Outdoor wood burners, also known as outdoor wood boilers or outdoor furnaces, provide an alternative way to heat your home and water using wood as fuel. Understanding how an outdoor wood burner works can help you decide if this heating option is right for your home.
What is an Outdoor Wood Burner?
An outdoor wood burner is a standalone unit installed outside of a home to provide heat and hot water. It burns wood to heat water that is circulated through insulated underground pipes into the home’s existing heating system.
The key components of an outdoor wood burner include:
- Firebox – This is the chamber where the fire burns and heats the water. It is typically made of welded steel plates and has an insulated double wall.
- Water jacket – The firebox is surrounded by a water jacket or heat exchanger that holds the water to be heated.
- Chimney – Exhaust gases and smoke exit through the chimney, which is typically 14-16 feet tall to facilitate optimal draft.
- Air intake – Allows air to enter and fuel the fire. Some models have adjustable air intakes to control burning.
- Water connections – Insulated underground PEX pipes deliver the heated water to the home and back to the boiler.
- Fuel – An outdoor furnace burns wood, such as logs, lumber scraps, sticks/branches, and some models can burn pellets.
How Does an Outdoor Wood Boiler Work?
Outdoor wood burners work by heating water that is circulated through pipes into the existing heating system of a home. Here are the basic steps for how the system works:
1. Loading the Firebox
Wood fuel such as logs or lumber scraps are loaded into the firebox through a front-loading door.
2. Lighting a Fire
Kindling and newspaper are used to start a fire in the firebox. As the fire starts burning, the smoke exits through the chimney.
3. Heating the Water
As the fire burns in the firebox, it heats the surrounding water jacket filled with water. The heat is transferred from the fire to the water.
4. Circulating the Water
The heated water is pumped out of the boiler through insulated underground pipes to the home’s existing heating system, where the heat is transferred to heat the home.
5. Returning Water to Boiler
Cooled water returns to the outdoor furnace through the underground pipes where it is reheated, completing the closed-loop system.
6. Regulating the Burn
The fire is regulated based on the desired boiler temperature. Air intakes control oxygen levels, allowing the wood to burn cleaner at high temperatures.
This closed-loop heating process continues as long as the fire is burning in the outdoor furnace and there is demand for heat from the home. The boiler can also heat water for domestic use when connected to water pipes entering the home.
Key Benefits of an Outdoor Wood Burner
There are several reasons why homeowners choose to install an outdoor wood furnace:
- Lower heating costs – Burning wood fuel from your property is less expensive than conventional heating fuels like propane or heating oil.
- Self-sufficiency – Having an independent, off-grid heating source gives you control over your heating costs.
- Abundant renewable fuel source – Wood is a renewable fuel you may have available on your own property. There is no need to continually buy fuel.
- Fewer indoor emissions or risks – With the furnace located outdoors, there are no risks of carbon monoxide buildup indoors. Smoke, ashes, and wood smells stay outside.
- Heat multiple buildings – Outdoor furnaces can be connected to heat a home, barn, workshop, greenhouse, pool, and more.
- Hot water – Get your domestic hot water from the burner for free rather than running an electric water heater.
How to Install an Outdoor Wood Boiler
Installing an outdoor wood furnace requires planning to determine the optimal location, properly size the unit, and integrate it with your existing heating system. Here are the key steps for installing an outdoor wood burner:
Choose a Location
The outdoor wood furnace should be located:
- At least 50 feet from the home (to prevent risk of fire)
- Near an adequate wood supply
- With good drainage
- Upwind from living spaces
- Following all local codes for clearance requirements
Prepare the Site
- Create a solid, level foundation using concrete or bricks to keep the furnace level.
- Construct a shelter around the furnace to protect it from weather if desired.
Install the Boiler
- Set the outdoor wood furnace on the prepared foundation.
- Install the chimney up through the shelter according to the manufacturer’s directions.
- Run insulated underground PEX pipes from the furnace to the home.
- Connect the PEX pipes to the existing heating system and hot water heater inside the home.
