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Old 01-23-2020, 08:51 PM   #1
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Figuring BTU’s used per gallon

How do you figure the BTUs or gallons of propane you may burn per night with 50000 propane furnace?
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Old 01-23-2020, 09:03 PM   #2
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How do you figure the BTUs or gallons of propane you may burn per night with 50000 propane furnace?
Depends how much it runs. About 91,000 btu/gal.
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Old 01-23-2020, 09:07 PM   #3
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How do you figure the BTUs or gallons of propane you may burn per night with 50000 propane furnace?
There are 91,547 BTU per gallon of propane. So, about 1 hour and 50 minutes per gallon if the furnace is running continually.
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Old 01-24-2020, 08:54 PM   #4
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RV furnaces average about 60% efficient. So you would only get around 1 hour per gallon of furnace run time instead of 1 hour 50 minutes you would get if the furnace was 100% efficient. How much you would burn in a night would depend on outside temp, thermostat setting, R value of your walls and ceiling, air infiltration rate and other variables we can't predict.

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There are 91,547 BTU per gallon of propane. So, about 1 hour and 50 minutes per gallon if the furnace is running continually.
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Old 01-24-2020, 09:12 PM   #5
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RV furnaces average about 60% efficient. So you would only get around 1 hour per gallon of furnace run time instead of 1 hour 50 minutes you would get if the furnace was 100% efficient. How much you would burn in a night would depend on outside temp, thermostat setting, R value of your walls and ceiling, air infiltration rate and other variables we can't predict.
Um... no. The furnaces are rated at input. Assuming the above efficiency of 60% this would result in a net out put of 30k btus.

Slightly less than two hours of burner time assuming all is correct, line pressure, orifice, etc.
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Old 01-24-2020, 09:13 PM   #6
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Originally Posted by hohenwald48 View Post
RV furnaces average about 60% efficient. So you would only get around 1 hour per gallon of furnace run time instead of 1 hour 50 minutes you would get if the furnace was 100% efficient. How much you would burn in a night would depend on outside temp, thermostat setting, R value of your walls and ceiling, air infiltration rate and other variables we can't predict.

How does efficiency figure into fuel consumption? I was thinking it may not produce 50,000 BTU of heat but it consumes fuel at a rate of 50,000 BTU/hour.

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Old 01-24-2020, 10:12 PM   #7
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The gallon of propane number, ~91,000 Btuh as folks explained above, is the fuel input burned at full fire in heater. The output is that multiplied by efficiency, I agree likely only ~60-70% so I’d estimate ~59,000 btuh is the energy put out as heat.

I’d estimate a good RV has about 30-40 Btuh heat loss per sq ft of the inside heated area when it’s about 30F outdoors.

That is rough estimates of course
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Old 01-25-2020, 05:16 AM   #8
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Um... no. The furnaces are rated at input. Assuming the above efficiency of 60% this would result in a net out put of 30k btus.

Slightly less than two hours of burner time assuming all is correct, line pressure, orifice, etc.
I guess I missed the part where the OP specified his 50,000 BTU rating was an input rating and assumed it was an output rating. Any answer to the OP's question will necessitate a good amount of "guessing".
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Old 01-25-2020, 07:01 AM   #9
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Oh Duhh[emoji1781] I was typing without thinking ! The efficiency example I mentioned was related to a gallon of propane and using that to figure energy output per gallon based on an estimated furnace efficiency number.

Meaning that’s the amount of heat to the RV per gallon burned.

I got lost in the posts and never answered his question....sorry for the misspeak!
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Old 01-25-2020, 11:58 AM   #10
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A no cost option, other than the cost of propane, would be to start with a full tank, heat for a few nights or a week, then have the tank refilled. Divide number of gallons added by the number of days used. This method would give a reasonable average usage per day figure, under certain conditions. Reading the tank gauge would provide some data, but would be less accurate.

There are also WiFi tank monitors available.
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Old 01-25-2020, 02:12 PM   #11
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I guess I missed the part where the OP specified his 50,000 BTU rating was an input rating and assumed it was an output rating. Any answer to the OP's question will necessitate a good amount of "guessing".
Unless you dig into the operating manual, the quoted but burn rate is the gross burn and not the output. The reason is that most propane furnaces also heat the wet compartments as well as the living area. For instance my furnace is rated at 35,000 btu, but the actual output to the living area is 15,000 btu.
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Old 01-25-2020, 07:44 PM   #12
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Need to know rated input of furnace. A 30k btu/h input furnace will run roughly 3 hrs straight on a gallon. The equation is 91,547 ÷ (furnace rated input, 30,40, 50k) etc.

Efficiency has nothing to do with burn rate. Efficiency is how much heat goes into ductwork vs out the flue pipe.

Heat loss of rv and efficiency have nothing to do with burn rate
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Old 01-27-2020, 10:51 AM   #13
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Originally Posted by RVPioneer View Post
A no cost option, other than the cost of propane, would be to start with a full tank, heat for a few nights or a week, then have the tank refilled. Divide number of gallons added by the number of days used. This method would give a reasonable average usage per day figure, under certain conditions. Reading the tank gauge would provide some data, but would be less accurate.



There are also WiFi tank monitors available.
Or just weigh it full and then after a few days to get a burn rate.
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Old 01-27-2020, 02:23 PM   #14
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Hi - If you want to make this even more complex, it depends on where you buy the fuel. In southern areas you are likely not buying propane but butane or some mix.


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