Sizing your Fireplace for a Flueblocker

The Flueblocker is easy to use and durable. It comes in a number of size  variations, so you need to have an idea of the size and shape of the flue you are looking to plug.

Round Chimney Flues

Round chimneys are the easiest to measure and install. Here are a few steps to show you how to use a Flueblocker in a round chimney.

Step 1) Determine if you need to put the Flueblocker above or below the damper. You need about 1″ of uninterrupted vertical wall space above or below your damper.

  •  Example 1 is a perfect application to install a Flueblocker below the damper. There is an inch of vertical wall space below the closed damper and a Flueblocker can slide right in there.
  • Example 2 can go either way. You could install the Flueblocker below the closed damper, but you will need to cut the wool pad to accommodate the damper handle. cutting a slot in the pad may compromise the tight seal that the Flueblocker offers. So, you could install a Flueblocker above the open damper into the narrow chimney throat. If you choose this option, be sure to mark the firebox clearly that the Flueblocker is in place. It is easy to forget about a Flueblocker that is installed high up out of view.
  • In Example 3  the Flueblocker definitely needs to go above the open damper. There is no room below the closed damper to put the Flueblocker into.

Step 2) Take a ruler or tape measure and measure the diameter (distance from one side to another) of the hole you are going to plug. You will want to buy a Flueblocker that is an inch or two larger than the hole.

For example: If you measure a round opening of 8″ diameter, then buy a Round 9″ Flueblocker.

Make sure you have a long enough handle for the install. A Flueblocker comes with a 12″ handle. If you need a longer handle order some 6″ handle extenders rods.

Step 3) Once you have received your Flueblocker, you can install it. Press the Flueblocker into place. It should fit snug, but not pucker or gap around the edges. If your Flueblocker is too big, you can trim it to size with scissors for a custom fit.

Rectangular Chimney Flues

Rectangular Chimney Flues come in many shapes, sizes and damper configurations.

Step 1) Determine if you need to put the Flueblocker above or below the damper. You need about 1″ of uninterrupted vertical wall space above or below your damper.

  •  Example 1: A perfect application to install a Flueblocker below the damper. The worm gear damper is tucked way up by the damper door. There is plenty of uninterrupted space below the damper hardware, so you measure and install the Flueblocker there.
  • Example 2: This application can go either way. You could install the Flueblocker below the closed damper, but you will need to pull the cotter pin that holds the damper handle on. Once the damper handle is removed there is no obstructions to putting the Flueblocker below the damper.Another option is to install a square Flueblocker into the square flue tile that you can see when the damper is open. However you will need to use some handle extension rods to get the Flueblocker up that high.
  • In Example 3:  The Flueblocker goes right into the damper door opening. The side-handle is not removable, and the flue tile is too high to reach. So the Flueblocker is installed into the damper opening and a slot is cut in the wool pad to accommodate the damper handle.

Step 2) Take a ruler or tape measure and measure the lenght from (left to right) and depth (from front to back) of the area you are going to plug. You will want to buy a Flueblocker that is an inch or two larger than the hole.

For example: If you measure an opening of 12″x34″ purchase a 13″x35″ Flueblocker.

Make sure you have a long enough handle for the install. A Flueblocker comes with a 12″ handle. If you need a longer handle order some 6″ handle extenders rods.

Step 3) Once you have received your Flueblocker, you can install it. Press the Flueblocker into place. It should fit snug, but not pucker or gap around the edges. If your Flueblocker is too big, you can trim it to size with scissors for a custom fit.

You can also use scissors to cut a slot in the Flueblocker to accommodate damper hardware.