If you are looking for a more economical way to heat your home, today’s outdoor wood furnaces may be a great option, especially for homesteads and farms.

Outdoor wood furnaces have been around for centuries and are a popular choice for homeowners who want to save money on their heating bills.

Outdoor wood furnace showing an EPA certified model beside a traditional outdoor wood-burning furnace
Today’s EPA Certified and Traditional outdoor wood furnaces can eliminate heating bills

In this blog post, we’ll tell you how outdoor wood-burning furnaces work, discuss the benefits of using one, and the cost savings that can be realized by installing one for your home, or heating multiple buildings, with just one furnace!

Why can you trust us?

As a property owner with a passion for country living, I’ve covered a variety of topics and written several articles on everything from best firewood practices, and wood stoves, to DIY construction projects. This guide combines my years of hands-on experience, together with extensive research from experts on the topic to help ensure a well-rounded perspective.

Let’s get into it!

How do outdoor wood furnaces work?

Outdoor wood furnaces work by burning wood to heat water within the furnace. The heated water is then circulated from the furnace to the buildings being heated through insulated underground pipes which connect to the water heater through a heat exchanger.

From the heat exchanger, it connects to the home’s forced air, in-floor radiant, or boiler heating system to send heat throughout the home. The water is then sent back to the furnace through the insulated underground pipe to be reheated. 

Here’s a recap of how they work

  • Firewood is loaded into the furnace through the furnaces firebox door
  • The burnt firewood heats the water within the furnace
  • Heated water is circulated from the furnace to buildings being heated through underground insulated pipes.
Image courtesy of Central Boiler
  • The heated water then connects to the home/building’s hot water tank through a heat exchanger which then connects to the forced air, in-floor radiant, or indoor boiler heater.
  • Heat is then circulated throughout the home/building
  • Cool water returns to the outdoor furnace through the underground pipe to be reheated.
  • This heating system is controlled by a regular wall thermostat

What are the main advantages of an outdoor wood furnace?

One of the biggest benefits of using an outdoor wood-burning furnace is the cost savings that can be realized. In most cases, the annual heating cost for an outdoor furnace will be less expensive than a gas or propane furnace.

In fact, most outdoor furnace owners tend to live in the country or homestead environment with larger properties where trees are plentiful for their firewood needs. So, apart from their labor, they consider their fuel cost as being free.

Another benefit of using an outdoor wood-burning furnace is the amount of heat that can be produced, as well as an abundant supply of hot water, thanks to the water tank being used as part of the heating system.

Larger outdoor wood furnaces are often used to heat multiple buildings by running multiple underground pipes to other buildings, from one furnace. Some of the more common out-buildings include:

  • Garages
  • Workshops
  • Barns
  • Storage buildings

Added bonus: because the furnace is located outside the home, there is no need to worry about the mess of bringing firewood into your home.

Finally, outdoor wood-burning furnaces require very little maintenance in order to keep them running efficiently. In most cases, all that is required is a yearly cleaning and inspection, making them a very low-maintenance option for homeowners.

Additional advantages of an outdoor furnace?

  • No longer reliant on electricity or fossil fuels such as oil, propane, or gas
  • Carbon neutral: firewood releases the same amount of carbon as decomposing bio-matter, meaning they are carbon neutral.
  • An abundant hot water supply from the furnace boiler to the hot water tank
  • Can provide hot water for a swimming pool or hot tub
  • Works with forced-air, in-floor radiant, or indoor boiler systems
  • Some outdoor furnaces can burn wood pellets, corn, biomass, or coal

Is an outdoor wood furnace a good fit for you?

To help you decide if an outdoor wood-burning furnace is an ideal fit for you, our research team came up with the following disadvantages expressed by owners of outdoor furnaces.

However, all of these people said they are very happy with their purchase and would purchase one again.

  • The furnace needs to be fed twice a day, and on rainy cold days, this isn’t fun.
  • Outdoor furnaces consume a lot of wood. Count on 10 to 25 face cords per burning season, depending on many factors such as square footage being heated, climate, and your desired room temperatures.
  • The initial cost of the furnace and installation is a sizeable upfront investment. Tax credits may be available. Check with your local outdoor furnace supplier.
  • The system still relies on electricity for the pump and fan systems, although solar panels could be used to supply this electricity.
  • If you plan to cut your own firewood (as many outdoor furnace owners do), you may need to purchase equipment such as a chainsaw, log splitter, and trailer. And don’t forget safety-first if you plan to cut your own trees down. There are over 28,000 chainsaw-related injuries annually.
  • You’ll need somewhere to season and store a large quantity of firewood in wood sheds, or other protected storage areas.
  • Wood-burning furnaces do not require a lot of maintenance, but it is important to do periodic maintenance to ensure the furnace provides many years of worry-free heating.
  • Someone needs to always be available to feed wood into the furnace. This can be a challenge for getting away on vacations or multi-day getaways. 

There’s no question that an outdoor wood furnace comes with a lot of labor. But for many families with outdoor furnaces, living the country lifestyle, they all join in and turn the tasks of preparing their seasonal firewood into a fun outdoor activity full of fresh air and exercise.

What size furnace to purchase

It is important to choose the right size furnace for your home; too small of a unit will not be able to produce enough heat, while too large of a unit will be unnecessarily expensive to operate.

Wood furnaces have a Btu/hr. rating (see chart below) that you can use to help determine the right size furnace you will need.

