how do chimneys keep rain out

So how do chimneys keep rain out?

Chimneys are essential for proper ventilation and for keeping houses warm in the winter. Yet, they must be able to hold up in wet situations, too.

They are the unsung heroes of home upkeep when it comes to protecting a house from the elements.

In addition to keeping the smoke and gases outside, their ingenious construction also effectively diverts rain away from your warm hearth.

But what keeps rain from coming down a chimney?

It is because of the clever designs and constructions as well as the use of chimney caps and crowns that chimneys manage to keep the rain out. 

Learning More about Chimney Design and Function

learning more about chimney design and function

A chimney is a vertical flue used to vent smoke, gases, and other wastes from an indoor combustion appliance such as a stove, fireplace, or furnace outside the building.

Its major goal is to keep the air in the house free of harmful contaminants by allowing adequate ventilation of combustion appliances. 

The Design of Chimneys

For proper and safe operation of heating systems, it is important to understand how a chimney is constructed.

There are quite a few parts of a chimney, including:

  • The flue
  • The Liner
  • The damper
  • The smoke chamber
  • The hearth
  • The firebox
the design of chimneys

Smoke and gases are released mostly through the flue.

In order to preserve masonry and improve its functionality, it is commonly lined with clay, ceramic, or metal.

The smoke chamber, situated above the firebox, acts as a conduit for the smoke and gases coming from the firebox to enter the flue.

The damper is a moveable plate within the smoke chamber that opens and closes the chimney to control airflow.

Finally, the hearth is the extended floor of the fireplace, whereas the firebox is the chamber where the burning takes place.

Fact: The chimney liner is crucial for limiting heat transfer to flammable materials and shielding the chimney from corrosive gases while keeping a steady draft. 

How Do Chimneys Keep Rain Out?

how do chimneys keep rain from entering

So, you know the basic design of a chimney but how do you keep rain out of a chimney?

There are various accessories and parts of a chimney that help protect it from rain and water.

For instance:

  • Chimney caps
  • Chimney crowns
  • Chimney flashing 

Chimney Caps and Rain Protection

If you want to keep water, dirt, and animals out of your chimney, you need a chimney cover.

They sit atop the chimney flue, acting as a cover to keep water out while enabling smoke and gases to leave.

There is a wide range of chimney caps to choose from, each with its own advantages and visual appeal.

For instance: 

Metal Chimney caps

metal chimney caps

Metals including stainless steel, galvanized steel, and copper are commonly used for making chimney caps.

For long-lasting performance, stainless steel caps are highly recommended because of their resistance to corrosion.

Less expensive galvanized steel covers, however, are susceptible to rusting.

Fact: Copper chimney caps last longer than other types and look great, but they cost more. 

Single-flue Chimney Caps

They are made to fit over a single flue in a multi-flue chimney.

Attaching directly to the flue, single-flue caps shield just that flue while leaving the others exposed. 

Multi-Flue Chimney Caps

multi-flue chimney caps

Chimney caps that protect multiple flues at once are called “multi-flue” caps.

These caps are designed for chimneys that have more than one flue or a single flue with an unusual shape that makes installing a standard cap difficult. 

Custom Chimney Caps

Depending on the specifications of your chimney, a custom chimney cap may be the best option.

They provide the best possible defense against the elements and are aesthetically beautiful because they are custom-made to fit the specific measurements of each chimney. 

How Chimney Caps Prevent Rainwater Intrusion

how chimney caps prevent rainwater intrusion

Rainwater entering the chimney flue is something you want to avoid at all costs, and a chimney cover does just that.

The cap’s main purpose is to prevent the flue opening from being exposed to the elements.

Repairs caused by water seepage can be expensive, and may include replacing the liner, re-constructing the chimney, or repairing interior water damage. 

An Important Consideration

In order to prevent sparks from flying out of the chimney, modern chimney tops feature mesh or wire screens.

The chance of a chimney fire spreading to the roof or nearby flammable items is greatly reduced by using these screens.

