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Ok, November again. The election is finally over, everything is settled, and we can all get back to business. What? You're kidding! Still? Hmm. One thing is settled, though. Around the 25th of next month, all of our chimneys need to be in top condition. For those among us who walk on roofs, November is a good time to take a last look, presuming we get one more sunny day. Roof maintenance is a subject for another time; today we talk about chimneys. Fireplace chimneys got a good going over in last January's issue. (http://www.inspectimichigan.com/watsonsj/Jan00.htm ) but this time we'll talk about furnace chimneys.
The point where the roof meets the chimney is a frequent leak source, possibly the most frequent. Back in the olden days, when more roofers were craftsmen, they devised a system of metal flashings that would allow the roof and chimney to move independently of each other and still keep out the water. This was a 2-part system. The sheet-metal base flashing was woven into the shingles, and bent to run up alongside the brickwork. The counterflash was tucked deeply into the mortar joints and hung down over the base flash. If the roof sagged a bit under snow load, or if the chimney leaned a little under wind pressure, this flashing system could take up the movement and still keep out the water. However, this method takes a good deal of skill and time, so these days, various kinds of short cuts are taken. The least crummy is used often on new homes. They still have the two types of flashing, but the top edge of the counter flash is bent out away from the brick, and the resulting trough filled with caulk. This is probably half as reliable as the old-fashioned method, so you can probably ignore it until your new house is 10 years old or so. At the bottom of the reliability totem pole are 2 really short-lived methods. One involves just running the base flashing up the side of the chimney and then plastering it to the brick work with caulk. This is strictly an amateur trick, usually found on do-it-yourself roofs. It will work until the chimney or roof move, and then start leaking. The second method uses no flashing at all. The shingles just end next to the chimney, and the open joint is filled with caulk or roof tar. This is the most common method used on re-roof jobs. This will work until the caulk or tar dries out and gets stiff. Then it cracks, and a leak begins. It's this last method, though, that I find most frequently.
So, while you are up there walking (carefully!) around, look closely at the base of the chimney, and find the cracks in the sealant where water will enter soon. You can seal these areas with caulk or asphaltic roof cement, and it will be tight for another year or two. This is a regular maintenance item.
Next, check the chimney masonry itself. The brick may be starting to crumble, or some of the mortar may be loose. If this is limited to a few small areas, further work can be put off for a while. If you find more than a few soft or loose bricks, start looking for a chimmey mason to replace the brick and repoint the mortar. Is the chimney is leaning out of vertical, or curving in the top section? Call that mason. Remember, not every bricklayer understands chimneys. Try calling a good sweep, and getting a mason referral from them.
A lot of older chimneys have a stone or brick cap that sits on top of the other brick and overhangs it by an inch or so. This overhang is both decorative and practical. It allows rain that lands on top of the chimney to drip off without seeping down the sides, thus affording some protection from weathering. Over the top of this cap, hopefully covering all its open joints, is a layer of concrete or mortar, poured as a single piece and tapered to run water off. This is called the cement wash. It's a wear item that most people never see, because it's not visible from below. It usually crumbles over the years and needs to be replaced. When the wash gets too thin, water gets into the brick joints in the cap, destroying the mortar and brick as it freezes and thaws.
So far, most of these problems are things that have been going on for generations. But thanks to advancing technology, there is a whole new problem. (Surprised?) Consider for a minute what you get when you burn natural gas (methane) in air. The products of combustion are mainly carbon dioxide and water vapor. With old, inefficient furnaces, about 45% of the heat produced by combustion went up the chimney with the exhaust, warming up the brick, and keeping the water in the vapor state till it reached the atmosphere. Newer furnaces only waste about half that much heat, so the brick stays cold, and the water vapor in the exhaust stream cools and condenses inside the chimney. Some of the exhaust product is a mild acid (carbolic acid) which helps the water attack the masonry. The result is rapidly deteriorating brickwork in the upper part of the chimney. The clay liner tube can crumble so completely that the pieces fall down and block the flue. Now, the furnace exhaust can't make it out, and the result is a dangerous build-up of monoxide in the house. This doesn't always happen, and if most of the length of your chimney is inside the house, it may never be a problem for you. However, it's worth taking a look down the inside of the chimney to see what condition that clay liner is in. If it's cracked, broken or even flaking off the sides, it's time to have a metal liner installed.
The metal liners are the solution to this now-common deterioration problem. In the last 5 years, it has become standard practice to install such a liner whenever a furnace is replaced. However, from the early 80's till about 1995, a lot of efficient furnaces were vented into the old masonry chimneys, and the results are obvious if you just walk down your street and look at everybody's chimney. If you are in a 1950's -1970's neighborhood like mine, you will see lots of deteriorating or recently repaired chimneys. It took the heating industry a while to figure out what was going on!
So what if you are not the roof-dancing type? Or if your roof is just too steep or high to get to? There is another way! At the bottom of most chimneys, just below the point where the furnace connects to it, is an ash clean-out door. The original purpose of this was to allow access for regular cleaning, which is necessary if you burn coal or oil. This isn't necessary for gas-burners, but the builders generally weren't allowed to make assumptions about what kind of fuel a house would use. So, there is this little metal door in the basement wall. But wait a minute before you open it! Here's what I have found behind ash doors: Ashes, (built up deep from the oil-burner that was replaced in 1960), pieces of flue liner, chimney bricks, lost ladybugs, dead birds, live racoons, nesting material and guano! Yup, guano, look it up! So before you open the door, go get your shop vac and dust mask. Then rap on the door, and listen. If anything raps back, or squeaks or buzzes, call Critter Control. If not, go ahead and open it. After you vacuum out the crud, you can stick a mirror in and look up the chimney. If there isn't a little piece of sky looking back, you need to find out why.
If all this is a bit too much, there are professionals who can do this kind of work. Chimney sweeps aren't just for fireplaces any more. They can check the liner, tuckpoint the brick (or refer a good mason) and lower a video camera down the flue so you can see it's condition on your TV. Make sure you get a sweep who is a member of the Chimneysweeps Guild, so you know he or she is competent.
One more November item: Hose faucets. Also known as sill cocks and hose bibs. The faucet should be dry during winter so it doesn't freeze and burst. First, disconnect the hose. Then find the valve in the basement that shuts off water supply to the faucet. Turn it off, and if it has a little brass knob on the side, remove the knob. Have a cup handy to collect the pint or so of water that will drip out. If there's no brass knob, go back outside and open the faucet, and leave it open till spring. If you have a freeze-proof faucet, all you have to do is disconnect the hose. How do you know? If the stem that the outside handle is on is parallel to and concentric with the pipe coming out of the house, then it's probably freeze-proof. With this type, the valve that is operated by the outside handle is actually a foot or so back inside the house, so the freezable part empties itself every time you turn off the faucet. No worries!
Now, go change that furnace filter, test all the smoke alarms, and relax. Don't forget to Give Thanks!
P.S. This newsletter is a 2-way street. If you have any questions or concerns, please use the e-mail link to let us know.
copyright 2000 Matthew J. Bezanson