How to Stop Cold Air from Entering Through Your Fireplace

There’s nothing cozier than sitting beside a crackling fire on a cold November night unless cold air is pouring into your living room through the fireplace.

If you feel chilly drafts even when the fire isn’t burning, your fireplace may be working against you. In fact, an unsealed or poorly functioning chimney can cause significant heat loss, drive up your energy bills, and make your home less comfortable.

Here’s what causes cold air to enter through the fireplace and how to stop it with practical solutions from True Ventilation, Catskill’s chimney and venting specialists.

1. Damper Left Open or Leaking

The damper is a metal plate that opens when you’re burning a fire and should be fully closed when the fireplace is not in use.

Problems arise when:

• The damper is accidentally left open
• It doesn’t close all the way due to warping, rust, or debris
• It leaks air around the edges even when closed

Fixes:

• Check and fully close the damper
• If it’s stuck or leaking, True Ventilation can adjust, reseal, or replace it
• Consider upgrading to a top-sealing damper

2. Unlined or Oversized Flue

Older chimneys or ones that were retrofitted for wood stoves often have oversized or unlined flues. This makes it harder to maintain a proper pressure balance, especially when the chimney gets cold.

Result: The cold air in the flue sinks and pushes into your home.

Fixes:

• Install a stainless steel chimney liner to resize the flue
• Line and insulate older masonry chimneys to reduce air exchange
• A properly sized flue improves both draft and efficiency

3. Negative Air Pressure in the Home

Tightly sealed homes, bathroom fans, kitchen exhausts, or HVAC systems can create negative pressure that pulls cold air down your chimney.

Symptoms:

• Cold air flows through the fireplace when fans or appliances are running
• Drafts get worse on windy days
• Smoke is occasionally pushed into the room

Fixes:

• Crack a window near the fireplace to relieve pressure
• Install a top-sealing damper or chimney balloon
• Consider an outside air intake for your fireplace if one isn’t already installed

4. Missing or Damaged Chimney Cap

A chimney cap keeps out rain, animals, and cold air downdrafts. If your cap is missing, damaged, or poorly fitted, cold gusts can enter the flue directly.

Fixes:

• Install a properly sized chimney cap with a wind shield
• Make sure the mesh is intact and properly seated over the flue
• Consider a vacuum-style cap to improve draft and reduce downdrafts

5. Masonry Leaks and Gaps Around the Firebox

Cracked mortar or loose bricks around the firebox and chimney breast can let in outside air from the attic or walls.

Fixes:

• Have your fireplace inspected for structural gaps or loose joints
• Seal with fire-rated mortar or masonry repair products
• Apply chimney waterproofing to reduce infiltration and heat loss

Top-Sealing Dampers

Mounted at the top of the flue rather than the throat, these dampers:

• Create a tight seal against cold air
• Prevent heat loss
• Keep rain and animals out
• Are easier to operate with a cable-pull handle inside your fireplace

They are one of the best investments for Catskill homeowners facing regular cold drafts.

Chimney Balloons or Draft Stoppers

Inflatable or foam stoppers fit snugly into the flue when not in use, stopping air transfer completely.

Important: Always remove before lighting a fire.

Insulated Glass Fireplace Doors

If your fireplace has an open hearth, adding doors can block cold air from entering the room even if your damper isn’t perfectly sealed.

Full Chimney Inspection

If you are not sure what’s causing the draft, schedule a chimney inspection. We check:

• Damper functionality
• Cap integrity
• Flue condition
• Structural gaps
• Pressure and airflow problems