MASONRY CHIMNEYS
Masonry Chimneys
Keep your eyes to the sky. Chimneys are one of those house components that if you notice a problem early on, it can be a fairly inexpensive repair. But if you notice something wrong and ignore it, it can mean tearing down the chimney to the roof line and that’s big bucks.
First lets learn some of the terminology of the different parts of a chimney.
1. Chimney foundation (The footing that supports all of the masonry).
2. Firebox, metal damper and flue (The firebox is the actual chamber the wood burns in, constructed of firebrick; a brick that has a low thermal conductivity. The damper is the metal divider just above the firebox that opens to let the smoke rise out of the firebox when burning wood. The flue is usually clay tiles, or a metal duct to funnel smoke and carbon monoxide out of the firebox to the exterior.)
3. Masonry chase (The chase can be almost any material. It’s the surround that frames the working parts of the fireplace, basically the flue. On a masonry chimney it is brick).
4. Chimney cap (The cap is like a hat. It is the very top of the chimney. On a masonry chimney it is usually concrete or steal).
I am going to discuss the two most common issues that homeowners have with chimneys.
1. Smoke coming out of the firebox into the house.
2. Exterior brickwork deteriorating on the chimney.
First – Lets go inside. Does your fireplace, also known as a firebox, smoke into the house when burning wood? Check your damper and make sure its fully open. The damper is the metal barrier inside your firebox just above the firebox opening. It has a metal lever that opens and closes the barrier to let smoke out when burning wood and inward (closed position) to keep the heat inside the house from escaping up the chimney flue. Right above the damper at the back of the chimney is called a smoke shelf. Make sure that it is cleaned off, debris can gather there. Wire brush your damper so that your damper opens and closes properly. If the metal damper is broken it can be replaced by a mason. If your damper works but it still smokes that usually means you are not creating enough draft to pull the smoke up. Chimneys are designed and built to use a formula that mandates a relationship between the firebox opening and the flue size (these charts can be looked up on the internet). If the sizing is incorrect, the draft created by the heat will not have enough draw or pull to move the smoke out of the firebox and up the flue. There are electrical caps you can install to create pull or it may be possible to reduce the firebox opening to meet the correct firebox/flue ratio. This can be done by using a good custom door or screen that reduces the firebox opening size. Another factor can be down drafts caused by trees and/or adjacent buildings.
Second – Lets take a look on the exterior. First look at the chimney cap; you may notice cracks on the edge of your cap. Are there any mortar joints or bricks showing signs of discoloration? Are any bricks cracked or missing? Are any bricks spalling? Spalling means the surface of the bricks are breaking down and delaminating. If you notice any one of these things you should have a fully insured mason go up and take a close look inside and outside of the chimney. If the cap is cracked, and depending on the severity of the water damage, the minimal you will have to do is replace the cap. More severe damage would involve replacing the flue liner and possibly the brickwork, down to where the damage stops.
Don’t forget early detection is key.
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Mike Gosser