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Wood Furnace Basics, A Guide To Heating With Wood

Our wood furnace guide will help you to understand the basics of heating your home with hot air from burning wood. These units can be installed indoors or outdoors depending on the model/brand you choose. An indoor model can be more convenient to put the wood in but this can be messy. An outdoor model takes that mess outside but they can also lose some of the heat to the colder outdoor air.

In many areas, regulations determine which unit you can install. The regulations govern the amount of particulates (smoke) that can be released into the surrounding air. The EPA regulates the particulate emissions from the units and it is based on the type of combustion system they use. There are two basic types; those that use a catalytic combustor and those that do not.

For wood burning appliances that use a catalytic combustor, the limit for particulates is 4.1 grams/hour while the limit for units without a combustor is 7.5 grams/hour.

A catalytic combustor is a device that resembles a honeycomb and has a noble metal (usually palladium) in it. The gases that are given off as wood burns will burn if the temperature is about 1000F. The noble metal in the combustor lowers the burn temperature of the exhaust to around 500 degrees which means less smoke is released. The catalytic combustor usually only lasts about five years and then it requires replacement. They can fail sooner (crumble) when contamination occurs from burning foreign materials.

The non-catalytic units usually use a small fan to force the exhaust gases down around the burning wood where the temperature is the highest and allows the smoke to be burned.

Wood Furnace Operation

The operation of a modern wood furnace begins by starting an initial fire with kindling and/or another fire starting material. Wood is added once the fire is started and it burns slowly until there is a call for heat from the thermostat. When the thermostat calls for more heat, a combustion blower starts and blows air into the heat exchanger causing the wood to burn faster. When the temperature of the air surrounding the heat exchanger gets high enough (normally around 200 degrees), the blower starts and air is pulled through a return duct from the home. The fan blows the air around the heat exchanger where it picks up heat from the burning wood and then it is delivered into a supply air duct system. This process continues until the thermostat says that no more heat is required and the combustion fan is turned off. The blower motor usually continues to run until the furnace is cooled down below a setpoint (typically around 175 degrees).

Older, more basic units have manual controls for the combustion air and burn at a set rate. In this case, the thermostat usually controls the blower motor to deliver warm air to the home. These units are much less efficient.

Some manufacturers include a coil in the furnace to produce hot water for the home. This can lower your use of gas, electricity, oil etc. Some offer the coil as an added optional while others include it as standard.

Before you purchase a wood furnace, you can check out our ratings page to compare the brands. Our simple system of from 1 to 5 stars will help you to quickly find the right unit for your home.

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