How do you cap off an unused chimney?

Author: Ernest Goodwin  |  Last update: Sunday, December 28, 2025

How to Cap a Chimney Instructions
  1. Measure the flue. ...
  2. Select a chimney cap that fits the flue. ...
  3. Slide the cap over the flue or insert into flue depending on design of cap.
  4. Leave at least 6 inches of space between top of cap and flue edge.
  5. The cap should come with self-tapping screws.

Is it okay to block an unused chimney?

As one of the biggest causes of a draughty home, it can make sense to block a chimney opening, especially for larger unused fireplaces. Fixing a draughty chimney not only makes your home more comfortable, it helps to lower energy costs too.

What is the best cap for an unused chimney?

Our disused chimney cap cowl (aluminium) is designed to cap off unused chimneys and prevent rain, birds, leaves, and vermin from getting into the chimney stack. This chimney cowl is made from aluminium which is beneficial as it is a corrosive-resistant material.

What do you do with an unused chimney?

If it is truly unused, you can have a roofer or chimney guy fix a simple sheet metal cap to it it doesn't need to be an actual ``chimney cap'', that allows gasses to pass, just a thick piece of sheet metal, glued down. It should extend past the edges, so water sheds away, past the opening and bricks.

How to seal off an unused chimney?

Chimney capping is one of the ways you can deal with the challenges of an unused chimney. You can block the top of your chimney using a flue ventilator or chimney cap with mesh, leaving space for chimney ventilation.

Chimney Capping - How to Cap off a Chimney and Seal

Is it safe to cap an unused chimney?

Capping your chimney will help reduce heat loss and keep your home more comfortable. The bottom line is that capping your chimney is always a good idea, even if you don't use your fireplace. It will save you money in the long run and keep your family safe and healthy.

Can you cap a chimney yourself?

Most DIYers with the right tools and safety equipment will be able to install a chimney cap themselves, though if the roof is too steep or there isn't enough room to safely maneuver, then it's a good idea to hire trained professionals to get the job done.

What are the disadvantages of chimney cap?

Chimney cap mesh sometimes has very small openings that are easily clogged with creosote. Anytime firewood is burned, some creosote is deposited in the flue lining; and it can also become attached to the mesh of the chimney cap. The oxygen needed for the fire can be cut off as a result of an obstructed chimney cap.

Should you remove an unused chimney?

You should only reduce or remove your chimney if you're absolutely sure it isn't providing ventilation or being used as a flue by any heat-producing appliance.

What happens if you don't have a chimney cap?

Without a cap, water, sleet, snow, and hail can enter your home and cause damage to your flue.

What's the difference between a chimney cap and a flue cap?

There are two basic types of covers for the flue. There is the smaller, less expensive “Chimney Flue Cap” which only covers the flue opening, and there is the "Custom Sized Outside Mount Chimney Cap” which covers the entire chimney top and chimney crown.

Does an unused chimney need sweeping?

An unused chimney should always be swept and given a little ventilation top and bottom. Ask your Guild sweep how best to do this for your situation.

Does a capped chimney need to be vented?

Even when you have retired your masonry fireplace from use, yes, venting an unused chimney is important. It is vital to allow for continued airflow, and that's not the only issue. Safety experts recommend annual inspections for retired, blocked off, and unused chimneys.

Are chimney balloons a good idea?

Chimney Balloons can deflate over time and can be prone to puncturing. Re-inflating them every three months can become tiresome and even messy. Unless you don't mind getting in your hands and knees to re-inflate or re-install your balloon every 12 weeks, we recommend that you get a Chimney Draught Stopper.

Do unused chimneys lose heat?

In fact, chimneys are designed to draw air out and expel it outside. This is so, when you light a fire, the smoke can be carried outside rather than blown into your home. However, when a fire isn't lit, warm air that's created by your heating system can be lost via the chimney.

How much should a chimney cap cost?

The average chimney cap costs $300, but often ranges between $75 and $500, depending on size, shape, and materials. The average chimney cap replacement cost is $300, though it can range between $15 and $1,000.

How to close off a chimney permanently?

This can be done by installing a chimney cap or cowl at the top of the chimney. This method of blocking off a chimney is considered one of the most secure.

Is capping a chimney a good idea?

Do I need a chimney cap if my chimney is not in use? Yes, capping an unused chimney is important to prevent moisture buildup, downdraughts and animal intrusion which can cause damage over time.

How to block an unused chimney?

Chimney sealing options
  1. Chimney Cowl. A chimney cowl often resembles a hood and is placed over the chimney hole. ...
  2. Chimney Balloon. A balloon can also be used to seal off the chimney. ...
  3. Chimney Cover Clamp. ...
  4. Damper Clamp. ...
  5. The Permanent Chimney Cover. ...
  6. Metal Mesh Coverage.

What is the difference between a chimney cap and a chase cover?

Also, the chase cover has a center collared hole that fits over the flue to allow the venting of fumes. A chimney cap is attached to the collar to keep water, pests, and debris out of the flue.

How much does it cost to uncap a chimney?

The cost of opening up a fireplace in the UK generally ranges between £500 and £3,000. This wide range reflects various factors such as the complexity of the work, materials used, and labour requirements.

What should you do with an unused chimney?

Unused chimneys not only waste a lot of heat, they also pose a potential damp problem as well as being a cause of smoking fireplaces and stoves. You should cap any unused chimneys with a flue ventilator. Flue ventilators can be found on our chimney pot page.

How hard is it to cap a chimney?

The installation process is pretty straightforward: once you have the correctly sized cap for your chimney's dimensions, slide the cap's band over the top layer of chimney brick.

Does a chimney cap cause creosote buildup?

The openings in the chimney cap screens are sometimes very small, and they can become clogged with creosote. Creosote is buildup caused by wood smoke and is not only deposited on the flue lining, it can also clog the mesh.

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