Caps, Dampers and Waterproofing in Windy Lehi

Sustained wind is a different problem from gusty wind

A chimney that sees the occasional squall can get away with a lot. One that spends whole days in a steady thirty-mile-an-hour flow cannot. Two things happen. Fastenings work loose through hours of vibration rather than failing in one dramatic moment, and a lightweight cap that was pressed on rather than bolted eventually walks off the flue. We find them in yards and gutters every spring.

So the specification matters more here than the price does. Stainless or copper, sized properly to the flue rather than nearest-fits, and mechanically fastened with screws into the tile or a band clamp that is actually tightened. On the exposed high ground on the bench, that is not over-engineering. Lehi has been settled since the 1850s and then took on most of its population after 2000, so the job here is either an aging clay-tile flue in the old grid or a framed chase up on the bench, and the fastening detail is not the same on the two.

Driven rain finds the windward face

The second consequence of sustained wind is that precipitation arrives sideways. Rain that would run harmlessly down a stack instead gets pushed into the joints on one side of it, and snow packs against the same face and melts there. Over a few winters that produces a chimney with one visibly deteriorated elevation while the other three look almost new. A breathable masonry repellent on sound brick helps considerably. A shiny film-forming sealer does the opposite, because it traps water that entered from the crown and cannot now escape.

Top-sealing dampers, and the wildlife argument

The old cast-iron damper in the throat of a fireplace leaks even when it is closed, and in a wind that leak becomes a draft you can feel across the room. A top-sealing damper puts a gasketed lid at the top of the flue, operated by a cable from the firebox, and it seals against both air and weather.

It has a second benefit worth mentioning in a city sitting on the river and lake corridor at the north end of Utah Lake. There are a lot of birds around here, and a warm vertical shaft is attractive to all of them. A top-seal damper or a screened cap closes that opportunity, and we always confirm a flue is empty before we close it, because trapping something in there is a worse outcome than leaving it open.