The screens protect the chimney from debris like leaves and tiny animals that may try to enter the flue and cause blockages or even risks.

Fact: Rainwater can cause damage to the chimney's construction, liner, and interior components like the damper and firebox, but chimney caps help prevent the issue. 

Chimney Crowns and Rainwater Diversion

Crowns on chimneys provide the important function of keeping water out of the masonry.

The crown is the overhanging horizontal surface at the very top of the chimney that may be seen even when the stack itself is not in view.

chimney crowns and rainwater diversion

It creates an impermeable barrier between the weather and bricks and mortar of the chimney, protecting the latter from deterioration.

The chimney crown is an integral part of keeping the chimney safe and sound.

Bricks and mortar can crack or decay as a result of freeze-thaw cycles brought on by water infiltration

A well-designed and well-maintained chimney crown can help prolong the chimney’s life and prevent the need for major repairs by effectively diverting rainfall away from the chimney. 

Reasons Why Chimney Crowns Keep Rain Out

reasons why chimney crowns keep rain out

Rainwater cannot get into the chimney because the crown is built with certain details.

These structural features prevent water from entering the chimney and keep it in good working order.

For instance: 

Sloped Design

The slanting slope of the chimney crown is a crucial design element.

With this angle, rainwater is channeled away from the flue and toward the chimney’s outer borders, where it cannot pool and cause damage to the masonry. 


overhang chimney

A well-designed chimney crown will have an overhang or drip edge that goes beyond the exterior walls of the chimney.

This overhang deflects precipitation away from the sides, where it would otherwise run down and harm the stonework.

Fact: To effectively divert rainwater, the drip edge of an overhang needs to be at least two inches broad. 

Expansion Joints

Chimney crowns require expansion joints to accommodate the natural expansion and contraction of the chimney’s masonry as a result of temperature changes.

Flexible sealant is used to fill these joints so the crown can expand and compress without cracking or damaging the chimney.

Water cannot seep through the expansion joints in the crown and enter the masonry. 

Suitable Materials

Chimney crowns are made using various suitable materials, such as:

  • Concrete
  • Pre-cast concrete
  • Stone
suitable materials

These materials ensure the crown stays in good condition while being exposed to the weather by providing a strong, long-lasting barrier against water penetration.

Crowns can deteriorate and fail prematurely if improper materials like common mortar are used. 

Proper Sealing

Waterproofing is ensured when chimney crowns are properly sealed to the flue and chimney stack.

To accomplish this, a flexible, weather-resistant sealant can create a watertight barrier between the crown and the chimney.

To ensure the sealant on the crown remains effective, it must be checked and maintained regularly. 

Chimney Flashing for Waterproofing

chimney flashing for waterproofing

Flashing around a chimney is an integral part of its waterproofing system, as it seals the transition between the chimney and the roof.

When placed and maintained correctly, chimney flashing prevents water from entering the chimney and extends the life of the roof by keeping water away from the roof and chimney intersection.

Fact: Most chimney flashing is made from aluminum, copper, or stainless steel since these metals are long-lasting and resistant to corrosion and rust. 

Types of Chimney Flashing

types of chimney flashing

Several types of flashing for chimneys are available but step flashing and counter flashing is probably the most common. 

Step Flashing

Chimneys with shingles, tiles, or other overlapping roofing materials typically use step flashing, a common type of flashing.

Step flashing is a metal flashing that is put in a sequence of L-shaped pieces along the sides of the chimney at its point of contact with the roof.   

Counter Flashing

counter flashing

Another method of preventing water damage is to place counter flashing, also called cap flashing, directly on top of the step flashing.

Watertight counter flashing is either embedded into the masonry of the chimney or sealed to it with a sealant.   


How do chimneys keep rain out?

Well, chimney accessories like crowns, caps, and flashing work along with the chimney’s innovative designs and constructions help keep water out of the chimney and away from the toasty fireplace.

It is important that you do not ignore the need to use these accessories and always check your chimney regularly to spot any issues early.