Weather Stripping & Draft Stoppers: Find the Leak First

Quick answer: find the leak before you buy the seal

Weather stripping is for moving joints. Caulk and other sealants are for appropriate fixed joints. Window film and insulated coverings address a different problem again.

That distinction matters because a window can feel brutally cold without outside air leaking through it. Cold glass can pull heat from you by radiation and cool nearby room air so it falls toward the floor. That indoor downdraft can feel remarkably like a leak.

Start by finding where air is actually moving.

Natural Resources Canada makes the same basic material distinction: caulking, tapes and gaskets join air-barrier materials at joints that do not move; weather stripping is used at joints that do move. See Keeping The Heat In: materials and weatherstripping.

Draft diagnostic

What’s causing your draft?

Pick where you feel the problem and when it shows up. This does not guess a product. It routes the symptom to the joint or building-envelope category worth checking first.

Where do you feel it?Not sure yetAround the sides or top of a doorUnder a doorAround a moving window sashAround a fixed window frame or trimThe whole window feels cold, but I cannot feel a clear leakAlong a baseboard, floor edge, or trimAround a pipe, cable, duct, or utility penetrationNear a fireplace or chimneyAt an attic hatchIn several rooms / all over the houseWhen is it most noticeable?Not sure / variesMostly when it is windyMostly during very cold weatherMost of the timeMostly noticeable near the floorMostly noticeable upstairsWhat kind of opening is involved?Not sure / not applicableExterior hinged doorSliding / patio doorCasement or awning windowSliding windowSingle- or double-hung windowFixed windowOther opening

Best next path

Confirm air movement before buying a seal

Start by separating an actual moving-air leak from a cold surface or a concealed envelope path.

Check this first

1. On a cold or windy day, move a tissue or thin plastic strip around door/window joints, trim, baseboards, hatches, and accessible penetrations.
2. Look for daylight, damaged seals, loose hardware, staining, frost, or condensation.
3. If the whole pane/surface feels cold but the tissue does not move, treat that as a heat-transfer clue rather than proof of air leakage.

Repair category

Diagnosis first. Choose weather stripping only for a confirmed moving joint; use caulk/sealant for appropriate fixed joints; use insulation/secondary layers for conductive problems.

Don’t shortcut this

Do not use candles, lighters, or matches as draft detectors, and do not deliberately depressurize the house around fuel-burning appliances without understanding the combustion-safety implications.

If you cannot isolate the path, a blower-door assessment is the cleanest next step.

This tool identifies a diagnostic path, not a guaranteed cause. Moisture, damaged assemblies, combustion venting, electrical/gas penetrations, and widespread leakage can require professional assessment.

Air leak or just a cold surface?

There are several ways a window, door, or wall can make you uncomfortable in winter.

Air leakage is bulk outdoor air moving through a gap because there is both an opening and a pressure difference across it. Wind can push air through the windward side of a house. Winter stack effect tends to draw outdoor air into lower parts of the house while warmer indoor air escapes higher up.

Conduction is heat moving through the solid building assembly. Heat still moves through glass, frames, doors, walls, and other materials even when the assembly is perfectly airtight.

Radiant discomfort happens when your body exchanges heat with a much colder surface. Sitting beside cold glass can feel chilly even when a thermometer in the middle of the room looks fine.

Indoor convective downdraft can happen when room air is cooled by cold glass, becomes denser, and falls down the face of the window. You may feel the moving air at floor level even though that air started inside the room.

NRCan’s fenestration guidance explicitly separates conduction, convection, radiation, and air leakage as different parts of window energy performance. See its technology primer for windows, doors and skylights.

The practical rule is simple: do not diagnose an air leak solely because something feels cold.

How to find drafts safely

Do the detective work on a cold day. Windy weather can make leakage easier to find.

1. Look before touching anything

Check for:

• daylight around a closed door;
• cracked, missing, folded, or permanently flattened weather stripping;
• a door or sash that sits visibly out of square;
• loose or worn locks and latches;
• gaps at casing/trim joints;
• staining, rot, frost, or active water entry;
• dirty streaks at trim or carpet edges that may indicate long-term air movement.

2. Use a tissue or thin plastic strip

Hold a light tissue or strip of thin plastic near the suspected joint. Movement at one specific joint is better evidence of a leak than a cold hand alone.

