Wood Stoves That Hook Up to Your Hot Water Boiler

Hot Water Units

• Several companies manufacture outdoor wood-fueled boilers that can be connected to your existing hot water heating system. These systems allow you to keep your existing gas- or oil-fueled boiler. There are also hydronic indoor fireplace inserts that fit into an existing masonry fireplace and tie into your existing hot water heating lines. These essentially are fireplaces surrounded by a water jacket with a small circulating pump. But many wood-heat advocates say the outdoor wood boiler is the simplest and most efficient way to heat their homes with wood.

Packaged Units

• Outdoor wood boilers come preassembled in steel enclosures that look like a small free-standing shed. They typically are installed on a concrete slab. Most outdoor wood boilers are atmospherically vented and non-pressurized, but some units operate under pressures of 10 to 12 pounds per square inch. Pressurized units include relief valves and other safety devices to relieve excess pressure and replace water losses. Most outdoor boilers have automatic combustion air controls and need to be loaded with wood only once per day. Some outdoor wood boilers have backup gas or oil burners to keep the water from freezing when you can’t keep a wood fire going.

House Connection

• The boiler is connected to the house by insulated pipes buried below the local frost line. A 1/20 horsepower circulating pump keeps the water moving from the outdoor boiler to the house and back to the boiler. The lines from the boiler terminate in a water-to-water heat exchanger located in the hot water lines at a point between the existing boiler and the thermostatically controlled zone valves. A small “wraparound” pump continually circulates boiler water through the heat exchanger to maintain water temperature in the existing boiler. This allows you to continue using your existing thermostats to control room temperatures.

Boiler Location

• An outdoor wood boiler typically is installed 30 to 200 feet from the house, depending on lot topography and local code requirements for outdoor boilers. But they can be installed as much as 500 feet away. A single outdoor boiler can heat outbuildings as well as the main dwelling. Some outdoor boiler models can also heat domestic hot water through a separate water-to-water heat exchanger and wraparound pump installed next to the existing water heater.