Air Leakage: Outlet Boxes Above Zero Clearance Fireplaces

Over the last few years it has become common for new homes to install flat screen televisions above zero clearance gas fireplaces. This location calls for an outlet to be installed and in many cases conduit for cables such as HDMI and ethernet that are attached to the backside of the television and run behind the walls to another location.

Most if not all gas insert fireplaces will be installed inside of a framed wall area. If located on an interior wall minimal insulation if any will be used along with little to no air sealing. This location and design creates an opportunity for air to leak into the home from vented attics and potentially unconditioned basements. Located on an exterior wall the inserts will/should have insulation and gypsum installed around them. The gypsum is typically installed just above the top half of the gas insert creating a nice air barrier for the installed gas unit. The problem is the outlet/conduit boxes will be installed above this location outside of any air sealing measures thus leading to unnecessary air leakage at the exterior wall.

Potential Air Leakage Points:

  • Vented Attic
  • Vented Vaulted Ceiling
  • Soffit Vent (if inside a “bump-out”)
  • Cantilevered Floor
  • Wiring holes from wall cavities
  • Around the electric/conduit opening at the surface of the wall

Figure 1 is of a gas insert fireplace installed on an interior wall of a house. When a blower door test was conducted air-leakage was detected at all four locations shown in the image. The movement of air can be traced back to the vented vaulted ceiling and no air sealing measures employed from the ceiling down to the framing around the fireplace, wall cavities and cold air return along with electrical boxes.

Figure 2 has the fireplace located on the exterior wall and does a much better job of air sealing prior to gypsum going up. The location above the electrical and conduit opening has been sealed with gypsum and spray foam thus stopping air leakage from above. The framed wall with air permeable insulation in it still needs to have an air barrier installed to stop/decrease air movement. The flexible blue conduit was also caulked on the outside at each stud interface that it ran through until it terminated at a wall opening. During blower door testing for Figure 2 no air leakage was detected on this wall.

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