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Measurements to Gather for Gas Chimney Liner Installation

Installing a chimney liner for a gas appliance is an easy way to bring your chimney back to life without having to rebuild your existing chimney. Cracked flues and large flues are the two most common reasons a chimney liner is required for a gas appliance. To do this job properly, you will need to gather some information about your appliance and chimney setup to determine the correct size liner for your appliance.

Why does the proper size Chimney Liner matter?

First, let's discuss why the correct size chimney liner is so important to the functionality of the gas appliance. By just installing whatever size liner would fit down your flue can hinder draft, causing the appliance limit switch to flip. When this happens, the appliance will fail to run. This is a result of the chimney liner being too small for the appliance.

On the flip side, if the chimney liner you install is too large for the gas appliance, it will cause the liner to condensate more. The condensation can spill back in the appliance and cause the appliance to rust. Having too much flue area causes the gas to be lazy and condensate inside the chimney. Installing the correct size chimney liner will ensure that the chimney vents properly without issue.

Measurements Needed from the Gas Appliance

With a little information on the gas appliance, it is easy to determine the correct size chimney liner.

  • The first piece of data we need is the BTU capacity of the appliance. If you are connecting multiple gas appliances together, you must add the BTU capacity from each appliance.
  • The next piece of information that is needed is the measurements of the existing chimney. What is the height of the chimney? What are the exact inside measurements of the chimney?
  • Lastly, we need to look at the pipe configuration of the connector pipe in the furnace room. Each 90 degree elbow in the connector pipe will reduce the BTU capacity by 10 percent. Each 45 degree elbow will reduce the BTU capacity by 5 percent.

Once you have all this information you can contact a Rockford Chimney Certified Technician to properly size the liner for you. Or, fill out our gas chimney liner measuring form!

Connecting the Gas Appliance to the Chimney Liner

Furnace ConnectionOften times, gas water heaters are venting into the same flue as a gas furnace. There are a few different ways that these are configured. In some cases, you have two pipes entering the chimney separately. Other times, the two connector pipes tie in and tee together before they reach the chimney and only one pipe enters the chimney. A custom Double Snouted Tee can be used to connect the flexible chimney liner to the connector pipe without having to change your thimble hole configuration. For installations where the connector pipes tie in together, you may use a standard tee connection.

Chimney liner installation for gas furnaces are generally the easy if you do your due diligence ahead of time. Now that you know what to look for to plan the installation, this will ensure a successful installation.