Confessions of an Ex-Outdoor Boiler Maker
Valuable lessons, learned the hard way
I read with interest the reactions to outdoor wood furnaces. Let me give my background so you know where I am coming from. I was an outdoor wood stove manufacturer and went out of business and have no intention of going back into business. This gives me two unique qualifications to comment on outdoor wood furnaces. I have a great deal of experience in the design, installation and operation of outdoor wood furnaces and I have no vested interest in any design or manufacturer.
We went out of business about four years ago out of a combination of too much money spent in design, some bad business decisions and some unforeseen circumstances. We would have run into warranty problems also if we had stayed in business a couple of years longer. My weakest area of design was in the metallurgy and our mild steel boilers in two of our designs were prone to corrosion after about five or six years.
We have recently purchased a home and I will be installing an outdoor wood furnace (which I will build) and have been researching the current market. I must say I am appalled at the lack of progress in outdoor wood furnace design. Almost all of the furnaces on the market four years ago were very inefficient (in spite of their claims) and very smoky. Most of the manufacturers have not improved their design at all!!!
One of the largest obstacles to an efficient design (70% or higher efficiency is possible) is the amount of money needed to develop the design and the cost of producing such a furnace. Most consumers can not justify 8 or 10 thousand dollars for a furnace. Our last production model was a wood/oil combination which was very low in particulate emissions (smoke) and very efficient (72% on wood and 81% on oil). This is not a trumped up marketing ploy, (remember I am no longer in the business) it was a scientifically verifiable number. It did have some other problems which I dealt with in the next generation design that never got into production and which I will finally get to build for my own home. I am saying this to say that it is possible for manufacturers to build an efficient, reliable, easily operated stove. However, be prepared to pay for it.
As for the current situation and what to do about buying an outdoor furnace.... I still believe it is the most comfortable, healthy, easiest and practical way to use wood heat. If you are in a rural location and the smoke won't bother you or your neighbours by all means buy an outdoor furnace. Shop carefully. Some manufacturers (one of the largest) lied about their true efficiency ratings. Some had bad design. Some are not reliable (unfortunately some of our stoves fell into that category).
A simple firebox and baffle design (which most are) does not reburn any significant amount of flue gasses and cannot be efficient. Stainless is the only way to go for the firebox and tank. The installation is critical, with special attention needed in insulating and waterproofing the underground lines. Pump location is also critical in proper operation of the furnace. Insist on talking to several owners who have had the model you are interested in for at least two years.