I need a good new stove......

Hush your mouth.....

 

Well, not to worry with the gov't shut down.

 

As for OWB design, I would use a good thick mild steel; SS is way harder to weld, does not expand as well and cracks, and is not as good for heat transfer. Then add a good anti-corrosive to the primary boiler loop, like the stuff that CB sells. It works, and is the best stuff according to several chemist friends. Thermostat controllers are easy to get to control the damper door. Run a Taco circulation pump, and put a 10 foot rise in the line after the pump to keep down cavitation. I would use an open vent rather than pressure loop system. I would also use flat plate heat exchangers for an isolated hydronic floor loop and/or DHW. Put the DHW Hx at the bottom of the tank loop and convection will do the heat circulation w/o a pump. I use one inch pex which matches 3/4 copper for inside diameter of the water lines for main runs. I bury the pex sleeved with pipe insulation stuffed into 4" corrugated drain pipe. The biggest losses from buried lines come from water in contact with the pex. Bury the pex lines 6 inches below the frost line.

I would design the firebox with just steel and no firebrick, and add an air injection system using one inch galvanized steel pipes with holes drilled into them running at the top of the firebox. Similar to any non-cat EPA stove. I would have a boiler tank of about 100-200 gallons around the firebox. Again, I would vent it so that if there is a boil-over, it just boils over and takes all the heat energy with the steam. Then plumb that to your holding tank and whatever Hx you have. Use a mixing valve if you run the loop into a hydronic floor loop (directly or through a Hx to a separate floor loop).

 

Good stuff.

I've been studying this for several years.......I tend to think long.

It would be a simple system with a heat exchanger in the existing duct work.

You lost me on the ten foot rise though. At best I could do a three foot....

 

If you want it to burn clean and hot, don't count on any steel anywhere near the combustion zone. My simple passive designs will eat any steel in a surprisingly short time. Add in forced air and not a chance. Low density insulating castable refractory with a skin of high density where the wood might abrade it is how I would approach the burn areas. Make sure the heat exchange is far enough downstream to not quench the burn and you can get a really clean burn and still deliver max heat to the exchanger. Insulation is your friend here, from wood feed all the way to the exchange.

 

I have designed and installed several CB OWB systems. The 10 foot rise is to give the pump enough head and back pressure to reduce cavitation. Pump cavitation is one of the biggest problems with a non-pressurized loop. Just run the pex into your house and up into the attic and back down again, and put a set of bleeder valves at the apex. I add a cross over there with three inline ball valves (one on each line and one for the bypass) and 2 hose bibb bleeders, and make the whole H shaped header out of copper/brass so the Hx side can be bypassed and air bled from the lines in one place. Adding the rise works, as the original Taco pump I installed in the first system is still in use after 8 years. I got the rise idea from a plumber I used to work with/for in California.

 

Somewhere I have the designs (1975 approx) of an outdoor wood heater, but at this minute cannot find the plans!

A 12'x12'x6' high cement block structure filled with sand, with stainless steel 1" piping running through the sand as a heat exchanger taking the heat stored in the sand to what ever you are heating with water.
The fire box is made out of high temperature fire brick much similar to the design of the Garn with the exhaust flues running through the sand much again similar again to the Garn including blower placement.
The expensive part is the stainless steel piping. Copper apparently cannot withstand the high temperature that the sand achieves as apposed to water in the Garn.
I have often wondered if this is where the Garn design came from?

It was featured in Harrowsmith around 1974 or 1975.

Allan

 

Above I have just remembered one filled with sand. Just an old fart blowing hot air!

 

Unless you get all the materials for free I don't see building a boiler coming out ahead financially.

You can get a downdraft gasser for under 3k, plum it into that 500 gallon tank and you have a proven clean reliable system that should last 20-30 years.


These boilers were for sale last spring for I think 2500ish, I know they were under 3k
http://www.newhorizonstore.com/Products/275-eko-line-25.aspx

 

I see now......


Mike I already have most everything I need. Time is the one thing I don't have a lot of though.....

 

We built one with sand, we got the plans from mother earth magazine and it worked for awhile but something happened and we had a melt down in the maze of copper pipe running through the sand....

 

If you still had the plans and could post both the plans with pictures ,many on this site including myself would be interested ! The unit was supposed to be clean burning and very efficient !

 

Sorry that was over 30 years ago....I believe it was called a Hausa, we burned green pine slabs in it, you could of cremated bodies in it....Lol...We went heavier on the steel plate in the firebox but I don't remember the thickness....Sorry I can't be of more help...I can't remember chit anymore...

 

Mastermind. Have you ever considered buying a used gasser? I have no experience with this seller, but have seen his stuff on e-bay when I was thinking of buying a used boiler. For that kind of a price, if you could get it cheap enough, then use your know how and stuff you have to come up with some storage you could .................

http://www.ebay.com/itm/HS-TARM-MB-...232?pt=LH_DefaultDomain_0&hash=item3a866e5a78

I have always heard good about HS Tarm boilers. Something to consider. You would not necessarily have to buy something that old either. Sometimes you can find one for sale on craigslist or the like because someone bought one and then decided burning wood was not for them.