The Outdoor Wood Furnace: New Thoughts on Keeping Warm

The firebox of a wood burning furnace.

Every winter as I turn on my oil burner heat unit I do so with a touch of trepidation and guilt. I pride myself on living as sustainably as possible and on my pursuit of environmentally friendly practices. Using oil heat to warm my home is not exactly in line with my beliefs. Granted, I have only lived in my home for just over a year now and have been conducting research on alternatives since I moved in.

What I have found is that as energy costs continue to skyrocket, many people are seeking alternative ways to keep warm. Some are doing so because they want to reduce their enormous heating bill, while others are just tired of taking from the earth when there are other alternatives. Whatever the case may be, I am definitely not alone in my search for an alternative heat source.

When one of my neighbors began welding and hammering in his backyard early this fall I took a trip down the street to see what all the fuss was about. It appeared, from a distance as if he was making a new shiny metal shed with a chimney. Upon closer inspection, I realized he was building an outdoor wood furnace.

Outdoor wood furnaces are stand-alone units that look somewhat like a metal shed on the outside and a wood-burning furnace on the inside. Constructing an outdoor wood furnace requires some experience with metal work and piping. However, plans to build an outdoor wood boiler are readily available, and my neighbor told me that his cost under $2,000 to build. I believe that price could be reduced if you could find some salvaged parts.

What Does an Outdoor Wood Furnace Heat?

furnace fire

Any building, commercial or residential space can be heated with a versatile outdoor wood furnace system. You can also heat the water in your home, hot tubs, or swimming pools. Some people use larger systems so that they can simultaneously heat workshops, barns, and their home.

The Anatomy of an Outdoor Wood Furnace

The actual guts of an outdoor wood furnace are relatively simple. At the heart is a fire chamber. Of course, this is where the wood burns. A water jacket surrounds this fire chamber. Several thick layers of insulation are placed around the unit. When the fire is lit, the water is heated. The hot water runs to the home and cold-water returns to be reheated. The forced air furnace inside the home provides radiant floor heat; radiant baseboard heat or an existing boiler may be used for heat distribution.

Installation Requirements

Made popular in agricultural communities, outdoor wood furnaces have some specific installation guidelines to follow. For starters, they must be at least 100 feet from other buildings and have a chimney that is at least two feet higher than the roofline of the building using the furnace.


Once the furnace is installed, my neighbor assured me, operation is simple. Many units require a wood fill once in 24 hours. On very cold days or in extremely cold climates, twice a day may be required. Ash needs to be removed only once every three or four weeks using a garden shovel.

Benefits of Outdoor Wood Furnaces

stack of firewood

Low Operational Costs - Because most people who install outdoor wood furnaces live in rural areas, wood is plentiful or at least reasonably priced. With free or low cost wood, operational expenses are extremely low. Most people who switch from conventional heating find that they save up to 75 percent on their heating costs, even when they have to purchase wood. The annual costs to run the pump, fan and exterior light bulb should not increase your electric bill by more than $3 per month.

Safe - With the wood furnace outside there is a low risk of combustion inside of the dwelling. Most units are located at least 30 feet from your home and a chimney cap also keeps sparks contained.

Environmentally Friendly - There is quite a lot of discussion these days relevant to the use of renewable energy. Fossil fuels, which are used to heat the majority of homes in America are not renewable. Wood, on the other hand, is renewable. When we burn wood, there is no change in greenhouse gas emissions because it is carbon neutral.

Flexible - As mentioned above, with multiple heating lines and the appropriately sized unit, multiple dwellings can be heated, increasing the efficiency and cost effectiveness of the unit.

When I look down the road and see a steady stream of smoke flowing from my neighbor’s outdoor wood furnace, I am reminded that there is a better way. Maybe next winter!