Block-Off Plate Installation
Whenever this appliance is installed with a direct connection a block-off plate, or other non- combustible seal-off device (e.g. damper adapter), will need to be installed. This device is used to seal the chimney, insuring no smoke enters the home and providing the chimney system with a seal to promote draft. The directions below detail the steps for construction and installation of a block-off plate.
1.Determine a location for the block-off plate at the top of the firebox below the damper area (make it high enough to allow installation of the connection pipe). The location should be level and in an area where it can be mounted easily. Measure the width at the rear ("A") and front ("B") of the firebox at the height where the block-off plate will be installed (see the illustration below). Then measure the depth of the location where the block-off plate will be installed ("C").
NOTE: Most masonry fireplaces have square fireboxes while certain zero-clearance (metal) fireplaces often have domed firebox tops. This makes zero-clearance block-off plates more difficult to install. To simplify the procedure, insulation may be used to seal the rounded edges.
2.Make a cardboard template of the measurements, but add a 2" flange to each side. This flange will be used to mount the block-off plate to the inside of the firebox. Bend the flanges downwards on the template and place it inside the fireplace. If the template fits correctly in its planned location, go to the next step. If it does not, make a new template with the appropriate corrections until it fits correctly.
3.With the template in place, mark the location that is centered in the fireplace and 9 1/4" back from the fireplace opening. This location approximates the center of the flue when the insert is in place (a slight offset may occur based upon insert and block-off plate placement). Remove the template and cut a 6 1/4" diameter hole centered on this mark.
4.Make the block-off plate of 24 gage or thicker steel to match the template. Drill two holes in each flange for mounting the plate.
5.Mount the block-off plate using masonry screws.
NOTE: Use sheet metal screws on zero-clearance (metal) fireplaces (screws need only be long enough to penetrate the first layer of metal).
6.Insulate the block-off plate using high-temperature fiberglass insulation (Kaowool® or equivalent) and furnace cement (allow the cement to dry for at least 24 hours before burning).
7.After placing the appliance and installing the pipe through the block-off plate, use high- temperature fiberglass insulation and furnace cement to seal any cracks between the pipe and block-off plate.
Block-Off Plate Template
