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Old 03-06-2019, 07:06 PM   #1
MaxwellD
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Heating while away

I have been deliberating on whether to leave the furnace on a low setting (50 degrees) versus a higher setting 65-70 degrees while the rig is parked and plugged in unoccupied for a time. Obviously it doesn't need to be at 65 degrees and the logical choice is a lower setting. But the question is: will a furnace cycle more to maintain a higher temp or cycle more if the lower temp is set? To me, it would seem that colder, denser air would be more stable and the unit should cycle less to keep it at 50 degrees instead of 65. But I don't know. All I do know is that my 3730 FL is a propane hog either way. Can someone shed some light on this question? All of this assumes no effect from insulation - maybe that is not a safe assumption?
Thanks in advance.
Max
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Old 03-06-2019, 07:34 PM   #2
DQDick
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We use 55 degrees when we are away. Haven't worked out the science, just know it works and stuff doesn't freeze.
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Old 03-06-2019, 09:45 PM   #3
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We leave ares around 45 to 50 when gone haven't had any problems.
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Old 03-07-2019, 05:05 AM   #4
WeBeFulltime
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You say "unoccupied for a time" which is a broad statement. Your LP supply has it's limits.
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Old 03-07-2019, 06:14 AM   #5
MaxwellD
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Quote:
Originally Posted by WeBeFulltime View Post
You say "unoccupied for a time" which is a broad statement. Your LP supply has it's limits.
Obviously, but the question I am trying to answer is which setting (higher or lower) will cause more cycling to maintain that temperature setting, ignoring the effect of insulation and assuming unlimited gas supply. Ideas?
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Old 03-07-2019, 08:42 AM   #6
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The lower the heat setting the less cycling. Think about it this way say it’s 50 outside and you have the heat set at 80 it will cycle more than if the heat is set at 51 degrees.
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Old 03-07-2019, 08:59 AM   #7
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The rate of cooling (dropping of inside temperature) is going to be dependent on the differential between the outside temp and the inside temp. So if the outside temp is 20 degrees and the inside temp is 70 degrees (differential of 50 degrees), the rate at which it drops the inside temp will be faster than if the inside temp is at 50 degrees (differential of 30 degrees). Since the furnace will kick on when the temp drops 2-3 degrees below thermostat set point, it will cycle more at the higher temp. If the outside temp were 50 degrees, it would not cycle at all if set for 50 inside, whereas it would if set for 70.

Newton's Law of Cooling states that the rate of change of the temperature of an object is proportional to the difference between its own temperature and the ambient temperature (i.e. the temperature of its surroundings).
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Old 03-07-2019, 08:06 PM   #8
TennTom
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BB beat me to it. It's all about the differential of temp.
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Old 03-13-2019, 01:25 PM   #9
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We did that just recently because the low was going to be in the low 20s. Set stat on 48. The unit cycled and kept the inside at 38. - 10 degrees off from setting. My mechanical/solid state stat in S&B bottoms at 55. I was curious how low the Dometic digital stat could be made to go. Anybody try really low? Just watch the propane! When it's being used, a good way to check the level is with a Fluke 62 Max IR Thermometer. Just point near the bottom of the LP bottle and slowly move up while squeezing the trigger. Where the temp makes a jump warmer is the line the liquid is in the bottle.
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Old 03-13-2019, 01:48 PM   #10
MJD
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Dont do it. Furnaces etc should only be run when your with the unit. They are not that reliable.
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Old 03-13-2019, 02:02 PM   #11
masterdrago
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They have safety mechanisms out the wazoo. The technology has been around since Adam & Adam. But then again, most of it is probably China's finest! So right, might not be the best idea to trust it, so be in it when the thing malfunctions.
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Old 03-14-2019, 03:16 PM   #12
Mark N.
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No physics to have to figure out here. It's simply this: If you're asking a furnace to keep the inside of your trailer at a higher temperature, it will run more often. Period. No other way to look at it.
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Old 03-14-2019, 03:38 PM   #13
MaxwellD
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Your point is good and i get that. The diferntial between the higher inside temp versus the outside temp thiough, is what brings the physics into the question. Apparently, keeping a cold area warm (enough) causes the futnacr to cycle less if a lower set point is chosen. Clearly, the question has been over-thought by me to begin with.
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Old 03-15-2019, 01:05 PM   #14
Dixie Flyer
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Heating while away.

Quote:
Originally Posted by MaxwellD View Post
I have been deliberating on whether to leave the furnace on a low setting (50 degrees) versus a higher setting 65-70 degrees while the rig is parked and plugged in unoccupied for a time. Obviously it doesn't need to be at 65 degrees and the logical choice is a lower setting. But the question is: will a furnace cycle more to maintain a higher temp or cycle more if the lower temp is set? To me, it would seem that colder, denser air would be more stable and the unit should cycle less to keep it at 50 degrees instead of 65. But I don't know. All I do know is that my 3730 FL is a propane hog either way. Can someone shed some light on this question? All of this assumes no effect from insulation - maybe that is not a safe assumption?
Thanks in advance.
Max

The lower the temperature the less your furnace will cycle. That being said we have a 3611rl Montana and during the winter months I use two electric heaters in the camper to keep it warm. I place them in the living room, kitchen area facing each other. Our camper sits in our back yard hooked to a 50 amp service with the slides out. I have never had a problem doing that and it saves on propane. It does run the power bill up but I figure it is a trade off, either you buy propane or you pay the power bill.
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