Outside boiler

[Admin]

Last week I posted a link to a woodburning kitchen stove that had a coil inside the firebox for heating water. When the water got hot inside the coil it would rise up the coil causing cold water to fall, causing the water to circulate to the resiviour through this thermosyphon process. I thought this was the cats a** cause you can plumb the woodstove right to a regular water heater and maintain the temps without running the gas burner. This would be just the ticket and my hot water solution for my next homestead. Since this simple conept will work why can't I get a yardsale woodstove, stick it outside, insert the coil into the firebox and plumb it underground back to the house to my water tank? or... get some firebrick, block and flue tile, build an permanent firebox outside with a coil in it and plumb it back to the house in the same fasion??? If a simple coil inside the firebox of a woodburning kitchen stove can heat 40 gallons per hour, why won't this simple outside structure work? I figure I could build it out of firebrick and stone for maybe an hundred bucks or so. So why spend 6 grand on an outside boiler??? All I want is simple hot water for showers and dishes. Is there something I'm missing here??? this just sounds too simple to me

[acewoodsman]

it looks like a good idea to me, jc i don't see why it wouldn't work i'll have to explore it a little more i'm always looking for ideas like that good thread karma coming at ya

[wrightbrothers]

Been thinking the same since seeing this in Mechanics illistrated several years ago.

The one thing you may not of thought of is an expansion tank. Make darn sure the pop off on water heater is working too.

The way I picture it is metal tubing coiled around the stove pipe.

Perhaps we have a steam fitter or boiler maker who will post thoughts?

I'm all ears on this topic, opinions wanted.

Going now to search JCs last week post.

[Admin]

This is the link to that kitchen stove. www.antiquestoves.com/kitchenqueen/

It has a coil embedded in the firebox that circulates hot water to a reservoir entirely from the thermosyphon without the use of a pump. If it works with this stove, why not an outdoor firebox? I just can't see spending 5 to 8 grand on something I can make for around a hundred bucks

[mooreorless]

JC, every time I look at a new purchase I do the same thing. Check it out, break it down, and convince myself that "I can build it". Then I usually hear my wife growl and then laugh and ask "when are you going to have time to do that?". Then I come back to the real world. She don't doubt that I can, she just knows that I won't, due to lack of time.
Anything can be done if you are determined enough. When I was in high school I had a friend whose dad was way before his time with his wood burning fireplace. He had made an insert with 3" pipe making a cradle to burn the wood on. They started at the bottom sticking out of the 1/4" plate face and made a u-shape coming out above the door with a circ fan blowing all the time to heat the house. Then he had 2 old cast iron radiators, one on each side of the firebox that were plumbed up to the hothingyer heater. I remember him having to get up in the middle of the night to run the hot water, because the pipes would be rattling.
I've got about 10 grand wrapped up in my central boiler, but I bought one that has the capacity to heat a couple shops as well as the house, also located about 160' from the house to be closer to the wood shed and centrally located between the house and shops, and heat the domestic hot water all of which adds cost to the initial investment. In the 3 yrs that it's been in it has paid for itself.
The hothingyer kit that I put on my unit is pretty simple, it is a 11/2" copper pipe surrounding 3/4" copper pipe which goes from the bottom of your wtr htr where the drain is and goes in at the top,which creates a loop and the heating is a convection process as you mentioned with the hot water rising and pushing the cold water down thru the tank,thru the 3/4 pipe to be surrounded by the hot water from the boiler. You would be amazed at the heat transfer in 2-3' of 11/2" copper.
Sorry for running on. Hope it helps. ;D

[bigpat]

Jc the only thing to be aware of is the pipe has to be pitched up all the way from the stove to the tank, and down all the way from the tank to the stove. If you have a high or low spot in the wrong place it will create a "heat trap". This will stop the heat syphon.

[Admin]

Good point Pat. I have plenty of time to learn all the details before I try to put this plan in to action. How do these outside boilers work? do they have a pump of some sort to circulate the water to and from the house? I'm not concerned with having a large system to heat a home like most guys, just enough to heat water for showers and such.

[mooreorless]

Yes, JC, the circ pump runs 24/7 on the central boiler pumps water thru a 1" pex line into the domestic hot water heat kit, then a heat exchanger in the plenum of the furnace, and back to the wood furnace via the return 1" pex line. When the thermostat in the house calls for heat the fan on the house furnace comes on. This is a closed loop sytem.

[denisbarclay]

I have coal boiler that heats my 10 room , 105 year old house. I put a 1 1/2" galinized loop in the fire box and plumbed it in to a 30 gallon water tank for storage using 3/4" copper. This feeds my electric water heater, so it doesn't cost much to heat water as long as I have a fire going. As someone mention before make sure you install a pop off vavle in the storage tank . If I don't run any hot water for a long peroid of time it will get hot enough to pop off. Thats about 240 f. ( the 30 gallon tank is a old eletric tank that doesn't work ) It can be kind of dangerous if you have kids, It will take the hide off if you are not carefull. The longer that you in the shower the hotter the water gets. Like I said , you have to be carefull with kids.
Denis

[patricimo54]

I think it was in my off the grid thread I spoke of my wood fired hot water heater. It was like a 8"or 10" pipe inside a 12" pipe with tubing or pipe coiled between them. It was 18" to 24" high with an ash dump in the bottom. I have often thought how to duplicate this unit. Soft copper comes in 50' coils. Do a dry run around a length of 8" or 10" pipe to see what would be needed to accommodate the coil or you may what to try 100' by splicing 2 together. Then cut a section of 12" to match, drill holes to allow entry and exit of the tubing, slide flare fittings into place, make flares, weld base with legs, cap with flue flange and here you go. I would suggest adding a flat bar frame around the smallest door opening possible to not interrupt the copper coil and to provide a flat square surface to mount a door.

[patricimo54]

Another thought would be to have it load wood from the top so there wouldn't be any interruption in coiled tubing.

[billfosburgh]

i doubt thermosiphon would work in that application. we have an outdoor shower that we use with 50 ft of black waterline laying in the yard to heat the water in the summer. when the temp drops in the fall of the year i have a 30 gal steel drum with 50ft of 1/2" copper line coiled on the inside. the barrel sits on 2 cinder blocks. i fill the drum with water & build a fire under it. i run my water supply to one end if the copper & out the other end to my shower. never run out of hot water. i use mostly junk pallets cut up for fire wood. dont take long for the water to get hot & boil. the water in the drum stays hot a long time after the fire is out. we have at times used this system into Dec. befor draining it for bad weather