Protect Your Chimney
While it was not common practice to install a rain cap on masonry chimneys years ago, those without caps are more likely to develop internal deterioration from exposure to the elements and normal use for the venting of exhaust gases from heating systems and fireplaces over the years. Whether or not you see evidence of damage to your own masonry chimney, don’t be surprised when the next time you have your chimney and fireplace cleaned the technician recommends adding a chimney cap. You may question the recommendation, thinking the chimney hasn’t had a cap since it was built 40+ years ago and there haven’t been any water seepage problems -- so why do I need one now? Is the technician just trying to add to the bill?
This skepticism is understandable. But there are definitely benefits. A chimney cap (aka flue guard or rain guard) helps prevent rain water from entering a chimney and causing leakage in a house. But a cap also helps prevent the deterioration of the venting components or the unit itself for a fireplace or heating system. A chimney cap can also help keep leaves and other debris as well as birds, raccoons and other creatures out. So whether it is absolutely needed or not, it can be well worth it, particularly considering the relatively low $50-100 cost for a basic metal cap with screening.
While all chimney exteriors are also subject to deterioration from long-term exposure to the elements, the potential for internal damage can be more significant a concern as any rainwater entering the flue can mix with the exhaust gases to create acids that deteriorate the masonry. This concern has been compounded in recent years with the introduction of high-efficiency heating systems that operate at lower exhaust temperatures. This means a greater potential for condensation within the chimney flue, which only adds to the potential for deterioration.
A basic properly sized and pre-fabricated cap is all that is needed to provide protection; however, caps come in many shapes and sizes. Custom designed or field- constructed caps add a unique touch to a chimney, but there will be a price to pay.
Adding a rain cap on a masonry chimney may not be critical unless there are already ongoing issues, all metal chimneys and vents need a cap to prevent corrosion of the metal. Even if the metal chimney is made of stainless steel a cap is required. Manufacturers of prefabricated chimneys and vents supply the appropriate cap and other components for their proprietary venting systems. While another brand cap or other component may seem to fit, alternate components should not be used unless the manufacturer confirms compatibility.
Use of the improper type/size vent can cause venting problems that could lead to a safety hazard as the restricted flow of the exhaust gases could cause a backdraft and possibly the buildup of toxic carbon monoxide in a house.
In areas of high fire risk or when there is a wood roof, a chimneys cap should also have spark screening to prevent the spread of embers. Only caps and screening specifically designed and listed for this purpose should be used.
Note: These tips are only general guidelines. Since each situation is different, contact a professional if you have questions about a specific issue. More home safety and maintenance information is available online at www.housemaster.com.