Wood Stove, Fireplace and Fireplace Insert Installation
There’s a romance attached to wood stoves that people don’t feel for their gas or oil furnaces. The reasons include economics, aesthetics, efficiency and environmental concerns. Today, wood stoves offer homeowners the promise of a heating system that’s independent of local utilities, plus the lure of cozy evenings by the gentle flickering flames.
It is extremely important to note that wood-heating technology and its safe installation have become much more complicated in recent years. No longer is it sensible or wise to simply “”hook up”” a wood stove to an existing chimney and begin using it for heating.
If there’s a wood stove in your life (or in your future) and you already have a masonry fireplace in your home, it’s likely that you have used (or wish to use) your fireplace’s chimney as the chimney for your wood stove or wood burning fireplace insert. Such a choice would seem both sensible and economical. However, any heating system works best when all its parts are designed to work together. A wood stove, fireplace or fireplace insert operates best when the flue size of the chimney is carefully matched to the wood stove, fireplace or fireplace insert capacity, so a wood stove, fireplace and fireplace insert is safest and most efficient when attached to a chimney whose flue size most closely matches the flue collar outlet of the stove. While wood stoves can be successfully connected to fireplace flues (a flue is the inner section of a chimney and is designed to carry away smoke and other toxic products of combustion), certain standards must be met.
Fireplaces aren’t designed to vent (or carry away combustion by-products from) wood stoves or wood burning inserts. They are a uniquely designed solid fuel burning system in their own right. The fireplace system consists of the firebox, a damper (the mechanism that regulates air flowing up the chimney), a smoke chamber (the area between the damper and the flue) and a flue (a passageway inside the chimney through which the smoke rises). Together, they draw off the smoke and gases produced by burning wood. How well the firebox, smoke chamber and flue are in correct proportion to each other determine the system’s performance. The applicable rule of thumb (which is included in many local codes) is that the area of the firebox opening should only be about 10 times larger than the area of the flue’s interior dimension – a 10:1 ratio.
There are three types of wood stoves that can be connected to fireplace flues: freestanding wood stoves, fireplace inserts and hearth heaters. Freestanding stoves can be connected to chimneys built especially for them. The chimneys may be of masonry construction or be a factory-built metal system that’s been designed, tested and listed for use with wood burning appliances.
Freestanding Stoves, Hearth stoves or Hearth Heaters
Freestanding stoves also can connect to an existing fireplace chimney, if the height and position of the stove’s flue collar permits it. When this type of installation is done, the stoves may be called hearth stoves or hearth heaters.
Fireplace inserts are a special type of wood stove and are specifically designed to fit into the firebox of an existing fireplace and to use the fireplace flue to vent smoke and other by-products of combustion. Since the insert must be smaller than the fireplace opening, there is usually a surround panel attached to the stove, which extends out around the fireplace opening to seal the firebox from room air.
The size of an insert’s firebox is smaller than that of the masonry firebox, so the existing masonry flue may now be proportionately too large. An over-sized flue causes a reduction in the speed at which air moves out of the chimney. This lets the smoke that exits the wood stove linger inside the chimney, cool down and deposit condensed creosote on the chimney interior.
Creosote is a brown or black combustible deposit – given off when smoke condenses which must be monitored and swept out to keep your system safe. Major creosote deposits are created when wood stoves or inserts do not meet the proper installation standards, and vent smoke directly into the fireplace or smoke chamber. Smoke condenses inside both the firebox and smoke chamber and may produce a ceramic-hard glaze of condensed creosote – which is hazardous, difficult and potentially expensive to clean… and which damages masonry materials through the corrosive action of acids it contains. Never permit continued use of this type of installation, even if your stove is old enough that manufacturer’s instructions do not require the connector to extend all the way to the top of the chimney. Insist on a safer installation for the safety of your home and your family.
An approved wood stove-to-fireplace installation will help assure your safety. Annual inspections and cleaning of these systems by a WETT Certified Chimney Sweep will enhance their safety and efficiency.