NRCan’s older Improving Window Energy Efficiency guidance specifically recommends tissue or thin plastic for this purpose. The current Keeping The Heat In guide also describes smoke-based leak detection.

3. Smoke can work, but it is not the first tool you need

NRCan describes using burning incense as a simple smoke indicator. That is authoritative guidance, but it still involves a hot, smouldering object. Keep it well away from curtains, paper, aerosols, foam, and other combustibles.

Do not use candles, matches, or lighters as draft detectors. They add an unnecessary open flame to a job that can usually be done with tissue, visual inspection, or professional diagnostic tools.

4. Treat infrared images as clues, not proof

A thermal camera sees surface temperature patterns. A cold streak might be moving outdoor air, missing insulation, a thermal bridge, reflected radiation, or another surface-temperature effect.

NRCan says infrared scanning is particularly useful with a blower-door test for locating air leakage and missing insulation. A blower door intentionally creates a controlled pressure difference so leakage paths become much easier to identify.

If drafts are widespread, the house has natural-draft combustion equipment, or you keep finding cold areas without a clear path, an energy advisor or experienced air-sealing contractor can be money better spent than buying ten different rolls of foam tape.

Cold air around the sides or top of an exterior door

This is where door weather stripping actually belongs.

But inspect the door before deciding the gasket is the problem.

A good perimeter seal has to make consistent contact when the door closes. A sagging slab, loose hinge, misaligned strike, warped door, damaged frame, or obstruction can leave one corner uncompressed even when the gasket itself is new.

Check these in order:

1. Close and latch the door.
2. Look at the gap around the top and sides. Is it reasonably even?
3. Confirm the latch actually pulls the slab against the stop and seal.
4. Inspect the gasket for tears, missing sections, hardening, or permanent flattening.
5. Test the suspected area with tissue or thin plastic.
6. Replace the weather stripping with a profile that suits the joint and gap, not merely the thickest one on the shelf.

NRCan recommends adjusting and squaring windows before installing replacement weather stripping, and the same principle applies to doors: a seal cannot compensate indefinitely for poor geometry.

Which door weather stripping should you use?

There is no universal winner. The joint determines the material.

NRCan’s current material guide specifically notes that some weather-stripping products harden and become less effective in cold weather, recommends flexible products that spring back quickly, and warns against products that make the window or door difficult to operate.

That is better buying guidance than pretending EPDM always wins or attaching a universal temperature limit to every product made from the same polymer. Product formulation, profile, installation method, and joint type still matter.

Canadian context

Canadian winter adds one boring but important installation constraint: self-adhesive products may have minimum application-temperature and surface-preparation requirements. Read the exact product instructions. A gasket that performs in deep cold can still peel off if its adhesive was applied to a dirty, wet, or too-cold frame.

Cold air under the door: sweep, bottom seal, or threshold?

The bottom of an exterior door is its own joint.

A door sweep attaches to the door and uses a flexible fin, pile, brush, or similar edge to reduce the gap at the floor or threshold.

A door bottom or shoe fits over or into the bottom edge of the slab and may use multiple flexible fins or a gasket.

A threshold seal is part of the sill/threshold side of the joint. Some thresholds are adjustable so the contact height can be tuned to the door bottom.

An automatic door bottom uses a mechanism that drops a seal when the door closes and retracts it while the door swings. It is a real category, but it is more specialized than most homeowners need for an ordinary exterior door.

NRCan notes an important trade-off: sweeps are generally easier to install and more durable, while thresholds can provide a more effective seal but take more abuse from traffic and weather.

What about a door draft stopper or draft snake?

A fabric draft stopper can reduce the sensation of air moving across the floor. That does not make it equivalent to fixing the exterior-door assembly.

A loose draft snake:

• is not mechanically compressed into the joint;
• does not seal the bottom corners consistently;
• moves when the door opens;
• may interfere with normal use;
• can get dirty or wet near an exterior entrance.

Use one as a temporary comfort measure, not proof that the underlying door is sealed.

Drafty windows: moving sash versus fixed frame

This is the other big fork in the road.

Air around a moving sash

That is a weather-stripping job if the hardware and sash alignment are sound.

Casement and awning windows: these commonly use compression seals. Closing hardware needs to draw the sash into the gasket. If the window does not close squarely, replacing the gasket alone may accomplish very little.

Sliding windows: these commonly use brush/pile weather stripping. Track dirt, roller wear, sash alignment, and worn pile can all affect the seal.

