going.

I have narrowed it down to either a leak or some type of control issue with the system that is not allowing the furnace to shut down. I did a little research and have read that the second issue is not unheard of with this *rediculous* Dometic digital T-stat, the 4-button Comfort Control Center.

Since the problem seems to be intermittent, I am assuming it is electrical, and my research indicates it could either be a bad wall stat or a bad relay in the roof unit control board.

Let's see, some other details. The rig has two rooftop units; the front is a heat pump and the rear is A/C with a heat strip. The front unit and the furnace are both in Zone 1, the rear unit is in Zone 2. The heat strip in the back comes on when requested on the T-stat but the heat pump does not seem to come on at all in Zone 1, although the furnace will come on when selected. Also, I replaced the T-stat about 4 years ago with a rebuilt one.

I called the local mobile repair guy to come and look at it, his best advice was "I can't make it use less gas." So, although I'm ill-prepared to troubleshoot this myself that's how it's shaping up.

That said, anyone have experience with this situation? How does one isolate the root cause? Are there other possible causes?
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Old 12-10-2013, 04:34 PM   #2
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RV Heat pumps don't function at low temps - if it goes below 37F, you're going to default to the furnace, so if the overnight temp really drops, you're using the propane sucking furnace.

My FIRST thought would be clean the filters on the A/C - Heat Pumps. If they've gotten dirty and air isn't circulating, then the heat pumps wouldn't be able to raise the inside temp. and the furnace might go on.

Next, get a propane sniffer and check for leaks around your tanks, hoses and regulator. Again this MIGHT be as simple as loose hose fitting.

Next, walk around your unit holding a candle. Check the windows, doors and vents. You want SOME air circulation, but if you find a vent cover broken, or a kitchen fan vent lodged open you could be heating the great outdoors.

And that's where I call in a pro... Just don't know enough to mess with anything else.

Best of luck and I hope it's something simple. Paula
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Old 12-10-2013, 04:39 PM   #3
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I can't speak at all about your ccc.

You can check the gas connections with soapy water.

Set the tstat for 45* when you leave.

A 34 likes propane, there's lots of space in there.

If it works fine during the week, but goes bonkers on the weekends, maybe someone found a nice party hut while you're gone!!!

John
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Old 12-10-2013, 04:49 PM   #4
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Hi TX_Streamer

If you are using the furnace as the sole heat source you will burn a good deal of propane. Also, in cold weather, the water heater will burn a good deal of propane if it is in on, and you should leave it on so it doesn't freeze (unless you have the electric element too in which case you can run that instead).

If you have the CCC set to run the heat pumps it will switch to the furnace as outside temps drop. I'm not sure what the transition point is but around 40 degrees or so. As a result, if everything is working perfectly, you will use no gas when the temp drops to 40 degrees and a great deal of gas when the temp drops to 35 degrees.

As a practical matter I can offer several solutions.

1) Get a pic-a-watt electric wall heater. I have a thread on the hows and whys, search for it. It will work regardless of outside temperature.

2) Get a local propane dealer to bring out propane in larger quantities, either two 100# tanks or a 100 gallon tank. This will be cheaper per gallon and more convenient.

Jammer
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Old 12-10-2013, 06:05 PM   #5
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If it works fine during the week, but goes bonkers on the weekends, maybe someone found a nice party hut while you're gone!!!

John
I was thinking that or a free propane tank exchange.
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Old 12-10-2013, 10:21 PM   #6
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The set point is 25 degrees for the switch over from heat pump to furnace.

We have a '97 31' and we set the heat pump at 60 degrees. We supplement that with 2 1500 watt ceramic heaters-one in the lounge and one in the bedroom.

Check the furnace discharge port-is it sooty(black around the out side) If so, you are getting incomplete combustion. Too much fuel. Make sure the air intake under the cabinet is clear. Clean the exhaust tube/combustion chamber from any soot or foreign debris. Use soapy water to check for leaks at all connections especially at the tanks. If the hose fitting is not centered in the valve it will leak.

This is about all you can do for yourself.
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Old 12-11-2013, 07:46 AM   #7
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The heat pumps don't have a backup heating element? It won't keep it toasty warm in there but it ought to keep it from freezing. The stand alone space heaters are not a bad idea but it is easy to trip a breaking doing that.

Perry
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Old 12-11-2013, 10:18 AM   #8
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The heat pumps don't have a backup heating element? It won't keep it toasty warm in there but it ought to keep it from freezing. The stand alone space heaters are not a bad idea but it is easy to trip a breaking doing that.

Perry
The heat pumps will go into a defrost mode periodically. No they do not have auxillary heat like your house. Their auxillary heat is the furnace which becomes activated when the outside sensor reaches 25* Then, the CCC switches to furnace and starts the furnace. Once the temp goes back above 25* then it switches back to heat pump.

To date I have not blown a breaker using the ceramic heaters as on low setting they are below the amp load. Most of the time with them on the heat pump does not even come on.
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Old 12-11-2013, 10:28 PM   #9
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On our 34', During two weeks freezing here in Austin area I used a bit over 40 pounds of propane. If you are using that much I suspect a leak or theft.

We left temp set at 65 to keep belly and pipes from freezing. Worked fine.

Really, to use both tanks that quickly something's up.
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Old 12-12-2013, 05:50 PM   #10
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Besides a leak or equipment malfunction, do you know for sure you're getting a full tank when you get it filled? A full 30# aluminum tank should weigh about 47#.
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Old 12-12-2013, 06:05 PM   #11
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I am for the thermostatically controlled space heater. One 1500W heater should keep things from freezing. It might make sense to separate the functions and nix the comfort control center. I think most of the HVAC problems on here deal with problems with those things. You could probably add a heater strip to the heat pump/AC and do it that way also. I use the furnace for emergency heat only or to get the trailer warmed up and then use resistance heating after that. You might be able to put an external thermostat on the furnace and set it to come on at a lot lower temperature.

Perry
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Old 12-12-2013, 09:28 PM   #12
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Adding electric heat is fine but won't add heat to the belly for keeping things thawed. The furnace is only way to get air in the belly pan... Right?
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Old 12-12-2013, 09:38 PM   #13
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Adding electric heat is fine but won't add heat to the belly for keeping things thawed. The furnace is only way to get air in the belly pan... Right?
That's right unless you add skirting and a source of heat under the trailer.
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Old 12-12-2013, 10:02 PM   #14
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That's right unless you add skirting and a source of heat under the trailer.
Thank ya!
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