Should you try to inspect the top of a metal chimney in a wood frame?
Always. Often, the metal flue and metal chimney cap are improperly installed. Leaks at a metal chimney cap can result in damage to the flue, damper and firebox.
Sometimes a metal flue is hidden
Let’s look at a good chimney cap (Illustration F031). A factory-manufactured metal flue often is installed within a wooden chimney chase that may be covered with siding or faux stone. Normally, you can identify a metal chimney by looking at the metal flue. A storm collar has been installed above the metal cap to deflect water.
Look at the chase, which is the structure around the metal flue pipes. The metal cap over the chase should be sealed to the flue. This cap should have a raised crimp from corner to corner to allow drainage from the center to the edges. Also, the cap should have a drip edge of at least one inch that overhangs the chase. The drip edge enables the structure to shed water properly.
Typical problems to watch for
Now let’s examine typical problems with a metal chimney (Illustration F032). The metal cap sits tightly on the wood chase with no drip edge. The center of the cap is not raised for drainage. The flue pipe is not sealed to the cap. Storm collars are missing. These defects allow water to leak into the appliance (fireplace) below and water will damage the siding on the chase.
Moving on, the example shown in Photo 1 depicts a metal cap with obvious problems: no slope and no clearance to the chase. Water ponds on the flat surface, creating rust. Because rust has crept over the edge, it is visible from the ground. There is a drip edge, but it’s too close to the wood frame. And where is the storm collar?
During another inspection, I found a chimney with a misguided attempt at repair (Photo 2). The cap is not pitched for drainage and there is no drip edge. The storm collar is missing and some kind of rubberized sealant was applied to secure the flue to the metal cap. Most likely, this assembly leaked before the sealant was applied.
What should you look for?
During an inspection, always try to see the top of the chimney so you can check the details. If you don’t have access to the top, look for rust on the sides or damage to the siding—these are signs of a poor cap. Always check the metal fireplace below for signs of water. Water and fireplaces do not mix.
Whenever you see a missing storm collar, missing sealer, rust, poor pitch or a poor seal, the chimney needs further evaluation.
To learn more, attend Tom’s technical presentations at educational sessions for ASHI chapters. Tom will present “Basement Inspections, Reporting and Identification of Defects” at ASHI InspectionWorld® 2020 in New Orleans.
Tom can also provide his knowledge for your educational event; contact him at Tom@HTOYH.com.