Heating with an Outdoor Furnace

In northern areas of the United States the outdoor furnace has revamped the heating requirements of many homes. In fact, outdoor furnaces not only can heat one household but several homes and out-buildings as well.

An outdoor wood burning furnace, or OWB, is a small, metal shed that houses a wood-fired boiler. A liquid containing glycol is heated in the boiler and a small pump moves it through insulated, underground pipes to the home and other buildings. These end uses include hot water tanks, barns and swimming pools. The heated water can be fed into a standard hydronic - or hot water-heating - systems or it can be directed into a heat exchange system where a radiator and fan system can direct heated air through exiting home ductwork.

Multi Fuels

Outdoor furnace units normally burn all types of wood products from chips to four-foot logs. However, many models can burn almost any combustible substance as long as it complies with local and state air quality and pollution guidelines.

The most common fuels are logs destined for wood splitters. These are cut into four-foot section and between one and three of them will keep a 2,000 foot home for a winter's day. In most cases logs are pilled beside the OWB where a sheltered table is used to load the logs into the firebox. These places can vary from a carport-like structure to a coverd barn where the wood is kept out of the snow and rain.

The Advantages of the Outside Furnace

1. Fuel Costs: Since OWB's are wood burners they can burn scrap wood, scrub brush, dried corn husks and almost any other organic waste including sawdust. Many OWB owners mix logs with other types of burnable materials so that they are not constantly feeding the firebox. For example, a truck-load of construction scraps can keep the firebox going for two to three days.

2. Fire Hazard-Free: The outdoor furnace units are situated far enough away from structures that there is no chance of fire. In fact, all approved units are cool to the touch and will not give off any airborne burnables. In addition, the codes demand that the units be built on concrete pads.

3. No Carbon Monoxide Threats: One of the deadliest killers in the home is odor-less carbon monoxide. This is not only relevant in oil-burning furnaces but is also a danger from propane and natural gas units as well. Having the heating unit outside completely negates this threat.

4. No Mess: Heating units that burn wood can give off ash when the firepots are cleaned out. Even wood pellet stoves can produce a film of dust on furniture. Because OWB's are only connected to the home by underground tubes the interior of the home is clean.

The Economics of an Outdoor Furnace

A recent study of outdoor wood furnaces taken in Wisconsin showed that the average owner used 10-13 cords of wood a year depending on whether it was hard or softwood. Hardwood, naturally, would be more expensive however it does burn more efficiently and cleanly than softwood. Most of the OWB units studied are designed to take up to four foot lengths of non-seasoned logs so this brings down the price over traditional, stove-length, split wood. At an average price of $125 a cord for unseasoned hardwood in four-foot lengths the heat and hot water bill for a 2500+ sq. ft. home would be less than $1500 per year.

Farmers, ranchers and other commercial operations that could get scrap wood for cheap prices or almost free were the ones that benefited the most from OWB's. One small furniture plant in Nova Scotia heats its operation entirely on waste wood products, a free byproduct the business.

Cost of Setting Up an Outdoor Wood Furnace

The cost for setting up an OWB can range from $3500 to $12,000 depending on the size of the unit, the excavating costs and amount of extras, such as a shelter and loading table. Many users of outdoor wood boilers use their present oil or gas furnace as a back-up. Also, the shipping costs can add to a unit as well as the amount of pipe needed to join the OWB with the areas to be heated.

Air Quality Concerns

There have been quite a few debates on outdoor furnaces regarding air quality. The design of most units revolve around a "slow burn," for the enhancement of heat transfer and to lessen fuel consumption. However, in many cases these cooler fires have been reported to be the source of bad smells and pollution due to creosote build-up and from burning trash and even tires.

The intervention by the Environmental Protection Agency has prompted newer designs where smoke is brought back into another chamber and combusted somewhat like a turbo-charger. This not only has cut down on emissions but has also increased the heat efficiency. In farming areas new outdoor furnace designs burn hay and other silage like dried flax and cereal chaff. These fuels have proven to have higher BTU levels than wood.

For more information on outdoor furnaces in your area consult our Contractor Directory or post your project online.

Posted by: kim
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