Furnace using too much propane

[allersj]

This all happened last spring, but I never addressed the issue. Our first day/night of camping was chilly. When we got to the camper, the temperature was about 50 degrees. I started the furnace, we went out to dinner, and by the time we got back, the camper was comfortable. For sleeping, I set the thermostat at 65. The temperature that night got down to 30. We awoke at 5am freezing. We were out of gas. I was positive that the tank had been full, but was cold enough to not care at the time. I went out and switched over to the other tank. Heat came back on. The temperature that day got to 65. The furnace didn't run much at all. That night got down to 30 again and I woke this time at 4am, once again freezing. I was pretty sure that my second tank was full, but admittedly I didn't check it the previous morning. I luckily had a spare 3rd tank. I know this one was full. I connected that and got the heat back on. Fast forward to the next (early) morning, and that tank is now empty as well. I went through 3 thirty pound tanks in 3 nights. The long weekend was over and our next trip back wasn't for a few weeks, so the weather was warmer. The remainder of of camping that year, we used electric heaters as needed. I leak checked all the connections and all the pipes. Nothing. The other two other things in our camper that use gas are the hot water heater and the stove. We used those for the whole summer and only went through 1 thirty pound tank.

So, here's what I know: the furnace alone is the culprit. But what I don't know is why. If it's a gas leak, it's only when the furnace is running. But it seems like if there was a gas leak right there at the furnace, something would have ignited. (Insert "shudder" here) Could something cause a furnace to run so inefficiently that it would use that much gas?

I'm going to guess that the number one suggestion will be "You should take it in." Because that would be my suggestion. There's a few reasons that's not going to happen: it's very difficult to get it out of its permanent site, the trailer is not plated, the nearest repair place is over an hour away, I wouldn't trust the tires to go 10 miles, etc. Also, I'm somewhat handy, so if the options are taking it someplace or installing a new furnace, I'd chose the latter. And I do feel that if I know what I need to fix, clean, or replace I could do it myself. I just don't know what to look for or where to start. I'm hoping someone has had a similar experience and can point me in the right direction.

Thank you.

[pianotuna]

allersj wrote:

facalton wrote:
If hooked to park electric use a ceramic space heater. More efficient, safe and much cheaper.

It's a seasonal, so I'm on a meter.

It still may be cheaper--and certainly more convenient.

Try this:

http://www.maxmcarter.com/fuels/fuelscalc.html

[allersj]

facalton wrote:
If hooked to park electric use a ceramic space heater. More efficient, safe and much cheaper.

It's a seasonal, so I'm on a meter.

[facalton]

If hooked to park electric use a ceramic space heater. More efficient, safe and much cheaper.

[allersj]

For the people who asked, yes, they are single pane windows and they were dripping.

Once I can camp again, my first thing to check will be any potential air leaks. I was sure it had to be something with the furnace, but the more people mention the air leaks, the more it makes me wonder. My kids weren't camping with us that weekend so I'm not sure if I even went into their bedroom. The roof vent may have still been open a bit. Also, I previously mentioned the gap in the one slideout. If cold air is getting drawn in and the hot air is escaping, I bet that uses lots of gas.

Of course, until I get out there and try it, it's all speculation. I will update after I do. Fingers crossed.

Thanks again.

[allersj]

larry cad wrote:
So as I set here, it occurs to me that the water heater also uses propane, and could be using more than normal.

I ran the hot water heater (and stove) for the remainder of the season and only used 1 tank.

[BurbMan]

When we ordered the Terry TT we spec'd all factory options including the dual-pane windows. The lack of condensation was a huge plus, and a side benefit we didn't expect was how much quieter the camper was, the dual-pane windows do a lot to keep out exterior noise.

We just camped in this new 5er last weekend, with temps 27* the first nite. Even with only single pane windows, we kept the day/nite shades down and that air layer in front of the window kept condensation from forming at all. What's interesting is that this 5er with single pane windows and 3 slides stayed warmer with less furnace runtime than the Terry TT that had dual pane windows and one slide. While those are factors for sure, the thicker walls and insulated/heated basement also help quite a bit.

Worth noting, if the tanks are new and aren't properly purged on the first fill, the air inside compresses and you only get about half as much propane in the tank as you should.

