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How do I know what size liner I need?

Choosing a Length

The best way to size your chimney liner is by dropping a tape measure from the top of the chimney crown and measure the distance from that point to the thimble or opening where your appliance or stove will connect to the chimney. It’s always a good idea to add an extra foot or two just in case.

Choosing a Diameter

A general rule of thumb is to see what size outlet is on your stove or appliance. In most cases, fireplace inserts require 6 inch diameter chimney liner. Woodstoves generally require between 6-8 in diameter chimney liner.

In any situation you should first consult the manufacturers instructions of your appliance before installing a liner.

Open Fireplace Liner Sizing Guide

The chart below uses a 10-1 ratio. A 10-1 ratio should be used for chimneys less than 25 feet in height and a 12-1 ratio for chimneys greater than 25 feet in height.

Fireplace OpeningLiner Diameter
Up to 600 sq. in9″
601 – 760 sq. in.10″
761 – 942 sq. in.11″
943 – 1140 sq. in.12″
1141 – 1356 sq. in.14″
1357 – 1846 sq. in.16″

Below is a chart for sizing gas appliance liners:

View our chimney appliance sizing chart

Choosing a Diameter for Non-Round Pipe

These charts will help you find the dimensions of ovalized,squarized, and rectangularized pipe. Start by finding the pipes minor outside dimension from the left side of the chart. Move across to the right to find the major outside dimension. Then move up to the topmost header. This will give you the round pipe size you will need before ovalization.

Oval Shape

Rectangle Shape

Square Shape








    *Note: If you have a terra cotta clay chimney
    flue lining, be sure to measure the true length and width of the
    inside of your chimney flue space.

    *If there is a terra cotta clay flue liner, does it protrude out of
    the top of the chimney at least 2 inches? If there are at least 2
    inches and the terra cotta clay is in good condition, you will use
    our stainless steel, terra cotta top plate that has a 1 1⁄2inch edge
    that goes all the way around (like a shoebox lid).

    *If your terra cotta clay flue is in bad shape at the top, you may
    need to just take a hammer and tap all around that terra cotta,
    taking it away to make the surface flat at the top of your chimney.
    In that case, you will simply use the flat top plate that comes with
    our liner kit.



    *Note: If you have a terra cotta clay chimney
    flue lining, be sure to measure the true length and width of the
    inside of your chimney flue space.

    *If it is on the back of the stove, is it parallel with the back of the stove or is it at an angle, like 45 degrees?

    *If it is at an angle you will use an insert stove adaptor (an insert liner kit) rather than a two-part tee with cleanout cap.


    Usually pellet stoves have an exhaust hole id of 3 inches. However, if you are going up more than 15 feet to the top of your chimney you need to use a pipe and/or flex liner that is 4 inches diameter.





    If you are only venting a hot water heater then the exhaust hole diameter is probably 3 inch diameter. If it is 3 inch diameter and you are going up more than 15 feet to the top of your chimney, you must use a 4 inch diameter flexible liner or ridged pipe for proper draft. We also suggest to go ahead and use a 4 inch diameter flexible liner or ridged pipe even if the total length is 15 feet or less.


    Not the depth or any other dimension inside your fireplace.
    Most gas log fireplaces require an 8 inch liner kit or rigid kit. But do not assume that is the case for the gas log fireplace kit you are installing. Obey the requirements for that specific unit that are in your installation/instruction manual.