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Open Roads Forum  >  Tech Issues

 > Furnace using too much propane

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bucky

Raleigh metro

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Posted: 03/31/22 05:56am Link  |  Quote  |  Print  |  Notify Moderator

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


2005 Cummins 3500 2WD LB quad cab dually pulling a 2014 Blue Ridge 3025RL


dougrainer

Carrolton, Texas

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Posted: 03/31/22 08:48am Link  |  Quote  |  Print  |  Notify Moderator

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

allersj

Hastings, MI

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Posted: 03/31/22 01:05pm Link  |  Quote  |  Print  |  Notify Moderator

bucky wrote:

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


No.

Dusty R

Charlotte Michigan 48813

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Posted: 03/31/22 05:20pm Link  |  Quote  |  Print  |  Notify Moderator

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.

BurbMan

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Posted: 03/31/22 06:08pm Link  |  Quote  |  Print  |  Notify Moderator

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....

valhalla360

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Posted: 04/01/22 12:26am Link  |  Quote  |  Print  |  Notify Moderator

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.


Tammy & Mike
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jkwilson

Indiana

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Posted: 04/01/22 08:27am Link  |  Quote  |  Print  |  Notify Moderator

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?


John & Kathy
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jodeb720

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Posted: 04/03/22 08:17am Link  |  Quote  |  Print  |  Notify Moderator

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.

philh

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Posted: 04/03/22 07:21pm Link  |  Quote  |  Print  |  Notify Moderator

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.

pianotuna

Regina, SK, Canada

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Posted: 04/03/22 09:54pm Link  |  Quote  |  Print  |  Notify Moderator

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


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

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