The cost to cap and seal a chimney costs between $250 and $650, but expect to pay $500 for the average-sized chimney.
It’s not just blowing smoke to say that your chimney endures a lot—from dirt and debris to vagabond critters looking for shelter. A chimney cap is the best way to keep these stowaways out while still allowing ventilation for your cozy, crackling fireplace. In many cases, you might also need to seal the chimney to prevent any cracks or other damage from getting worse. Getting everything done in one trip might cost anywhere between $35 and $1,350, depending on the price of the cap, as well as a number of other factors. We stack up your potential costs below.
Sealing a chimney involves first having a chimney without any damage. A chimney inspection is a good idea to make sure there’s nothing wrong with your chimney before you potentially seal in damage.
Although it won’t have a large effect on the total project cost, you need to decide if you need to seal or waterproof it. The differences between the two are subtle, but choosing the right one the first time will save you time and money in the end.
| Sealing | Waterproofing |
|---|---|
| Creates protective barrier | Fills minor cracks |
| Cost-effective | Stronger weather resistance |
| Does not address underlying issues | More thorough and lasting protection |
Chimneys tend to be similar in height to fireplaces, which are usually on the first floor of a house, with the chimney extending one or two floors above that. The good news is that waterproofing or sealing a chimney from the top down (which is done 99% of the time) takes a similar amount of time, and size shouldn’t be too much of a consideration.
However, size matters if you have a chimney with a double flue. There is a much larger amount of surface area to waterproof, so the cost increases. Any large or ornate chimney cap will also increase the labor and materials costs if it’s larger than average.
Material costs vary quite a bit based on the size of your chimney and what you plan on sealing it with. The two main choices are silicone and polyurethane. Most pros will recommend silicone instead of polyurethane as silicone has a much longer life span, cures quickly, and works well at any temperature.
Because silicone is made from inorganic materials, its life span is often double that of other sealant materials. Other materials are also used in sealants (like rubber and polyester), but they aren’t as common as polyurethane and tend to be more expensive. A pro will help you decide which material is best for your unique chimney.
| Type of Sealant | Material | Average Cost per Gallon |
|---|---|---|
| Black Diamond | Polyurethane | $55 |
| Chimney Saver | Siloxane | $90 |
| Flex Seal | Liquid rubber | $35 |
| LastiSeal | Polyester/Polyurethane | $60 |
| Masonry Defender | Silane/Siloxane | $38 |
Labor is an interesting aspect of chimney sealing, as sealing is a multi-step process. First, you need to clean the chimney. This costs, on average, $130 to $380. Professional chimney sweeps charge around $300 per hour, but they might not even need that long to thoroughly clean a chimney. Unfortunately, this isn’t a job you want—or could—do yourself.
Prepping a chimney for waterproofing or sealing mostly comes down to inspection. You want to make sure you’re applying the desired compound on a clean and undamaged surface; otherwise, the sealing may not be effective.
Some of the prep required for sealing a chimney:
Inspect the chimney for existing damage or cracks.
Thoroughly clean the chimney (hire a pro for this), and remove any debris.
Check and repair the flashing where the chimney meets the roof.
Replace or repair a damaged chimney cap.
Check that your chimney cricket still diverts water.
There are a few reasons why someone wouldn’t do the prep work themselves, with the most obvious being that the chimney is on the roof. Injury, fear of heights, and difficult chimney access are all reasons why you should not prep or seal your chimney yourself. Hire a local chimney repair professional to handle the work.
You might think that sealing a chimney just involves spraying some sealant on the surface, but it can be significantly more complicated when dealing with damage or, in many cases, just getting to the chimney itself. For this reason, we don’t really recommend this as a DIY project.
You will save money on labor costs, but there is a high possibility of performing the work incorrectly. Waterproofing or sealing isn’t as cut-and-dry of a job as hanging drywall. Any money you save on labor costs by doing the work yourself isn’t worth the potential injury and skill set required to seal a chimney. This is a job best left to a professional.
Chimneys should either be sealed or waterproofed, which is different from sealing off—closing at both ends—a chimney. Waterproofing and sealing are both crucial steps to take to prevent water damage and the chimney leaking inside the house. While waterproofing is more comprehensive, both help safeguard your chimney, extending its life span and preventing expensive repairs.
Waterproofing a chimney increases the resale value of your home and can lower insurance costs as well. It means that no moisture enters your bricks, which, over time, causes them to crumble. You can consider waterproofing a chimney inexpensive if you contrast the cost with the amount of money you save by preventing future damage.
You should waterproof a chimney when any previous waterproofing isn’t effective anymore, which is usually somewhere between 8 and 12 years. A pro can tell you if you need to apply more waterproofing solution, or you can see it yourself if you notice any damaged bricks. However, the best idea is to receive an inspection from a professional to avoid further damage.
Yes, you should seal an unused chimney. Even if it’s not in use, the structure is still susceptible to moisture damage, which can lead to problems like cracks, spalling, efflorescence, and damaged mortar joints. But you should also cap the chimney to prevent blockages while still allowing for air ventilation (which also prevents moisture damage). Also, continue to get an annual chimney inspection to prevent other issues with the structure.
