The wood boiler is the ‘engine room’ of your system. The firebox of the boiler - where the wood burns - is surrounded by water. Note: at start up time you fill your boiler with water then start your pump in order to test your lines for leaks with unheated water.

A thermostat on the boiler with a hi/low setting regulates the operation of an air injection blower, usually built into the firebox door. When the water temperature drops below the low point, typically around 160° F, the blower is automatically activated and air will blow into the firebox at velocity, transforming it almost instantly from a dormant state to an intense burn. When the temperature of the water reaches its high limit, typically around 180° F, the blower cuts out. Once the fire no longer has air blowing across it, it will return to a dormant state, burning increasingly little wood until the cycle repeats itself. In this way the stove regulates itself within a pre-determined range of water temperature; the temperatures mentioned here being typical of the ‘out of the box’ manufacturer’s recommended settings.

Most of the time your boiler will be in a state of controlled burn (think, smolder) with water temperature hovering between the high and low settings on your burner control, punctuated by an occasional blast from the blower. One of the benefits to a wood boiler system you will enjoy is that a boiler will burn just about any wood you throw in, including wet or rotten logs. You can also use logs that are up to four feet in length. No arduous splitting required!

Additionally, depending on the quality and type of wood you use, you can expect to have to fill your firebox as seldom as once a day. Likewise, since your system will be more or less airtight very little water gets lost to evaporation. Most owners find they have to top up their boiler water level (indicated by a gauge on the control panel), only once or twice during a heating season.

The hot water emanating from your system is pumped to and from your building(s) in a continuous loop 24 hours a day. The sort of pump you will buy is built to run non-stop. A ‘hot’ line transports the hot water from the stove to the building, and a return line brings the cooler water back to the stove for re-heating. A circulating pump located somewhere on this loop drives the water through the system. Within the boiler itself convection moves the water around.

Once the heated water reaches the building it can be used for heating, typically in one of two ways. Where there’s an existing hot water system the boiler water can be incorporated directly using a water-to-water heat exchanger; when a forced air heating system is already in place, a water-to-air exchanger (radiator) can be installed in the plenum of your existing furnace. Air is blown over this heated radiator and hey presto, hot clean air in the house courtesy of your outdoor wood boiler.

Other options for employing your new heat source include water baseboard heaters and in-floor heating. Individual set-ups require a thermostat to ensure a constant temperature in the building or space being heated. Usually the existing heating method is retained as a backup and for ‘vacation’ coverage.

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