How do you close an unused chimney?

Having an unused chimney in your home can present safety risks and energy inefficiencies if not properly closed off. There are several methods for closing up an unused chimney depending on your needs and budget. In this comprehensive guide, we will walk through the pros and cons of various chimney closure options to help you determine the best solution for your home.

Why Close an Unused Chimney?

There are several important reasons to close off an unused chimney in your home:

• Prevent heat loss – Open chimneys can let heated air escape from your home, driving up energy costs.
• Keep out pests – Birds, raccoons, squirrels and other animals may enter your home through an unused chimney.
• Eliminate drafts – An open chimney flue can create uncomfortable drafts in the house.
• Improve safety – Blocking off the chimney reduces the risk of fires and ember sparks entering your home.
• Prevent water damage – Closing the chimney prevents rain and moisture from seeping into the unused flue.
• Meet code requirements – Most building codes require unused chimneys to be sealed to prevent safety hazards.

Clearly there are many benefits to closing up an unused chimney flue. The key is choosing the right chimney closure method for your specific needs.

Chimney Closure Options

There are four main options for sealing an unused chimney flue:

1. Chimney cap
2. Chimney balloon
3. Chimney sealant (crown or bottom)
4. Chimney removal

Let’s look at the pros and cons of each approach.

Chimney Cap

A chimney cap is a metal or concrete barrier installed on top of the chimney crown at the roofline. Here are the benefits and drawbacks of using a chimney cap:

Pros

• Inexpensive – Chimney caps range from $100-$500 on average.
• Quick installation – Can usually be installed in just a few hours.
• Removable – The cap can be taken off to convert back to wood burning use.
• Prevents animal access – A proper cap keeps pests out of the chimney.

Cons

• Leakage – Poor fitting caps may still allow some water intrusion.
• Maintenance – Caps should be inspected annually and repaired as needed.
• Limited insulation – Does not provide complete sealing or prevent drafts.

A chimney cap offers a fast, affordable way to block off the chimney opening. However, it does not seal the entire length of the flue or provide insulation. Caps may need repair if damaged by storms or animals.

Chimney Balloon

Chimney balloons are inflatable pillows made of durable plastic that are inserted into the flue. Here are the main pros and cons:

Pros

• Inexpensive – Usually $100-$300.
• Easy installation – Can be inserted through the damper.
• Insulates – Fills the entire chimney space to prevent drafts.
• Removable – Can remove later to convert back to wood use.

Cons

• Durability issues – May need replacement every few years.
• Improper installation – Balloon could come loose and fall down chimney.
• Limited lifespan – Exposed to weather extremes and creosote buildup.

For the cost, a chimney balloon provides very good insulation and sealing. However, it may not be the most permanent solution and requires proper installation.

Chimney Sealant

Specialized sealants can be applied to the crown or bottom of the chimney flue. Here are the main advantages and disadvantages:

Pros

• Airtight seal – Completely seals the flue from air flow.
• Permanent – Long lasting solution when properly installed.
• Prevents water leaks – Sealant blocks moisture intrusion points.

Cons

• Labor intensive – Requires proper prep and application.
• Not removable – Difficult to reverse once sealed.
• Brittle over time – Seal can crack and deteriorate.

Applying chimney sealant provides a robust air blockage solution. However, installation is more involved and the results are not easily reversible.

Chimney Removal

For a permanent closure, the entire chimney stack can be removed. Here are the main pros and cons of full chimney removal:

Pros

• Permanent seal – The opening is fully enclosed.
• Eliminates maintenance – No more inspections or repairs needed.
• Improve home value – Removing an unused chimney improves aesthetics.

Cons

• High cost – Chimney demolition and repairs cost $2,000-$5,000 typically.
• Damages – Risk of damage to roof and interior finishes during removal.
• Non-reversible – Cannot convert back to wood burning use.

Chimney removal provides the most complete form of closure. But it is expensive and results in permanent changes to the home.

Key Considerations

When deciding how to seal your unused chimney, keep these key considerations in mind:

• Temporary or permanent? Do you want the ability to use the fireplace again in the future? This impacts the best closure approach.
• Accessibility. Consider how easily the chimney can be reached for inspection and repairs.
• Roof type – Flat or sloped roofs require different installation methods.
• Chimney material – Brick, block, or metal chimneys have different sealing requirements.
• Cost – Select a closure method that fits your budget constraints.

Taking measurements and assessing your specific chimney will help determine the optimal sealing approach.

How to Seal a Chimney

Once you select the appropriate chimney closure method, proper installation is critical. Here is an overview of how to seal a chimney using each approach:

Installing a Chimney Cap

1. Measure the chimney crown opening size
2. Select and purchase a cap based on chimney shape and material
3. Apply waterproof caulk between the cap and crown
4. Secure cap firmly in place with screws drilled into the chimney
5. Seal any gaps with high-heat caulk or mortar
6. Paint the cap to match the roof shingles

Inserting a Chimney Balloon

1. Measure the flue size and purchase proper balloon size
2. Inflate balloon according to product instructions
3. Deflate and insert through damper into the chimney flue
4. Re-inflate balloon to create tight seal
5. Use rope to secure balloon in place

Applying Chimney Sealant

1. Select quality polyurethane or silicone sealant
2. Mix sealant according to manufacturer instructions
3. Use wire brush to remove creosote deposits
4. Apply generous amount of sealant to top and bottom of flue
5. Seal all joints and gaps completely
6. Smooth and shape sealant to shed water

Removing the Chimney

1. Hire qualified chimney demolition contractor
2. Obtain all required permits for removal work
3. Disconnect and cap fuel line supply if present
4. Demolish chimney stack above roofline
5. Remove sections below roof and repair surfaces
6. Permanently enclose fireplace opening

Always follow all manufacturer instructions and building code requirements when sealing a chimney flue. Use proper safety protection for working at heights.

Conclusion

Sealing up an unused chimney improves home safety, energy efficiency and comfort. Four main options exist based on needs and budget. A chimney cap offers a quick DIY method while full removal provides maximum permanence. Considering the pros and cons of each approach will lead you to the best chimney closure solution for your specific home.