Outdoor Wood Furnace Info
Outdoor Furnaces - Manufacturers with NON EPA-Certified Models Only => Home Made => Topic started by: Pulseingenuity on March 01, 2014, 09:28:35 AM
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Hello,
Drew up a rough sketch of my pool heater last night at work, excuse the rough drawing, was drawing it in my spare time waiting for trucks on dozer. Anyway, Im looking for suggestions or comments, any input at all. I have a few questions aswell,
1; first off, will this design work?
2; is it possible to remove too much heat from a fire?
3; will this design burn smoky?
4; can you use a blower to extract the smoke instead of using a blower to force air through?
5; how large of a setup will I need to take a 1 inch feed of 15-20 degree water to 30-40 or more degree water?
Any comments or suggestions are appreciated !
Thanks!
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I heat my pool all summer and fall the key to no smoke is not to over load it a little at atime
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I'll try to answer your questions as I see them.
1 I would say your design would work. It is fairly similar to my design. This design is a hybrid between a conventional "barrel in a barrel" OWB and a full blown gassifier. I am happy with mine, there are some quirks that I don't like but I believe it is a fairly efficient unit. This season I have used it every day since mid October and we have had a couple of minus 40 days (central Ontario) and tons of minus 30's days and up to the end of February have gone though about 5 1/2 cords of wood to heat my shop and a medium sized old, poorly insulated, farm house.
2 It is possible to remove too much heat. You want a stack temp above 250. Lower temps will cause creosote and form condensation. This is usually controlled by the amount of airflow, higher airflow (within reason) equals higher stack temps.
3. As is, I am thinking it would smoke. I fire brick lined my firebox to promote a good hot fire and good combustion in the firebox and try to get the heat transfer in the heat exchanger. (Some stuff on this at woodheat.org). BTW, this design is more maintenance prone. You will likely find that you will have to brush the tubes every week or so. It takes me less than 10 minutes to brush 6 tubes.
4. I think you are better off with a forced draft fan. It will blast air into the fire zone and promote good combustion. If you find draft is an issue then you could either add an induced draft fan (which are normally designed different because they handle higher temps and volumes) or you could try a higher stack. My stack is about 7 or 8 feet and draft seems OK. You may also consider trying to get some air up into your secondary smoke box to help promote a 2nd burn. I can't say for sure that it will work - this has been on my to-do list for 5 years.
5. Have a look at a commercial unit and see how the firebox is sized. Mine is about the size of a large woodstove and the water capacity is 250 gal but I am not using it to heat a pool and I have no idea what sort of load that would take. To prevent corrosion, boiler water should be chemically treated with chemicals specific to OWB's. Your boiler should operate above 150 and you should have a separate heat exchanger for the pool water. You would have no problem heating 15 deg (C - ?) to 40.
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If you go with a forced draft or draft induced design you can drop your rear baffle much lower. Not sure I'd mess with ripple top boxes anymore. The last boiler I built I had that rear baffle within six inches of the floor on a natural draft stove.
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Thanks a lot for the input, the whole boiler willl be built from stainless so I won't need a heat exchanger, im thinking my fire box will be about 3x3x3, and the exchanger tubes will be 1.5 inch tubing. Hopefully 4 runs should do it for the exchanger. I'm hoping this new design will bring my 8000 liter pool from 15ish degrees to 25 in a few hours, I have a natural gas boiler with a heat exchanger that can maintain the tempeture, it just isn't big enuf to overcome the loss from atmosphere if it's too cold
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Finally pulling the trigger and buying the stainless steel, I have a few questions though,
Ive attached a drawing of the design,
My firebox will be 28"w x 38l x 38d
total area of approx. 23 cubic feet.
1st question is, How large of a chimney should I require for this size burner box?
2nd, Should the intake be the same size?
3rd How many BTU will this burner yield?
Thanks in advance!
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A six inch stack should be good for up to around 170,000 BTU's.
Look at commercial units, compare your size firebox to theirs then see what size stack they use.
If it's going to be a forced draft a 6 will be plenty, an 8 might work better with natural draft.
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An update to the build, almost finished, stainless is very tough to work with, but its almost done!
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I see a lot of time invested, looks very nice, nice job! are you going to put any brick inside the burn chamber?
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I haven't decided yet if I will or not, im not sure if it will be necessary. If need be then I will, the plan is just to run it as hard as possible till the pool reaches a reasonable temperature then just let it burn down. Guess I'll see when I get it all up and running.
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It will burn cleaner with firebrick!
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Well, it's up and running, took the pool from 18 c to 35c in 3 hours, outlet tempetures reached 55 degrees. Needless to say it works amazing, except it's really smoky, not sure if it's because there are a few small leaks in the exchanger or if it's because it sweats so much or what the deal is.
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It will burn cleaner with firebrick!
and a door
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Great point!
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Wow. Lot of cash in stainless there..
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Yeah, I didn't have time to cut the hinges, my cnc plasma table was down with a stripped sprocket. What kind of brick is fire brick and where can I get it?
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Most any masonry supply house stocks it locally in varying sizes.
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Menards has it too.
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I priced a lot of refractory brick on line. Local masonry supply is the cheapest. Not sure how wide spread they are but I got some thru Old Fort Building Supply.
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Just finished the door and added fire brick, had fire burning for about 2 hours still kinda smokey, measured stack temp with infared gun, was about 100 degrees F, does that seem too low maybe?
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I'm definitely no expert, but your going to have smoke. Your not re-burning the exhaust gases, only routing them through heat xchange to utilize more heat.
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Yes, very low if you measured it at the breech and used a temp probe, what is your water temp?