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Installing a Nature’s Comfort Outdoor Wood Furnace

Installing a Nature’s Comfort Outdoor Wood Furnace 2017-06-13T13:32:18+00:00

We will be happy to assist you any way we can with installing an outdoor wood boiler!

Every furnace comes with a complete detailed installation manual with lots of pictures and diagrams!

If you have any technical questions or need any help whatsoever, please call Randy at (608) 399-4847.

How to install an outdoor wood furnace can be broken down simply. The wood furnace installation parts needed will usually cost about $1,100.


40′ – 1″ red PEX
20′ – 3/4″ red PEX
1 – 1″ MPT x PEX valve
1 – 1/2″ MPT x PEX valve
1 – 1 x 1 x 1/2″ PEX T
1 – 1″ PEX x MPT fitting
2 – 1″ PEX x Fem Sweat fitting
2 – 1″ PEX couplings
12 – 1″ PEX cinch clamps
3 – 1/2″ PEX cinch clamps
1 – PEX cinch tool
4 – 1/2 gal boiler treatment (enough for up to 400 gallons)
1 – Boiler Treatment Test Kit
1 – 1-1/4″ black pipe 90
1 – 1-1/4″ x 1″ black pipe bushing
1 – 48″ Single Wall Chimney Extension (Specify:  CP548 or CP648)
1 – Chimney Cap w/Spark Arrestor (Specify: CPC5 or CPC6)
1 – 20 plate water to water heat exchanger
1 – water to air heat exchanger
50 – Platinum 3 Wrap Insulated red&blue 1″ Pipe


wood furnace installation

A.  Location of Boiler

The NCB boiler must be located to comply with the clearance requirements. Keep the firebox door positioned so as not to point toward a structure so all fire danger is removed from the home. The boiler may be installed as much as 250 feet away using an appropriately sized pump and piping and still heat the house and hot water. However, if the boiler is located more than 100 feet away, you may experience inefficiency and heat loss. A larger pump than the one supplied may be needed for distances over 100 feet and/or any rise in elevation over 15 feet.

Locate the NCB boiler where it will be convenient for refueling and wood storage. Pex pipe and power lines are to be installed underground between the house and the boiler and must be buried below frost lines.

Failure to keep the boiler area clear and free of combustible materials, gasoline and other flammable liquids and vapors can result in severe personal injury, death or substantial property damage.

A full concrete pad or footings just under the feet are not necessary for the wood boiler installation, but is recommended to prevent frost heaving. Four concrete footing blocks 8” X 16” X 4” will suffice if desired. You may add additional layers of blocks for ease of loading wood. The figure below is for outside foot dimensions.


B.  Chimney

A 6” stainless steel rain cap must be purchased separately for your outside wood furnace installation and can be obtained from Randy. If installing extensions, use supports as directed by pipe manufacturer. It is recommended that the boiler be located with due consideration to the prevailing wind direction.

1 It is recommended that the stack be at least 2 feet higher than the peak roof line the nearest residence.

2 If located more than 100 feet but no more than 150 feet to any residence, it is recommended that the stack be at least 50% of the peak roof line of that residence, plus an additional 2 feet.

3 If located more than 150 feet but no more than 200 feet to any residence, it is recommended that the stack be at least 25% of the height of the peak roof line of that residence, plus an additional 2 feet.

Example of chimney height relative to nearest downwind neighbor


C.  Underground Insulated Pex Pipe

You must use underground insulated pex pipe for transferring the heated water from the boiler to the home. Minimum pipe size permitted is 1”. Platinum 3 wrap (4” drain tile) & Platinum 4 wrap (5” drain tile) insulated pipe is available for purchase through Randy by going to the pex pipe page. It may contain twine for pulling electrical wire. If possible, do this with the pipe laid out straight for ease of pulling.


Bury the underground insulated pipe below frost lines (or just above water table level) and keep underground as it enters the house. The depth of the trench varies in different regions of the country. I have included a frost line depth chart photo below.

frost line depth chart

Be completely sure about the correct depth needed before the insulated pex pipe is installed underground. Contact your local building inspector’s office for this information. Make sure to seal around the corrugated pipe to prevent water from entering. If conditions require the pipe to be above ground for entering the home, make sure to insulate thoroughly.

Note: If only one color of PEX pipe is used, label the water lines or connect and test them before back filling over pipe and lines. If you have rocky ground, make sure you use clean fill or place straw or landscape fabric around the pipe before back filling, giving extra protection against punctures.

If more than one building is to be heated, additional pipe and pump must be installed.

D. Plumbing Hook Up

Plumbing connections should be well insulated after installation. Cover bottom access holes as well.

Minimum pipe size permitted is 1”. Install the outgoing pex line on the pump flange that is already mounted to the lower end of the circulation pump. Install the return line on the 1-1/4” fitting located in the top-middle of the rear control area. Add a valve to the return line so if repair or service is needed on lines or equipment, the water in the boiler can be isolated without having to be drained. (Valves and PEX fittings can be purchased from Randy.)

