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.

[allersj]

philh wrote:
Two questions, are you sure the tanks were full? Take them to tractor supply, their personnel always seemed to be well trained.

2nd question, are you sure they were empty. If it's too cold out, the propane may not turn into gas to supply the furnace. I had that issue at my park model, **** tank froze up while feeding a generator.

I will say that I was not positive that the first 2 tanks were full. I was about 90% sure. However I know the third tank was full, and it did the same thing that happened to the first 2. And all the (empty) tanks did end up at the local TSC and they were filled by weight.

[joerg68]

Many years ago, something very similar to the OP's experience happened to us. We had bought a tank of butane in summer in Southern France, not knowing about its "special properties".
Cue forward to a truck camper rallye in late October, with night temperatures in the 20s.
We were woken up in the middle of the night by the low voltage alert of the LPG monitor in a freezing cold camper - the butane had "run out", and the furnace fan just kept on running until the battery was low (Suburban heater I believe, not sure why there was no safety circuit for this condition, but that is what happened).
After some initial confusion from being woken up by the alarm, we got it sorted out and replaced the seemingly "empty" tank with a fresh one with regular propane, and went back to sleep.
It was not until the next morning that we learned about Butane not evaporating below freezing, and that our tank had been, in fact, not empty.
This is why I suggested to the OP upthread to investigate in this direction.

[pianotuna]

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

[philh]

Two questions, are you sure the tanks were full? Take them to tractor supply, their personnel always seemed to be well trained.

2nd question, are you sure they were empty. If it's too cold out, the propane may not turn into gas to supply the furnace. I had that issue at my park model, **** tank froze up while feeding a generator.

[jodeb720]

For years, my heater would run - incessantly - and very little air volume wasn't come out of the registers.

If my wife set the temperature at 65, the heater would run for 20 minutes only to barely raise the temperature from 62 to 65.

Last year, after a catastrophic failure - we decided to redo the inside of the trailer (think RV makeover) and part of the process was to determine what was going on with the heater.

The design of the airflow was to pass down into a plenum under the heater, (located on the passenger side of the 5er) then to a central plenum that ran under the floor from front to back with the registers connected to the plenum.

What I found was the plenum under the heater had both sides not closed. Think of a cube - with the left and right sides opened, not closed.

All the heat that was generated was blowing under the 5er not passing to the plenum in the middle redistributing the heat.

During the redesign, I sealed the plenum off - and with some help from some folks here (Thanks Doug) I was able to utilize the 4" duct connectors and imagineer a solution that works.

The key is to understanding the flow of the air, the volume the heater needs to pass through the ducts without restricting the airflow and causing the heater to hit the high temperature limit safety switch.

Since I've made that change, my heater cycles much shorter (only a few minutes - generally less than 5) and my consumption of propane has been reduced dramatically.

The OP has an issue - consuming that much propane in that short a period of time there is something seriously wrong. I'm wondering if the regulator is freezing up staving the heater of propane and being misdiagnosed as being empty?

I'm at a loss of another explanation - but there's something awry with this situation.

[jkwilson]

A couple folks have mentioned it already, but I’d chase the idea that you have an air leak. If you have a rig that uses the underbelly as a plenum to help warm the tanks, a leak in the belly material results in heated air blowing directly outdoors.

Another possibility is ductwork detached from the furnace or pinched restricting circulation.

Finally, do you know where the air returns are in your rig and have you checked that they aren’t blocked?

[valhalla360]

Dusty R wrote:
It's been a few years since I've looked, but a RV furnace is the most in- efficient furnace there is. It has 2 fans, 1 motor. 1 pushes air threw the inside of the combustion. The other circulates air over the outside of the combustion chamber, that is heated to warm the RV. When the T-stat calls for heat the fan motor turns on for a pre set time, to purge the inside of the combustion chamber with air from outdoors, before the burner lights. When the RV T-stat reaches the set temperature the burner turns off and fan motor continues to run until cooling the combustion chamber to a preset temperature.

It seems to me that it wood be better to put a dampers on the combustion chamber to turn the air flow on/off.

30 seconds at the start and end of a heating cycle isn't using a lot of power and certainly has nothing to do with the OP's propane loss.

Air to Air heat transfer isn't the best but reality is most RVs only rarely use the furnace, so there isn't much to gain by upgrading the furnace.

Example: Last winter we spent around 6 months traveling with a good bit of time in areas where the temps dropped to freezing. This is very heavy use compared to the average weekend warrior. Including cooking, we went thru 4 - 20lb tanks.

Not much room to save a lot in propane with a more efficient furnace design.

[BurbMan]

Yes it's an air-to-air heat exchanger just like they used on the 60's-70's VWs. The old joke what the heat on those VWs had only 2 settings: too hot and too cold. Sounds a lot like how RV heat works....

[Dusty_R]

It's been a few years since I've looked, but a RV furnace is the most in- efficient furnace there is. It has 2 fans, 1 motor. 1 pushes air threw the inside of the combustion. The other circulates air over the outside of the combustion chamber, that is heated to warm the RV. When the T-stat calls for heat the fan motor turns on for a pre set time, to purge the inside of the combustion chamber with air from outdoors, before the burner lights. When the RV T-stat reaches the set temperature the burner turns off and fan motor continues to run until cooling the combustion chamber to a preset temperature.

It seems to me that it wood be better to put a dampers on the combustion chamber to turn the air flow on/off.

[allersj]

bucky wrote:
Have you got a roof vent open somewhere or even worse a quiet roof vent fan running?

No.

[dougrainer]

Dutch_12078 wrote:

dougrainer wrote:
Propane tanks can be filled by weight or volume.But according to DOT regulations, propane tanks with less than 200 pounds capacity must be refilled by weight. The proper refilling procedure is detailed in the CETP handbook.

Yes, DOT says fill smaller cylinders by weight, but my preference is refillers that fill by volume using the 80% Fixed Liquid Level Gauge to determine when the cylinder is full, just as they do for the permanent ASME tanks. There's no fudging on the weight settings then.

True, but that does not make it right or legal or safe. I would lose my LP license if I get caught violating Railroad Commission regulations. There is a REASON they have these type laws/regulations. Every 3 years we have to go to 8 hour Texas LP safety Seminars to keep our individual license. You would be amazed at some of the issues that come up about filling. Doug

[bucky]

Have you got a roof vent open somewhere or even worse a quiet roof vent fan running?

[Dutch_12078]

dougrainer wrote:
Propane tanks can be filled by weight or volume.But according to DOT regulations, propane tanks with less than 200 pounds capacity must be refilled by weight. The proper refilling procedure is detailed in the CETP handbook.

Yes, DOT says fill smaller cylinders by weight, but my preference is refillers that fill by volume using the 80% Fixed Liquid Level Gauge to determine when the cylinder is full, just as they do for the permanent ASME tanks. There's no fudging on the weight settings then.

[dougrainer]

Propane tanks can be filled by weight or volume.But according to DOT regulations, propane tanks with less than 200 pounds capacity must be refilled by weight. The proper refilling procedure is detailed in the CETP handbook.

[dougrainer]

2oldman wrote:

dougrainer wrote:
The correct way to fill tanks is by weight.

Don't find that too often in western states.

Nobody ever said the Western USA was enlightened(Seattle/Portland/San Francisco/Los Angeles):B. Just because you have never seen it does not mean it is required. LOTS of Texas LP fillers do not fill by weight, even tho they are licensed and required to do so. Doug