Modified New Englander wood stove to water boiler stove

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Hi, I am converting a New Englander wood stove with a blower on to a water stove. The air chambers will become water jackets. The flue will have a 5 foot stainless water jacket around it as well. I plan to have storage by using 3 or 4 -50 gallon water heater tanks less the heating elements. This system will be connected to an existing 164,000 btu propane boiler with radiant baseboard heat.The house is 2000 sq. feet in N.C. I realize this set up may or may not heat my house in full, but I do not want to spend thousands of dollars on a new ready made water boiler as I may not be living in this house the rest of my life. I am just trying to get all the heat possible out of a modified wood stove turned into a water stove. Does anyone have any thoughts on plumbing and controls or a drawing I could see? Thanks for the help!


Steelbear

 

[Eric Johnson]

Hi Steelbear. Welcome to the Boiler Room.

Unless you're one heck of a welder, I wouldn't attempt to build a pressurized vessel from a wood stove. It's a potential bomb.

You can pick up a decent, used wood-fired boiler (Tarm, Royall, etc.) for probably less than $500 and way less than that if you shop around. It's a much safer, easier-to-configure way to go, and you'll get much better results.

A boiler is not all that hard to plumb up and control, but you need tappings in all the right places so that you can install your aquastats, drain, pressure relief valve, domestic water feed and other essential elements in the right places.

 

[stoveguy2esw]

i cant put into words how strongly i emphasize that you do not do this. modifications to any UL listed appliance voids its listing which will pretty much void your homeowners insurance as well. any damages caused will not be covered by your homeowners.

designing a boiler retroactively into a device not intended for the purpose is not a trivial task, also it could damage the origional woodstove which could lead to failure of the home made boiler system as well. remember you are talking about welding stanless steel to carbon steel which isnt a good match especially under pressure.

my advice is to follow BB's advice and look for a "purpose built" appliance rather than attempt what you are intending , the risk doesnt match the reward.

 

[Dune]

You need a dedicated circulator swicthed on by an aquastat when the water reaches a preset temp, say 165F. The aquastat should be in a well in a tapping in the water jacket. You will need to install an additional pressure relief valve, one specificly rated for wood fire. You will want to install your stove in parralell to your gas boiler, meaning you should interupt the heat loop before it returns to the propane boiler, intall a flow check and a tee, insert your new circ, run through your stove, install another tee on the output side of the gas boiler, and pipe in from your stove there. When you are done, there must be two flow checks, one for each boiler. I would also install ball vavles on your new piping,both sides, so you can isolate the stove and still have gas heat if there is a problem. You will need to increase the size of your expansion tank to acount for the additional volume of the stove and piping, and disregard the idea of storage until you get a real tank. The aquastat alone must run the new circulator, it cannot be hooked up to the thermostat AT ALL IN ANY WAY WHATSOEVER, REGARDLESS OF WHAT ANYONE TELLS YOU< INCLUDING PLUMBERS< HEAT TECHS OR ELECTRICIANS.
All your thermostat can do is regulate your gas boiler. Set it so that if the house starts to get cold, the gas will kick on. (fire goes out, gas boiler kicks on) I am sure you already know this, but when welding stainless steel to steel, use 309 s.s. rods, stick or tig. Finaly, you must pressure test your rig to at least 100 P.S.I. Do this part before you do the plumbing. That way when the walls of the stove bow out, you will not have wasted as much time and money.

 

[Gooserider]

Agreed w/ previous posts - BAD idea Note that "StoveGuy" is one of the senior people at Englander, so he is very famiilar with the stove you want to modify...

If you are dead set on doing this, you may well end up living in whats left of that house for the rest of your life... As others have said, home-brewed-boiler is potentially an alternative spelling of "BOMB"

That said, I would add to DuneBilly's comments that you should carefully plan out what happens if you have a power failure shortly after having fired the stove - how does the water continue to circulate? What other alternatives do you have to keep the water in the system from boiling and building up pressure?

While it isn't a bad idea to want to heat w/ a wood fired boiler, or to want to save money, you would be much better off to look for a used boiler that was designed to be a boiler from it's original construction.

Gooserider

 

[[email protected]]

Hello guys,
Thank you all for the fine advice, not to pursue the modified Englander wood stove into a boiler, that you gave me last month. I will heed your advice. However, I stll have the stainless flue coming up from the wood stove and into the thimble. The 6 inch stainless flue is about 5 feet in length and has a water jacket around it with water ports at the top and bottom. I hate not to use this free heat going up the flue and outside. I have an existing 164,000 BTU propane boiler with radiant baseboard heat 20 feet from my wood stove. Why can't I circulate water from the flue jacket to my boiler and only use one of my three zones to help heat one room. Of course, I would not fire the boiler with propane. Any thoughts on this idea? Thanks for your time.


Steelbear

 

[Dune]

Can you describe the stainless flue in more detail?

 

[Gooserider]

Hello guys,
Thank you all for the fine advice, not to pursue the modified Englander wood stove into a boiler, that you gave me last month. I will heed your advice. However, I stll have the stainless flue coming up from the wood stove and into the thimble. The 6 inch stainless flue is about 5 feet in length and has a water jacket around it with water ports at the top and bottom. I hate not to use this free heat going up the flue and outside. I have an existing 164,000 BTU propane boiler with radiant baseboard heat 20 feet from my wood stove. Why can't I circulate water from the flue jacket to my boiler and only use one of my three zones to help heat one room. Of course, I would not fire the boiler with propane. Any thoughts on this idea? Thanks for your time.


Steelbear

For starters, your propane baseboard system is almost certainly pressurized - what is the pressure rating on your flue jacket? If it isn't intended and designed from the start to be used in a pressure system, it shouldn't be, as it will probably fail, often catastrophically.

The second big issue is "fail-safeing" W/ dino-boilers, this is really easy, and relatively automatic... They put in various sensors for temperature and such, and if a sensor trips, the fire shuts off... If the power goes out, the fire shuts off. If a pump quits, the boiler temp goes up, and trips the overheat sensor, and the fire shuts off... Etc... If all this still fails, there will be a pressure relief valve on the boiler to vent off excess pressure safely...
With a pellet burner, you get a similar pattern, but any other sort of solid fuel burner, the fire is very hard or impossible to shut off, especially in a stove where this isn't normally seen as an issue. This means that you have to be EXTREMELY cautious in your system design to ensure that it CAN'T over heat, and that there is adequate means for pressure relief if it does in spite of your cautions...

This generally means gravity circulation only, no pumps (what do you do if the power goes out or the pump quits just after you've gotten a new load of wood going?) or at least enough of an automatic gravity "dump loop" to get rid of ALL the heat production... It also means that you need to have properly working pressure relief valves and expansion tanks that are close enough to the jacket to protect it, and where they CAN'T be shut off by a valve.

This sort of thing can be done, but it takes a lot of careful engineering and design work, and all the parts have to be up to the task in the first place.

A third big issue is over cooling the flue... Modern EPA stoves are designed to burn very cleanly, and send just enough heat up the chimney to make a good draft and carry away the water vapor and any remaining combustion byproducts. Most of the heat produced should be leaving from the stove body. If you remove too much heat from the stack, which your jacket will almost certainly do, you will kill the draft and cause the stove to burn badly. Worse, you will cause the smoke to condense in the stack, which will give you creosote buildup problems at the least, and probably a good deal of corrosion and stack damage from the drippings... On top of this, you won't get all that much heat... An older "smoke dragon" if you run it hot, might give you more stack heat, but that would come only at the cost of greatly increased creosote buildup...

Gooserider