Install a fill line from the domestic water into the return line at the house using a T, 2 valves and a union to disconnect or a backflow preventer when not using to keep 100% isolated so no boiler water can ever enter the domestic side if pressure is lost.

Use sweeping bends for PEX pipe keeping 90’s to a minimum (no more than 6) as each one adds 1 foot of head pressure, reducing the rate of water flow. For tight radiuses use ¾” rubber heater hose in short lengths (fits 1” PEX fittings and is available by calling Randy).

For a forced air system, run the line from the pump first to the heat exchanger for the domestic hot water then to the one in the furnace plenum. For a hydronic radiant system, reverse this order.

Note: For larger homes, 1-¼ pipe may be needed for maximum BTU output. A 1-¼” pipe can carry up to 37% more BTUs due to higher water flow. The fittings above would need to be changed to accommodate 1-¼” Pex. The Armstrong E9.2 pump available from Randy has the ability to do this in a 1” pipe within distance & height limitations.

E. Wiring the Boiler

A qualified electrician must wire this boiler in accordance with the National Electrical Code. A dedicated 15amp, 115vac circuit needs to be installed to power the GFCI. Land power & neutral wires to the back of the GFCI and wire nut the ground wire to the green wire that is fastened alongside the ground of the GFCI. See controls section for an electrical diagram.

The size and type of electric wire to be installed depends on the distance from the boiler to the house. If the boiler is less then 100 feet from the house, #14 AWG UF cable is the smallest wire that may be used. If the distance is greater than 100 feet, #12 AWG UF cable must be used.

A maximum of 5 amps is used by the boiler if all standard equipment is running. The extra outlet will provide a total of 10amps for convenience use.

For ease of loading at night, it is suggested to install an outdoor light on a pole, 10’-20’ from the front of the boiler and offset slightly so a user can see inside the firebox when loading.

F. Forced Air Systems – Thermostat Wiring

The next example drawings are for controlling the blower on a forced air system independently of the existing heat source (i.e. propane, electric, fuel oil, etc). Randy can provide custom diagrams for other types of control setups as well upon request.

Use this example diagram if you have a typical, basic 4 wire system


Use the example drawing below if you have a 2 wire system or the thermostat is the advanced computerized type that communicates back and forth between the furnace (typically found on heat pump systems). Do not use this method if your HVAC system utilizes a multi-speed blower. All of the parts below are available through Randy.


G. Adding Bypass Valves

Adding a bypass valve system (3 valves, 2 T’s and unions) at each heat exchanger is a good idea so that if there is a potential problem such as a stopped up heat exchanger, it can be diagnosed & serviced easily as well as being used for a summer bypass as explained in the “operation” section of this manual.

H. Installing A Water-To-Air Heat Exchanger

The heat exchanger should be installed above an air conditioning condenser coil and must be placed at least 2” above it so any ice that may from on the condenser due to improper operation won’t touch the new heat exchanger.

No air can be allowed to flow around it or out of the ductwork. Use adhesive backed foam tape (used for insulating doors and windows) to seal around the frame and foil tape to seal off the opening you make in the plenum heat for the heat exchanger.

Make sure the fittings for the supply and return lines are easy to get to once the heat exchanger is installed.

You should be able to find a heat exchanger to fit most popular sizes of plenums. If you are unable to the ductwork must be modified to accept the heat exchanger. Wear proper protective gear. (gloves, safety glasses, etc…)

Measure the width of the heat exchanger (Dimension A in next diagram). Measure the thickness of the heat exchanger (Dimension C).


Start by cutting a hole in the side of the ductwork the thickness of the heat exchanger (Dimension C) and the full length of the ductwork (usually Dimension A).

WARNING! Metal edges are very sharp! Wear protective gloves and use caution!


Slide the heat exchanger into the hole for a test fit. Ideally the header and tubes (F) should stick out of the plenum.

While test fitting try to determine how much tape is needed around the frame of the heat exchanger to seal and keep air from flowing around it. A different amount (thickness) may be needed on different sides.

The heat exchanger must be secured so it won’t move up or downstream in the plenum. Fabricate some ‘L’ shaped braces and install the proper width apart as shown below (Dimension C). Secure in place using pop rivets or self tapping screws.


Slide the heat exchanger carefully into the plenum to check the fit again. Once proper fitting is verified, you can seal off the ends of the heat exchanger and the hole you made in the plenum with foil or duct tape.

I. Installing In A Small Plenum

You can install a heat exchanger in a plenum that is smaller than the length of the heat exchanger as follows. Make cuts at the top and bottom of the plenum, usually 4 inches long (the width of the heat exchanger) as shown below. You may need to do this on both sides of the ductwork depending on the heat exchanger size.


Slide the heat exchanger through the front hole to the back hole so it protrudes out the front and back of the plenum the same amount. Ideally the core of the heat exchanger will be entirely within the plenum.

Crimp the sheet metal to the edge of the heat exchanger (item G) using channel-lock pliers. This not only forms a virtually airtight seal, but also supports the heat exchanger as well.

J. Adjusting Plenum Air Flow

The motors on most force air furnaces have three speeds to provide various rates of air movement. Please consult a local furnace specialist if you want to change the airflow of an existing furnace system.

