What Is a Forced-Air Outdoor Wood Furnace?

Heating your home by burning logs might seem old-fashioned, but a modern forced-air wood furnace simplifies using wood as fuel. If your house is on forested land or you have access to free or low-cost firewood, this could be an efficient, budget-friendly way to heat your home.

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What Is an Outdoor Forced-Air Wood Furnace?

An outdoor forced-air wood furnace is a wood-burning heater with the firebox, which holds the fuel, located outside. A fan pushes heat generated by the unit through insulated pipes into the ductwork in your home to provide consistent, reliable warmth in every room.

Step by Step, How Do Outdoor Wood-Burning Stoves Work?

Forced-air furnaces operate through a fairly simple process of heat generation and distribution. Here's a basic step-by-step explanation of how a wood-burning forced-air furnace works:

• Load up the firebox. The process starts when you load the steel firebox with wood and turn on the ignition. The firebox is typically lined with heat-resistant bricks for better efficiency and has a bottom grate to collect ash and soot.

• The heat exchanger warms up. Once the fire gets going, this heats a metal heat exchanger situated inside a separate chamber in the furnace. Air inside this heat exchanger warms up even though it's not in direct contact with the wood burning in the furnace.

• The blower turns on. A large fan attached to the back of the furnace pushes the hot air from the heat exchanger into pipes connected to the ductwork that leads to each room of your home.

• The blower shuts off once the set point is reached. When the house is heated to the temperature you've set on your thermostat, the blower turns off. The thermostat tracks the indoor temperature and turns the blower on and off automatically to maintain a consistent temperature throughout your home.

• Smoke and gases are removed via a chimney. Since burning logs produce smoke and gases in addition to heat, these need to be removed from the firebox. The outdoor wood furnace has a chimney that allows these byproducts to escape.

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What Types of Fuel Can You Use?

An outdoor wood-burning furnace is designed to work with seasoned firewood, but some other forms of fuel may also work. Seasoned firewood is wood that's been dried, which makes it burn more efficiently than wet or damp wood. Wood pellets are often a suitable option for burning in a wood furnace when seasoned firewood isn't available.

Some outdoor forced-air furnaces work with coal or shelled corn, but you should check the manufacturer's instructions before using them. You may need a different type of grate system to burn fuel other than firewood or wood pellets.

How Do Forced-Air Wood Furnaces Differ From Outdoor Wood Boilers?

The main difference between a forced-air outdoor furnace and an outdoor wood boiler is the use of air rather than water. While a forced-air furnace uses a blower to move heated air through ducts, an outdoor wood boiler instead heats water that flows through piping to heat emitters throughout the home, such as baseboard heaters, radiators or radiant in-floor systems.

Both the pump for a wood boiler and the blower for a forced-air furnace run on electricity, so these systems could stop working during power outages. A generator or solar battery could power the pump or blower to keep the heater running even when the electrical grid is down.

Reasons to Choose a Forced-Air Wood Furnace

Cost is a major reason people choose to install a forced-air wood furnace. In places where firewood is plentiful, this type of furnace can be cheaper to operate than a gas furnace or electric HVAC system. Since wood is a renewable resource, this can be a sustainable heating option compared to units powered by coal, gas or electricity.

Another reason to consider an outdoor forced-air furnace is energy independence. Using a generator or residential solar power system makes it possible to install this type of system in a remote location that isn't connected to the electric power grid.