How to Measure for a Chimney Cap (and Install It Yourself)
Measuring for a chimney cap takes about five minutes and a tape measure. The rule that matters: a single-flue cap is sized to the outside of the flue tile, not the inside and not the brick crown around it. Get that right and the cap fits the first time. Every cap below ships with No Sales Tax in any state.
Quick answer: measure the outside length and width of the clay flue tile where it sticks up above the crown, and order that size, for example an 8" x 13" tile takes the 8" x 13" HomeSaver Pro stainless steel chimney cap. Two or more flues? You need the outside measurement of the whole group for a multi-flue chimney cap. All our caps are on the chimney caps page.
Before you climb: stay safe
Only go on the roof in dry weather, with a ladder that extends at least 3 feet past the roof edge and someone at the bottom. On a steep or high roof, use a roof harness or measure from a ladder against the chimney. If any of that sounds like a bad idea, a chimney sweep will measure and fit the cap for you, usually during a sweep.
Step 1: Work out what's on top of your chimney
The cap you need depends on what sticks out of the top. Look from the ground with binoculars first, or take a photo from a ladder.
| What you see | Cap that fits | From |
|---|---|---|
| One square or rectangular clay tile | HomeSaver Pro stainless steel chimney cap | $74.99 |
| One round clay tile | HomeSaver Pro round chimney cap | $131.99 |
| Two or more tiles on one crown | HomeSaver multi-flue chimney cap | $203.99 |
| Clay tile on an open fireplace with a broken damper | Lock-Top II damper & cap | $344.99 |
| A round stainless pipe coming out of the tile (a liner) | Forever Flex liner rain cap | see page |
| A metal chimney (Class A pipe, no brick) | Ventis Class A chimney cap | see page |
Metal chimneys and liners take the cap made for that pipe. Don't put a masonry cap on them.
Step 2: Measure a single square or rectangular flue
- Measure the outside of the tile. Run the tape across the outside of the clay flue tile in both directions, at the top. Write down both numbers, for example 8 1/2" x 13".
- Measure how far the tile sticks up above the crown. A bolt-on cap clamps around the exposed tile, so there has to be enough tile showing for the screws to grip. If the tile is flush with the crown, you need a multi-flue (crown-mount) cap instead, even for one flue.
- Check the tile. Cracked, crumbling or loose tiles won't hold a clamp. Fix those first.
- Pick the size. Match your measurement to the nominal size in the chart below. Clay tile is sold by nominal size, so a tile that measures about 8 1/2" x 13" is an "8 x 13" tile.
Common chimney cap sizes
| Flue tile (nominal) | Also called | Stainless cap | Lock-Top II damper |
|---|---|---|---|
| 8" x 8" | 9" x 9" | $74.99 | $344.99 |
| 8" x 13" | 9" x 13" | $79.99 | $411.99 |
| 8" x 17" | $130.99 | $493.99 | |
| 12" x 12" | $96.99 | — | |
| 13" x 13" | $92.99 | $448.99 | |
| 13" x 17" | 13" x 18" | $144.99 | $440.99 |
| 17" x 17" | $190.99 | $529.99 | |
| 12" x 16" | $234.99 | — | |
| 15" x 15" | $219.99 | — | |
| 9" x 18" | Hy-C, $91.99 | — | |
| 13" x 18" | Hy-C, $119.99 | — |
Prefer a lower-cost cap? The HomeSaver Pro galvanized chimney cap comes in the same sizes from 8" x 8" to 17" x 17", but stainless lasts much longer. Round clay tile comes in 8", 10" and 12": measure the outside diameter and use the round chimney cap.
Step 3: Measure for a multi-flue cap
A multi-flue cap sits on the crown and covers every flue at once. Take three measurements:
- The flue area: the length and width around the outside edges of all the tiles together.
- The tallest tile: how high the tallest tile stands above the crown.
- The crown: the length and width of the flat top of the chimney.
Choose a cap that's at least as big as the flue area and still fits on the crown. Its screen must be taller than your tallest tile, with room to spare so smoke can get out under the lid. Our HomeSaver multi-flue caps have a 10" screen and come in 13 sizes from 13" x 13" to 21" x 41". If your crown is cracked, repair it before the cap goes on, because the cap will hide the damage. See chimney crown repair.
How to install a chimney cap
Single-flue (bolt-on) cap
- Install when the fireplace or stove has been out for at least a day, so the tile is cold.
- Clean loose debris, nests and soot off the top of the tile.
- Loosen the clamp screws on the cap and set it over the tile so it sits square.
- Tighten the screws a little at a time, working around the cap, until it's snug on all sides. Don't crank one screw down, it can crack the tile.
- Give the cap a firm tug. It shouldn't move.
Multi-flue cap
- Assemble the cap on the ground if you can. Knock-down caps ship flat and go together with the hardware supplied.
- Set it on the crown, centered over the flues, with the lid level.
- Mark the mounting holes, drill the crown with a masonry bit and fasten the cap with masonry anchors.
Lock-Top II top-sealing damper
The Lock-Top II mounts on top of the flue tile and a cable runs down the flue to a handle in the fireplace. Follow the instructions in the box: it takes longer than a plain cap, but it's still a one-person job for most homeowners.
Mistakes that lead to the wrong cap
- Measuring the inside of the tile. Single-flue caps go by the outside.
- Measuring the brick. The crown size only matters for multi-flue caps.
- Buying a masonry cap for a metal chimney. Class A pipe and stainless liners need their own Class A cap or liner rain cap.
- Buying galvanized to save a few dollars. It rusts out much faster in wet weather. In the small sizes our stainless cap costs about the same.
- Forgetting the mesh. A screen clogged with creosote chokes the draft. Check it every fall when you clean the chimney.
Common questions
Are all chimney caps the same size? No. Single-flue caps come in sizes to match standard clay tiles, from 8" x 8" up to 17" x 17". Multi-flue caps are sized to the area they cover.
Do I need a chimney cap? Yes, on any chimney you use. It keeps out rain, which rusts dampers and cracks masonry, and animals, which block the flue. See what a chimney cap does and when to replace it.
What if my measurement falls between two sizes? Send us the two measurements and a photo and we'll tell you which cap fits.
Related guides
- Chimney caps and liners: what you need and why
- Chimney crown repair
- How to waterproof a brick chimney
- How to clean a chimney yourself
Shop all chimney caps at StoveSource: authorized dealer, No Sales Tax in any state, free shipping over $300. Not sure which size? Email info@stovesource.com or text 1-888-866-8206 with your measurements.
Updated October 2026