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How can I replace my fireplace damper?
8 December 2007

Q. My wood burning fireplace was built in 1966 and it has been enjoyed through the years. I noticed that the frame of the damper flue is rusting at the back and the cement caulking is falling out. This frame rests on the fireplace box. Can this old damper be removed and replaced by going through the back of my brick chimney? If so, do you know the size and where I can purchase a new one? The brick chimney has been inspected periodically and appears fine.

A. Replacing that damper mechanism with one just like it will create great expense and mess. You could have avoided this had you had a rain hood and bird screen over the top of your chimney to keep-- among other things-- water from getting down there to rust out the damper frame. Youíre not expected to know that but whoever inspected your chimney would have served you better by suggesting one.

We average about 40 plus inches of precipitation each year and with your top flueliner open to the sky that translates into a column of water almost three and a half feet tall pouring down the chimney annually. That water doesnít do the metal of the damper or the masonry any good. Why itís not part of the building code to install a rainhood at the time of construction Iíll never know. Even if you enjoy using your fireplace frequently, it isnít burning every day and certainly not in summer to dry things out by use.

It took 41 years for this to happen with your damper and that tells me itís a cast iron damper mechanism that comes manufactured as one piece with the damper plate and hinges integral to the system. Itís placed over the firebox during construction and forms both the damper and the throat-- the opening into the flue-- and the smoke shelf. The smoke shelf is a space behind the damper where air mixes with the hot flue gasses and creates the draw. This combination of technologies is over 200 years old and was developed by both Ben Franklin who gave us the damper and Benjamin Thompson, the inventor of the Rumford style fireplace, the first to employ a smoke shelf.

Heatilator type fireplaces, with a metal firebox that heats up and has vents on the bottom, sides and top that convect and heat house air around the metal firebox were, and are, popular with a lot of builders and homeowners but their dampers are rolled steel and if the chimney isnít kept dry with a rain hood will rust out much faster than any cast iron damper.

When and if the damper mechanism gets rusted to the point of being nonfunctional then I would recommend a spring loaded chimney top damper be fitted to your fireplace and chimney system and the old rusted one be abandoned. I see that done quite often.

The damper is mounted to the very top of the chimney and the old damper at the firebox is either removed if itís loose and unhinged or left in the open position. There is a stainless steel cable that drops down through the chimney and is connected to an anchor that is installed on the inside of the firebox on the side and towards the front opening. When you want to use the fireplace you just pull down on this cable and slide it out of the restraining slot on the anchor and let it go. The spring at the top pops the damper open and youíre ready to light the fire. After the fire goes out and youíve waited a safe period-- about 24 hours-- you reverse the process closing it again. Leaving the damper open will continuously vent your heated house air out through the chimney. I like these chimney top dampers because they perform all the important functions at once. They keep out birds, critters, leaves, rain and cold air when closed. Cost runs about $400. installed.

Cutting into the back of the chimney and replacing the damper mechanism and rebricking things I would estimate is in the $2500. cost range. And a masonry repair always looks like a masonry repair- Iíve rarely seen one blend perfectly with the old.

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