As a rule of thumb to calculate your needs, for colder climates, you will need about 30 to 40 BTUs for every square foot of space. For moderate climates, use 20 to 30 BTUs per sq. ft.

Photo courtesy of Pinterest

Be sure to include all buildings in your calculations and think ahead to include any future buildings on your wishlist.

Maintenance: Recommended Do’s & Don’t’s

Don’t

  • Burn garbage; garbage impurities have a lot of moisture
  • Burn green firewood; cools the firebox, contains a high percentage of moisture, and wastes Btu’s
  • Burn below 150 degrees; creates condensation

Do

  • Burn at recommended 185 degrees
  • Maintain the furnace water; use manufacturers recommended water conditioners and corrosion inhibitors to keep the water balanced
  • Stir ashes daily to help minimize moisture in cooler ashes
  • Empty the ashes when they get too built-up
  • Scrape built-up creosote off the firebox walls as needed
  • Ensure the furnace is hooked up to a grounding rod
  • Use a chimney cap in off seasons to keep rainwater out

One more preventative maintenance recommendation is to purchase a quality PEX underground insulated pipe. There are several types of insulation materials such as polypropylene warps, foil wraps, and polyethylene foam, each with its own R-value.

Purchasing a quality insulated pipe and burying it deep enough to prevent it from damage is well worth the time and money.

For a short YouTube video from a leading manufacturer on this topic, click here.

How much do outdoor wood furnaces cost?

Don’t be surprised if the cost of the wood furnace only accounts for half of the installed cost for the entire system. For example, a high-capacity furnace costing about $8,000 to $10,000 will still need:

  • Inground insulated PEX pipe costs about $1.50 to $2.00 per foot
  • Excavation to bury the pipe, depending on distance and the property could cost another $1,500 to $2,000 – or more.
  • A cement foundation for the furnace to sit on
  • Heat exchangers
  • Pump(s)
  • Fittings and sundry plumbing supplies
  • Hiring a licensed plumber to connect everything

In the end, it’s not hard to see how the overall cost of an installed heating system and furnace can end up costing as much as the furnace alone. But if you can do some of the work yourself, and you shop around for the best deals, you can reduce the capital cost and therefore the time it takes to get a return on your investment.

Do outdoor wood furnaces come in different sizes?

Outdoor Wood Furnace – Examples

Below is an example of the various sizes of outdoor wood furnaces available. The examples below are from Wood Master, a leading U.S. manufacturer of outdoor wood furnaces, based in Minnesota.

ModelsCleanFire 300CleanFire 500CleanFire 700CleanFire 900
Btu/hr.150,000200,000245,000400,000
Firebox Cu. ft.10 cubic ft.14 cubic ft.23 cubic ft.32 cubic ft.
Water Capacity150 gal.205 gal.330 gal.420 gal.
Wood Master, Inc. CleanFire EPA Certified Wood Burning Furnaces

Summary

An outdoor wood furnace isn’t designed for traditional homes in the suburbs. But for homesteads, farms, or country homes with a good size lot, an outdoor furnace can be a viable option to reduce heating costs.

The real cost savings begin to add up when multiple buildings are heated by the same furnace. The Btu’s available from today’s wood furnaces can handle the heat requirements for a home – or two, plus a garage and workshop.

But as a single-purpose furnace for an average size home, a large high-efficiency wood stove may be a more economical option.

However, for outdoor lifestyle families that enjoy the thrill of being off-grid from fossil fuels and don’t mind putting in the labor to keep a consent supply of seasoned firewood on-hand at all times, an outdoor wood furnace can be a perfect fit.

Finally, it is important to have the furnace properly installed by a professional in order to ensure optimal performance and safety.

Recommended YouTube Video

We chose the video below because the homeowner has used his outdoor wood furnace for over 4 years to heat multiple buildings.

If you’re still undecided on whether an outdoor wood furnace is the right fit for you, but you still like the idea of burning wood as a primary or secondary source of heat, we have a great article to help you explore your options.

Related article: How to choose a wood-burning fireplace

FAQ’s

What is “decomposing bio-matter” and why is it considered to be carbon-neutral?

Decomposing bio-matter is the process by which organic matter is broken down and recycled into simpler forms. This process is a key part of the global carbon cycle and is considered to be carbon-neutral.

Bio-matter includes all living things, as well as any dead organic matter. When an organism dies, its body decomposes, releasing all of the carbon it contains back into the atmosphere. This carbon is then used by plants to create new organic matter, completing the cycle.

While decomposing bio-matter is considered to be carbon-neutral, some greenhouse gasses are produced during the process. These gases include methane and nitrous oxide, which can trap heat in the atmosphere and contribute to climate change.

However, the overall effect of decomposing bio-matter on the climate is still considered to be neutral.

There are many reasons why it is important to recycle bio-matter. First, it helps to keep the carbon cycle going, which is essential for life on Earth. Second, it reduces the amount of waste that ends up in landfills.

And finally, it helps to combat climate change by reducing the emission of greenhouse gasses.

So, next time you compost your kitchen scraps, remember that you’re playing a small but important role in preserving our planet!

Is there a lot of heat loss from the underground pipes?

A quality underground insulated PEX pipe loses less than 1 degree per 100 feet.

What s the best firewood to burn in an outdoor wood furnace?

Always burn firewood that has had 4 to 6 months to season. You can tell seasoned wood by its greyish color, or even better, buy a moisture meter to measure the moisture content f the wood.

Ideally, you’re looking for less than 20% moisture content.



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Greg Jones

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