Multi Fuel Stoves

Multi-Fuel/Wood stoves are becoming increasingly more popular because of economics, aesthetics, efficiency and environmental concerns.  Today, these stoves offer home-owners the promise of a heating system that's independent of local oil and gas suppliers, plus the lure of cozy evenings cheered by gently flickering flames.

If there's a multi-fuel or wood stove in your life (or in the 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 stove or fireplace inset. Such a choice would seem both sensible and economical.

However, any heating system works best when all it's parts are designed -at the outset-to work together. Just as a furnace operates best when the flue size of the chimney is carefully matched to furnace capacity, so a multi-fuel or wood stove is safest and most efficient when attached to a chimney whose flue size most closely matches the flue collar outlet of the stove.

There are two types of multi-fuel/wood stoves that can be 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)  freestanding stoves and fireplace insets. Freestanding stoves can connect to an existing fireplace chimney, if the height and position of the stove's flue collar permits it.

Fireplace insets are specifically designed to fit into the firebox (where logs normally go) of an existing fireplace and to use the fireplace flue to vent smoke and other by-products of combustion.

Fireplaces aren't designed to vent (or carry away combustion by-products from) multi-fuel/wood stoves or insets.They are a uniquely designed solid fuel burning system in their own right.

Whenever a multi-fuel/wood stove or inset is vented through a masonry fireplace chimney-the ratios on which efficient operation of that masonry system initially was based may be changed.For example, the size of an inset'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 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 multi-fuel/wood stoves or insets 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. Insist on a safer installation for yourself and your family.

For those committed to the use of a multi-fuel/wood stove or inset for heat, a more efficient, easier to maintain and ultimately safer method is available. That method calls for the vent pathway to extend from the stove collar all the way to the top of the flue-creating a new chimney liner within the chimney.(see figure 1.)

This new chimney liner is sized correctly for the multi-fuel/wood stove or inset, so drafting the smoke out of the system is less likely  to be a problem. In addition it is an easy and economical way to extend the life of your chimney, since the new liner protects the existing structure fromheat deterioration and acid-based smoke condensation. 

Stainless steel chimney liners run from your stove to the top of your chimney and should include an insulating system to assure stable temperatures within the flue and help prevent heat transfer to combustible parts of the house.