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Chimney Liners – What are they for?

Tuesday, October 22, 2013

Chimneys may seem somewhat obsolete in our homes nowadays since many of us no longer use the fireplace as our main heat source. The question is then, other than for Santa, what and how are chimneys used?  Well, it depends on the type of furnace you have, but chimneys are generally used as a way to ventilate the released steam from the furnace.  However, since as time goes on furnaces become more and more efficient, our chimneys have to adapt to these changes, which is why we have chimney liners.
 

Older, less efficient furnaces do not need a chimney liner.  This is because the steam they release can be up to 700 degrees Fahrenheit. That means that the steam uses the entire space of the chimney as it travels outwards. More efficient furnaces, such as those at 80% AFUE, use the chimney for ventilation as well.  Conversely, the steam that they release has a much lower temperature at only 400 degrees Fahrenheit.  Hence, the entire space of the chimney is not necessary.  That is why they use a chimney liner.  A chimney liner is a device that lines the inside of a chimney.  They are essentially metal tubes inserted into the chimney that reduce the size of the space so that the steam of more efficient furnaces can take up the entire area.
 

So, why does the steam need to fill the whole space of the chimney?  If it didn’t, moisture could build up along the sides of the chimney, which could lead to chimney destruction due to acid seeping in through the mortar.
 

That doesn’t sound good, right?  In order to prevent this, it is important to find out if you need a chimney liner.  You do not need a  chimney liner if…
 

You already have a chimney liner.  It’s possible a chimney liner may already exist in your home, and then you do not need to worry about anything.  You can tell by taking a quick look at your chimney.  If you see a metal pipe or top coming out just over the top of your chimney, that is most likely a chimney liner.
 

Your furnace is very old and inefficient.  If your furnace is really, really old then most likely it’s too inefficient to need a chimney liner.  If you aren’t sure, feel free to call A.B. May to find out more about the needs of your furnace.
 

You have a 90% AFUE furnace or above.  Steam from high efficiency furnaces (90% AFUE and above) is too low for even a chimney liner to work. Instead, these units need a separate ventilation system consisting of PVC pipes coming out the side of the home.
 

You have a newer home.  Generally newer homes have chimneys that are thin and made of metal.  They are already ready for more efficient furnaces that need a smaller ventilation space.

 If you would like to learn more, please feel free to contact A.B. May!

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