How Outdoor Wood Furnaces Work and FAQ’s

Why look for wood furnaces that are EPA Phase 2 Qualified?
Effective 12/31/2015, the EPA has imposed the requirement that all wood burning heating units are EPA Phase 2 qualified. The benefits of these units are much lower exhaust emissions, much more efficient wood burning (which means using less wood to provide the same heat), better for the environment and typically much less work to operate.
You can still buy outdoor wood furnaces from Wood Boiler USA. We are prepared for the future of highly efficient, lower emission requirements. The Wood Boiler Blaze HE and the Wood Boiler E4 are an EPA Qualified units.
Please look at our videos demonstrating what is required to operate, install and maintain one of our qualified units.

How do Outdoor Wood Boilers (Wood furnaces) heat my home?
An outdoor wood boiler also known as an outdoor wood furnace is a heating appliance that sits outside the home while providing heat to the home. The boiler is a wood fired combustion chamber that is surrounded by a water jacket. The water in the jacket is heated and pumped underground through insulated pipes to the home that is to be heated. Inside the home, the heat is put into the existing furnace via a liquid to air heat exchanger and into the water heater via a water pre-heater attachment. Once the heat is used, the cool water is returned to the boiler to be heated again. This cycle occurs over and over as the heat demand increases or decreases. See the videos on “How It Works”.

Is the Outdoor Wood Boiler (Wood furnaces)  safe?
The boiler is located a safe distance from the home.  It is constructed of thick steel. There really is nothing in the boiler to burn but the wood you put it. It keeps the fire out of your home yet you feel the warmth inside.

Can an Outdoor Wood Boiler (Wood furnaces)  “blow up”?
The simple answer is No. Many ask this funny but legitimate question.  The boiler is open vented meaning that there is no pressure to build up.  There are no components that can “blow up” or explode.  There are two open vents on the boiler.  These should never be plugged or resticted in anyway.  These open vents is what keeps the boiler from building pressure.

How much wood will I use?
This is a very good question and our consultants can help you by looking at your old utility bills and give you an estimate based upon our BTU Conversion Calculator.  This formula is an exclusive product of Wood Boiler USA.  We believe it is very accurate.  Do not believe a dealer or salesperson who believes they can tell you without knowing how much energy you used in the past.  Ask for us give you an accurate estimate.

Why is it called an Outdoor Wood Boiler (Wood furnace) ?
The name is a little misleading as it does not actually boil water, it heats it to a safe 150-185 degrees. Water actually boils near 212 degrees. Our wood boilers allows the user to adjust the temperature of the water to your preferred level.

How does the Outdoor Wood Boiler (Wood furnace)  control the temperature of the water?
The wood boiler’s burn chamber is surrounded by water. When the temperature drops below the setting on the thermostat the automatic air induction system activates and burn chamber is inducted with air.  This air forces the fire to ignite and heat is produced. Once the turn-off temperature is reached, the induction system disengages and the fire returns to a near dormant state.

Can an Outdoor Wood Boiler (Wood furnace)  heat my pool and/or spa?
In our history, you will see this was one of the challenges we wanted to address. The simple answer is Yes.  Using a liquid-to-liquid heat exchanger, we found a solution. There are multiple types liquid-to-liquid heat exchangers available.  When you purchase, please work with our design consultants for the best match to your needs. See the videos on Heating your Pool/Hot Tub.

Why are there no ash trays or grates?
During the design and testing process, we installed grates and ash trays trying various configurations to attempt to get the boiler as easy to maintain while being as efficient as possible.  We found that the grates of all metal types break down and will require replacement frequently.  We also determined there seemed to be no savings in wood usage by having grates.  Here is a  picture of a cast iron grate used for only a few months:

Cast Iron Grate
The use of ash trays seem like a good idea until you attempt to use one.  They get clogged up, they are hard to manage and they actually make cleaning ashes a real pain.  Watch our video on cleaning our Blaze HE unit.

Why are Wood Boiler USA products better than your competitors?
Here are a few reasons:

  • Our boilers are made of thick steel
  • Our loading doors are water cooled some models
  • Our firebox is welded inside and out; not just one side
  • Our boilers are EPA qualified (some models)
  • Parts are easily replaced and are readily available
  • You are working with the designers and builders not a third party contact

What is involved in cleaning the boiler?
It depends on the boiler model. Some models are easier to clean than others. Some of the more high efficient and low emission models have more places to clean. See the videos on “Cleaning”.

Can I make my own underground pipe?
Below are pictures of a customer that made their own pipe as you see the pipe leaked and what appears to be rocks is actually dried mud inside the pipe.  The heat loss was tremendous and ultimately the customer purchased professionally made pipe and as a result has cut their wood usage greatly.  Needless to say we would recommend buying professionally made pipe.

Broken Pipe

Broken Pipe 2

Broken Pipe 3



For some additional information and to see our boilers in action, visit our Videos page.

If you have questions or if you would like to see more, we invite you to provide suggestions or feedback using our Contact Us form. Click here.