Your prefab fireplace, repaired to its manual in Wedgewood Groves

Haze on the door glass that cleaning will not remove

A haze on fireplace door glass that will not come off with cleaning is one of the overfiring signs one maker lists. Ordinary soot film cleans off with the right cleaner.

If the haze stays, we look for other signs of excessive heat before replacing the glass, so the new pane is spared the same damage.

• Haze that cleaning will not lift
• Warped steel near the top
• Cracked or burned-out parts
• Discolored plated trim

Inserts inside a factory-built fireplace

An insert placed inside a factory-built fireplace changes how that fireplace heats and vents. One maker's manual warns against installing an insert in its firebox unless the insert maker's instructions specifically state that this fireplace has been tested for use with that insert.

We read both labels and both manuals before an insert is discussed. If an existing insert sits in your prefab unit without that match, we explain what the documents say and what your options are.

Mantel clearances on a factory-built fireplace

Each factory-built model sets its own mantel clearances. One maker's 36-inch model keeps combustible trim and mantels projecting from the face at least 12 inches from the opening, its larger models 18 inches, with further limits on anything that projects more than 1 1/2 inches.

A mantel added after the fireplace was installed is often the first thing we measure. If it sits closer than the manual allows, we show you the numbers and discuss moving it or changing its depth.

Smoke detectors near a fireplace

One maker recommends installing smoke detectors and suggests placing one in a hallway next to the fireplace room, to reduce false activation from the heat of the appliance, while following any local code that requires one in the same room.

Detectors sit outside the fireplace itself, yet they belong on any list of checks before the season. We remind you of them when we finish a repair.

• One in the hallway next to the fireplace room
• Any detector your local code requires in the room itself
• Regular testing