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1. Senior Member Rank 2
Join Date
Mar 2009
Posts
238

## chimney liner

I have an existing brick chimney partially lined with clay tile but the clay is cracked and shifting so i want to line it with a stainless steel liner. The run is only 30 feet but im not sure what size i need. How can i calculate the diameter of the needed liner? Water and boiler for baseboard heating vents through the same line. The boiler vent is a 4 inch line for 70,000 btu and the water heater is a 3inch line for 40,000 btu

2. Senior Member Rank 2
Join Date
Feb 2010
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South*East
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## Re: chimney liner

This was told to me by a old mason. It is the way they determined the flue size. Draw two connecting line in the shape of a L. In your case one line would be 4" and the other 3". Then connect the two line to form a triangle. The length of the line to form the triangle is the minimum size your flu should be.

John

3. Senior Member Rank 2
Join Date
Mar 2009
Posts
238

## Re: chimney liner

Thats a great tip if someone can back it up. In this example i would need a 5" liner but would there be anything wrong with gettin a 6 inch? Assuming it fits the only issue i can think of is drawing too much air out of the house including the warm air that i want to stay in but i assume i could solve this with a damper of some sort?

4. ## Re: chimney liner

The area of a 3" pipe is 7.07 sq. inches, a 4" pipe 12.57 sq. inches total 19.64 sq inches, the area of a 5" pipe is 19.63 sq. inches, so a 5" pipe has the same area as a 3" and a 4" combined.

If a 6" fits in the existing chimney it won't draw out any more air than the existing flue and if the existing flue worked with the boiler and WH, then the 6" should actually work a little better.

Jack
Last edited by JLMCDANIEL; 10-12-2011 at 11:32 PM.

5. Senior Member Rank 2
Join Date
Mar 2009
Posts
238

## Re: chimney liner

Thanks, the 6" sounds good to me but should I worry about the existing space around it? For example, is it normal practice to backfill the remaining space between the new liner and the existing chimney?

6. ## Re: chimney liner

If you back fill you would need to use light weight concrete, but normally a liner and cap is installed without back fill. The chimney cap keeps water out of the chimney.

Jack

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