Plans for an outdoor wood furnace?

Simple one is an old oil drum. What are you trying to do? If you're trying to heat a space that's one thing (called a wood stove), if you're trying to heat water, that's another thing. "outdoor wood furnace" seems a little vague to me.

Grant

This question has come up before and I suggested to the poster to find and purchase cheaply an old outdoor boiler with a hole in the firebox. (something that happens quite frequently from corrosion) and rebuild it. This way you will have the aquastats, forced draft blower and a good plan. Steve

----- Original Message ----- From: Newsgroups: rec.crafts.metalworking Sent: Wednesday, September 07, 2005 1:20 PM Subject: Re: Plans for an outdoor wood furnace?

I would start by placing an ad in the local paper.

An outdoor woodstove would do that. Here is a high efficiency stove I thought was interesting. Burns cleaner with less wood.

I think they're all gone, you should probably give up. It'd be easier to just get another job instead of trying to build one anyway..

John

Many years back Mother Earth News magazine had an article on building a remote from the house wood fired boiler.

At least 20 years back as I recall but perhaps a search of their archives would produce result.

Errol Groff

Instructor, Machine Tool Department

H.H. Ellis Technical High School

New England Model Engineering Society

Unless you want to have a similar problem with wood that you have with propane, here are the requirements:

1. Combustion air must be supplied from outside the house and the draft must be controlled to limit the rate of burn. Controlled draft is a stove, uncontrolled draft is a fireplace.
2. Cold air to be heated must be drawn from inside the house and returned to the interior of the house; some type of forced-air is very desirable.
3. The heat-exchange efficiency of the device will improve if the firebox is insulated and the forced-air reclaims heat from the chimney stack of the stove.
4. Your comfort will increase and less cold air will be admitted to the house if the fuel introduced into the firebox does not require you to make frequent trips outside to add wood.
5. Safety will be improved if the hot surfaces of the stove are covered if not insulated.
6. If you want water to be heated, it should have some type of pressure-relief system built into it. Consider using the wood heater as a pre-heat mechanism going into your normal hot water heater.

Take a look at this system:

Guy down the road built one out of an old 250 gallon heating oil tank . No idea how well it works but His wood pile if all 3 to 4 foot long pieces . His is just under a small roof mounted on poles sunk in the ground . A better system is dug int a bank and covered all sides except the front with sand . Luck Ken Cutt

I have heard that the outdoor furnaces have a reputation as smokers. The thermostatcally controlled draft can extend the burn cycle but makes for inefficient combustion, makes lots of smoke. The smoke might be acceptable in a rural area where neighbors aren't too close.

Those with boilers have major issues with corrosion, the piping can freeze during the winter. An effecient wood fire must burn hot. , combustion temperatures should reach 1,500 F. A metal boiler which surrounds the firebox will extract too much heat and lead to inefficient combustion. The firebox should be massive masonary construction to hold the heat and slowly release the energy. When heat is extracted to a boiler the flue tubes should be well above the firebox. Consider the boiler flue design in an old Case steamer.

Well engineered systems probably exist, but have questionable cost benefits over a modern wood stove, which are pretty good these days. Most companies who build the external furnaces with boilers go out of business.

I have heard that the outdoor furnaces have a reputation as smokers. The thermostatcally controlled draft can extend the burn cycle but makes for inefficient combustion, makes lots of smoke. The smoke might be acceptable in a rural area where neighbors aren't too close.

Those with boilers have major issues with corrosion, the piping can freeze during the winter. An effecient wood fire must burn hot. , combustion temperatures should reach 1,500 F. A metal boiler which surrounds the firebox will extract too much heat and lead to inefficient combustion. The firebox should be massive masonary construction to hold the heat and slowly release the energy. When heat is extracted to a boiler the flue tubes should be well above the firebox. Consider the boiler flue design in an old Case steamer.

Well engineered systems probably exist, but have questionable cost benefits over a modern wood stove, which are pretty good these days. Most companies who build the external furnaces with boilers go out of business.

Tim