What Are Chimney Dampers?

There’s several brands of dampers that I will cover, but first I’ll distinguish between two basic damper types: Top dampers and throat (or bottom) dampers.

Understanding Top Dampers

  Top dampers are usually installed in damper repair situations where the original damper is missing or beyond simple repair. They are fairly air tight, particularly if your chimney has been relined or in excellent condition. They have a rubber gasketed surface and can be purchased with or without an animal guard/fly ash arrestor and rain cap. The rain cap and mesh animal guard feature comes into play during the hours your damper is left open. The damper itself keeps critters and rain out very well when the fire is out and in the off season. Top dampers also keep out most insects like flies, bees, mosquitoes, etc. Bottom dampers are far less effective at this and never keep the critters out of the chimney itself. My favorite setup is a throat (bottom) damper (if one is already in place) and a top damper with its control cable run through a tiny hole drilled into the throat damper frame, giving double insulated protection.

  The down side of a top damper is that you are not sealing the large, dense and cold chimney off from living space. However you are providing the best airtight seal available, preventing outside (cold) air from entering and inside (warm) air from escaping. Overall it is generally the best choice for repairing broken or no damper situations.

Understanding Throat Dampers

Throat dampers sit just above the fireplace opening and are used primarily in new construction. They are set on top of the top course (layer) of firebrick and then regular brick are layed on top of the throat damper’s frame making the frame very difficult to remove or replace. Generally this cannot be done without removing several courses of firebrick and even then the frame may require trimming with a metal cutting saw.

  If the damper frame is already in place and in good shape, it may be possible to replace the damper plate (door) if one buys a new assembly and scraps the frame (roughly $70 – $100) or has a plate made (roughly $200 – $300) but these prices do not include labor and 2 trips out (to measure and install) and another trip to and from a welder or brickyard, so be prepared for another $300 – $400 for the leg work. And, if your damper is 50 years old or unusual, it may be hard to replicate and impossible to find for sale.

Pros and Cons of  Throat and Top Dampers

In 98% of the cases I’ve been involved with, a top sealing damper was chosen as a simpler, cheaper and less problematic choice, even though I like throat dampers. Top dampers install easily. are relatively inexpensive and fairly air tight. They also reduce smoke cross-over at the chimney top.

 I like like throat (bottom) dampers because they close off the chimney closest to the living space, separating me from a large, dense and cold masonry chimey.  But, they are not practical to install or replace after the chimney has been consstructed. What I don’t like about them is they leak cold air because they are not gasketed and the mating surfaces are rough and leak and they usually have holes in them to attach differenttypes of  handles that are optional. Incidentally,  older throat damper handles are very hard to get and also even harder to replicate. In new construction a throat (bottom) damper is a good idea and in retrofitting such as repair situations, top dampers are a good choice.