[larry_cad]

Been watching this thread for a while, and even put in my 2 cents a while back. Reading this morning and it seems like there is nothing wrong with the heater and nothing wrong with the plumbing for the propane, and "probably not" the ducting.
(Please excuse the use of the word plumbing there)

So as I set here, it occurs to me that the water heater also uses propane, and could be using more than normal. Water heaters use two thermodiscs, one to control the water temperature, and the second, redundant one to act as a safety. I've had personal experience with mine where the water tank had vibrated away from the two thermodiscs to the point that neither were regulating the water temp. I realized this when I took a shower and the water was REALLY hot.

The problem for me at least, was the crappy factory installation which was falling apart, allowing the tank to fall slightly backward, and the foam sheet that holds the thermodiscs tight against the tank, had a small gap instead of actually touching tank surface.

I never thought of propane usage, I just wanted to get my water back into normal temp range. Also, water heaters burners occasionally get out of tune and burn yellow instead of blue.

Just a suggestion, but it might be worth checking the "other" propane user. Check for blue flame, correct water temperature, and a mud dauber home in the chimney.

Just a thought that may be way off, but won't take long to verify.

(That will be 2 cents please.)

[valhalla360]

JaxDad wrote:
Lots of misinformation here. It’s not propane, it’s LPG, Liquified Petroleum Gas.

It mainly consists of propane (C3H8) and butane (C4H10) or a mixture of both with several other light hydrocarbon compounds. Like gasoline it’s components usually vary depending on where and when you buy it. Buying LPG in south Florida and then heading to the frozen north of the continent might not work very well.

In the USA, it's typically Propane with just trace amounts of other components. So calling it "propane" is quite reasonable and you are unlikely to find significant differences between Florida and Indiana.

In some other countries (typically where they don't experience extreme cold), they may use a larger percentage of butane.

Of course, this is largely irrelevant to the OP find the leak in his system.

[JaxDad]

Lots of misinformation here. It’s not propane, it’s LPG, Liquified Petroleum Gas.

It mainly consists of propane (C3H8) and butane (C4H10) or a mixture of both with several other light hydrocarbon compounds. Like gasoline it’s components usually vary depending on where and when you buy it. Buying LPG in south Florida and then heading to the frozen north of the continent might not work very well.

[JBarca]

allersj wrote:
Thank you all once again for the suggestions. The one that I am definitely going to check out is the air leak theory especially around the slideouts. It never occurred to me that that could be the issue. I do remember that around June of last year I had to adjust my one slideout. The top was sealed up tight, but the one bottom corner (about 3 feet from the furnace return), had a sizable gap. I did get it adjusted so that it closed up. But I'm sure it was like that from when I opened the camper up in the spring. If the furnace was just constantly sucking in cold air those nights, I would bet that would make it use quite a bit of gas.

Hi,

I'll throw my experience into the mix as we have winter camped a fair amount, and I have an above the average RV'er understanding of the Atwood hydroflame furnace. At least I think anyway.

What is the brand and model of your furnace? It can help give better answers to your exact furnace, but the Suburban works very similar in the big picture to the Atwood.

Some comments that may help spark some ideas for you to check.

Doug R gave a lot of good facts on the furnace system. I'll add a few extra. You stated the furnace system used to work correct in your mind, and now it appears to be burning through a lot of propane, what changed? In the furnace there are 2 areas that I will explain to help you think, maybe it is OR is not the furnace?

A. In the furnace, there is a gas jet at the end of the gas valve, that jet orifice is precision machined to deliver a certain BTU rating at a certain gas pressure (11" WC pressure). The only way to get more gas through that same size hole is, the hole got bigger or the gas pressure was higher. Flow is proportional to the pressure drop across the orifce.

B. The furnace has a high temp limit safety switch. If that high temp switch is tripped, it shuts off the gas valve until the switch and furnace cool down to it's differential setting, and then the gas valve opens back up. You can hear the burner cycle, the fan keeps running, the burner goes on an off. If the system is ducted and sized correctly (many campers are not) that switch should never trip as the air flow over the heat exchanger inside the camper should be cooled enough to not over heat. And if the gas side of the heater exchanger is blocked, the gas fumes can't get out and that too will cause the high limit to trip.

