How Dampers Work

A barometric damper typically consists of a round tee on your boiler's flue, with a round door and adjustable weight. The weight is used to control the opening and closing of the door, regulating the amount of air that can enter the flue and chimney while your boiler is running. If a damper is not installed, or if your damper is not working properly, it can cause too much draft, which leads to increased heating costs, or too little draft, which can cause incomplete combustion, soot buildup and carbon monoxide leakage.

Opening and Checking Dampers

Open the damper and look inside. Depending on whether your boiler's damper is installed on a horizontal flue pipe or a vertical flue pipe, you should be able to see inside. Dirt, debris, soot buildup and rust damage may be visible, in which case your system will need to be cleaned. Excessive buildup can in some cases prevent a damper from opening and closing as it should. More likely, though, buildup is causing air flow issues in your chimney or flue, which only appear to be a damper problem.

Common Problems

If a barometric damper is shared between your boiler and another piece of equipment, such as a furnace or water heater, it cannot be tuned to optimal performance, because each piece of equipment has different specifications. If the damper is broken, damaged, or has missing parts it cannot do its job properly and will need to be replaced. If the weight has been changed or removed the door may not open and close right. If your damper has been blocked, plugged or wired shut, this probably means that someone else tried (unsuccessfully) to fix some underlying problem, such as a blocked chimney. If the damper is stuck in the open position, it is probably due to a mechanical defect or missing weight.

Considerations

Dampers and flue pipes can get very hot while furnaces are in operation, so turn your boiler off and let it cool down before you attempt to fix or inspect your damper. Do not adjust the weight or attempt to wire your damper shut. In most cases, damper repairs will need to be done by a trained HVAC professional.