In this blog post, you'll learn how to install and mount an outdoor wood furnace. Find out about the things you need to take into consideration before making your wood furnace at home. Learn all the best practices before, during and after the installment.



Project Description: Wood Boiler Heat Exchanger


Wood Furnace House

Wood Furnace House

So what I'm going to do is go through with you the history of how I got here. When I first got my first stove, it was actually a central boiler. I took my dog bed and put it right where the central boiler was when I first got it. I basically took the underground installation and laid it on top of the ground and went to my home, which is over here on my left side, and it's about 40 feet away.

First of all, the reason I put it here was that I didn't know where I wanted to put it, and I bought it in the fall like most of us do. I think the ground was frozen like it is now and I also wanted it so I could plow in front of the unit. The front door of the unit was right about here, looking this way. So I plowed my wood up right here and then I would fit it in. I'm glad I didn't put it in right away. I did this for about three years because I found out that this furnace right here, even though very easy to access every day, required wood twice a day.

It was badly placed, simply because it got in the way of a lot of my kid's activities. If we had a gatherings or parties, it was always the center point, they're always asking me what it was.

So every year, I would take it and move it with my backhoe.

This is where I would put it and roll up the underground installation. So where I'm going with all of this? Well, this is how I came to my final position and how I finally built what I call the carriage house for the wood stove.

I took the time and the money, and I dug into the hill and built a concrete foundation and a concrete wall to hold back the material and the dirt. Then I wanted to build a carriage house look.


The Carriage House

The Carriage House

The primary reason for the carriage house roof is that, it gives me more exposure to the southern sun, which gives me a lot more heat to help with drying the wood. In here, I actually have a greenhouse roof, which we will go inside in a minute, and you're going see how it works. When choosing your location for your wood stove there are a few things to consider. For example, if the wood stove is going to be initiated by itself, and the air currents. By air currents I mean how the smoke is going to react to your house. As you can see my stove doesn't smoke very much. It's properly done and taken care of, and it's a good quality stove. Outdoor wood stoves don't smoke more than an indoor wood stove.

Outdoor Wood Boiler - Power and Water Lines


A few of the commonly asked questions I receive are, "How much power should I bring from my house to the woodshed? And how many water lines? And what should I put in the trench before I actually put my stove down?" I ended up running a 12/3 wire, which allows me to put a power box in there, so I can have lights, I have power to my unit, and I also have a ventilation fan in there to remove any of the smoke if I'm loading the furnace.

Water Lines

I also run two zones of water lines to my house that is about 3,800 square feet. This was done not because I wanted to run two zones of water lines to heat the whole house because I can't do that with just two sets of water lines. I wanted to do this because I also have a water pool that I've set up and I heat with my wood furnace. Also, I wanted to be able to heat my garage. I have a nice three car garage, where I keep all my tools, cars, and my toys. Now I have more heat than I would ever need, and that's the reason I ran two zones of water lines.

With that apart of your thought processes, what will you want out here? Identifying your preference when you're digging that trench will help you only have to dig it once.

How to Install an Outdoor Wood Boiler Inside a Building - The Elements


Where to install an outdoor wood boiler

Where to install an outdoor wood boiler

So what I'm going to talk about now is how I installed the wood boiler inside the building.


Greenhouse Roof

Greenhouse Roof

So the wood shed, as you can see, has a nice greenhouse roof, and it provides a nice lighting. When you’re in the greenhouse it also provides shelter from the rain or the snow that might be happening outside or during the winter seasons. Believe it or not, the unit doesn't provide too much heat. This building ends up being around 55, 60 degrees, so it's not all that cold.

Wood Boiler Timer Switch




One of the first things I do when I come into the unit is I ‘feel’ the unit out. What I will do is I'll first come over here and I'll hit this timer switch so it turns on for 5, 10, 20 minutes and then it turns off.

When I open the unit some smoke will come out but it will also make it tolerable. So I'm not breathing in all the smoke. So I'm going to turn that off.

Interior Lights Switches


Interior Lights Switches

Interior Lights Switches

As I previously mentioned, I wanted plenty of lights in the greenhouse. Above you can see I have my light switches that have lights in outside the buildings. I did this so when the kids are playing in the summer or fall, I actually have lights outside. I also added in lights inside the greenhouse to provide more ambient light along with plug outlets and everything else. This way, if I'm working in here I can have outlets to use.

Other Purposes for the Outdoor Shed

The shed also serves a variety of different purposes. One of them being I store a lot of my tools in here. In the image below you can see a picture of my old military generator that I use if the electricity goes out. This ensures that I have plenty of power to run my whole house if necessary.


Diesel powered military generator

Diesel powered military generator

How Much Wood Should You Store in the Building?

