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Old 12-04-2008, 08:07 AM   #1
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How long would a furnace run on 2 40 gallon lp tanks?

If say the furnace ran three times a day for three hours a day to keep at set temp? Just out of curiosity.
(ps... do they make auto switch regulators for the lp tanks..)
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Old 12-04-2008, 08:31 AM   #2
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That would depend on so much.. Outside temp, btu on furnace, how big of a trailer, how many vents on the furnace.

I haven't ran mine all the time, and not in the winter, but in 8 days I used one tank and a little... Cooking and heater at night, plus hot water heater. But there are four of us with the kids and my wife likes her hot showers... And I don't know how full the tank was to begin with...

This is what you do.. When someone comes to visit, Or you can just pretend. turn the heat on and try it out... I think every set up will be a little different.
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Old 12-04-2008, 08:54 AM   #3
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Well, as Jason pointed out, there are variables out the wazoo, but if it's really cold (around -15 at night, around 15 during the day), then I generally wind up filling one seven gallon cylinder every two days to keep folks going. But, again, that's VERY much a rough estimate.

(Your Airstream probably has forty pound cylinders, not forty gallon cylinders. That's a little over nine gallons per cylinder.)


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Old 12-04-2008, 08:56 AM   #4
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I agree with purman -- a lot of variables are in play. A tank will last most of the summer. I camp in weather around freezing quite often, running the furnace only at night. It seems a tank can last a couple weeks with nights around 30 +/- and shutting it off during the day. I get too hot sleeping if the thermostat is above 60 degrees.

While underway on a 350 mile drive in upper teen temps, I once had the furnace on with the thermostat set to about 62 degrees -- mistake! The breeze from driving took away a lot of heat and I used up most of a tank in that one drive -- it emptied toward the end of our first night camping.

I haven't had to drive in weather that cold again but I'd probably set the thermostat in the low 40s and set a thermometer next to the waterpump, checking that once down the road a bit.

You'll find the furnace cycling on and off quite a bit the colder it gets. 3 hrs a day might be conservative if you're running it all day and night and the temps are in the 20s. In frigid conditions I'd recommend winterizing if you are away from any trailer more than a day. One mistake or malfunction could cause a lot of very expensive damage.

Here's a pic of frost on my Safari last month in Oklahoma. Note the conduction heat loss through the ribs. nickcrowhurst posted last weekend talking about insulation he puts in his windows -- look that up if you're interested.
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Old 12-04-2008, 09:20 AM   #5
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I can relay my experience with two 30 pound tanks and my 25 foot Tradewind. I live in it full time and right now tempperatures range from 1 celcius lows at night and 8-10 celcius highs during the day. I run the furnace from early evening until I leave for work in the morning, so around 10-12 hours. I also use my oven and stove for cooking each evening and for morning coffee. My water heater runs on both propane and electric, but I only use it in electric mode. One thirty pound tank lasts me 6 days. So as soon as I switch to the full tank, I go refill the empty one. By getting in the habit of doing this, I'm never without propane. I hope my experience helps you.
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Old 12-04-2008, 09:27 AM   #6
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Quote:
Originally Posted by CanoeStream View Post
I agree with purman -- a lot of variables are in play. A tank will last most of the summer. I camp in weather around freezing quite often, running the furnace only at night. It seems a tank can last a couple weeks with nights around 30 +/- and shutting it off during the day. I get too hot sleeping if the thermostat is above 60 degrees.

While underway on a 350 mile drive in upper teen temps, I once had the furnace on with the thermostat set to about 62 degrees -- mistake! The breeze from driving took away a lot of heat and I used up most of a tank in that one drive -- it emptied toward the end of our first night camping.

I haven't had to drive in weather that cold again but I'd probably set the thermostat in the low 40s and set a thermometer next to the waterpump, checking that once down the road a bit.

You'll find the furnace cycling on and off quite a bit the colder it gets. 3 hrs a day might be conservative if you're running it all day and night and the temps are in the 20s. In frigid conditions I'd recommend winterizing if you are away from any trailer more than a day. One mistake or malfunction could cause a lot of very expensive damage.

Here's a pic of frost on my Safari last month in Oklahoma. Note the conduction heat loss through the ribs. nickcrowhurst posted last weekend talking about insulation he puts in his windows -- look that up if you're interested.
Was that picture after had towed with it ?
Only reason I ask is I am woking on my trailer right now and I have my forced hot air ready heater going for about 30 minites then I have to shut it off it gets to about 75 degrees and it lasts about a hour in the 70's WITH windows open . So I bet my trailer will hold heat well if I seal it up.
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Old 12-04-2008, 09:55 AM   #7
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30k BTU/hr furnace, 93kBTU/gallon fuel means about 3 hours of furnace time per gallon of propane. 40# propane is about 10 gallons so it would be good for 30 hours furnace run time.
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Old 12-04-2008, 08:31 PM   #8
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Was that picture after had towed with it ?
It was dawn frost -- temps about 28 degrees. Furnace set during night at about 58 degrees.
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Old 12-04-2008, 09:47 PM   #9
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Here's another frost pattern

from rye patch reservoir a few years ago. (from a rally photo gallery)

