Heating H2O with Wood

[secureland]

An open discussion of water-heating with wood. Who's doing it, What's safe, What's dangerous, How to do it.

Here's a start;
http://www.woodheat.org/dhw/dhw.htm

 

[Mike Van]

Good link - Some scarey looking "prototypes" there. I use a Harmon wood/coal boiler tied to my oil boiler, 10 years now, no problems. Free hot water all winter.............priceless

 

[Butch(OH)]

I had long thought about heating domestic water with wood and foresaw most every problem they speak about there except I didn't think about this one,,

"There are major insurance consequences with wood heated DHW. For example, we don't know of any insurance company that will cover custom systems like the last three above."

Insurance is a no worry,,, until you need it

Looks like you have the choice of a low cost system that is unsafe, doesn't heat much water and voids your insurance policy or a higher priced system that heats little more water, is unsafe and voids you insurance policy. Not much for choices there IMO. Only good info there for me is don't build one that is direct fired. When I was thinking about doing such things I kept coming to heating circulating water with wood, then heating the domestic water with the circulating water via some type of heat exchanger. The circulating water being a "buffer"? for lack of a better term, between the fire and my domestic water system. An outdoor boiler is perfect for that, I have one now,any chance of boil over, steam etc is outside and separated from my domestic water. Without some kind of real fancy controls and equipment I just cant see doing it directly fired.

 

[Coldfront]

I have been thinking about it also. I figure I spend at least $500 per year heating hot water with natural gas hot water heater. I wish I could harness all the heat that goes up the chimney but like they say it would affect creosote build up.

 

[mtfallsmikey]

It's fairly safe with an open system (OWB) and closed system with an HX setup, but grafting coils on woodstoves is not...I'm trying to find an indirect heater with 2 electric elements instead of one (a couple of mfr. make them) so I can run it as a "normal" electric hot water heater in summer, heated by wood in winter. The ones that buy gasifier-type boilers have to use some kind of storage tank anyway, so DHW heating is easy. A common method is to use an old LP tank, put a 100' roll of 3/4" copper tubing in it, but vendors are clamping down on sales of these tanks due to liability exposure.

 

[secureland]

I'm considering contacting the engineering and environmental studies departments of the local colleges to ask them to take on a design project. Design a wood heated domestic hot water source that could be made for $500.

 

[Crofter]

Heating of domestic hot water with wood has some difficult problems to overcome. Possible loss of of feed water supply and no way to instantly shut down a loaded wood stove. You get steam then and you need much higher temperature connections and piping. You have created a system that would call for a stationary engineers ticket to operate at least to satisfy insurance or liability issues, so I dont think it is going to happen. I am a certified steamfitter but that would not legally qualify me to operate a steam generating system over 15 psi.

That said, there are two sleeved openings in the brick wall behind my new Kitchen Queen wood cookstove that are graded to line up with the two holes in the rear of the firebox; my crystal ball tells me there is a future connection.

 

[secureland]

Heating of domestic hot water with wood has some difficult problems to overcome. Possible loss of of feed water supply and no way to instantly shut down a loaded wood stove. You get steam then and you need much higher temperature connections and piping. You have created a system that would call for a stationary engineers ticket to operate at least to satisfy insurance or liability issues, so I dont think it is going to happen. I am a certified steamfitter but that would not legally qualify me to operate a steam generating system over 15 psi.

That said, there are two sleeved openings in the brick wall behind my new Kitchen Queen wood cookstove that are graded to line up with the two holes in the rear of the firebox; my crystal ball tells me there is a future connection.

What about safely located pressure release valves? Also a tempering valve of some sort might allow cool water in to modify the temp.

 

[CUCV]

My father has been doing it for over 30 years. He has a copper coil wrapped around the stove pipe on his home made FHA wood furnace. The water circulates naturally through the coil back to an 80 gal tank. He runs a CAT in the furnace so the stove pipe temp is already relatively low. You can touch the stove pipe after the hot water coils and the CAT chamber is well over 1000 degrees.

 

[Crofter]

A temperature / pressure release valve should be on every system. Their vents have to be piped to a drain because if for some reason they vent into the room there is a scalding problem or zero visibility in the fog of steam. On a city water supply often there is a anti backflow valve at the service connection and no water pump storage tank cushion so it is easy to get a locked in pressure build with temperature that will pop the relief valves. Losing water supply with the fire on is a problem as is having too much coil area and overheating if unattended and no hot water being used. You cant readily turn the water off to the system without bad results and the only way to shut down is rake the fire out.