Alright, pull up a stool. Let me explain your chimney to you with total confidence and zero slides. If your house has a wood-framed chimney (the kind wrapped in siding instead of brick), the metal lid on top is called a chase cover, though plenty of folks call it a chimney cap. It’s not the bank, and nobody is chasing anybody. It’s a sheet metal cap that keeps rain, leaves and the occasional squirrel with real estate ambitions out of the chase. When it fails, water runs straight down into your framing, and around Huntsville and Madison we see a lot of them fail.
Most replacement covers are custom made, which means the measurements you hand the metal shop are the whole ballgame. Measure twice, cut once. If you cut three times, call us.
Why Old Chase Covers Fail in North Alabama
The original covers on a lot of homes here were made from thin galvanized steel. Galvanized holds up for a while, but our humidity, long wet springs and baking summers chew through the coating, and once rust starts it doesn’t stop. Rust never sleeps, and honestly, neither do I when it rains. Flat tops make it worse, because water sits on the cover instead of running off, and that puddle eats a hole right where the pipe comes through.
Signs yours is on the way out include rust stains running down the siding, a top that sags or holds water, water stains on the ceiling or wall near the fireplace, and a collar around the flue pipe that’s cracked or caulked within an inch of its life. Our article on custom chimney chase cover installation goes deeper on what a good cover does.
What You Need Before You Measure
You need a tape measure, a pencil, something to write on, and a way to tell north from south. The compass app on your phone works fine. If the chimney is on a steep roof or you’re not comfortable up there, stop right here. No chase cover is worth a trip to the ER. We’ll come out and measure it for you during a free roof inspection.
How to Measure a Chimney Chase Cover, Step by Step
Here’s the whole process in order. The tool above follows the same steps, so you can fill it in as you go.
- Measure the length and width of the chase. Measure the outside of the chase, siding to siding, not the old cover. Old covers can be bent, oversized or just plain wrong. Measure both ends of each side, because chases are rarely perfectly square, and use the larger number. Call the east to west side the length and the north to south side the width.
- Measure from each side to the flue pipe. From the north edge of the chase, measure in to the closest edge of the pipe. Do the same from the south, east and west. Four numbers, one per side.
- Let the math find the pipe. The chase length minus your west and east numbers equals the pipe diameter. The chase width minus north and south should come out the same. If they’re off by more than a quarter inch, one of your measurements is wrong or the pipe isn’t round, and the tool will flag it.
- Pick a skirt drop. The skirt is the part that hangs down over the siding. Three inches is a good standard. Go deeper if the top of the chase is uneven or the siding is wavy.
- Choose a drip edge. A small 45 degree kick at the bottom of the skirt throws water off the siding instead of letting it run down behind it.
- Set the storm collar height. The collar is the raised ring around the flue hole. Two to three inches keeps standing water from running down the pipe opening.
- Choose the metal and the top shape. More on both below.
Why measure from the sides instead of finding the center of the pipe? Because on a roof, nobody can find the exact center of anything. Edges you can hook a tape on.
Why North, South, East and West?
Because “left” depends on which way you’re standing, and the guy reading your notes at the metal shop wasn’t standing there. Compass directions don’t change. If you write “west side 19 inches,” everybody knows exactly which side you mean, today and five years from now when the next cover needs ordering.
Choosing the Right Metal
This is where people try to save a few bucks and end up buying the same cover twice. Here’s how the common options stack up.
- 304 stainless steel is what we recommend for most homes. It resists rust in our humidity and holds its shape.
- Copper lasts a very long time and turns that green patina over the years. It’s a premium look at a premium price.
- Kynar-coated steel gives you a painted finish, like black or charcoal, to match the trim.
- Galvanized steel is the least expensive option up front, and it’s usually what rusted out in the first place.
Whatever you pick, ask for a cross-break or crowned top. Those creases give the cover a slight peak so water runs off to the edges instead of sitting in the middle. A flat pan is basically a birdbath with a mortgage.
Reading the Shop Ticket
When you hit “Copy the shop ticket,” the tool writes up everything a sheet metal shop needs in plain text. It adds a quarter inch of ease to the length and width so the cover slides over the chase without scraping off your siding, and it sizes the flue hole 3/8 inch larger than the pipe so there’s room for expansion and a proper seal. It also lists your four side measurements and the pipe center, measured from the west and south sides, so the hole lands where the pipe actually is. Paste it into an email or a text and you’re done.
The tool was designed by Patrick White, 256-ROOFERS LLC, to make ordering a custom chase cover faster and more accurate for homeowners, roofers and metal shops alike. It’s free to use, so feel free to share it with your crew or your fabricator.
Common Measuring Mistakes
Measuring the Old Cover
The old cover is the thing that failed. Don’t let it vote. Measure the chase.
Rounding to the Nearest Inch
Sheet metal doesn’t do “about.” Measure to the nearest 1/8 inch. Your tape has those little lines for a reason.
Forgetting the Siding Isn’t Flat
Lap siding and corner trim can add bulk at the top of the chase. Measure right where the skirt will sit, not a foot lower.
More Than One Flue
This tool handles one round flue pipe, which covers most homes. If your chase has two pipes or an odd-shaped vent, give us a call and we’ll measure it in person.
Want Us to Handle It?
Plenty of folks use this tool to get a ballpark and then decide they’d rather not hang off a chimney with a tape measure. Totally fair. We fabricate and install custom chase covers across Huntsville, Madison, Owens Cross Roads and Hampton Cove, Meridianville, Harvest, Hazel Green and New Market, and we’ll check the chase framing, flashing and siding while we’re up there. If water has already gotten in, our chimney repair page explains how we fix the damage underneath. Got a roof leak that might not be the chimney at all? Our roof repair team can track it down.
Call 1-256-ROOFERS for a free estimate. We’ll measure it, build it, and put a lid on the problem.
Alright, that’s my two cents. Go find your tape measure.
FAQ
How do I measure for a chimney chase cover?
Measure the outside length and width of the chase to the nearest 1/8 inch, then measure from each side of the chase to the nearest edge of the flue pipe. Add 1/4 inch of ease to the chase size and choose a skirt drop, usually about 3 inches.
How big should the flue hole be in a chase cover?
Cut the hole about 3/8 inch larger than the outside diameter of the flue pipe. That leaves room for expansion, and a raised storm collar keeps water from running into the gap.
What is the best material for a chimney chase cover?
For most homes in North Alabama’s humidity, 304 stainless steel is the best balance of durability and price. Copper lasts longer and costs more. Galvanized steel is the least expensive but tends to rust sooner.
How do I figure out my flue pipe size?
Subtract your west and east measurements from the chase length. The result is the pipe diameter. Do the same with the north and south measurements and the width to double-check it.
Do you install chimney chase covers in Huntsville and Madison?
Yes. 256-ROOFERS measures, fabricates and installs custom chimney chase covers in Huntsville, Madison and nearby communities. Call 1-256-ROOFERS for a free estimate.
Is a chimney chase cover the same as a chimney cap?
Not exactly, though people use the names interchangeably. A chase cover covers the whole top of a framed, sided chimney and has a hole for the flue pipe. A chimney cap is the smaller hood that sits on top of the flue to keep rain and animals out. Most framed chimneys have both, and this tool sizes the chase cover and the flue opening it fits around.