Single- and double-hung windows: NRCan specifically discusses V-strip/tension seals at sash channels and compression material at the sill. The meeting rail and sash lock matter too.

For modern units with factory weather stripping, NRCan’s advice is delightfully unsexy and correct: remove a sample and take it to the manufacturer or supplier to match the replacement.

Air around the fixed window frame or trim

That is not a sash-weather-stripping problem.

NRCan recommends interior caulking around appropriate window-trim joints. If the trim can be removed, gaps between the frame and rough opening may need insulation plus caulk, backer rod, or low-expansion foam intended for window/door use.

The key word is appropriate. Exterior window assemblies also need to manage water.

NRCan specifically says storm-window weep holes must remain open to the outside and emphasizes flashing and a properly detailed drainage plane as the stronger defence against rain entry.

What if the whole window feels cold but you cannot find a leak?

Stop buying weather stripping.

If tissue does not move at the sash or frame joints, the window closes correctly, and the seals are intact, your comfort problem may be the thermal performance of the window itself.

Three different strategies can help, depending on the window:

• Seasonal heat-shrink window insulation film creates a tight interior storm layer over the opening. NRCan says these kits can provide an excellent seal, but the tape can lift paint and the window cannot be opened without removing or puncturing the film.
• Reusable interior storm panels provide another sealed interior layer and can reduce leakage around the original window when fitted tightly.
• Insulated curtains or cellular shades can reduce heat exchange and improve comfort, but they do not repair a leaking sash or frame.

Those are substantial enough commercial intents to deserve their own ReadyHome pages. This guide keeps them in their proper role: secondary thermal strategies after you have diagnosed whether an actual air leak exists.

No fake R-value for shrink film

ReadyHome does not assign one universal R-value to a plastic window kit.

The performance depends on the original window, air gap, leakage, installation quality, frame effects, and test method. NRCan describes the system and its sealing benefits without giving one universal R-value. That is the standard we are following.

Thermal curtains: useful layer, wrong repair for a leak

NRCan says curtains and blinds can reduce radiant heat loss through windows during heating season, and insulated drapes offer somewhat more benefit than ordinary drapes or blinds.

There is a catch: window coverings can also isolate the glass from warm room air. NRCan warns that closed drapes and blinds can reduce air circulation at the glass and contribute to winter condensation.

A sensible routine is:

• fix actual sash/frame leakage first;
• use a well-fitted covering as an additional layer;
• open coverings when useful winter sun can warm the room;
• close them when that solar gain is gone;
• monitor for condensation behind tightly fitted coverings.

Blackout describes light blocking. It does not automatically tell you how well a curtain controls heat flow.

Rope caulk and removable seasonal sealing

Removable or strippable caulk can be useful for windows or joints that are intentionally taken out of service for the winter.

NRCan recommends strippable caulk for windows that are never opened, with an important qualification: do not seal a window shut if it is required for ventilation or emergency escape.

This is different from permanent caulk around a fixed casing joint and different again from weather stripping on an operable sash.

Drafts along baseboards, trim, and rim joists

A draft near a window does not prove the window caused it.

NRCan lists baseboards, trim, sill/header areas, service entries, plumbing penetrations, attic openings, chimneys, and basement/header joints among common leakage locations.

If cold air seems to emerge along a floor edge or baseboard:

1. Trace the symptom along the wall rather than staring only at the closest window.
2. Inspect the basement or crawlspace rim/band-joist and sill area below it if accessible.
3. Look for fixed joints and penetrations where outdoor air could enter.
4. Choose the air-sealing and insulation method for that actual envelope boundary.

Weather stripping belongs on a moving joint. A rim joist is not a moving joint.

Attic-hatch drafts

NRCan says to treat an attic hatch much like an exterior door:

• caulk the fixed frame/casing joints;
• weatherstrip the hatch perimeter;
• use a latch or hook arrangement that actually holds the hatch against the gasket;
• insulate the hatch itself.

That advice is strong enough without inventing a universal R-40 or R-50 requirement for every hatch in every Canadian jurisdiction.

Attics also contain fire-clearance, electrical, chimney, recessed-fixture, moisture, and sometimes asbestos/vermiculite issues. If the job is no longer “replace a gasket on an accessible hatch,” broaden the safety assessment before you start spraying foam around things.

