Properly installing a fireplace will increase comfort and safety, as well as reduce the amount of heat required from the HVAC system.
In production homebuilding, there are three main types of fireplaces: direct vent gas fireplaces, B-vent gas fireplaces, and electric fireplaces. Direct vent gas fireplaces have a sealed combustion vent system. With a sealed combustion vent system, combustion air is drawn from the outdoors into a sealed firebox through a flue. The flue consists of two concentric circles—outside air is drawn through the outer pipe while combustion gases are exhausted outdoors through the center pipe. This way, air from the home isn't used to fuel the fireplace. Direct vent fireplaces are the most efficient type of fireplaces on the market.
Traditional B-vent gas fireplaces take combustion air from inside the home and vent the exhaust air outside the home. A typical B-vent flue consists of two circles—combustion gases are exhausted through the center circle, while the outer circle is used solely to provide a cooler layer between the center circle and any materials surrounding the flue.
In production homebuilding, electric fireplaces are hardwired to the home's electrical system. They don't have a flue, as there's no need to bring in combustion air or exhaust combustion gases. They're typically installed in multi-family homes.
Framing
Before installation, inspect the rough framing, making sure all of the specified fireplace clearances are met. In addition, make sure the side and top framing are positioned to receive the attachment ears and framed to support the mantel or surrounding trim. The front framing should be plumb.
Insulation
If the fireplace is located against an exterior wall, make sure insulation is installed in all wall cavities between the fireplace unit and the outdoors, so the unit is within the thermal enclosure. If the fireplace is located in a bump-out, insulation should be installed in the exterior walls, as well as at the top of the fireplace cavity and in the cantilevered floor. If the fireplace is located mid-plan in a single story home, insulation should be installed at the top of the fireplace cavity.
Draftstopping and air sealing
Draftstopping encapsulates the insulation and creates an effective air barrier. Before installing the fireplace unit, install a continuous rigid air barrier of wood sheathing, drywall, or Thermo-ply® along the exterior walls. If the fireplace is located against an exterior wall, draftstop the wall. If the fireplace is in a bump-out, draftstop the exterior walls, the top of the fireplace cavity, and the underside of the cantilevered floor. If the fireplace is located mid-plan, draftstop the top of the fireplace cavity. After installing the draftstopping, make sure all corners, edges, and seams have been thoroughly sealed with foam. Use fire-rated sealant to seal the area where the heat shield meets the exterior wall.
Fireplace unit
Build a raised platform for the fireplace unit. Make sure the platform is secure and level. Check that the back and side clearances between the platform and the surrounding framing are adequate. Make sure the location of the gas lines, electric lines, and combustion air duct don't interfere with the position of the fireplace unit.
The fireplace unit should be level, flush with the front framing, and centered side-to-side. Check that all required clearances are met. Make sure the tabs on the top and face of the fireplace unit are fastened to the rough framing. If it's a gas fireplace, make sure the gas line and shutoff valve are roughed-in. If it's an electric fireplace or a gas fireplace with an electronic ignition or blower unit, ensure that all electrical connections have been made. Make sure the flame sensor is positioned properly in the flame and that it’s functioning properly. During construction, leave a temporary cover on the face of the fireplace unit to protect it from damage.
ProTip!If installing CSST gas piping, make sure it’s bonded and grounded at the service entrance and at any transition between CSST piping and rigid black iron piping.
Combustion air duct
A combustion air duct is an additional pipe that’s attached to a B-vent fireplace to prevent backdrafting. A combustion air duct brings combustion air into the fireplace, so the B-vent unit doesn't draw air from inside the home. The combustion air duct inlet should be level with or lower than the firebox. If it’s installed level with the firebox, install a small dip in the duct, known as a cold air dip, to prevent the flow of cold air. Make sure the combustion air duct is connected to the unit and sealed where it penetrates the exterior wall.
Flue
Install the type of flue recommended for the fireplace unit. A direct vent flue (or concentric flue) has two concentric circles, one for intake air and one for exhaust air. A B-vent flue has two circles—the center circle is for exhaust air and the outside circle provides a cooler layer between the center circle and any material surrounding the flue. A triple-wall flue has three concentric circles—the center circle is for exhaust air, the middle circle is an insulation layer that keeps the center of the flue as warm as possible, and the outside circle provides a cooler layer.
For a horizontal termination, make sure the framing hole is a minimum of 10” x 12”. Install a wall shield firestop and integrated heat shield where the flue penetrates the exterior wall to protect vulnerable materials from contact with the flue. Don’t pack insulation around the flue. Install an elbow pipe as part of the flue. An elbow adds resistance to the flue and prevents air from traveling down a direct path to the pilot light. When installing the flue, attach it to the top of the fireplace, rather than to the back; attaching it to the top will help keep air from moving the pilot light. At the termination cap, make sure the termination clearances required by the manufacturer are met. When a vent is adjacent to a traffic area, an additional heat shield can be installed to protect homeowners from accidental contact with the hot flue surface.
For a vertical termination, make sure the framing hole is a minimum of 10” x 10”. Install a ceiling shield firestop where the flue penetrates the ceiling plane; the firestop protects vulnerable materials from coming into contact with the flue. In the attic, install an attic insulation shield or framed end dams to maintain a clear space around the flue where it penetrates the attic. Don't pack insulation around the flue. Support the flue according to the manufacturer’s specifications. When the pipe runs vertically, support it every 8’ after 25’. When the pipe runs horizontally, support it every 5’. Use a vent support or plumber’s strap for support. At the termination cap, make sure the termination clearances required by the manufacturer are met.
ProTip!er insulation is blown in the attic, verify that no insulation has fallen between the attic insulation shield or framed end dams and the flue pipe.
Termination cap
Termination caps are fabricated to provide weather resistance, redirection of hot gases, and access to combustion air. Termination caps don't require any adjustment. Simply check that the cap hasn’t been damaged, bent, or otherwise harmed. A vertical termination cap requires an additional piece called a storm collar that protects the transition between the pipe and roof flashing. Make sure the pipe-to-boot flashing and the storm collar-to-pipe joint are caulked.
ProTip!When installing a horizontal termination cap in a brick wall, make sure the two sections of the heat shield overlap properly.
