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How To Install A Prefabricated Fireplace

Manufacturers of prefabricated fireplaces, as shown in Figure 1, generally provide you with lots of literature and instructions on the installation and maintenance of their specific product. It is important that you follow them carefully.

Prefabricated Fireplace

Figure 1 - Prefabricated Fireplace

When foundations are required, the installation of a prefabricated fireplace unit, like that of a traditional fireplace, starts with the foundation work. Use the foundation procedure as described for traditional fireplaces. Prefabricated fireplaces may come with or without a hearth. Those units that come complete with a hearth only require anchoring onto the foundation walls. Those fireplaces that do not come with a hearth involve the pouring of a hearth onto the foundation walls before the fireplace can be installed. The hearth pouring process is similar to that of a traditional fireplace.

When foundations are not needed, simply position the fireplace on the sub-floor. To find the precise placement, drop a plumb bob from the place where the chimney punctures the roof and any other floor level. Make sure that the location of the chimney on the roof corresponds to the location of the chimney opening in the fireplace unit. Before framing in or encasing the unit, erect the chimney. Chimney installation has to be handled by two persons; one to hold the section and the other to lock it in place. Install the first section of chimney over the fireplace unit, as shown in Figure 2. Follow the manufacturer’s instructions to lock it into position. Proceed to install the intermediate sections in the same fashion until the to section extends through the roof.

connecting first piece of flue to prefabricated fireplace

Figure 2 - Connecting first piece of flue to prefabricated fireplace

Note: Flues are slender vertical elements requiring support to prevent them from buckling under their own weight. Install the chimney support boxes where the chimney passes through the ceiling into the attic. In multistory homes provide fire stops as the chimney punctures each floor, as shown in Figure 3.

fire stop

Figure 3 - Fire stop

Once the chimney is above the roof, close the leftover opening and apply flashing on top of it. Fit the flashing over the flue and nail it to the roof frame. Roofing is applied to cover the flashing except for the lower flange. This one laps over the roofing instead, to divert water away from the structure, as shown in Figure 4. The remaining components of the chimney are locked into place. A storm collar is inserted in the flue over the flashing and the joint sealed with waterproof mastic. If there is a chimney cap, it is now attached, as shown in Figure 4.

chimney flashing and cap

Figure 4 - Chimney flashing & cap

The fireplace unit is now framed or encased according to your design. The last step is to apply the finishing material for the front hearth.