Electrical, plumbing, cable, and utility penetrations

These are fixed joints, but the safe sealant depends on what passes through the hole.

Ordinary exterior-wall penetrations may be sealed with a compatible caulk, gasket, or foam. Gas lines, electrical equipment, chimneys, vents, and fire-rated assemblies can require specific materials and clearances.

If you cannot identify the service, do not bury it in foam because a blog post said “air sealing good.”

Fireplace and chimney drafts

A fireplace is not a giant drafty window.

A poorly sealing damper or chimney pressure can move a lot of air, but a chimney or flue may also be an active combustion pathway. NRCan’s combustion-spillage guidance explains how house depressurization can reverse flow in natural-draft equipment and pull combustion products into the home.

Never permanently plug, foam, or caulk an active flue, draft hood, chimney, or required combustion-air opening.

If a fireplace or natural-draft appliance is involved, use the manufacturer instructions and an appropriate chimney/fireplace, HVAC, or fuel-appliance professional rather than improvising an airtightness retrofit.

Air sealing, humidity, and condensation

Air sealing changes the house.

NRCan warns that as an envelope becomes tighter, indoor humidity can rise. That can increase condensation risk on cold glazing if moisture production and ventilation are not managed.

There is no responsible one-number rule such as “keep every Canadian home at 30% RH all winter.” NRCan’s own condensation table shows that the maximum indoor relative humidity before condensation varies with outdoor temperature and window performance. Better windows can tolerate more indoor humidity before their interior surfaces reach the dew point.

Use these principles instead:

• persistent condensation means the glass/frame is cold relative to the moisture level indoors;
• colder outdoor weather generally reduces how much indoor humidity a given window can tolerate;
• better-performing glazing generally keeps the interior surface warmer;
• closed blinds/curtains can lower glass temperature by blocking room-air circulation;
• an HRV/ERV, exhaust fans, moisture-source control, and normal heating/air circulation can all affect the result;
• condensation between panes of a sealed insulating-glass unit points to a failed sealed unit, not a weather-stripping problem.

If you see active water staining, wet drywall, rot, or leakage from outdoors, diagnose that water source before sealing over it.

When air sealing and combustion safety intersect

Replacing a worn door gasket is not inherently dangerous. The concern is comprehensive tightening of a house that depends on natural-draft combustion appliances or fireplaces.

NRCan says fuel-burning furnaces, water heaters, fireplaces, woodstoves, and similar equipment need combustion air and a reliable route for exhaust gases. It also warns that strong exhaust appliances can depressurize a house enough to contribute to backdrafting.

That is why ReadyHome does not publish a magic “5 Pa” homeowner cutoff or an ACH50 number that supposedly tells everyone when an HRV becomes mandatory. Appliance type, venting, exhaust equipment, code requirements, and the actual building all matter.

Professional assessment is warranted when:

• you are doing extensive whole-house air sealing;
• the home has atmospherically vented/natural-draft combustion equipment;
• a fireplace or chimney shows signs of poor draft or spillage;
• a large range hood or other exhaust equipment creates obvious pressure problems;
• you are unsure whether an opening is intentional combustion/makeup air;
• you need blower-door or combustion-spillage testing to understand the house as a system.

Why this matters during a winter power outage

Air sealing does not create heat.

It can reduce uncontrolled air exchange and therefore reduce one part of the home’s heat loss. That may help the building cool more slowly when the heating system stops.

But there is no universal answer to “how many extra hours will weather stripping keep my house warm?” Cooling rate depends on outdoor temperature, wind, air leakage, insulation, window area and performance, solar gain, building geometry, thermal mass, and the indoor starting temperature.

That is why the outage connection is a resilience handoff, not a runtime claim:

• If electricity is what stopped the heating system, use the furnace power-outage guide.
• If the home is cooling in severe weather, use the frozen-pipe prevention guide.
• For the rest of the household dependency chain, start with what to do during a power outage and the backup-power hub.

What should you buy first?

Use this order.

1. Confirm the leakage path

Tissue/plastic, visual inspection, correct closure, and a cold/windy day are enough for many localized problems.

2. Fix alignment and hardware

If a door or sash is not reaching the seal, replacing the seal alone can be a waste of money.

