Wood Stove and Fireplace inserts
In the early 1980’s, the cost of heat had reached an all time high. The return of wood burning spread throughout the United States. Steel manufacturers begin manufacturing fireplace inserts and wood stoves. These heavy steel stoves were great conductors of heat. When home owners burned fires inside these units, the heat would radiate throughout the home and less wood was required to produce a good amount of heat.
The problem. – Chimney fires!
A strange thing occurred during the 1980s. A significant amount of chimney fires occurred in homes that purchased wood stove inserts. Many of these chimney fires spread to other areas of the home and caused structural damage. This spike in chimney fires alarmed the home owner insurance companies and they begin to take various measures regarding wood stove inserts. Since these units were relatively new, home owner’s insurance companies would require homes with wood stoves to have their chimney inspected by chimney sweeps to report on the condition of the chimney. Even with inspections, chimney fires still occurred. Everyone was stumped.
Chimney professionals during their cleanings of these wood stove inserts would find significant amounts of creosote. Many times the creosote would build so much that it would block the flue passage or stage three glaze creosote would form. Creosote is very flammable and is the main fuel source for chimney fires. The question chimney sweeps wondered was “what’s causing the excessive build-up of creosote?” The answer was “draft.” This is a little complicated but here is the watered down version. Draft is the flow of smoke through a chimney flue. There are two main requirements for draft. The opening of the fireplace and the size of the chimney liner. If you have a big fireplace opening (place where you burn wood) than you will require a bigger flue to draft the smoke up the chimney. Usually the ration is about 10:1 but shape and height of liner can cause minor variations. Here is where it gets a little tricky. If your chimney liner is too small, smoke will back up into your house because the liner will not properly vent the fireplace opening. On the other hand, if your chimney liner is too big, the smoke travels up the chimney very slowly and the flue gas cools. When flue gases cool, creosote drops out of the gas and forms on the chimney flue liner. A well drafted chimney will expel the gases out of the liner before significant amounts of creosote can form. So what is causing wood stove inserts to form creosote. The answer is the opening of the wood stove. When wood stoves are inserted into a fireplace opening, the area of the fireplace opening is now greatly decreased from the original opening to the opening of the wood stove doors. Installers simply placed these units inside the fireplace and did not bother to modify the area of the chimney liner. Small fireplace openings require smaller liners. With a small fireplace opening and a large liner, the smoke will take a long time to draft up the chimney. The flue gas will cool and creosote will form. Lots of creosote will form!
Wow, so all these houses are burning down because the liners are too small. Chimney sweeps begin to tell home owners there was a problem but home owners assumed the wood stove manufacturer would have known if there was a problem. They’ve been burning the stove for years and there hasn’t been an issue. They just wanted the stove cleaned and “see you next year.” Finally, in the late 1990’s, the National Fire Protection Association specifically addressed this problem in there NFPA 211 code book.
188.8.131.52 – A natural draft solid fuel-burning appliance such as a stove or insert shall be permitted to use in a masonry fireplace flue where the following conditions are met:
1) There is a connector that extends from the appliance to the flue liner.
2-8) a bunch of other requirements. 7 – says it needs to be able to be cleaned and inspected.
So what does this say? Basically, the wood stove insert has an opening in the front and an opening on the top of the appliance. The top of the appliance is the proper flue size for the unit. You need to place a direct connector from the opening of the top of the unit and run it up to the first chimney flue liner. Most home owners simply “slip in” the unit and vent it into the fireplace opening. Smoke needs to work its way out of the firebox, through the damper and past the smoke chamber to the flue liner. This process takes too long and the flue gas cools and large amounts of creosote forms. NFPA says to connect the wood stove to the chimney liner with a connector.
More problems! Go figure.
The politics and engineering of building codes is twice as bad as the red tape in the government. There are many boards involved with many different industries voicing their opinions. The facts were simple. The wood stoves were causing chimney fires. The reason was the liner size issues. Their solution was to install a short liner to the first flue tile. The problem is that now it is nearly impossible to clean. The chimney brush gets stuck where the larger chimney liner meets the smaller appliance connector. Even worse, the larger liner requires a larger brush and the smaller liner requires a smaller brush. A chimney sweep needs to disconnect the connector, remove it, and re-install it. Since these connectors are usually bolted to the wood stove, the process is very difficult and frankly stupid. The codes (7) require the appliance to be able to be cleaned and inspected. It doesn’t say that the cleaning should be easy.
The easy solution would be for NFPA to say to install the connector to the top of the chimney with a full reline. Basically install chimney liners to the top of the chimney. To clean these systems, simply open the wood stove damper and sweep a brush from the top of the chimney down the inside of this new liner. Clean the debris out of the wood stove opening and everyone is happy. The wood stove manufacturers would not vote on this idea convinced the Environmental Protection Agency to develop the “Great American Wood Stove Change Out.” Keep America safe and sell more stoves! Bottom line – A Step in Time recommends the installation of full reline chimney liners to connect wood stove appliances to the top of the chimney.