Is it normal for cold air to come through fireplace?

Quick Answer

It is normal for some cold air to come through a fireplace when it is not in use. This occurs because fireplaces are designed to let air flow easily in and out. When there is no fire lit, the chimney acts as a large open flue that allows outdoor air to descend through it and enter the house. A certain amount of airflow helps carry smoke up the chimney when a fire is burning. However, too much airflow when the fireplace is inactive can lower indoor temperatures. There are some steps homeowners can take to minimize cold drafts coming down the chimney.

What causes cold air in an unused fireplace?

Several factors lead to cold air entering through an inactive fireplace:

Chimney draft

The chimney is essentially a large vertical tunnel that runs from the fireplace up through the house to the roof. Even when no fire is present, the chimney can facilitate air movement between the house and outdoors due to something called “the stack effect.” Warm air inside the home rises and escapes through the chimney, leaving behind an area of lower pressure. Meanwhile, cool external air is drawn down to fill this void. This constant convection cycle causes a draft through the chimney and fireplace. Draft strength depends on the temperature differential between indoor and outdoor air. Larger chimneys allow more airflow.

Loose damper

A damper is a metal plate inside the chimney that opens and closes to regulate airflow. When open, the damper allows smoke and gases to vent up the flue. When closed, it seals off the fireplace opening to prevent indoor air from escaping. An unsealed, loose, or warped damper can let cold outdoor air leak into the fireplace and circulate into the living space.

Missing chimney cap

A chimney cap is a covering piece that sits on top of the chimney’s exterior opening. Its role is to prevent rain, debris, animals, and birds from entering the flue. A chimney without a proper cap is fully exposed to the elements. This allows cold air to easily flow down the length of the chimney and through the fireplace.

Cracked or missing mortar

Most chimneys have an inner liner surrounded by brick, stone, or metal on the exterior. Mortar seals the gaps between these materials. Over time, weathering and damage can cause cracks and missing chunks of mortar. These openings give cold outdoor air a direct route into the chimney and fireplace.

No fireplace doors

Fireplaces designed for open burning often lack doors or screens covering the firebox opening. When not in use, the exposed firebox allows room air to freely circulate up the chimney flue. Adding tightly-sealing glass doors can help reduce cold drafts.

Is some cold air normal?

A small amount of cold airflow down an unused chimney is normal. Completely sealing off the fireplace is generally not recommended or possible. However, homeowners do not need to tolerate excessive cold drafts. The appropriate amount of natural airflow helps the chimney system function safely and efficiently. Too much airflow starts to sacrifice indoor comfort.

Here are some guidelines on normal versus abnormal cold air in an inactive fireplace:

Normal airflow

– A light breeze through the fireplace opening.

– Enough draft to carry smoke up the chimney but not drastically lower the room temperature.

– Slight airflow from chimney even when damper is fully closed.

Excessive airflow

– Strong, noticeable drafts coming from fireplace.

– Cold air rushing down the chimney.

– Significantly colder room temperatures around fireplace.

– Damper position does not affect airflow amount.

– Loud noises from air movement in chimney.

Steps to reduce cold air drafts

Here are some steps homeowners can take to cut down on excessive cold air entering through the fireplace:

Check the chimney damper

Make sure the damper is properly closed when the fireplace is not in use. Test its seal by feeling for airflow around the edges. Repair or replace the damper if it is warped, rusty, or otherwise unable to form an airtight seal.

Seal the fireplace opening

Keep glass doors or screens closed over the firebox opening when not burning a fire. For fireplaces without doors, install a new set or use an inflatable chimney balloon to seal the opening. Remove inflatable seals before lighting a fire.

Plug the chimney flue

Use an inflatable chimney plug to seal the flue opening itself when the fireplace is inactive. Remove plugs before building fires.

Install a chimney cap

Properly cap the top of the chimney to prevent exterior cold and moisture from entering. Make sure the cap fits securely and allows proper ventilation.

Repair mortar joints

Refill any cracks or missing mortar around chimney bricks and liners with new mortar to close up cold air gaps. Let mortar fully cure before using the fireplace.

Insulate the chimney

For severe drafts, installing fiberglass insulation around the chimney through the attic can help moderate airflow. Use fire-rated insulation products only.

Block vents near fireplace

Seal off nearby air vents and returns to prevent cold drafts from being drawn in and circulated. Open vents back up before making fires.

Upgrade the damper

Some new chimney dampers come with improved sealing features like vinyl gaskets, flexible brackets, or weighted flaps. Install an upgraded damper for maximum airtight capability.

Have the chimney cleaned

Creosote buildup and other blockages in the flue can hinder proper ventilation and allow cold air to leak through. Schedule a professional chimney sweep to clean and inspect the system.

Conclusion

Some cold airflow through an inactive fireplace is expected, but excessive drafts can cause discomfort and energy loss. While a completely airtight seal is not recommended for safety reasons, homeowners have several options available to reduce unwanted cold air coming down the chimney. With a few upgrades and proper maintenance, fireplaces can be enjoyed without sacrificing indoor temperatures. Addressing damper issues, sealing openings, and improving ventilation are key steps to prevent problematic cold drafts. With the right troubleshooting and preventive measures in place, fireplaces can function properly while minimizing unintentional heat transfer to the outdoors.

Cause of Cold Air	Solution
Chimney draft	Install chimney plugs or balloon
Loose damper	Repair or replace damper
Missing chimney cap	Install proper chimney cap
Cracked mortar joints	Refill mortar gaps
No fireplace doors	Add glass doors or screens

Normal Airflow	Excessive Airflow
Light breeze through opening	Strong, noticeable drafts
Minimal temperature change	Significantly colder room air
Slight airflow when damper closed	Damper does not affect airflow
	Loud noises from air movement