Unlined Chimneys may leak noxious gases into the living space.
If used for gas, modern appliances have such low-temperature flue gasses that they produce huge amounts of condensation. With an unlined chimney, the condensation is allowed to adhere to the actual masonry. This ruins wall paper in the house, and the freeze-thaw cycles in the winter slowly demolish the masonry chimney. If the chimney is used for wood burning, the condensation can also help form tar and creosote, which is flammable. In this case, they pose an unnecessary fire danger. When you make a change to the construction of a structure, the system must come up to building code standards. So if you have a new furnace or boiler, a woodstove or insert, the chimney must be lined at that time.
Block Chimneys in Old Houses
Block chimneys do work, but as a general statement they are less than desirable. Block chimneys are really meant to be surrounded with bricks. They are more subject to cracking, leaning and leaking; all most any problem you can imagine. As a general statement, if you have a block chimney built right against the house it’s probably not legal and if you have a wood-frame house you probably ought to just tear it down. However, if you can build brick around all four sides, unlikely in most situations, you can get the clearance to combustibles called for in the codes, the chimney can be serviceable.
Old Brick and Mortar Chimneys
Old brick chimneys have their own set of problems. Fortunately, older bricks are often actually better than newer bricks. It’s the way they were fired that makes the biggest difference. That’s why you see some houses from the 1800s or even 1700s where the bricks are still in great condition. Yet you’ve also probably seen modern houses with the faces of the bricks popping off. So if you have an old house, you probably have pretty good bricks!
Shifting Ground and your Old Chimney
The ground is always moving a little bit. Fortunately houses are actually a bit elastic, or at least allow enough give that they don’t split in half when the ground heaves an inch. But over time, those stresses can break bricks. If you have that problem in your chimney or walls of the house, it’s probably visible. Broken bricks are just a fact of life sometimes. You might need to replace them eventually.
Old Masonry Chimney Degradation Due to Weather
Sun, wind and rain are hard on any masonry work, especially the mortar. There are so many different types of mortar and concoctions of mortar cement that there’s no guessing how long your mortar is supposed to last, but suffice to say 60 years on a chimney is a long time.
When the mortar wears out it’s either time to rebuild or re-point. Re-pointing is the process of grinding out about an inch of the old and broken up mortar and putting in new mortar without removing the bricks. Unless your chimney is quite large, it may be just as easy to dismantle it and rebuild using the same bricks.
Chimney Crown (Or Lack Thereof?)
There’s another aspect of the chimney that’s almost always lacking on older homes, and that’s the chimney crown. The crown is the cement part on top of the chimney that keeps the rain from going into the structure below. The crown catches more sun, wind and rain than all the rest of the chimney, and it is usually not as thick as a brick. Crowns are almost always cracked. If the crown is bad enough, it needs to be taken off and re-laid. If it is cracked but still structurally sound there are good materials to coat the crown, which will save money.
The way to deal with that is to make sure you have a liner installed to zero-clearance (insulated). The only alternative is to tear out the walls and cut away the wood. Practically speaking, nobody is going to do that, and even if you do, there’s no guarantee you’d get it far enough away. Take a look in the attic and remove wood you find against the chimney up there. That’s not so hard to do.
Removing Debris and Blockages From Your Chimney
At the base of an old heater flue, usually in the basement, there can be all kinds of debris. Sticks and leaves, dead birds, or maybe a lot of soot. Old oil furnaces may have released sulfuric acid in the chimney for years and worn the chimney out from the inside. Aside from that though, the bases are often just blocked by debris. Just be sure to have a chimney sweep come out to make sure it’s open. If you have flue that was converted from oil to gas, you would be venting carbon monoxide into the house. Be sure to have this checked, and especially if you or your family have a lot of colds or headaches because thus could very well be carbon monoxide poisoning.
With regards to that debris in the chimney, many older homes are surround by large trees or perhaps in a semi-rural setting with lots of animals and leaves. That being said, a chimney chase cover is a smart addition to any chimney to prevent debris from building up as well as protection from harsh weather conditions.