K. Installing On An Existing Indoor Boiler

The NCB boiler may be connected to an existing boiler system. A water-to-water plate heat exchanger is needed to transfer heat from the outdoor boiler to the indoor hydronic system so that the two systems remain isolated (see next diagram).

how to install an outdoor wood furnace

As shown in the above figure, the two systems are totally isolated from each other so that the existing hydronic system remains undisturbed and functions exactly as it did before. Water that circulates through the outdoor boiler is never circulated through the home’s hydronic system or vice-versa.

All pumps and controls remain essentially the same on the existing system but you will need to keep the burner on the hydronic furnace from firing.

This can easily be done by strapping a thermal snap disc limit control to the incoming line from the outdoor boiler and wiring it in series with the indoor boiler’s aquastat (see next drawing).

This provides the means to solely heat the home with the outdoor boiler if the water on the incoming line is over 140F. If it ever falls below 120, the indoor burner will fire again to keep the home warm and also reverse heat the outdoor boiler to keep it from freezing.


The electrical diagram on the next page shows a typical control setup for operating a 2 zone radiant system for a new installation that does not use an existing hydronic furnace. Part numbers are noted on each item for ordering from Randy.


L. Filling the Boiler with Water

Inspection: Before filling, inspect the pump shaft by removing the large silver screw to expose the top of the shaft and turn back and forth with a screw driver to make sure the shaft was not broken during shipping. Broken shafts are not covered under warranty unless found and noted before outdoor wood stove installation and startup. Also read maintenance section in full.

Once all piping connections are complete, flush about 20 gallons of water into the float stack and drain, repeating until it comes out clean. Close drain valve and pour Nature’s Comfort boiler treatment in – required for warranty. Fill the boiler with a hose through the float stack or if you have installed a fill line, open the valve and allow it to fill, stopping once the float starts to rise.

Use water that is softened and has low iron content if possible for maximum boiler and pump life.

Do not start circulation pump until boiler is FULL and the impeller and bearings have been primed! After filling, remove the top screw on the pump until a steady stream of water flows and all air has been purged. Being a wet-rotor unit, if the pump runs dry at all, it will seize up as the bearings rely on lubrication from the water. See maintenance section for full details on pump operation and care.

During the first heating cycle the water might expand and overflow. This is normal and will occur anytime too much water has been added. Open the drain valve to keep the float indicator at the bottom of the rubber cap. Any higher than this and hot water may push the float out and also cause scalding water to spill out. (NOTE: You must over-fill when the boiler is shut off and not in use)

After water has circulated for 1 hour, test Nitrite level to assure required 1,000-1,500ppm and add treatment if below this level. Submit a water sample to Nature’s Comfort for official warranty Nitrite testing and also once a year thereafter. REQUIRED! See warranty for full details.

Below is a pictured sample of our outdoor boiler water treatment from Nature’s Comfort.

outdoor boiler water treatment

M. Float Level

After priming and starting the circulation pump and bleeding the heat exchanger (see next section), let the boiler heat up and run for 24 hours then top off the water if needed. The ideal water level is at the beginning of a heating cycle for the level indicator to be at the bottom of the rubber cap. The water level will rise and fall during operation as water expands and contracts with temperature changes. Be sure to keep the boiler full of treated water at all times including through the summer as this will keep the boiler free from corrosion and when in use, from overheating causing circulation pump failure.

N. Bleeding the Heat Exchangers

With the pump running (prime and flush bearings first!), simply close a valve on the return side, hold for 1 second then open quickly. Repeat the procedure four times or until you cannot hear air rushing through the line.

O. Pre-conditioning Rope Seals

Option 1: (Good) Wet the rope seals with WD-40 before firing the boiler to keep prevent hardening from smoke and creosote and re-apply 1 or 2 times during the heating season or as needed.

Option 2: (Better) Purchase a tube of high temperature caulk and lay a bead of caulk on the impression of the door jamb in the rope seals, placing a 2” strip of wax paper over them. Over-extend the latch open and bounce the door/ash pan closed, then leave open to fully cure before starting a fire to get a custom seal. Once cured, wet the rope seals with WD-40 to prevent hardening from smoke and creosote and re-apply 1 or 2 times throughout the heating season or as needed.

Option 3: (Best but more hassle and messy) Purchase a tube of high temperature caulk and brush over the entire surface area of the rope seals to permanently seal out smoke and creosote. Place a 2” strip of wax paper over this. Over-extend the latch open and bounce the door/ash pan closed, then leave open to fully cure before starting a fire to get a custom, long term seal.

NOTE! Adjust fuel door if you ever see any amount of smoke. See maintenance section. Door adjustment is done at the factory but may be required again after outdoor wood boiler installation and before starting a fire as the seals compress over time. See maintenance section for complete adjustment and care instructions.


Check out this diagram for information on how to install a water to water plate heat exchanger!

The above video courtesy of Biomass Direct shows how to install a water to water plate heat exchanger!

If you have any installation questions at all, please call Randy at (608) 399-4847!

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