Anyone built a woodburning heater?

keithw

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Mar 30, 2007
303
Virginia Beach
I am planning on building one this fall. I had seen one somewhere floating around on the internet and it looks pretty easy to install. 55 gallon drum split in half. Put wheels and frame on bottom half, plumb a bunch of 3/4" copper piping in the top half, add a pump and some garden hose and you are good to go. It's portable so when your done you drag it away and store it. Wondering how quickly it will heat up my 6700 gal fiberglass pool....
 

The Mermaid Queen

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Mar 28, 2007
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Northern KY
I saw a grill heater last season that somebody rigged up, similar to what you are describing... they also had a pool under 10K gallons, here is a link... maybe it will help
 

duraleigh

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keith,

caution on the heater.......it takes a TON of btu's to heat water and I doubt that heater can do it to any appreciable extent.

I have a pretty sophisticated whole house 150,000 btu wood heater and it can barely dent the temp in my pool. I've got a big pool but the energy required to be transferred to your water is significantly more than most folks expect.
 

ric

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Apr 27, 2007
217
Ohio
hi KEITHW
you might want to rethink about the copper with your glass pool. most heaters now are getting away from the copper.
 

KurtV

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Mar 29, 2007
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SE Louisiana
6,700 gallons of water is about 56, 000 (55,811) pounds.

It takes 1 BTU to raise each pound of water 1 degree F.

Therefore it will take about 56,000 BTUs for each degree F of temperature increase.

A cord of firewood contains somewhere between 12 and 25 million BTUs depending on species. Let's assume you're burning white oak at roughly 25 million BTUs/cord to make the arithmetic easy.

Let's assume 50% efficiency for your heater. IThat's just a guess, but I bet it's no higher than that.

I'm also going to asume you need to raise the temperature of your water by 15 degrees F. Again, no basis; another SWAG.

So, the Total BTU requirement to raise the pool temperature by 15 degrees F= 56,000 BTU per degree * 15 degrees = 840,000 BTU

BTU realized per cord of wood = 25,000,000 BTU per cord * 0.5 (efficiency factor) = 12,500,000 BTU

That means that each cord of wood would raise the temperature of your pool by 15 degrees F about 15 separate times. 12,500,000 BTU / 840,000 BTU per pool heating session = 14.88 pool heating sessions

If the assumptions and my arithmetic are correct, even allowing for some additional inefficiencies not accounted for here, a cord of wood would probably easily get you through a 4-6 week shoulder season of weekend pool heating.
 

KurtV

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Mar 29, 2007
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SE Louisiana
Lump or briquettes?

Lump has about 13, 000 BTU per pound.

Briquettes about 9,700 BTU per pound.

With all other assumptions remaining the same it would take about 130 pounds of lump or 173 pounds of briquettes to raise the pool temp by 15 degrees F.

Hey, you asked.
 

duraleigh

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KurtV said:
6,700 gallons of water is about 56, 000 (55,811) pounds.

It takes 1 BTU to raise each pound of water 1 degree F.

Therefore it will take about 56,000 BTUs for each degree F of temperature increase.

A cord of firewood contains somewhere between 12 and 25 million BTUs depending on species. Let's assume you're burning white oak at roughly 25 million BTUs/cord to make the arithmetic easy.

Let's assume 50% efficiency for your heater. IThat's just a guess, but I bet it's no higher than that.

I'm also going to asume you need to raise the temperature of your water by 15 degrees F. Again, no basis; another SWAG.

So, the Total BTU requirement to raise the pool temperature by 15 degrees F= 56,000 BTU per degree * 15 degrees = 840,000 BTU

BTU realized per cord of wood = 25,000,000 BTU per cord * 0.5 (efficiency factor) = 12,500,000 BTU

That means that each cord of wood would raise the temperature of your pool by 15 degrees F about 15 separate times. 12,500,000 BTU / 840,000 BTU per pool heating session = 14.88 pool heating sessions

If the assumptions and my arithmetic are correct, even allowing for some additional inefficiencies not accounted for here, a cord of wood would probably easily get you through a 4-6 week shoulder season of weekend pool heating.
Hi, Kurt,

My experience tells me it won't work...remember his original question?
Wondering how quickly it will heat up my 6700 gal fiberglass pool
"quickly" is the rub....I doubt that barrel stove would consistently produce more than about 20,000 btu's. The loss thru the thin barrel walls and the pipes to the pool is huge. Secondly, the loss to the evaporative process in the pool is even largerl. (gotta' have a solar cover 24/7 to offset it.)

All that aside, I think it will take more than three days to get the pool up 15 degrees.....that's stoking the fire 24/7. Even assuming that stove capable of 40,000btu (that's a real stretch) you'd still have to stoke 24 hours straight....all the time losing heat in the pool itself and never getting the plus 15 degrees you wanted.

I had high hopes my wood stove (100,000 realistic btu) would heat my pool......wouldn't move it one degree in 15 hours (uncovered)
 

KurtV

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Mar 29, 2007
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SE Louisiana
I forgot this was to be a drum stove. The efficiency would certainly be much less than 50% in one of those.

Do you have one of the outdoor wood furnaces? Those are typically set up with high efficiency boilers for forced hot water heat. I would think you could easily use one of those to heat a pool.

One thing in the OPs favor is that he has a pretty small pool.
 

duraleigh

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Do you have one of the outdoor wood furnaces? Those are typically set up with high efficiency boilers for forced hot water heat. I would think you could easily use one of those to heat a pool
. Yeah. The mistake (which seems completely stupid, now) was not to get exact specs on it's btu capacity....it's rated at 150,000 so, realistically, produces less than that. I've got it attached to the pool with a water-to-water exchanger (500,000btu) which virtually sucks the life out of that stove if I leave it wide open. The same company makes a 400,000 btu stove that would work but it takes an enormous amount of wood......far too large for my house so it doesn't make sense.

I've got a new strategy to try with it this fall but my bet is I end up with solar to provide the majority of my heat for the pool. I should've researched the numbers more carefully for the pool but the stove is the perfect size for my house, work shed, and hot water heater so I'm willing to accept that as it's primary task.
 

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