What is the Purpose of a Chimney Cap?

There are several functions of a chimney cap. You may already know that an obvious one is to keep the rain and snow out of your chimney. But do you know why it is important to keep water out of your chimney? Chimney caps will cost a little money in the beginning but can save you a lot of money and potential headaches in the long run.

Keeping Your Chimney Dry

You may think there is no need to keep the rain and snow out of your chimney because the heat from the fire will quickly evaporate any water that gets inside. This can be true if you keep your fire hot all the time. But in most cases people don’t keep their fire going 24 hours a day 365 days a year and at some point it is going to get very wet inside a chimney.

Over time water can be damaging to a chimney, especially if it is masonry. Both brick or tile chimneys will absorb water. When you don’t have a fire the inside of a chimney isn’t exposed to the sun and wind so it can stay wet inside for a long time. This can start to damage the masonry over time with extreme temperature changes that happen inside a chimney. When you build a fire and get a sudden extreme temperature change a wet flue can be more likely to crack. In cold weather the water can freeze which can break apart masonry.

A metal liner may be less susceptible to water damage but with some materials like galvanized steel the water can lead to rust. The extreme heat and the chemicals in the smoke and creosote mixed with water can create an environment for corrosion. Not only for your chimney liner but your stove or fireplace can fill with water and the ashes inside can hold moisture for a long time. In one big rain storm I had a stove fill up with water and run out all over the hearth which made a wet ashy mess. The wet ashes and creosote can also produce odors.

Keeping Animals out of Your Chimney

Birds, squirrels, raccoons, rats, mice, cats, all these animals can find their way into an open chimney. Some of them can find their way in and then become trapped and die. In most cases you probably won’t know they are there until the odour pervades your home.

Sometimes birds will build a nest inside your chimney and that will plug it up and the nest will have to be removed before you can build a fire.

I knew a woman who had honey bees build a large hive inside her chimney. She figured that out after she noticed a constant buzzing coming from her wood stove and noticed swarms of bees flying in and out of her chimney. It was kind of funny, most people have smoke coming out of their chimneys but she had bees coming out of hers.

Spark Arrestors Could Save Your Home

Chimney caps with spark arrestors have a screen that is designed to block sparks from coming out of your chimney and starting a fire. Sparks can ignite a roof, walls, or nearby objects such as trees, shrubs and can start wildfires. In some areas a spark arrestor is required by local building codes. Spark arrestors come in different size mesh screens. Some areas like California require a minimum mesh size so check with your local building codes.

Chimney Caps Can Help Prevent Downdrafts

Some chimney cap models are designed to keep air from sinking down your chimney which is called a downdraft. A downdraft can bring cold outside air into your home when your stove or fireplace is not in use. Or when it is in use it can cause smoke to flow into your home instead of out the chimney.

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