How Do I Choose A Chimney Cap For An Air-Cooled Chimney

Choosing the correct chimney cap is very important to ensure your fireplace or heating appliance vents properly. The most common mistake when choosing a chimney cap is guessing the flue pipe type and size without measuring it. Choosing the correct chimney cap doesn't need to be difficult. Understanding the flue type and size will make choosing the correct chimney cap much easier. Below, I will go through the six most common types of flue pipes, how to measure them, and the best chimney cap for each flue type.  

Air-cooled chimney pipes are most commonly used to vent pre-fabricated fireplaces. Pre-fabricated fireplaces are framed in the home and a wood framed chimney chase is constructed to conceal the pipe. Air-cooled chimney pipes are often double or triple-wall flue pipes that require a 2" clearance from combustible material. Air cooled pipes rely on a vented air space just underneath the base of the rain cap, allowing the inner exhaust pipe to breathe at the top of the chimney. This allows the radiant heat from the central / inner exhaust pipe to escape through the top of the chimney. The air gap is part of the reason the pipe is safe to be 2" away from any wood framing. It is very important not to close the air gap. If the gap were restricted, the pipe could overheat and potentially cause a fire.

Once you understand what an air cooled chimney pipe is, identifying an air-cooled chimney cap is simple. Look under the main exhaust section of the cap and look for vents directly under that section of the cap. These vents are often a mesh screen, steel webbing or louvered. Here are some examples of the vents that primarily identify air-cooled chimney pipes. 

The most common mistake when replacing the rain cap for an air-cooled chimney is sizing the cap. The original chimney rain cap from the pipe manufacturer most likely attached to the outer pipe. However, since it is probably an older venting system, there is a good chance the manufacturer is no longer in business or no longer makes that particular model. There are aftermarket caps that work great as a replacement rain cap. For these aftermarket caps, you will need to measure the innermost pipe diameter & the outermost pipe diameter. The new aftermarket caps will attach to the inner pipe and rest over the outer pipe with spacers to allow the outer pipe to breathe. 

There are a few options for air-cooled chimney cap replacement. Each option has a specific feature that will make it the best choice for your pipe configuration. 

The Weathershield Air-Cooled Chimney Cap is a perfect option for an air-cooled chimney pipe where all pipe layers terminate at the same height. The Weathershield air-cooled chimney cap has a 4" long pipe extension to connect to the inner pipe. The cap is also equipped with spacers to ensure the pipe can breathe, enabling air cooling. 

The WeatherShield Tallboy Air-Cooled Chimney Cap is a great option for an air-cooled pipe where the inner pipe is recessed below the outer pipe at the top of the chimney. This happens when you remove the existing chimney cap and a long section of the inner pipe comes out with the rain cap. The Tallboy replacement cap has a 15" pipe length to reach the innermost pipe, which may be recessed below the outer pipe. The cap is also equipped with spacers to allow the pipe to breathe & air cool. Three tie down straps are bolted to the spacers that allow you to screw the straps to the outer pipe, ensuring the cap doesn't rattle around inside it. 

The VacuStack Air-Cooled Chimney Cap is a great choice if your fireplace or wood stove is experiencing wind-driven downdrafts. Strong winds blowing in certain directions can cause fireplaces to emit smoke into the home. This unique chimney cap prevents downdrafts by creating an upward vortex when wind hits the cap, which generates an updraft for the flue pipe. The VacuStack Chimney Cap has a 4" long pipe to connect to the inner pipe - use when all pipe layers terminate at the same height. The cap is also equipped with spacers to ensure the pipe can breathe & air cool.