Here’s What Happens to Your Chimney When It Rains

Having a fireplace to curl up close to on those cold rainy days could be a lifesaver, but as the fire protects you from the cold and the chimney protects the fire from the rain, what protects the chimney from the rain? And what exactly happens to your chimney when it rains? 

When it rains, your chimney may accumulate excess water if you don’t have a chimney cap. Water can also leak through if you don’t have dampers installed, or if your chimney was constructed poorly.

In this article, I’ll take a closer look at what happens to your chimney when it rains. I’ll also explore what a chimney cap is, and how to protect your chimney from water damage. Keep reading to learn more.

rain flows down from a roof down

How You Can Stop Rain From Entering Your Chimney

A chimney is constructed to let out smoke from a fireplace and prevent rain, snow, and wind from coming down the structure excessively. 

If rain enters your chimney, there are several ways to prevent it, and a chimney cap is one of them. A chimney cap could make all the difference between your chimney staying dry during the rainy season and being filled with water as it rains. 

What Is a Chimney Cap?

A chimney cap is a flat roof-like structure, usually built with metal, that is situated atop the chimney. Its main purpose is to deter excess water from entering the flue and pooling around the base of the chimney.

Chimney caps also have legs that prop them up, creating a defined space between the top of the flue and the cap. This is to allow room for smoke to rise out of the chimney and prevent rain from pouring into the chimney. 

The chimney cap works similarly to an umbrella by shielding the chimney from downpours and pushing water away from the opening. Some are even built with screens to keep birds and other pesky animals from the chimney shaft. 

Why Do You Need a Chimney Cap?

Every chimney can benefit from a chimney cap, though not all homeowners decide to invest in one. This is mainly because most people believe a chimney shaft is waterproof and is built to absorb any water that trickles down the shaft. And while this is true, it is only partially so. 

You need a chimney cap to deter as much water as possible from entering the chimney’s shaft. The building material can absorb some moisture, but only a cap can divert enough water to prevent excess water from pooling around the chimney’s base.

The masonry of a chimney is usually built with waterproofing in mind, with the bricks lining the chimney shaft. They’re constructed in a way that enables them to absorb as much water as they can before the water reaches the fireplace below. 

But what most people don’t know is this is supposed to be a secondary protective measure, with the chimney cap being the first line of defense against rain. 

Why You Can’t Depend on a Chimney Cap Alone

While having a chimney cap at the top of your chimney is advisable, it shouldn’t be the only waterproofing method you implement. This is because, even though chimney caps may be effective against rain, they are usually quite small, with even smaller openings, to allow smoke to rise out of the chimney crown. 

Therefore, it is possible for wind and rain to still find ways into the chimney, which is where the quality of your chimney’s masonry comes in. 

A masonry chimney is the overall build of the chimney involving the flue tiles, the bricks in the chimney wall, and every other component that makes up the chimney. These components determine the stability and the water and fireproof nature of the chimney. 

If these components are not up to code, it could lead to rainwater seeping in through the walls and damaging the chimney’s structure. Rainwater making its way into a subpar chimney could lead to it losing stability, becoming less secure, and degrading its fireproof nature. 

In addition, using a damper is a great way to prevent rainwater from entering the chimney’s flue. A damper controls airflow in and out of the flue with an opening and closing mechanism. It has a switch to let out smoke when the fireplace is lit and closes when not in use. 

It can serve as a reservoir for any rainwater that makes its way down the flue, holding it long enough for the heat to evaporate it over time before it causes any damage. 

Checking for Water Damage Periodically Can Save Your Chimney

Due to the tricky nature of water, a chimney cap, quality masonry, and even dampers can sometimes only do so much in keeping water out of your chimney. 

Water can cause small and gradual damage, with no apparent effect until the damage is already too significant to fix. That’s why it is important to carry out occasional inspections. 

Also, water finding its way through the chimney’s flashing can cause slow and undetectable damage. 

The chimney’s flashing is a tight stripe that seals the space between the chimney and the house’s roof, preventing water from coming in. 

If the flashing is damaged over time, rainwater can get in and break down the chimney wall, the surrounding ceiling, and roof areas. This can lead to even more expensive and extensive repairs. 

Therefore, having a professional perform quarterly or annual checks on the chimney will go a long way in detecting underlying damages caused by rain. 

Ultimately, this could save you a lot of time and money spent on repairs. It will also keep your home and family safe.


Rain can be a real hassle on chimneys, especially if your chimney isn’t constructed with quality, or doesn’t have a chimney cap to keep out water. 

Using the right equipment and structures in addition to routine maintenance should keep your chimney safe and functional for a very long time. 

Dan Westfield

Hi everyone! My name is Dan and I currently have two fireplaces, a wood-burning and a gas one. I cannot live without them and love to share my passion with you all!

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