Chimney Work for South Salt Lake's Older Houses

The houses along the older grid here are small, tightly spaced and mostly pre-war. Their brick went up when a fire in the room was how you heated the room, and the flue was sized for that. Everything since then has been fitted into what was already standing: a gravity furnace, then a forced-air one, then a high-efficiency replacement, plus a gas water heater teed in beside it.

The chimney's real job has changed

On most of these properties the fireplace is now the least important thing attached to the stack. The furnace and the water heater are what matter, and they are the reason an oversized old flue is a hazard rather than a curiosity. Modern appliances produce cooler and wetter exhaust than the coal and early gas equipment these chimneys were built around. Given too much cross-section, that exhaust slows, cools and condenses on the way up, and the condensate is acidic. It works on the mortar joints from the inside, and the first thing anybody notices is white staining or crumbling brick on an outside wall a floor or two below the top.

The remedy is nearly always a correctly sized liner rather than rebuilding anything. That is a smaller job than it sounds, and it is the single repair we end up recommending most often in this part of the valley.

There is a second thing worth knowing before anyone starts pointing up your brick. Old brick is soft. It was fired at lower temperatures than modern brick and it was meant to move and to let moisture out through its face. Modern mortar is harder than the brick it sits between. Repoint a century-old chimney with a standard bagged mix and the joints will outlast the brick, which spalls away on either side of them instead. A softer, lime-rich mortar is the right answer, and it is fair to ask anyone quoting the work which one they plan to use.