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Old 03-31-2016, 06:17 PM   #1
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calculating the BTU's you need to stay warm

So i have been researching to find out what a good R value for a schoolie would be for full timing it. i ran into this calculation to help me, hopefully it can help you as well.


take the area of the wall, floor or ceiling, multiple by the difference of the schoolies internal temp(or the temp you wish to maintain) and the current temperature outside then divide that total by the r-value of each surface.

Example: and 8 ft x 10 ft wall = 80 sq ft, the temp inside the bus is 70 and the outside temperature is 30 or a 40 degree difference, the R value we will call it 14 for this "wall"

(80 * 40)/14=229 btu's are required to maintain 70 degrees for that wall

a better example would be

24 ft by 3 feet for wall 1 and 2

(72 * 40)/14=206
206 * 2 as the both walls will be the same
so 412 BTU's for those walls

now lets assume you have a 26 ft by 10 feet wide roof/ceiling

(260 * 40)/14 =743 btu's

and for ease of math we will assume the floor takes up as much space so we just double that.

743 * 2 = 1,486 Btu's

1486 + 412 = 1898

1,898 BTU's needed to maintain the temp of 70 inside your schoolie when its 30 degrees outside with r 14 insulation. i grant these are brick and mortar numbers and you would probably need to add 10-15% more BTU's based on heat loss from windows and general heat loss. But it is still extremely manageable at 2,300 BTU's. A Mr. Heater portable buddy on 4k btus covers that easily with a box fan to move the heat around a bus.

How Insulation Works, What R-Value Means, and How to Calculate Heat Loss/Gain for your house | BrainStuff

is where i got my numbers.so hopefully this will help you plan and stay warm and toasty in your schoolie in the winter.
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Old 03-31-2016, 06:58 PM   #2
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so hopefully this will help you plan and stay warm and toasty in your schoolie in the winter.
This is how I plan to stay warm and toasty in my skoolie-

(And, IMHO, Rachel Nichols looks sooooo much better as a redhead)
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Old 03-31-2016, 07:07 PM   #3
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Originally Posted by Scooternj View Post
This is how I plan to stay warm and toasty in my skoolie-

(And, IMHO, Rachel Nichols looks sooooo much better as a redhead)
well you cant argue with that lol
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Old 03-31-2016, 07:41 PM   #4
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Scooter's plan looks very hot and very expensive.

i used the btu calculator found here:

Home Heat Loss Calculator

if i recall, i used a (-20) for my outside temp and (70) for an inside. my 30' bus needed about a 30K btu furnace.

i have 2" of spray foam insulation that was about R4.
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Old 03-31-2016, 09:04 PM   #5
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That's all the R value there is from 2" of spray foam?
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Old 03-31-2016, 09:17 PM   #6
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its been awhile since i did it.... perhaps that was R4 for each 1" of foam.
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Old 03-31-2016, 09:35 PM   #7
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Foam board is higher in R value, isn't it? I thought the R value of spray foam was better than that, especially considering the expense.
Perhaps the main idea of spray foam is how it does a good job of reducing the sweating because of its direct contact with the metal.
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Old 03-31-2016, 11:11 PM   #8
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Foam board is higher in R value, isn't it? I thought the R value of spray foam was better than that, especially considering the expense.
Perhaps the main idea of spray foam is how it does a good job of reducing the sweating because of its direct contact with the metal.
it depends on the board, the r-10 value is 2 inches thick, the r-4 value is 1-1.5 in thick. they were solid foam board, Spray foam is a different beast, but i believe they calculate the R value for each inch of insulation added that way. so initial r value of 3 for one inch, 6 for two inches and so on. Each spray foam will have information on how the R-value is calculated on the manufactures website. That is always the best source of information and also most of the time the most detailed.

side noted once you calculate the area once you wont have to ever do it again nor will your r value change. so the only thing that changes is the temp difference. But you can just go worst case scenario. which -20 would work lol.
664 x 90/14 =4,269
4,269 with 15% added heat loss
4,910
man 14 r value is kinda boss...
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Old 04-01-2016, 12:54 PM   #9
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This is per Secret Agent Google:

Closed-cell spray foam provides a higher R-value per inch (6.5) than less expensive insulation types like cellulose and fiberglass (3.5 to 3.7). Most spray polyurethane foam is called "two-component" foam.

I've been planning (hoping) that the roof ribs with 3/4" of plywood furring strips will = 2" depth. Sound reasonable?

Also, I have to point out that the green energy solution is almost always the most expensive choice.
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Old 04-01-2016, 01:32 PM   #10
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Originally Posted by Scooternj View Post
This is how I plan to stay warm and toasty in my skoolie-

(And, IMHO, Rachel Nichols looks sooooo much better as a redhead)


Daaaammmn, she's hot. I like redheads.
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