Piping & Wiring for an Outdoor Wood Boiler


Outdoor wood boilers for home heating are popular in certain parts of the country where wood is cheap and plentiful. Installing any outdoor wood boiler involves building a support pad of block or concrete for the boiler to stand on, digging a trench below the frost line to your house, burying the pipe and wiring in the trench to link your boiler to your house, connecting the plumbing and electricity, filling the boiler and starting it.

Boiler Piping

  • Most outside hot water boiler installations use PEX piping of 1 inch in diameter to connect the outside boiler to the heat exchanger, which feeds boiler heat into the house heating system. PEX piping is flexible tubing made of cross-linked polyethylene plastic. The process of extruding PEX piping intertwines the polyethylene molecules to create molecular bridges between them. This gives the pipe the ability to resist heat up to 200 degrees Fahrenheit and freezing cold temperatures without bursting. It also resists most chemicals, including those used to condition boiler water.

Insulated Lines

  • PEX piping has been used successfully in the United States for over 25 years for potable water and other plumbing, water chilling and hot water heating. You can buy PEX pipe for boiler use with or without insulation. For use in harsh northern climates, most boiler makers recommend use of preinsulated PEX piping, which contains supply and return lines surrounded by foam insulation, all encased within a larger flexible polyethylene pipe. PEX is approved by most state and local plumbing and building codes. However, since the ultraviolet rays in sunlight are a major environmental enemy for PEX pipe, causing the polyethylene to break apart, PEX is approved only for indoor and underground use, such as for outdoor boilers.

Connecting Pipe

  • PEX pipe attaches at one end to the boiler and at the other end to a water-to-water or water-to-air heat exchanger installed at your boiler or furnace. PEX pipe doesn’t require solvents or cements for attachment. Instead, crimped or compression fittings are used to connect the supply and return lines at the boiler to the inlets and outlets at the heat exchanger. Most installations include a shutoff valve and drain valve for the lines.

Boiler Wiring

  • An outdoor boiler uses a 120-volt electric circulating pump to move water between the boiler and your house. Most boilers also have an outside light to illuminate the fuel loading area. Boiler makers recommend using wiring rated for underground installation with three #12 gauge conductors plus a ground wire. The third wire will allow you to tie your boiler pump to your home heater’s water pump or furnace blower, so the boiler pump will run only when your household thermostat calls for heat. Hook up the boiler’s wiring to a separate 15 amp circuit breaker at your house service panel. Outdoor boiler makers offer detailed installation manuals for plumbing and wiring their boilers.

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