I am currently running a Woodmaster outdoor wood boiler. I am totally happy with it and am heating a 10,000 sqft retail hardware store with it.
I researched wood gasification boilers from Tarm, Garn and Alternative. The initial cost of the gasification boilers is significantly higher than the less efficient outdoor wood boilers. The cost of the units would not allow me to recoup the cost of the more efficient gasification boiler in a reasonable amount of time.
The Tarm and Alternative boilers would have required additional water storage to keep up with the demand in my building. The additional water storage and associated parts would have added nearly $8000 to an already expensive boiler. The Garn has the water storage built in, but it is more expensive than any of the others.
In the end, my boiler system cost me $10,000 installed. A Tarm, Garn, or Alternative would have cost twice that to fulfill the requirements I needed. It would have taken 10 years to pay off the additional costs if I was purchasing wood. Since I have enough wood for three years, I wouldn't have realized a savings for 13 years if I was paying current prices for wood.
How much am I saving now? Last year I burned 4000 gallons of heating fuel in this building. At the price in September when I made the decision to purchase the wood boiler I would have spent about $14,000 on fuel this winter. Currently, since the price of fuel plummeted, I would spend about $10,000. I will require 30 to 40 cords of wood to equal that much oil. I am currently producing wood at about $25 a cord if I don't count my labor, just the labor of my helper and fuel for the machinery I use to move and cut the wood. I will most likely break even this year on the whole thing. Next year, if fuel doesn't go up or down I will save $10,000. In the next five years I will save a significant amount of money.
In the very near future wood supplies are going to tighten and the price savings may not be there. With my inefficient system you can count on a cord of wood equaling 100 gallons of heating fuel. At $250 a cord for wood I would not save any money. Since I need huge quantities I am entertaining putting my wood out to bid every year. Myself and a couple other outdoorwood boiler owners are also thinking about approaching the Borough or CIRI about purchasing trees from their property to secure a better long term source of wood.
More thoughts I had last night.
If you have a small home and it uses relatively little fuel to heat it also may take a long time to make one of these units pay. It takes roughly 1000 gallons a year to heat my 2000 sqft house. I have been agonizing over whether or not to buy some sort of wood heater for it. Under my current excellent insurance rate I am not allowed to use a wood stove. My only option would be a wood boiler for wood heat. If fuel stays stable (which I doubt it will) it will take me quite a while to pay off a wood unit. Now, my plans are to build a 2000 sqft shop for my heavy trucks and equipment. That will make sense then.
The othe concern is not being there all the time to feed the stove. You have two choices in this case. Run glycol in the system so you can shut it down when you are not there so you don't have to worry about it freezing. The other option is to have a fuel oil boiler to heat the house while you are gone. If you use one of the Alternative boilers this can be plumbed directly into it. If you use an outdoor boile the fuel oil boiler via a heat exchanger will heat both the house and keep the wood boiler system thawed.
It's a lot to think about.
I have thought of this type of furnace, but I would put in some kind of anti freeze, which also helps reduce scale build up. My brother installs geothermal heat pumps and uses a coolant mix that won't freeze and keeps the lines conditioned. My thinking was to make something like the cooling system on a car, low pressure and use the heat to circulate the coolant so you wouldn't have to run a pump. Keep in mind, I haven't really looked into it though, if the price isn't too great, it would most likely be better to go with a store bought boiler system instead of reinventing the wheel.
There is another thread on this later in the forum about this very same topic.
I am also like AKDoug.
This is the one that we have:
It costed us $6,995.00 and my husband did the full installation of it on his own which saved us quite a bit of money.
We decided not to have it outside, but inside of our hangar and we are going to get one of those stack robbers that pushes the heat out from the stack into our shop/hangar. Even with not having it, it still takes the nippy edge off of being inside of our hangar. Having it inside saved us money as well or else we would have had to purchase the actual shed that it goes into.
What we figured is that it would cost us about $17,500.00 to heat our place over the duration of the winter months. It would either be that or do what we are doing now. It took us 10 weeks to go through 4 cords of wood, but it has been worth it because we have only had to pay for 10 gallons of fuel since starting the wood boiler.
Honestly, if you are still debating on what to do, we were in your same boat this time last year. Make the transition. This decision was worth it for us and has saved us quite a bit of money in the long run!
Keep us informed on your decision on which boiler system you plan to use!