Insulating Around a Fireplace Insert

Four Places People Want to Add Insulation

When an insert goes into an old fireplace, there are gaps everywhere, and the urge to stuff them is understandable. Each gap has a different job, and only some of them may be filled. Here is where they are, from the room inward.

• Around the faceplate edge, where it meets the fireplace face.
• Behind the faceplate, in the space between the insert's body and the old firebox walls.
• Above the insert, at the old damper throat around the liner.
• Around the liner itself, inside the flue, all the way to the top.

What Counts as Noncombustible

The DuraVent DuraTech chimney instructions give a useful definition. They list building insulation among the combustible materials a hot chimney must be kept away from, alongside lumber, drywall and wiring. For insulation that may sit inside a required clearance, they ask for material that is noncombustible under ASTM E136, melts above 2000 F and resists water. Stone insulations, sold as rockwool or mineral wool, meet that; fiberglass insulation, they say, is not approved.

Those instructions are written for a chimney passing through a wall or ceiling, not for an insert, but the logic carries over. Near anything that gets hot, the only insulation that belongs is one a maker names, and it is never the kind sold for attics and walls.

Fiberglass and Paper Facing

Rolls of house insulation usually carry a kraft paper or foil facing, and the chimney instructions above class building insulation as combustible. Tucked against an insert's body or a liner, it fills an air space the insert counts on and puts a combustible material against hot metal, where trouble starts long before anyone sees it. Keep it out of the fireplace entirely.

The same goes for spray foam and loose fill. If a remodel leaves framing near the fireplace open, leave the gap for a crew to look at rather than filling it.

The Faceplate Strips

The one place insulation belongs on almost every insert is the faceplate. The Regency i2450-2 faceplate kit comes with two pieces of insulation, and the manual installs them between the faceplates and the fireplace face once the insert is connected. Their job is to seal the opening so room air does not leak into the old firebox and warm air does not leak out.

If those strips are missing, crushed or burned, replace them with the insert maker's part. Do not swap in a strip of house insulation.

The Liner Has Its Own Insulation

A chimney safety organization's FAQ for homeowners explains that liners serving wood appliances need insulation, either a blanket or an expanded mica or masonry type, while gas and oil liners do not. The DuraLiner instructions require insulation above the first flue tile, recommend it on the whole flex run, and specify at least 1/2 inch of their foil-faced blanket, taped and covered with mesh.

Those instructions also say no insulation or other material beyond what they specify may be placed around the liner or in its required air spaces. So nothing gets packed around a liner from below. If the liner's blanket is torn or missing, that is a relining question, covered in our guide on liners for inserts.

• Foil-faced liner blanket, wrapped lengthwise and butt-jointed.
• Aluminum foil tape along the seam.
• Protective mesh pulled snug over the blanket.
• Clamps at each end, then the liner lowered down the flue.

The Hearth and the Walls

Floor protection in front of an insert is a different kind of insulation: a hearth with a rated thermal resistance. The Regency manual lists noncombustible materials such as metal, brick, stone, mineral fiber board and concrete board, and asks for floor protection with an R value of 1.4 when this insert is raised only slightly off the hearth. Mantels, trim and side walls are handled by clearance distances in the manual, not by insulation.

Prefab Fireplaces Are Different

A factory-built fireplace and its metal chimney depend on open air spaces. The Superior wood fireplace manual says never to use blown insulation to fill the chimney enclosure and not to block the opening in the collar around the chimney at the top of the fireplace. DuraVent's DuraPlus instructions warn against filling chimney clearances with any material, especially home insulation. Section R1005.8 of the Florida Building Code, Residential, requires a steel insulation shield where a factory-built chimney passes through an insulated ceiling or attic, ending at least 2 inches above the insulation.

So in a prefab fireplace or its chase, the rule is the reverse of stuffing gaps: keep the air spaces clear and the shields in place.

Getting the Surround Checked

If you have found house insulation stuffed around an insert or a liner, stop using the insert and book a free inspection. Our fireplace insert installation crew removes what does not belong, replaces faceplate strips and liner blankets with the makers' parts, and writes up anything else in an estimate.

Family-owned, locally run and Proudly American, our experienced crew knows inserts, liners and which materials belong behind a faceplate. Spring Hill families get the same Proudly American crew from the first look to the last screw.