In my case, I thought two years was an ample amount of wood. Hindsight twenty-twenty if I were to do this again, I would probably change it to a years supply of wood for the wood boiler. Potentially a little bit more depending on how bad the winter is.

Removing the Ash of an Outdoor Wood Boiler

Wood Boiler Ash Removal

Wood Boiler Ash Removal

Now there will come a point where we will need to remove the ash from the wood boiler. I remove the ash by opening the door, in the image above, and I take a garden shovel and empty the ash into bucket of my backhoe. Then I let it sit in the backhoe bucket for a couple of days, and then I dump it into my gardens. The charcoal and the ash is fantastic for the soil. It's a great thing to put into your garden.

If you're burning any material with nails and stuff like that, try not to put that in your garden because that will your gardens soil.

Accessibility and Design of an Outdoor Wood Boiler

When I put the stove in I talked about the design of having one main beam going across the whole building here. So I can take out this wall easily, with just cutting some simple nails, and then I can just slide this thing out, which will allow me to take this whole furnace out through here. And I actually put the furnace in before the roof was in, but before the front was in. So this was just the foundation.

In my case, which I don't recommend, is I didn't pour concrete, but I put solid concrete blocks and then put the floor this way. As you can see here, the amount of ash, and dust, and things that fall onto it, it's a constant clean up battle. However, if you left it dirt or wood chips, there is really no cleaning to do. It is important to be careful when you get this much debris on the ground as you're throwing logs in charcoal and red hot will come out and land in the area. And you can actually see some of them where I actually will step on them and put them out.

This debris here is compressible which means you can start a fire. Please be careful about what you do to make your area clean so that if sparks do come out, you do not create a fire.

One of the other things that I found very beneficial when installing an outdoor wood furnace, depending on how many pups you have, put an external light switch on the back of the furnace where you can turn the pump on and off.

Wood Furnace Installation Checklist:

Choosing a Location: 

When installing your furnace, keep in mind the direction of the winds during heating months. Try to place the furnace in an area where smoke will not be a problem for yourself or your surrounding neighbors. Also, keep in mind that you will want an easy access to your furnace to feed and stock wood.

Placing the Wood Furnace:

Under normal conditions, four cement blocks are all that is required to support the furnace. Blocks should be at least 6 inches wide, 10 inches long, and 4 inches thick. Under very soft conditions larger concrete blocks may be needed. For model 4400 the pad should be no less than 5 feet wide, 6 feet long, and 4 to 6 inches thick. For the model 5500, no less than 6 feet wide, 7 feet long, and 4 to 6 inches thick. Always use a non-combustible base.

Remember to always call before you dig!!!

The Trench:

The trench should be 24 inches deep and 6 to 12 inches wide. It can be dug with a shovel or a backhoe. Place all the dirt to one side of the trench to allow room for working on the other side.

Place the electric supply in the bottom of the trench and cover with dirt. Electrical wire rated for underground use (14-2 +ground) can be buried in the same trench as the water lines but must maintain a minimum 24-inch depth. Remember to always follow state and local codes.

The remaining 18 inches of the open trench is where the water lines are placed. Use a one-inch water line with a minimum rating of 100 psi at 180 degrees, such as a pex line, and ensure that your water line insulation has a minimum R-value of eight in order to maintain adequate heating efficiency.

Note: Use only materials purchased through Alternative Heating & Supplies. If you use poor insulation for your underground insulation you will burn a lot more wood. This is not the place to cut corners on cost as it will have you incurring more costs in the long term!

Mounting the Water Pump:

Attach the 1″ X 2″ black nipple (BN001) and one-half of the flanges from the 1′ cast iron pump flange kit (PF001) to one of the hot water supply valves on the back of the furnace. All the material to do this comes in a kit FK00.


Furnace Installation

Furnace Installation - Pump

Locate one of the black rubber gaskets, and placing it between the pump and the mounted flange, bolt the pump to the flange. Make sure the arrow on the pump is indicating the proper direction of the water flow pointing down.

Hooking up the water lines: 

Hot water supply 1″ Pex x 1″ MIP (DP002) fitting to flange on the bottom of the pump. Then attach the hot water supply 1″ pex water line (DP001) to the fitting using 1″ pex crimp ring (DP007).

Cold water return: 

Attach the 1″ pex x 1″ MIP (DP002) fitting to the cold-water return valve on the same side of the stove on which the pump was attached. Then attach the cold water return 1″ pex water line (DP001) to the fitting using 1″ pex crimp ring (DP007.)


Furnace Installation

Furnace Installation - Pex

Wiring the Water Pump:

Remove the cover on the water pump. Then using an approved wire, connect the ground wire to the green ground screw on the pump. Finally, connect the remaining two white wires together and replace the pump cover.

Locate junction box on the back of the unit and remove the cover. Connect the running end of the approved wire coming from the pump to the junction.

