Community Forums

SkiSmuggs · 11-11-2017, 01:14 PM

I had my furnace set to 50 until I could complete winterizing. When I got around to it because temps were dropping, we found ice crystals in some water jugs. Puzzled, I turned the thermostat up. The furnace would ignite for 5 seconds then go out and did it repeatedly which explained the ice crystals. I had installed the Mopeka Tank Check sensors and they read 24%(LOW) and 81% so even though I have an auto switch valve, I manually switched to the fuller tank. Still the furnace kicked off after a few seconds. I did some research and found a suggestion to run my stove to get air out of the lines, and bingo!, the furnace started working. Just a suggestion for those RVing in the cold. But it seems 24% propane is too low for cold weather.
DW doesn't understand why I carry both an electric heater and a Mr Heater Buddy.

Gary RVRoamer · 11-11-2017, 03:01 PM

Yeah, if the LPG blend is just 24% propane, you are very likely to have problems at or even near freezing. Most of the remaining 76% is probably butane and butane stops vaporizing altogether at about 30 degrees and doesn't generate much vapor pressure as the temperature gets close to that. At a guess, I would think a 24/76 blend would quit working around 20 degrees and become unreliable much below 30.

If you want to make your own guess, there are engineering tables that give vaporization info for common propane/butane blends.
https://www.engineeringtoolbox.com/p...ix-d_1043.html

Loggenrock · 11-11-2017, 08:15 PM

I read that as 24% FULL, not 24% mix... Volume in the tank has only a little bit of issue with vaporization. The surface area is the limiting factor, usually, as to vaporization rate in the tanks. Vertical tanks have less surface area than horizontal tanks. With cold temperatures, the propane may not have been vaporizing at an adequate rate to keep the furnace running. Buddy just had an issue with a propane fed camp stove/griddle. Started fine, but developed weak flames in all burners. Swapped tanks, no improvement. Solved it by "resetting" the regulator. Shut off tank, turned on all burners to drain any residual gas. let it sit for several minutes, then burners off, opened tank, re-lit all burners - good flame all the way around. maybe something to think about for future issues. ST

SkiSmuggs · 11-12-2017, 05:55 AM

The Mopeka sensors measure % Full, not blend. Since my second tank had gone from 100% full to 81% full, I assume the auto switch valve had already switched over, but I manually switched it to be sure. Temps were teens at night and 20s during the day when I discovered the problem. There are no provisions for heating the LPG tanks, but I have read that some folks insulate them for better cold weather performance.
I had issues once with a 100 gallon propane tank for a heated out building freezing up at single digits. The tech added something like methane to the tank to help, but the ultimate fix was to bleed the tank to rid it of air and moisture as the regulator had ice crystals forming in it.

timjet · 11-12-2017, 06:10 AM

Quote:

Originally Posted by Gary RVRoamer

Yeah, if the LPG blend is just 24% propane, you are very likely to have problems at or even near freezing. Most of the remaining 76% is probably butane and butane stops vaporizing altogether at about 30 degrees and doesn't generate much vapor pressure as the temperature gets close to that. At a guess, I would think a 24/76 blend would quit working around 20 degrees and become unreliable much below 30.

If you want to make your own guess, there are engineering tables that give vaporization info for common propane/butane blends.
https://www.engineeringtoolbox.com/p...ix-d_1043.html

Seeing that we don't have much control over the blend and being in FL but traveling to colder wx, what is the fix to ensure we have a source of burnable fuel for the furnace.

SkiSmuggs · 11-12-2017, 06:17 AM

Quote:

Originally Posted by timjet

Seeing that we don't have much control over the blend and being in FL but traveling to colder wx, what is the fix to ensure we have a source of burnable fuel for the furnace.

Keep your tanks at 30% or higher. Blend was probably not the issue and, as you noted, we can't control that.

timjet · 11-12-2017, 06:28 AM

OK, I reread your 1st post and I think you have a TT and carry 2 tanks. You switched to the fuller tank and bled the propane lines of air to get a positive flow of propane to the furnace burner. I got it.

hohenwald48 · 11-12-2017, 07:37 AM

Auto switch over valves can be a little wonky at times. Also, a tank that is at 81 percent is actually as full as it can get. Remember, they can only be filled to 80 percent capacity.

I suspect that air in the lines from the second tank was your problem from the beginning. When you refill a tank, you should purge the lines on that tank or else you will have a problem when the auto changeover occurs.

SkiSmuggs · 11-12-2017, 08:06 AM

Quote:

Originally Posted by hohenwald48

Auto switch over valves can be a little wonky at times. Also, a tank that is at 81 percent is actually as full as it can get. Remember, they can only be filled to 80 percent capacity.

I suspect that air in the lines from the second tank was your problem from the beginning. When you refill a tank, you should purge the lines on that tank or else you will have a problem when the auto changeover occurs.

That tank had read 100% a couple weeks earlier so perhaps the Mopeka sensors take that into account. They don't weigh the tank as LP dealers do, but use sonar or something similar to measure the contents. They attach via magnet to the bottom of the tank and you set the app to the appropriate tank size which is 30# in my case (about 7 gallons). But you are correct in that they are only filled to 80% and you are probably correct about the rest of it.