homemade boilers

[mjs97]

i am thinking of building an outside boiler. i have read many posts on here which were very helpful, but i was curious of a few things. for those of you that have built them before, what would be some design features you would do if you could build it again?

i am planning a round firebox around 36" x1/4 thick mild steel. water jacket would be 48"x 1/8 steel (old fuel barrel). i will include a powerdraft. water capicity should be around 150-200gal. non pressurized probably.

stack out top or back? what kind of heat baffle? tubes thur stove or not? stack run thur water jacket or not? round door or square? grates or no grates? ash pan or no ash pan? many questions!!

any suggestions would be greatly appreciated.

thanks,
matt

 

[woodchop]

look on Ebay for plans. I just bought: http://cgi.ebay.com/Outdoor-wood-bu...ryZ41987QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[mjs97]

i guess i'll try the old trial and error method.

matt

 

[Patrick62]

I will toss in 2 cents worth

I have not built one, but thought about it once or twice.

Since nobody really wants to touch this subject... I will, carefully.

First thing is, you already decided on a non-pressurized system. That makes it fairly safe. After all I was thinking you wanted steam... until I re-read your post.

Okay, so we are building a "hot water heater". Kinda on the large size. Factory water heaters use the tube thru the tank, and I guess it works okay. Boilers tend to try and run multiple tubes thru the fire. What we are looking for here is effiency. The few I have talked to told me that outside boilers are great, but they use a LOT of wood. So the trick is to get the heat into the water, and not lose it somewhere else. I like your tank around another idea, but 150 gallons might be excessive... Slow to warm up, but slow to cool down as well.

Insulate the thing really well. High temp Fiberglass should be sufficient.

I would imagine you are going to use a 120V circulator pump?? Hook it to a 100 deg thermostat mounted on the boiler, okay now we have automation!

Use some creativity and figure a way that as the water temp increases past about 120 deg than a bi-metal spring will clost the damper/air intake effectivly regulating the fire. Make this with LOTS of adjustment.

One more suggestion, and a question. What is the working fluid? Water? Or antifreeze? If the fire goes out does the boiler and lines freeze?

If your system can handle it I would suggest reducing the capacity to some manageable size and use recycled coolant. Has the advantage of carrying a ton of heat without boiling. Just for giggles you could adapt a pair of necks removed from old car radiators soldered to the top and then screw in a pair of 7psi radiator caps. This allows the system to come up to a low pressure increasing the boiling point while still staying in some sort of comfort zone. Screw a pressure gauge in the top as well! It would look really nice up there. Once dialed in, the pressure will react to the temp of the water, and the amount of burn.

Good luck, don't blow yourself up
-Pat

 

[mjs97]

thanks for the input. water will be used at first, once everything is working good maybe then adding anti-freeze, i've heard antifreeze for these things is very expensive so we'll see.

i am planning on having an aquastat hooked to a power draft to keep the water temp between 160-180 deg. i was thinking of a 150gal because then the power draft won't be kicking in as often as say 80gal. hopefully saving in consumption of wood.

i don't see much advantage of pressurizing water jacket, although the fuel tank i will be using has a pressure cap on top of it so i could use that if i wanted.

they tell me running baffles through the firebox doesn't work because they can't hold up to the heat. that would be a great way to transfer more heat into the water instead of going out the chimney.

thanks,
matt

 

[Patrick62]

Pressure cap

I did not know the intended temp. Now I am sure you would want a pressurized system. Think of it like your old pickup. Just how far are you going to drive with the radiator cap removed?? Two things happen. Evaporation, and boiling.

Evaporation probably would not be a issue, but BOILING!! is going to be the problem. A little water makes a LOT of steam. But just raising the pressure a few pounds increases the boiling point substantially. Using antifreeze raises that even more, plus adding some corrosion protection.

Go check and see if your local radiator shop gets "recycled" antifreeze by the barrel. He might make you a sweet deal. Also check the junk yards they drain cars before they crush them, also a cheap source of coolant.

Forced draft... wow. Why does that thing in the back yard sound like a jet engine??