- Install a thermostat to control the boiler temperature.
- Add a domestic hot water coil to heat water.
Finish the Installation
- Seal all connections and insulate pipes.
- Test the system and all functions when started up.
- Enjoy a new cost-effective heating system!
Operating and Maintaining an Outdoor Wood Furnace
Proper operation and maintenance are key to gaining the most from your outdoor wood furnace investment. Follow these tips:
- Use seasoned/dried wood – Burning green or wet wood will create more smoke and creosote buildup.
- Start a hot fire – A hot fire promotes complete combustion. Allow 30-45 minutes to get the fire burning hot before adjusting the air control.
- Let the coals burn down – Don’t continually add wood. Let the fire burn down to coals before reloading.
- Remove ashes regularly – Ashes should be removed before they block airflow.
- Inspect chimney and flue – Check for creosote buildup in the flue monthly. Remove creosote to reduce risk of chimney fires. Have the chimney cleaned professionally if needed.
- Check for leaks – Inspect all water connections for leaks to avoid loss of heat. Repair leaks immediately.
- Clean air intake – Make sure the air intake is free of obstructions so proper airflow is maintained.
With the right operation and maintenance, an outdoor wood furnace can provide years of reliable, cost-effective heating.
Frequently Asked Questions
What are the disadvantages of an outdoor wood boiler?
Potential downsides to consider include:
- Higher startup costs – The initial investment is higher than a conventional heating system.
- Wood consumption – It takes a substantial amount of wood to heat for an entire season. You’ll need access to low-cost or free wood.
- Labor for wood processing – Time and effort are required to prepare, cut, split, stack, and load the firewood.
- Operation attention – The fire needs loading and tending daily during the heating season.
- Emissions and environment – There can be environmental impacts from smoke, particulates, and cutting trees. Newer models have lower emissions.
- Risk of corrosion/leaks – Leaks can develop over time in the pipes, boiler, or heat exchanger.
What are the best woods to burn in an outdoor furnace?
The best woods are those with low moisture content that provide high heat output. Top choices include:
- Oak – A dense hardwood that burns long and steady.
- Hickory – Burns hot with few sparks.
- Black locust – High heat value and low moisture.
- Apple and other fruit woods – Excellent fragrance and readily available for many.
- Ash – A classic firewood that splits easily and provides even heating.
Avoid softwoods like pine which burn faster and increase creosote buildup in the chimney.
How much wood do you need for an outdoor wood boiler?
You’ll need 10-15 cords of wood (128-192 cubic feet) for the average heating season depending on your climate, home size, and boiler model. Well-seasoned hardwoods give you the most heat per cord. Have your wood supply ready before winter.
What maintenance does an outdoor wood furnace require?
- Remove ashes regularly from firebox
- Inspect and clean chimney and flue pipes
- Check for and repair any leaks in connections or pipes
- Keep air intake unobstructed
- Replace gaskets/seals when worn out
- Clean any soot buildup from firebox interior
Follow your manufacturer’s maintenance schedule for optimal performance. Expect to spend 1-3 hours per week on maintenance.
How long should a properly installed outdoor wood furnace last?
A quality outdoor wood furnace that is properly installed and maintained should have a lifespan of 20-30 years. Lower quality boilers may need replacement sooner. The water jacket and firebox are most likely to deteriorate over time. Maintain your furnace well for maximum lifespan.
Does home insurance cover outdoor wood furnaces?
Outdoor wood furnaces are generally covered by standard home insurance, but check with your insurer. Insurance should cover the boiler itself and attached structures like the shelter. Damage or injuries caused by the furnace may not be covered if it is deemed improperly installed, so use a professional.
Outdoor wood burners offer a self-sufficient way to lower heating costs by burning renewable wood from your property. While requiring an initial investment and operational labor, a properly run outdoor furnace can provide over 20 years of reliable heat. Locate the furnace safely, install it correctly, and practice good maintenance for optimal performance. With some planning and preparation, an outdoor wood boiler can be a smart and sustainable heating choice.