How To Buy The Correct Chimney Cap

Selecting a chimney cap often begins with the question of necessity. The answer, without question, is yes. If you have an active chimney, you need a cap. This is primarily due to fire safety concerns. When using your fireplace, sparks are created. While most of these are contained within the fireplace or base of the chimney, some can reach the top. Without a cap or screen, these sparks could ignite nearby flammable materials or your roof. Chimney caps also serve to keep unwanted guests out. Open chimneys can attract a variety of small animals, such as birds, squirrels, or raccoons, looking for nesting spots. These nests can be hazardous as any obstruction in the chimney could cause smoke build-up within your home. Additionally, animal waste can harbor illness and living above a working fireplace is dangerous for the animals themselves. By capping your chimney, you protect both your family and the animals. An uncapped chimney is also more susceptible to weather-related damage. Rain and snow can seep into the mortar joints of masonry chimneys, causing bricks to loosen. Water can also saturate bricks, resulting in cracking when it freezes. Excess moisture promotes mold growth and unpleasant odors. For metal chimneys, exposure to moisture can lead to insulation damage, rust, and shortened lifespan. Even if wind is not a significant factor in your area, it can affect your chimney's draft. Strong gusts can cause fluctuation in the draw of your fireplace or stove, leading to downdrafts, where smoke is blown back down the chimney. Installing a chimney cap can limit wind and help maintain a steady draft.

Understanding the type of chimney and flue you have is crucial before purchasing a chimney cap. This information determines the type of cap you can use and the measurements you need to take to ensure a proper fit. Continue reading to learn about the most common chimney constructions.

The two types of masonry chimneys are single-flue chimneys with extended flues and single-flue chimneys without extended flues. Single-flue chimneys with extended flues have single flues that extend above the crowns and come in various shapes such as square, rectangular, round, and oval. The shape of the chimney cap that can be used is determined by the shape of the flue. For square, rectangular, and oval flues with extended flues, caps that attach with clamps or screws can be used, while round flues can use slip-in caps or caps that attach with clamps or screws. Single-flue chimneys without extended flues feature a single flue that is flush with its crown. The shape of the flue determines the type of chimney cap that can be used. For square, rectangular, and oval flues that are recessed inside the walls of the chimney, legs or brackets are required to attach the cap. Round flues that are not extended can use bolt-on caps designed to slip into the flue's opening. Top-mounted chimney caps are suitable for covering single-flue chimneys of all shapes, including those with flexible metal liners. Multi-flue chimneys require top-mounted chimney caps regardless of whether their flues are extended or not.

The type of factory-built round metal chimney can vary based on the number of walls and the insulation used. Single-wall metal chimneys consist of a rigid metal tube and are commonly used for wood-burning stoves. When selecting a cap, it's crucial to choose one that works with a single-wall metal pipe. Chimney cap options include those that fasten to the flue exterior with clamps or screws, and those that slip into the flue and require adhesive for a secure fit. Double-wall air-insulated metal chimneys have two walls separated by open space and use air to cool the flue. These chimneys require caps specifically designed for use with a double-wall air-insulated pipe, preferably from the same manufacturer as the chimney. Double-wall solid-pack insulated metal chimneys also have an inner and outer wall, but use insulation to separate the two. Each type of double-wall solid-pack insulated pipe requires its own specific kind of chimney cap, and using a cap produced by the same manufacturer is recommended. Triple-wall air-insulated metal chimneys work the same way as double-wall air-insulated pipes, but have three walls instead of two. Caps designed to fit triple-wall air-insulated pipes are required and it is recommended to use a cap made by the manufacturer of the chimney. Triple-wall solid-pack insulated metal chimneys feature three walls separated by insulation, with some models leaving the insulation exposed and others covering it with a metal cap. Chimney cap choices are limited to those specifically designed to fit the specific kind of pipe.

Standard chimney caps are the most commonly used due to their cost-effective protection against weather and animals. However, there are five other types of chimney caps that address specific chimney issues while also covering the flue opening. Draft-increasing chimney caps improve draft, but if extreme winds are present, a standard model may not suffice to prevent downdraft issues. For such situations, a special draft-increasing cap can be used that relies on Bernoulli's principle to create stronger updrafts. Draft-increasing chimney caps force wind around their tops rather than allowing it through openings, which increases the air velocity and decreases the static pressure above the chimney. This creates a partial vacuum, forcing the smoke inside the chimney upwards. It is important to note that these caps can't solve draft problems unrelated to wind, such as air inversion or chimney top pressurization. Also, most draft-increasing chimney caps are designed for factory-built metal chimneys, so ensure the selected cap is compatible. Electric draft-increasing chimney caps act as both a chimney cap and a draft inducer, with adjustable electric fans that allow direct draft control. However, these products are more expensive due to their complicated nature and require professional installation. Chimney cap and damper combinations eliminate energy loss caused by a loose-fitting, broken, or missing damper mechanism, particularly if you were already planning to get a chimney cap. The dampers in these combo models function like top-sealing models, but are only available for square and rectangular chimneys. Outside-mount chimney caps provide excellent weather protection and fit over the crown and attach to the body of the chimney. Outside-mount caps are useful if you have multiple flues, oddly-shaped flues, or a poorly constructed crown. Due to variations in chimney dimensions, outside-mount caps are often made to order, but stock models are available that fit a range of dimensions. Flue stretcher chimney caps allow you to raise the height of your masonry chimney's flue by one or two feet while protecting your home from the elements and animal invaders. If structures are blocking the flow of air to your flue, or the flues for your upstairs and downstairs fireplaces are adjacent to one another, adding a flue stretcher can solve these issues. However, flue stretcher caps are only available for square and rectangular chimneys.