-Pat

 

[woojr]

I made a real jury rig about 20 years ago out of an old oil fired boiler mounted to the top of my home made firebox. It has tubes meant to take the fire. Welded an 8" round exit to the top side of where the tubes are. Used a conventional manual damper.
I ran it at the same pressure as the settings for the oil burner. Pumped up to the second floor.
Wrapped it with some expensive space age insulation and it is built right into a wood frame wall. It is still there but I stopped using it awhile back. Just use a freestanding stove now.
To regulate it I adjusted the aquastat up and down as outdoor temp called for more or less heat. I forget how many gallons it holds but was probably 120,000 btu or more rated. You get the hang of it quickly if you have a simple layout without too many zones and fancy instrumentation.
As an example, when it was in the thirties, I would set the pump to kick on at say 150 and if it got cool in the house, I'd add more wood and set up the stat abit. To make it more strange, I have part cast iron radiators and part baseboard. It was fun and works well when its colder and runs steady as opposed to taking the chill off fires in the spring (like now).
I am planning on removing it this summer (takes up allot of space) and will have to burn it out in place. If you decide to reuse or modify an old boiler, you should hydrostatic test it first. Also be sure to have the propet pressure relief devices in the system. I once lost my electric for the circulating pump and was making steam real quick. Had to put out the fire and bleed her down fast. I have three relief valves and they were spraying but the steam hammering sounded like the 3 stooges doing their best plumber
skit. Good luck, woojr

 

[bassman]

STOP!!!!!!!!!!!!!!!!!!!!

they make these things you know....
go to central boilers website and look and see how to do it right.
I have one and when i was looking for one to buy i saw all the pros and cons of home made units vs manufactured.
I am not saying you cant do it as heating water is not magic just do it right.
a few controlls and a little planing and you can make a relly good one .
but leave your rain barrel to collect rain please.
keep me posted .

shayne

 

[mjs97]

i looked at about every outdoor stove on the market (that i know of). i am comparing all models and trying to come up with the best design. problem is that everyone you talk to thinks theirs is the best and it is really hard to decide which design is the most efficient. i looked into buying one but they are crazy for what they want for one of these types of stoves.

central boilers firebox is not round and from what i have gathered round is the way to go. less welds, stronger, better heat transfer are some of the adv. i do like central's heat baffle design. i have been looking at aqua therm stoves. i like their concept but they exit the flue out the top with a baffle under to block heat. works but i don't think is as efficient as going out the back.

thanks,
matt

 

[bassman]

I have one and this is what i find is important.

fire box should be like a maze so you dont lose all your heat up the chimney.
BLOWER DAMPER is a must as you can then burn green wood or other hard to burn junk.
the water should only run around 165 to 185 so it wont boil and with that you need a controll system to run the damper but i am sure you could just use one from a stor bought unit.
ash pan is a bunch of crap!!!!!!!!!!!! mine has one and and it sucks!!! in order to fill it you have to use an ash rake but as you push it back and forth you stir up a wicked ash dust storm so i never do it and i just shovel them out about once a month.
back to the firebox.. if you could get the fire so it went from the back into a chamber that zig zagged and was all part of the water jacket you would use less wood.

then you get into how much water this thing should hold.
I like the idea of about 150 gallons then use big tanks indoors with heat exchangers so you have lots of thermal mass but only a small amount of boiler water you could then not have to worry about freeze up or if you use glycol you dont need 2 grand worth..

shayne

 

[mjs97]

i am the process of building this stove. any one see any disadvantages of making the door the full end of the firebox? it would be 36 in. in diameter. maybe weld in a 6 inch piece in the top to hold in heat and smoke. otherwise i don't see any problems. what di you think.

thanks,
matt

 

[MS-310]

I have made about 6 outside wood stoves each one is diff. then the other one and I can give you some really good ideas. If you want some more info and maybe some parts give me a P.M. and i will give you my cell number. I am a dealer for outdoor wood stoves (cant tell you what kind). If you like to make your own thats cool or you want a nice stove for the best price PM me.
Jack

 

[andy7spc]

outdoor boiler idea

anyone hear of buying a scraped out 500 gallon propane tank and cutting the domed end off of it and then cutting it to the desired length and re welding the original end piece back on .....then take and cut out 1 end to a square shape and weld angle iron into a square so it fits on the hole and there is the opening for the door .........wrap the tank with soft copper tubing or even space it a short distance away from the firebox

build a relatively small building out of concrete blocks and of course insulate it ......insert the firebox in the building and fill it with sand and if desired you could install some pex tubing in the sand as well .......sand would be a good heat sink

 

[hamradio]

Check this out-
http://www.motherearthnews.com/Homesteading_and_Self_Reliance/1980_September_October/Mother_s_Wood_burning_Hot_Oil_Furnace