The rising costs of heating oil and gas have led homeowners to look for cheaper and alternative energy sources. While some homeowners embrace new technology such as solar thermal, others turn to energy sources that may sound outdated, such as outdoor wooden furnaces. Aside from the significant savings of using wood (most energy sources are priced many times higher than wood), keeping the furnace outside may also reduce home fire hazard.
Installing an outdoor wood furnace is ideal for houses in areas that have an abundant supply of wood (free or low cost), as well as large outside property. The furnace can work with any radiant heating system and can also be used for domestic hot water supply (with a water-to-water heat exchanger). It can simultaneously heat multiple structures such as houses, garages, pools, etc.
An outdoor wood furnace is installed within 50 to 150 feet from the house on top of a specially constructed concrete pad. A trench, deep enough to be below the frost line, is then dug from the pad all the way to the house. The pipe is laid in the trench in order to keep it from freezing as well as to reduce heat loss, as ground temperature during winter is always significantly higher. Given that PEX is an inexpensive and proven material that is often used for heating, it is often utilized for wood furnace piping.
Using insulated PEX tubing will further minimize heat loss, resulting in less wood being burned. Insulated tubing consists of 2 PEX pipes wrapped in insulated material and placed together inside of a special plastic pipe. The inflow and outflow tubes, even though they’re in the same pipe, can’t be touching each other. An outdoor wood furnace is one of the most common applications where insulated PEX pipe is used.
Sizing the furnace is very important and because furnaces are expensive, there is very little room for error. The potential problem lies not with a furnace that’s too big for the house, but with one that’s not big enough to provide sufficient heat. Out of dozens of factors that are needed to be considered for sizing, the main ones include: area size, heat loss area and tubing insulation.
Even though burning wood to provide heat has been common practice since the beginning of human race, today many municipalities find the issue to be very divisive and a cause for debate. Moreover, some localities went as far as to issue a complete ban on the use of outside wood furnaces. The issue at hand is that burning wood produces smoke and reduces air quality in the area, both factors that many neighbors find unacceptable.