Herscher outdoor wood boiler flue: sweeping it before the first cold week

By Jacob Dove, Friendship Chimney Sweep

The job

A farm a few miles out of Herscher heats the house and the shop with an outdoor wood boiler. The owner had it installed two winters ago and had never had the stack swept. He called because the boiler had started smoking back at the door on windy days. When we opened the stack it had a solid quarter inch of glazed creosote from the firebox to the cap, in a single burning season.

Why boilers glaze

An outdoor boiler is a water jacket around a firebox. The water keeps the firebox walls cool, so combustion is cooler and smokier than a stove or fireplace, and most models smolder between calls for heat with the damper closed. Cool, smoky exhaust up a short, uninsulated stack that sits outside in a Kankakee County January is the perfect creosote factory. The smoke condenses almost immediately and the glaze builds fast. A quarter inch of glaze is the point at which a stack fire becomes likely, and a stack fire in a boiler next to a shop full of equipment is a bad afternoon.

The sweep and the advice

Glaze does not come off with a brush. We ran a rotary head down the stack and chipped it out, cleaned the firebox flue outlet and the connector, and checked the stack cap. Then we talked about wood. The owner was burning green ash cut the same fall. Boilers tolerate wetter wood than a stove, which is part of their appeal, but wet wood is still the main reason the stack glazes. Splitting a year ahead, keeping the pile covered, and running the boiler hot for a stretch each day instead of letting it smolder will cut the buildup by more than half. We will see him again next fall regardless. Boiler stacks get swept every year, no exceptions.

If this sounds like your house: we handle chimney and stove flue sweeping across Kankakee County, and our Herscher page covers what we usually find there. Call (815) 449-4264, 7am to 9pm, any day.

Quick questions