|unlined chimney in a home built before 1800|
Even though the use of clay flues was implemented to better contain exhaust fumes, older builders did not anticipate one day oil boilers and furnaces would become high efficiency units like the ones we see today.
Most oil boiler's installation specifics call for a 6 inch round flue to properly vent combustion fumes. Quite a difference from passages like the one illustrated above.
Bigger is not necessarily better in this case. One of the reasons newer appliances call for such smaller passages is to preserve the unit's efficiency.
Another, perhaps more important factor, is to better control the condensation of the fumes.
In the event of a chimney fire, smoke and fumes will transfer through the house since masonry is porous in nature. This is where a chimney liner makes the most sense. The stainless steel passage will effectively trap the fumes and safely conduct them outside of the house.
Older homes, not originally designed to accommodate a boiler or a furnace, have been typically adapted poorly to vent combustion fumes. Often, boiler/furnace fumes are vented right into a smoke chamber of an existing fireplace. By today's building codes, this practice violates every safety measure established against carbon monoxide poisoning.
A chimney liner installation in an unlined chimney can be quite simple in most cases. However, on a central common chimney that serves multiple fireplaces, and adapted to vent a heating appliance, the installation is far more complicated.
Divider walls will most likely be less than solid and may collapse and block the passage. The demolition to open up the space for the chimney liner is involved, but necessary.
Chimney liners are a sound investment into the safety of the home and its occupants. Liners safely contain toxic combustion fumes and guide them out of the home. Quality liners carry a lifetime warranty, typically built out of stainless steel that will not rust or sustain the type of water damage found in unprotected masonry.
An installation is only as good as the installer, which is why professional chimney technicians undergo extensive training and adhere to manufacturer's standards.
If you own a home built more than 80 years ago, it's likely your chimney is unlined. Consult with your chimney professional, and you'd be wise to explore the option of having a chimney liner installed for your heating appliance, or your wood stove, as discussed in an older post.
Stay safe, informed, and warm.
Javier A. Robayo
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