More on heating - Fiberglass RV


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Old 06-08-2007, 02:34 PM   #1
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Trailer: Trillium 13 ft
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Hi all, my dad provided some insight into this...

I asked about how many BTUs I need to heat my 1300.

I quote:
1. Surface area =~ 440 cubic foot ( 10 + 10 +7 + 7 ) * 13

2. Outside air temp. = 14 F

3. Inside room temp. = 75 F

4. Supply temp. of air just leaving the heater = 100 F ( assumed )

5. Coefficient of heat transfer ( U value ) = 0.3 ( for caravan sandwitch
pannels )

6. Air changes assumed = 2, giving CFM = 30 ( cubic feet per minute ).

Now , we have two heating loads :

A: Surface heat losses = 440 * 0.3 * 25 F( temp diff. bet. 100 F and 75 F
) = 3300. Btu / hr

B: Heat losses to warm some fresh air = 30 * 1.08 *( 75 - 14 )F = ~ 2000.
Btu / hr

Total load = A + B = 5300. Btu / hr

taking a factor of safety of 15 %, giving a total load = ~ 6000. Btu / hr


I pointed out that I am using Reflectix and insluation, and waiting for him to weigh in.




Mo
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Old 06-09-2007, 04:58 PM   #2
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Benita... we need the beanie!

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Old 06-09-2007, 05:23 PM   #3
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Most heaters will tell you how many sq. feet they will heat on the box or in the spec. sheet. Thats what I go by and have never been disapionted.
John
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Old 06-09-2007, 05:41 PM   #4
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That's very interesting! I have a fiberglass floored Boler. I hope someday to take out the old Suburban furnace (which actually works nicely) and replace it with a water heater and pump attached to a radiant heat system piped under the floor. I think a radiant system would be an excellent method for a small egg. Cheers, Alec
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Old 06-10-2007, 03:41 PM   #5
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The manufacturer's calculation of area which can be heated makes a bunch of assumptions about the construction of the building or RV which is to be heated. They may be way off of the actual conditions, which is why people seem to routinely report that RVs require much larger air conditioning (I know, this is heating, but it's a similar situation...) capacity than the home unit ratings would suggest.

In near-freezing conditions, a 1500 watt electrical heater has proven to be much more than we needed in our 17' Boler... but that's just one example.
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Old 06-10-2007, 03:44 PM   #6
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In answer to your question in English :-P

I heated my 13 with a 3kbtu Blackcat and a 2800 btu Olympian Wave 3. (Not at the same time, mind you)

Both would sweat me out in even below freezing weather.
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Old 06-11-2007, 07:55 PM   #7
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I am glad to know that the 2800 btu Olympian Wave 3 works.... I might end up getting one,,, and seriously considering a Mr. Heater Big Buddy.
To Brian's point... it depends on several conditions....
heat dissapation through windows, shell, floor, etc. outside temp, inside temp, insulation, etc.
I just thought it might be ammuzing/educational to read the "science" behind it.
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Old 06-12-2007, 12:39 PM   #8
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Quote:
...I just thought it might be ammuzing/educational to read the "science" behind it.
I agree! The many factors are why the manufacturer's ratings may not apply, and it would be interesting to get a complete calculation for the actual trailer situation. I thought someone took a shot at this a while ago in this forum, but I haven't really looked for it.

By the way, 1500 watts is about 5100 BTU/hour, so if a 1500 W heater is significantly more than required, that is consistent with the experience people are reporting with their portable propane-fired heaters.
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