Fireplace drafts: dampers, doors and inserts

First identify what is behind the hearth

An open wood fireplace, a fireplace fitted with gas logs, an enclosed wood insert and a sealed direct-vent gas appliance can look similar from across the room. Their air and exhaust arrangements differ. Record the appliance name and model, fuel, available manuals and inspection history. Have a qualified hearth or chimney professional identify an unfamiliar installation before selecting a draft-control product.

Not in use can mean different things: no visible flame, no fire this season, or permanently taken out of service. Those are not equivalent. A pilot may still be burning, embers may remain, or another appliance may need the chimney. A thermostat being off is not permission to obstruct an exhaust route.

Sources: [5] [8] [6]

Why an idle chimney can lose heat

Air leakage needs an opening and a pressure difference. In winter, differences between indoor and outdoor air density help drive stack effect; wind and operating equipment alter the pressures too. An open flue can connect the room to outdoors, allowing heated air to leave and replacement air to enter elsewhere. The cold draft you notice near another opening can therefore be part of the same airflow pattern.

Flow can also reverse. CSIA describes household pressure conditions that pull air and chimney odours down into a room. A chimney is consequently more than a hole with one fixed direction of flow. Weather and the rest of the house influence what happens at the hearth.

Sources: [1] [3]

There is no single heat-loss number

How much heat escapes depends on airflow, the indoor–outdoor temperature difference and how long those conditions persist. Flue size, damper condition, chimney location and house pressure all affect the answer. A percentage advertised for one product or house cannot establish the loss from yours. Heat from an active fire is a separate question from leakage through an idle fireplace.

Ask an energy adviser to explain the evidence behind a proposed saving and coordinate assessment with the chimney professional. Useful records include when drafts occur, whether the fireplace is active, and what other equipment is operating normally at the time. Do not create test conditions by running fans against a fire or temporarily blocking vents. Our air-sealing article explains controlled professional leakage testing.

Sources: [1] [2] [8]

The existing damper is the first discussion

A traditional throat damper is a movable closure near the base of the chimney, above the firebox. NRCan notes that a damper which does not close properly needs specialist repair, and that even a closed damper may leak. Establishing its condition and intended operation is a sensible first step before buying another device.

Energy-saving closure applies only when safe for that specific installation. An operating open wood fireplace needs its flue damper open as its manual requires. Do not close it over a fire or remaining hot embers, or use it to shut off a gas appliance’s required exhaust. Have the professional explain safe shutdown and reopening; no visible flames is an inadequate test by itself.

Sources: [2] [5] [8]

A top-sealing damper changes the closure location

A top-mounted damper closes near the chimney outlet rather than at the throat. CSIA identifies a tight-sealing top damper as one way to reduce unwanted downward airflow. Its relevance depends on the fireplace and chimney: an accessory that suits one masonry wood-burning installation is not automatically approved for a factory-built system or gas appliance.

Ask the chimney professional about compatibility, inspection access, maintenance and reliable operation before commissioning one. The proposal should identify how an occupant confirms the required open position before a fire. Roof access and installation belong with qualified trades. A tighter closure also does not diagnose the house-pressure problem that may be drawing odours downward.

Sources: [3] [5]

Glass doors are not the same as an insert

Glass doors can change airflow across an open hearth, but their fit and permitted operation matter. NRCan cautions that many fireplace doors do not seal particularly well. Adding a decorative door set does not, by itself, turn an open fireplace into a sealed combustion appliance.

Door position during a fire is model- and accessory-specific. For example, the Heat & Glo Exclaim 36/42 owner’s manual, revision C dated April 2026, permits its approved doors fully open or fully closed in its wood-burning configuration and warns against intermediate positions. That is an illustration of why the actual manual matters, not a rule for every fireplace. Have the professional verify the approved door assembly and explain operation for your exact unit.

Sources: [2] [5]

A balloon is a temporary obstruction with strict limits

An inflatable chimney stop forms a removable barrier in a flue. The Chimney Balloon manufacturer explicitly says to remove its product before lighting a fire. Treat such a device only as a possible option for a cold, dormant wood-fireplace flue after a professional confirms suitability. It must never obstruct a burning or smouldering fire, an active pilot, any operating fuel-burning appliance, or another appliance’s shared vent.

The manufacturer’s UK FAQ is evidence about that product, not Canadian or American installation approval. Its marketing claim that the material shrivels when heated is not a safe-use plan. If a temporary stop is approved, the household needs clear identification and a reliable removal check before reuse. Guests and future occupants must know it is present. Do not use an improvised plug; permanent retirement requires a professional plan for disconnection, remaining vent paths and moisture management.

Sources: [4] [8] [3]

An insert changes the appliance, not just the opening

An enclosed wood insert is a heating appliance fitted into a suitable existing fireplace. Health Canada advises choosing advanced-combustion wood appliances certified to recognized CSA or EPA standards to reduce particle emissions and improve efficiency. Certification does not make wood smoke harmless. Compare the intended heating role, fuel use, servicing and local restrictions as well as appearance.

A sealed direct-vent gas insert has an outside-air combustion supply and a separate exhaust path, with the combustion chamber separated from room air by its approved enclosure. A natural-draft gas appliance or gas-log conversion is not necessarily that system. With a wood insert, ask where combustion air comes from; enclosed does not establish a sealed outside-air circuit. Request the actual model’s performance and venting information rather than a generic savings percentage.

Sources: [7] [6]

Include the house in the assessment

NRCan explains that fuel-burning equipment needs both combustion air and a route for exhaust to leave. Air sealing and changes to exhaust equipment can affect those conditions. A chimney upgrade should therefore be coordinated with any wider insulation, air-sealing or ventilation project. Fixing a nuisance draft is not proof that combustion operates safely.

Ask who will assess the existing appliances and verify their operation after the change. Required combustion-air openings and appliance cooling paths are not ordinary leaks to cover. A proposal should distinguish those functions from unintended leakage around the building enclosure. The professional should also identify which observations require repair before an energy improvement proceeds.

Sources: [2] [9]

Compare options against the intended future use

There is no universal best device. A fireplace used regularly calls for an approach that preserves convenient, verifiable operation. An appliance intended only for occasional ambience may justify a different investment from one expected to provide useful room heat. If the fireplace will never be used again, ask about professional decommissioning instead of treating a temporary stop as a permanent solution.

Sources: [3] [4] [6]

Keep the safety information with the energy decision

Keep the inspection report, exact manuals and a record of approved modifications together. Health Canada recommends professional maintenance of fuel-burning equipment and annual cleaning for wood-fireplace chimneys. Confirm the schedule for your installation and arrange follow-up when operation changes, rather than assuming a rarely used chimney needs no attention.

Maintain smoke and carbon-monoxide alarms according to their instructions and local requirements. An alarm is a backup, not permission to obstruct a vent. If a CO alarm sounds, Health Canada advises leaving for fresh air immediately, calling 911 from outside and returning only after professionals have resolved the problem. Do not remain inside to find the source.

Sources: [9]