Let us show you how to select the right chimney cap

To select an appropriate chimney cap size, you must first identify your flue type and cap preference. Measuring your chimney is a straightforward process, but varying flue and cap types require different measurements. 

To measure for specialty chimney caps, the process is similar to measuring for standard models. Different types of caps require different measurements. For draft-increasing caps, the measurement process is the same as for standard caps, even if an adapter is needed for a masonry chimney. Chimney-cap and damper combinations can be measured by determining the inside length and width of the flue. Outside-mount chimney caps require measuring the length of each exterior wall and the height of the tallest flue, ensuring the selected model is at least five inches taller than the flue. Finally, flue stretcher chimney caps require measuring the outside length and width of the flue.

I Have No Flue

Most masonry chimneys come equipped with a flue, however, if you find that your chimney is one of the few without a flue, there is no need to worry. You can still purchase a chimney cap, but your options will be limited to those that can be mounted directly onto your chimney's crown. You have two choices: a standard flue cap with brackets or a model designed for multiple flues. Regardless of which type you choose, you will need to measure the length and width of your chimney's opening to determine the minimum area that your cap needs to cover. Alternatively, if your main concern is maximum protection, you can opt for a cap that covers the entire chimney. In this case, measure the length and width of your entire chimney to determine the largest cap you can use.

Chimney caps are typically made from galvanized steel, aluminum, stainless steel, or copper. The right material for you will depend on your budget, priorities, and preferences. Galvanized steel caps are inexpensive but less durable and prone to corrosion. While they may cost less initially, they may lead to higher maintenance costs and replacements in the long run. Aluminum caps, while similar in price, are also not particularly sturdy and easily disturbed by wind. However, they have a bright and shiny appearance and are resistant to soot buildup. Stainless steel caps strike a good balance between cost and performance, being slightly more expensive than aluminum and galvanized steel but much more corrosion-resistant and requiring little maintenance. Copper caps are the most aesthetically pleasing with a classic look that enhances most brickwork. They are durable, but also the most expensive and require regular cleaning and protectant application to maintain their original color.

Chimney caps are available with either 3/4" or 5/8" mesh, which refers to the size of the holes in the cap's screen. Though these models don't differ much in performance, the difference lies in fire safety and building codes. Some areas have laws requiring all chimney caps to have 1/2" spark arrestors, which means the mesh has to be small enough to prevent a half-inch sphere from passing through. Caps with 3/4" mesh cannot meet this standard, so people living in these areas needed an alternative, resulting in the 5/8" mesh chimney cap. Caps with 5/8" mesh have become the industry standard for areas that require 1/2" spark arrestors, often called California-style chimney caps. If your local building codes require it or if you live in an area with wooden structures or dry climates, investing in a chimney cap with 5/8" mesh would be beneficial. These caps do not cost significantly more than 3/4" models and offer additional protection.

Chimney caps typically do not require many accessories, though there are situations where additional items may be necessary. This guide provides information on the most common chimney cap accessories that one may encounter. Adaptors are the most commonly used chimney cap accessory and there are four basic types: Factory-Built to Masonry Chimney Adaptors, Flue Shape Adaptors, Legs, and Brackets. Factory-Built to Masonry Chimney Adaptors allow for specialty chimney caps that are typically designed for factory-built chimneys to be used with masonry chimneys. Flue Shape Adaptors enable the use of a chimney cap with a flue shape that it was not originally built to fit, but they are only available for masonry chimneys. Legs are utilized to use a standard single-flue cap with a square, rectangular, or oval masonry flue that is not extended. They are easily attached to the cap and slid into the flue, similar to a slip-in model. Brackets also allow for the use of a standard single-flue cap with a square, rectangular, or oval masonry flue that is not extended. However, brackets are more secure than legs in windy conditions because they are directly mounted onto the chimney's crown. Chimney caps can be secured with adhesives, sealants, or screws. If screws are required, they are typically included with the purchase of the cap. However, if an adhesive or sealant is necessary, it may need to be purchased separately. The installation manual for the chimney cap will specify what type of adhesive or sealant is needed. Most chimney caps do not require additional treatments to maintain their condition, but if a copper or aluminum cap needs to remain shiny, a protectant is required. These protectants usually come in spray containers and safeguard the chimney cap against fungus, oil, and water. The protectant dries clear and will not impact the appearance of the cap.

Selecting a chimney cap requires careful consideration, but it need not be overwhelming. When you have a clear understanding of your options and how to identify your specific requirements, the selection process becomes straightforward. In fact, once you've conducted some research, your biggest challenge will likely be retrieving your ladder from storage.