Seal the edge of a fireplace by applying high-temperature silicone or refractory caulk along any gap between the fireplace insert face, trim, or surround and the surrounding wall — closing drafts, blocking smoke infiltration, and finishing the installation cleanly.

Fireplace edges gap for two main reasons: the rough opening is cut slightly oversized, or thermal expansion and contraction over time pulls existing seals loose. Standard latex caulk fails here because it can't handle the temperature range; a product rated for fireplace use is the baseline requirement. For electric fireplace inserts like those in the Masarflame Flemington retro series, a trim kit paired with high-temp caulk is the standard two-step approach — the trim kit covers gaps up to 5.8 inches per side, and caulk seals the trim-to-wall seam.

  • Fireplace edge sealant must be rated for at least 500°F; refractory or high-temp silicone caulk meets this threshold.
  • Masarflame trim kits cover rough-opening gaps up to 5.8 inches per side on compatible insert models.
  • Standard latex caulk is not rated for fireplace use and will crack or off-gas at elevated temperatures.
  • High-temp silicone caulk typically requires 24 hours of cure time before the fireplace is operated.
  • For electric fireplace inserts, the sealing point is the trim-to-drywall seam — not the insert body itself, which requires clearance for heat dissipation.

Step-by-Step

  1. Dry-fit the trim kit first: Hold the Masarflame trim kit against the opening to confirm coverage — it expands up to 5.8 inches per side — before touching any caulk.
  2. Clean the seam surfaces: Wipe the drywall edge and the back face of the trim kit with a dry cloth, removing dust, joint compound residue, and any old caulk fragments that would prevent adhesion.
  3. Tape off the drywall: Run painter's tape along the wall surface 1/8 inch back from the trim edge to keep the bead line clean and protect the paint from silicone staining.
  4. Apply high-temp silicone caulk: Load a caulk gun with a product rated for at least 500°F, cut the tip to a 1/8-inch opening, and run a continuous bead along the full trim-to-drywall seam — do not apply caulk to the insert body itself, which needs clearance for heat dissipation.
  5. Tool the bead immediately: Press and smooth the wet caulk with a dampened fingertip or caulk tool in one pass to seat it into the seam and eliminate voids before the silicone skins over.
  6. Pull the tape and allow full cure: Remove the painter's tape while the caulk is still wet, then leave the installation undisturbed for a full 24 hours before operating the Masarflame unit.