With care, a tank of propane in conditions like this could last a week. With a bit more comfort, I'd wouldn't plan on more than 2 or 3 days. -

when you get conditions like Bob describes you can often see a frost line on the tank after the sun comes up that shows you just where the liquid level is.
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Old 12-10-2008, 02:29 PM   #10
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Quote:
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30k BTU/hr furnace, 93kBTU/gallon fuel means about 3 hours of furnace time per gallon of propane. 40# propane is about 10 gallons so it would be good for 30 hours furnace run time.
Ok I think next question is how long would it have to run to keep say 70' F temp if it stays in 70's for like three hours?
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Old 12-10-2008, 03:15 PM   #11
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Ok I think next question is how long would it have to run to keep say 70' F temp if it stays in 70's for like three hours?
I believe the part accented in the quote in red must be a typo.

I know that keeping it at 60 with outside temps in the 20s, it will run every 5 minutes or so for 2-3 minutes at a time. Set the thermostat at 70 in the same conditions and it runs nearly constant. I've spent sleepless minutes listening to the furnace cycle while I try to find a happy medium between some comfort and not using fuel at a high rate. Soft ear plugs work wonders during the shoulder seasons.

We use flannel sheets/down comforter or else sleeping bags in these conditions. It warms up pretty quickly when I get up in the morning and set it closer to 70 for comfort. Camping in the shoulder seasons, there are very few times when I have to run the furnace during the day.
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Old 12-10-2008, 04:18 PM   #12
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Mrcrowley, I think you'll have to experiment to have an answer.

How many windows and what kind of window coverings? We have some silver colored blinds on a lot of the windows, but if we wanted to conserve more, it would be a good idea to replace them with cellular shades. The front and back have supper thin curtains and they should be lined when someone around here (not me, I can't sew in any reasonable manner) has time to do so.

Are you talking about keeping it heated while having it parked at home? In that case, do you have a heat pump? Do you have a thermostat that will go as low at 40˚ and when the temp gets around 30˚, will automatically switch to the furnace? Probably not as only the newest ones have that thermostat (it's made by Dometic) and even if the A/C has a heat pump, it may not have the wiring to the thermostat for that kind of switching. When during the shoulder seasons we park it waiting for another trip, I plug in the shore power. I use the heat pump and furnace combo to keep the water tanks and lines warm enough. My electric bill goes up a lot, but some of that could be from house heating too, so I can't be sure just what is what.

These trailers are not well insulated and the more windows, the worse for heating and cooling. I think I was told by the dealer the insulation in the new ones was R-11, but it was only 1.5 to 2 inches of standard pink insulation, so think it's more like R 4 to 6. Plus, as well shown in the pictures above, the ribs radiate heat to the exterior rapidly. I am sure there are plenty of voids in the insulation and that's where a lot of heat would be lost. Modern insulating techniques are not used (yet) in Airstreams.

I don't like to leave home during the shoulder seasons because if the heat pump, thermostat, or furnace goes bad, life will not be good when the water lines defrost.

If you go boondocking when it's cold, you also have to watch the battery charge. A solar panel and a generator are backup because the furnace fan uses a lot of battery charge. If the temp is in the lower 20's at night the furnace will run a lot. Unlike Bob we can sleep through it, but I'll wake up in the middle of the night and worry about the batteries. If it's windy, that'll blow off a lot of heat too. We'll keep the temp around 55 to 60 to save propane and volts. The batteries that came with ours are the cheapest ones available, so we have to get better ones, but I'm waiting 'til these get bad. Even with a solar panel, short days in the Fall limit charging. So do clouds and trees overhead. Thus, a generator may be necessary.

Our propane tanks hold 30 lbs. each and a tank can be emptied in 2 to 3 days during nights of 15-25˚. We keep the temp in the evening at the low 60's and then lower it for sleeping. When we get up (not easy when it's 55˚ or less in the bedroom), we'll turn it up for a while. We only use the water heater twice a day—the water can stay hot for many hours after it's shut off.

So, there are so many variables depending on what you want to do, you'll have to experiment.

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Old 12-10-2008, 04:53 PM   #13
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On my last trip of the season the temperature was low 30's during the day and low 20's at night. The thermostat was set at 60 when we were out, 70 when we were there and 62 when asleep. At night one ceiling vent was open about 2" so as to reduce condensation. We run the water heater on propane and ran the fridge on propane while on the road. Used the range for only one meal (breakfast). Almost emptied one 30lb. tank in two days, but comfortable we were!
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Old 01-02-2009, 05:03 PM   #14
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2008 30' Slide Classic.
~28F day/~16F night (~10F with windchill)
furnace @ 55-75 depending on whether we were in/out/sleeping
fridge/water heater on electric
used range for every meal (seven mouths to feed)
emptied topped-off 30# tank in 50 hours
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