How often does a furnace flue need to be swept?
If it is a GAS furnace flue, the most common answer is: very seldom. If
the gas to air mixture is adjusted properly, the byproducts of burning
gas are various gases, including carbon dioxide and carbon monoxide,
and water vapor. There is a lot of water vapor. Not just a few cups, but

Older homes, that once had coal or oil furnaces, and now have a gas
furnace on the same flue, often have deterioration of the interior of the
chimney, whether it is brick or clay tile. Why is this? Coal  or oil residue
has sulfur in it.  Combine that with water, and you now have a form of
sulfuric acid. It can slowly deteriorate the lining, or lack of lining, in a
chimney. When this happens, debris from the interior of the chimney
starts to obey Newton's law of gravity. As the debris piles up on the
interior, it will eventually cover the opening where the furnace vent, and
possibly the hot water tank vent, enters the chimney. The carbon
dioxide that enters the furnace area is then burned again, thus
becoming carbon monoxide.

A multitude of illnesses can occur from over exposure to carbon
monoxide. Death can be a very real possibility. I cannot stress enough
the importance of digital carbon monoxide detectors. They are as
important as smoke detectors.

Another problem is not having a proper rain cover with animal guard on
the chimney. Animals, such as birds, squirrels, and raccoons can nest in
chimneys. This can result in a blockage.

If your furnace is on a clay tile liner that has only had a gas furnace on it,
then it can go for 50 years or more without needing to be swept. Of
course, that is assuming that you have the proper animal guard on the

What about
OIL? Oil does have more residue that can be very
destructive to a clay tile liner. Again, there is sulfur in the byproduct
that coats the interior of the chimney, so again, a light form of sulfuric
acid can eat away at the interior. Gravity applies, and the furnace
eventually will not be able to vent. I have come in behind several of
these events, some that happened when the family was on vacation and
the family pets were killed. Thank goodness the family was not home
sleeping. The entire house is filled with oil smoke that coats everything.
The house must be vacated until everything can be cleaned. Back in the
mid 1990's, I was told that the expense of cleaning a house came to over

So oil furnace flues need to be swept or at least inspected every year.

Again, the time of year when you are not using the furnace is the time to
get it serviced. I get calls during the "silly season" from people that
have no heat. We are already working seven days a week, so there is no
immediate spot to put in an emergency job.  I do not want to turn these
requests down, but I have learned that if we do not get enough sleep
during this time of year, it can be very hazardous to a sweeps health. All
of my falls from roofs occurred around Thanksgiving. Why? Because of
the number of hours worked and the lack of sleep. I do not want this to
happen to anyone else.

Actually, there are not that many companies that will do oil flues
anymore.  I don't blame them for that decision. The only job that is
worse, is dead raccoons in a  chimney.

Not to sound too repetitive, but check our website for discounts during
the slower months of the year.