Now understanding those two areas of the furnace, gas orifice jets do not wear out very fast, if ever. It takes a boat load of time and flow to erode the jet. What are the odds the jet got bigger from when the camper used to work until now? Slim I think, but ask your self that. If the jet did not change, then the LP burn per minute did not increase. So you can rule in or out the jet, I think anyway.

The main tank LP regulator is supposed to limit the gas pressure when the furnace is running. Doug can confirm this, but if the main tank regulator went up to 14" WC when the furnace was running, that is the max limit considered OK for a wide open main tank regulator. The 3" WC extra pressure could increase the LP gas flow through the same size orifice, (~ 28%) but the main tank regulator could of been doing that when the furnace worked when you thought it was working right.

If the furnace was using more LP for increased LP pressure, it would create more heat. The BTU's are being burned, the heat is coming out of the furnace. BUT there is the high limit safety switch that will shut down the gas valve if the heat exchanger gets too hot. With that high limit in the mix, how can the furnace create excess LP usage as the limit switch keeps shutting down the gas valve? You can hear the gas valve going on and off by the roaring burner sound of a 30K or 35K furnace without much trouble.

Think through the above, it can rule in and out the furnace is your issue. From what little we know about your furnace, odds are, the furnace is not burning more LP gas then it used to a year or so ago. You are loosing heat out of the camper or taking in more cold air.

You said you checked all the fittings for leaks and found none, well the fittings may not be leaking, the gas valves and gas regulators can, but still those leaks can be small, and it's hard to leak a good part of a 30# tank in 7 hours and not smell it. The water heater, the furnace, the fridge, the stove, the main tank and stove regulator can all leak, but again, you did not smell it. The stove is inside, that you can smell more easy, the rest of those valves/regulator are outside or closer to outside.

If you want to rule out the LP gas system itself, educate your self on these 3 LP gas checks. These are standard LP system gas checks. You need a manometer or a gas gauge to do them.

1. A system pressure drop test
2. A main regulator pressure set point test
3. A main regulator lock up or max pressure test

Those 3 tests will confirm you have "no" leaks in any of the LP system, it will confirm the main tank regulator is not passing very high pressure and if the main tank regulator is not too low in pressure. In your case, low LP pressure is not what you are seeing, but it's good to know so all LP systems are working right.

Once you rule out the furnace itself, you come down to, heat is escaping the camper, or too much cold air is entering the camper.

No one yet asked if the wind was blowing outside? Was it?

No one asked yet, do you have single pane glass windows?

You said you used to use an electric heater and that would keep the camper warm. A 35,000 BTU gas furnace can create a lot of heat if you actually burned a 30# tank over night, where did all that heat go?

How many electric heaters did you have? 1 heater, 5 heaters? Are they 1,500 watt heaters? If your camper is 30 amp service you only have so much power. If your on 50 amp, the wall outlets are still limited, you can only plug in so many heaters and not trip out the 15 amp circuit breakers. You need a lot of electric heat to create the amount of heat a 30# or 20# LP tank (if the tank was not full) can give you.

This comes back to, I think more cold air came into the camper, and or you lost more heat from the camper, or both, through ducts blowing in the wrong place, etc.

This much I can tell you from our winter camping. Single pane glass sucks for heat retention. The windows would be totally covered in wet condensation. Was yours?

Slide rooms, the rubber seals stink for heat retention and can allow cold air in. The slide floor is many times not insulated. You have 3 slide? We only have 1 slide on our 32 ft camper with a 35,000 BTU furnace. You have a lot more heat loss in the just slides.

If the wind is blowing, all the window leaks and slide leaks can overpower the furnace. We went to the shrink wrap on the windows for the single pane glass and that made a large difference in heat loss and cold air entry and dropped the wet windows to almost nothing. We also have to deal with all the humidity in the camper. We crack open one roof vent a good 1" up,(yes it lets heat out) we run a dehumidifier, we set the T stat at 64F at night, we run one oil electric heater and one ceramic heater powered by a separate 120 VAC power line into the camper (we only have 30amp hook up), we practice extra venting of the camper when we shower and when we use the range top for cooking to let out all that excess moisture. And I added 4, attic vents in the roof to let the excess moisture out of the attic to not all mold up the attic. Yes, the attic will mold up if you camp a lot in times of high internal humidity and do not deal with it to keep it in check. We camp down to 30F often, days are only about 45 to 50F but the sun helps heat the camper during the day.