Note: The wires from the water pump will have to be connected with the main power wires in the junction box along with the power wires from the ETC system.

The Home:

Entering the building with the water lines can be done underground or over the sill plate. Once inside the building the typical hookup would run first to the domestic hot water supply and next to an existing heating system such as forced air furnace or to a hot water heating system (boiler). Finally, before leaving the building, a fill valve must be installed near enough to the homes water supply for filling and flushing the boiler at the end or beginning of the season.

Domestic Hot Water:

The domestic hot water/ flat plate kit consists of a water to the water heat transfer unit and the fittings needed to hook it up. The unit goes on the top of the domestic hot water heater and is connected as shown below.


Furnace Installation

Furnace Installation - Domestic Hot Water

Existing forced air: 

A water to air plate heat exchanger is inserted in the existing plenum. In most cases the heat exchanger is placed in a horizontal position, keeping all four sides level. The air must be forced through the finned area of the heat exchanger evenly. The hot water line coming from the hot-water tube enters the bottom fitting of the heat exchanger and exits the top fitting, which returns to the wood furnace. If the plenum is too large or too small, it must be altered to fit the heat exchanger properly.

Note: The water to air exchanger must be installed below any existing off-peak electric coils already in the plenum.

After installation of a water to air heat exchanger in the plenum the fan speed of the existing furnace needs to be increased to compensate for the water to air heat exchangers resistance.


Furnace Installation

Furnace Installation - Water Supply / Return

Existing Hot Water Boiler: 

This is the easiest of all the setups. All we have to do with a boiler is to add a water to water plate exchanger to the existing boilers loop and keep the loop circulating. Which fools the existing boiler to think it is always at temperature and it doesn’t turn on.

Filling with water:

Connect your domestic water to the return line to the furnace using a ball valve. This makes it much easier to fill and flush the unit. Start filling the unit and inspect for leaks. Make sure the ball valves on the unit are open to the return and supply. Once the green light on the control panel goes on you are full. Or if it simply over flows, don’t worry this is not a problem.


Furnace Installation

Furnace Installation

Bleeding the Unit:

Routinely pay attention to the water level light. If the light is not lit, this indicates water level is low and the furnace may need to have water added. Add water until it over flows the vent pipe on top of the unit. It’s not a bad idea to check to make sure the light is working properly every now and again. Open the ball valve in back to see if the light goes out or check the over flow pipe with a flash light. The circulation pump will be very helpful in bleeding the air out. It can take several minutes to do this.

Installing your Ash Auger:

The ash auger is very simple to install. As seen in picture (left) place cork screw portion in first then insert long cork screw through the auger hole. Mount auger cover and handle. and finally, place the cover on the auger assembly.  Caution watch your back this is a heavy steel!


Auger Assembley

Auger Assembly

Firing the Unit:

Once you have determined that there are no leaks and all looks good. Paper and kindling should be used for starting the fire. Build a small fire, and add wood as needed. Be sure pumps are circulating when firing the wood furnace. You might notice some water on the inside walls of the unit, this is normal the furnace is sweating like a cold drink on a summer day. Once the furnace has reached 180 degrees, the furnace is ready to be filled to capacity. I recommend burning cut, split, seasoned wood. Do not overfill the unit so hot coals fall out when opening the door. The best is a well-controlled fire and when the wood gets low, rake the ashes exposing buried unburned coals. You will be surprised those coals will heat your home all day and then some.

Caution: Do Not Burn garbage, rubber, gasoline, or any oil products. Do not use chemicals or oil products to start a fire.

Ash removal, Rotation, and Disposal:

Maintain a good ash rotation. This should be done weekly. Remove ashes when the furnace is very low on wood. If your wood furnace is not equipped with an ash auger system use a shovel to take ashes from the front of the firebox and use a rake to pull ashes from the rear of the furnace to create a level bed of hot coals. Tip - Ashes are great for the garden. Ashes should be placed in a metal container with a tight-fitting lid. The closed container of ashes should be placed on a noncombustible floor or the ground, well away from all combustible materials, pending final disposal. Ashes should be retained in the closed container until all cinders have thoroughly cooled. At least 48 hours. (coals can live for a week or so) Keep this in mind when disposing ash and coals. Forrest fires!

Creosote Information and the Need for Removal:

When wood is burned slowly, it produces tar and other organic vapors, which combine with expelled moisture to form creosote. The creosote vapors condense in the relatively cool chimney flue of a slow burning fire. As a result, creosote residue accumulates on the lining. When ignited this creosote makes an extremely hot fire. The chimney connector and chimney should be inspected at least monthly during the heating season to determine if a creosote build up has occurred. If creosote has accumulated it should be removed to reduce the risk of a chimney fire.

I hope this blog post will make your life a little bit easier on deciding on how you want to place your woodshed and simplify the installation process of your outdoor wood boiler.

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