Gas Log Sets Dropped Into Salt Lake City Fireplaces

The appeal is obvious. An old fireplace that smokes, needs sweeping and takes effort becomes something you switch on. The problem is that the chimney above it was built for a large volume of hot coal or wood smoke, and a gas appliance produces a fraction of that volume at a much lower temperature.

Why an oversized flue works against a gas appliance

Draft depends on the exhaust staying warm enough to keep rising. A small quantity of relatively cool gas exhaust entering a tall, wide, cold masonry flue loses heat to the brick very quickly. It slows, and the water vapor in it, which is substantial, condenses on the flue walls instead of leaving the chimney.

Salt Lake City's older houses make that worse simply by being tall. A two-and-a-half or three-story house from the turn of the century carries a chimney to match, and where that stack runs up an outside wall it is a great deal of cold masonry for a small, cool gas exhaust to climb before it ever reaches daylight.

That condensate is mildly acidic, and in an unlined or old clay-lined flue it works on the mortar joints from the inside. Over years it degrades the very masonry the appliance depends on. The correct answer is a liner sized for the appliance rather than for the fireplace that used to be there, which keeps the exhaust warm and moving and isolates the masonry from it.

Vented log sets and the damper

A vented log set needs the flue open while it runs, which is why the damper is fixed permanently in an open position as part of a correct installation. If your gas logs went in without that being done, it is worth checking, because a closed damper over a running gas appliance is a serious matter. It is a small thing to verify and we check it on every visit.

What annual service covers

• Burner and pilot cleaned, ports cleared, air adjustment checked.
• Thermopile or thermocouple output measured, since a weak one is the usual cause of a fireplace that lights and then goes out.
• Logs or media returned to the exact manufacturer layout, because a log resting in the flame path produces soot and carbon monoxide.
• Glass and gasket on sealed units checked and refitted correctly.
• Venting and, on a masonry chimney, the flue condition looked at with a camera every few years.
• Gas connections leak-tested.

Carbon monoxide alarms

Any house with a fuel-burning appliance should have working carbon monoxide alarms, and in an older house with an old chimney that is not a formality. It is the one protection that does not depend on anybody having inspected anything.