We have an enclosed tank compartment and 2 heat hoses goes through that compartment to convect heat into the area of the tanks. I added extra insulation in the tank compartment to not loose excess heat. I also have a temp sensor in the tank compartment to know what the temp is. We have to have the furnace on to keep the tank compartment warm enough to not freeze a tank. All my dump valves in inside the tank compartment.

If you read all this this far down, what makes more sense to you? It points to, you lost more heat then usual and or, you took on more cold air, or both.

Hope this helps, and report back your findings. We all learn something from this.

John

[StirCrazy]

dougrainer wrote:

pianotuna wrote:
Philh,

I think you may mean the regulator. Propane itself does not freeze until -188 C. (-306 f). It does boil at -43 (-45 f)

The other thing that may happen is that sometimes there is a lot of butane in the mix. Butane boils at -1 c (30 f). So it can be a BIG problem.

In the summer time one is better off with butane as it has 102,600 btus per gallon and propane has 91,500 BTUs per gallon

Propane is stored within the tank as a liquid, which is then released through a valve as gas. However, when temperatures drop too low within the tank, right around -44 degree Fahrenheit, the propane no longer has the ability to convert into its gaseous form. IF you are in a RV in -44 degrees F, you have WAY MORE problems than trying to run your LP appliances:B Doug

PS, In the USA, you will have a very hard time finding Butane for DOT RV tanks. Butane has been phased out for years by LP dispensers and refinery's. I know Mexico has it and I guess Canada since you are in Canada

I have never seen butane here at propane places. but its a big country....

Steve

[pianotuna]

dougrainer wrote:

pianotuna wrote:
Philh,

I think you may mean the regulator. Propane itself does not freeze until -188 C. (-306 f). It does boil at -43 (-45 f)

The other thing that may happen is that sometimes there is a lot of butane in the mix. Butane boils at -1 c (30 f). So it can be a BIG problem.

In the summer time one is better off with butane as it has 102,600 btus per gallon and propane has 91,500 BTUs per gallon

Propane is stored within the tank as a liquid, which is then released through a valve as gas. However, when temperatures drop too low within the tank, right around -44 degree Fahrenheit, the propane no longer has the ability to convert into its gaseous form. IF you are in a RV in -44 degrees F, you have WAY MORE problems than trying to run your LP appliances:B Doug

PS, In the USA, you will have a very hard time finding Butane for DOT RV tanks. Butane has been phased out for years by LP dispensers and refinery's. I know Mexico has it and I guess Canada since you are in Canada

I got sold a butane mix once in Florida.

Of course if one is running the furnace at -44 f the boiling is not going to keep up with the demand. I carry a magnetic block heat for that purpose--but so far have not needed to use it.

I use it on the generator in extreme cold.

[allersj]

Thank you all once again for the suggestions. The one that I am definitely going to check out is the air leak theory especially around the slideouts. It never occurred to me that that could be the issue. I do remember that around June of last year I had to adjust my one slideout. The top was sealed up tight, but the one bottom corner (about 3 feet from the furnace return), had a sizable gap. I did get it adjusted so that it closed up. But I'm sure it was like that from when I opened the camper up in the spring. If the furnace was just constantly sucking in cold air those nights, I would bet that would make it use quite a bit of gas.

[dougrainer]

pianotuna wrote:
Philh,

I think you may mean the regulator. Propane itself does not freeze until -188 C. (-306 f). It does boil at -43 (-45 f)

The other thing that may happen is that sometimes there is a lot of butane in the mix. Butane boils at -1 c (30 f). So it can be a BIG problem.

In the summer time one is better off with butane as it has 102,600 btus per gallon and propane has 91,500 BTUs per gallon

Propane is stored within the tank as a liquid, which is then released through a valve as gas. However, when temperatures drop too low within the tank, right around -44 degree Fahrenheit, the propane no longer has the ability to convert into its gaseous form. IF you are in a RV in -44 degrees F, you have WAY MORE problems than trying to run your LP appliances:B Doug

PS, In the USA, you will have a very hard time finding Butane for DOT RV tanks. Butane has been phased out for years by LP dispensers and refinery's. I know Mexico has it and I guess Canada since you are in Canada