Installation Guide For: Multi Flue Top Mount Chimney Cap

So you have a multi flue chimney and want to install a top mount chimney cap to help keep your chimney working great? Then follow this handy guide to help you through the process. First thing you’ll want to do is to safely get on top of your roof so you can closely inspect your chimney. 

While you’re up there, you’ll need to accomplish three things:

  1. Inspect the flue holes for blockages, pests, etc.
  2. Determine the condition of the masonry surrounding the crown. If it is heavily damaged or worn down, then you may not be able to safely install a new chimney cap and you may need to reach out to a professional to get the masonry repaired or replaced.
  3. Measure the length, width, and circumference of your chimney crown, and flue vents. This is important because it will determine which type of cap and what size of cap you should buy and install.

What You’ll Need:

Now that you’re ready to get started in earnest and you have measured your crown for the proper cap type, here’s what you’ll need to have on hand in order to safely and effectively install a new chimney cap on your home.

  1. Safety ladder in order to access your roof (and a partner to help hold the ladder steady as you climb)
  2. Leather work gloves
  3. Safety glasses (you’ll be working with power drills on masonry which can flake off and possibly injure or irritate your eyes)
  4. High traction work boots or other appropriate footwear for work on a roof
  5. Construction pencil, paper, clipboard for noting measurements and other information as you inspect, install, and measure the flue for proper fitment
  6. Locking tape measure
  7. Dry paint brush or handheld brush broom
  8. (Optional) Digital camera or smartphone camera in order to take pictures of exactly what your crown looks like to help make buying the right cap easier once you’re away from the roof
  9. Cordless drill (higher torque recommended for drilling in masonry)
  10. 1 carbide tipped masonry drill bit, 3/16ths inch in diameter by 4 ½  inches in length
  11. 8 to 10 masonry screws. They should be ¼ inch around and 1 ½ to 1 ¾ inches long to get a real grip on the chimney crown
  12. New chimney flue cap
  13. (Optional) a bottle of high heat silicone sealant or heavy duty construction sealant calk gun compatible adhesives

Step 1: Get Your Roof Workspace Set Up Safely

Carefully climb the ladder with your needed gear in a construction grade leather or reinforced nylon gear bag or bucket. You can either attach the bag to your shoulder or back while climbing the ladder or have someone attach a rope to it on the ground which they can then toss up to you when you’re up there so you can safely pull it up. Make sure your hands are free while you are climbing the ladder so you can reach the roof safely.

Once you’re up on the roof and your tools and proper chimney cap (that you measured and purchased beforehand) are resting in a secure area near the chimney crown, then you can get started. Make sure that your tools and supplies are resting safely and not constantly slipping or rolling down the sides of your roof.

Step 2: Prep The Chimney Crown For Work

You’ll need to do a few things to ensure your new cap will be secure and leak free once it is installed. Visually inspect the crown for debris, loose rocks or pebbles, and animal droppings. Using a stiff handheld brush broom or dry paintbrush, brush off any loose sand, pebbles, or debris that has built up on the crown over time. Any debris left on top could inhibit the seal and fitment of the cap once it is installed. Ensure that your chimney is clean and free of clutter before installing your new cap.

Step 3: Place New Cap

Take your new chimney cap out of any packaging or container and carefully place it over your chimney crown. Ensure that the size and fitment is correct and that it completely covers all of your flue holes (if you have multiple) and that it fits around the chimney structure itself. There can be some wiggle room, but not a lot. The cap should fit snugly over the crown to ensure proper function.

Step 4: Mark And Drill Pilot Holes

Using your construction pencil, make a small mark around the crown indicating where each screw will go by lining up the screw holes in the chimney cap. There should be between four and eight total, typically one to two screws per each of the four sides.

Once you have the holes marked, take your masonry bit and drill a pilot hole down into the crown. The pilot holes only need to be about an inch to an inch and a half deep. About equal length to the screws themselves. Make sure to keep your drill perfectly perpendicular to your masonry surface area as you are drilling to ensure that the screws align properly and can sink straight down instead of at an angle which could lead to a looser seal or improper fit of the cap at the end.

Step 5: (Optional) Add The Silicone Sealant

Using a calking gun or by steadily squeezing the bottle of silicone sealant (depending on your bottle’s size and shape) run a thin line of sealant around the outside edge of the chimney crown. Then quickly run a small line around the inside edges close to the flue openings themselves. This will help the sealant grip all edges of the cap properly. 

Step 6: Carefully Place Cap Over The Crown

Make sure to align the cap with the drilled pilot holes so that you don’t misalign the cap as you insert and tighten the screws. The holes should line up properly and evenly so that the entire cap is flushly sitting on top of your chimney opening.

Step 7: Sink The Screws Half Way

If the pilot holes are properly aligned, then it should be easy to drop the screws into the pilot holes and sink them in on each side. Make sure that all screws are only sunk halfway before you move on to the next so that you can be 100% sure that everything is aligning and fitting properly.

Step 8: Tighten Screws

Once you have made sure that all of the screws are present and are fitted properly in the cap, then you can sink each one the rest of the way so they are pushing firmly and tightly against the cap, holding it to the structure. Once they are all sunk, then you can give each one a slight extra turn to ensure that they are fully engaged and tight.

Step 9: Observe Fit And Clean Up

Once your screws are tightly secured, then do another visual inspection around the entire chimney. Look to see that the cap is now evenly and properly aligned with the crown and that there are no gaps or holes around the edges. If the masonry looks like it is too worn or cracked, then you may have to do some repairs to get everything air and water tight again around the chimney base. Then, make sure that you have all of your tools and materials safely stowed in your bucket or bag and carefully lower it off the roof to your assistant. Then have them hold the ladder as you climb back down to safety. 

Congratulations! You have safely installed a new chimney cap. Check back in about 2 to 3 days to make sure that the wind or rain hasn’t shifted or damaged the new cap. As we mentioned before, it’s a good idea to inspect your chimney once a year or every other year to make sure that rodents or other pests aren’t making a home up there and that your cap is venting things properly and isn’t obscured.