3. Match the material to the joint

• moving compression joint → compression gasket;
• sliding joint → low-friction pile/tension seal as appropriate;
• door-bottom joint → sweep, fitted bottom, or threshold solution;
• fixed casing/frame joint → appropriate caulk/backer rod/low-expansion foam;
• whole cold pane with no leak → secondary glazing or window-covering strategy.

4. Escalate when the problem is not local

Widespread leakage, moisture damage, inaccessible assemblies, combustion appliances, chimneys, or complex attic/basement work can justify professional diagnostics.

Frequently asked questions

What is the best weather stripping for an exterior door?

There is no universal best material. The right choice must fit the existing door/frame geometry, gap, movement, compression, exposure, and installation method. NRCan recommends flexible material that springs back well and does not make the door difficult to operate. Modern prehung doors often work best with a matching replacement kerf-in profile.

How do I stop cold air from coming around my front door?

Close and latch the door, map the leaking section, and check alignment before replacing the perimeter weather stripping. If the slab does not sit square or the latch does not compress the seal, correct that problem first.

What is the best way to stop a draft under a door?

Inspect the existing door bottom/sweep and threshold. A properly fitted sweep, door bottom, or adjusted threshold is a real seal. A fabric draft stopper can be a temporary comfort aid but is not equivalent to repairing the door-bottom joint.

How do I weatherstrip a sliding window?

First clean the track and make sure the sash sits and closes correctly. Sliding windows commonly use brush/pile weather stripping that can be pulled from a channel and replaced with a matching size/profile. Avoid compression material that creates so much friction the window cannot operate normally.

How do I weatherstrip a casement window?

Casement and awning windows normally use compression seals. Before replacing them, make sure the locks and hardware pull the sash squarely into the frame. A new gasket cannot compensate for a sash that never reaches it.

Should I caulk around my windows for winter?

Caulk can be appropriate at fixed interior trim/frame joints and other fixed air-leak paths. It is not the right material for a moving sash. Exterior sealing also needs to respect flashing, drainage planes, and weep openings.

Do window insulation kits work?

They can. NRCan treats heat-shrink film as an interior storm-window option and says a properly installed kit can provide an excellent seal. It is especially relevant when the window itself is cold or leaky and a temporary seasonal interior layer is acceptable. The trade-offs include tape/paint damage risk and losing normal window operability while the film is installed.

Do thermal curtains stop drafts?

They can improve comfort and reduce heat exchange at a window, but they do not repair an air leak through a sash, frame, or wall joint. Fix the leakage path first. Also watch for condensation behind tightly closed coverings.

How can I tell whether my window is leaking or just cold?

Test the actual sash and frame joints with tissue or thin plastic. If you cannot detect airflow but the glass and area below it are cold, conductive/radiant heat loss and an indoor downdraft may be the issue. A cold surface is not proof of infiltration.

Should I use an infrared camera to find drafts?

It can help find cold patterns, especially when combined with blower-door testing, but it does not directly measure airflow. Use it as evidence to investigate, not as automatic proof that every cold patch is an air leak.

Sources

This guide was independently checked against current primary guidance on September 7, 2026. The main technical sources are:

• Natural Resources Canada — Keeping The Heat In: Section 2, How your house works
• Natural Resources Canada — Keeping The Heat In: Section 3, Materials and weatherstripping
• Natural Resources Canada — Keeping The Heat In: Section 4, Comprehensive air leakage control
• Natural Resources Canada — Keeping The Heat In: Section 8, Upgrading windows and exterior doors
• Natural Resources Canada — Condensation
• Natural Resources Canada — Combustion gases in your home: combustion spillage
• Natural Resources Canada — Improving Window Energy Efficiency

Methodology

Research method: ReadyHome started with Canadian keyword clustering and a dedicated technical research dossier, then independently re-checked the claims against current NRCan guidance and other primary/technical sources before writing this page. We deliberately excluded attractive-but-weak numbers where the evidence did not support a universal value, including fixed window-film R-values, exact heating-bill savings, universal humidity targets, fixed outage-survival times, and single pressure/airtightness thresholds for combustion safety.

Tool method: the “What’s Causing Your Draft?” helper is deterministic decision support. It maps the location and operating condition you select to a diagnostic path; it does not assign probabilities, estimate heat-loss percentages, or recommend a specific brand/product.

Authorship: Chris Gaglardi receives research and methodology credit for the ReadyHome implementation. This page does not present him as an energy advisor, HVAC contractor, window installer, or building scientist.