You feel cold air near a window, you check the lock, it’s closed, and the cold is still there. Frustrating. The honest answer is that “drafty window” covers about six different problems, and two of them are not air leaks at all.
Short answer: Most window drafts come from worn weatherstripping, cracked caulk at the frame joint, empty gaps behind the interior trim, or a sash that no longer closes tight because the frame has warped or shifted. But a good share of what people call a draft is cold glass, not moving air. Old single-pane and clear double-pane glass chills the air next to it, that heavy cold air slides down toward the floor, and your ankles read it as wind.
Key takeaways
- Air leaks and cold glass feel identical but need completely different fixes.
- Windows are only about 10% of a typical home’s total air leakage, according to U.S. Department of Energy figures. Floors, walls, and ceilings account for 31%.
- Weatherstripping, caulk, and loose hardware are cheap fixes and worth trying first.
- Rot, a racked frame, fogged glass, or a bad original install usually means the window itself is finished.
- If you do replace, the number that controls drafts is air leakage (AL), not U-factor. ENERGY STAR certified windows must test at 0.3 cfm/ft² or lower.
Is it really a draft, or is it just cold glass?
Do this before anything else. Hold the back of your hand about six inches from the center of the glass, then move it along the seam where the sash meets the frame.
| What you notice | What’s actually happening | What fixes it |
| Moving air at the sash joint, frame edge, or trim | Real air infiltration | Weatherstripping, caulk, hardware, or new window |
| Glass is cold but no air moves; cold pools at your feet | Convective downdraft off cold glass | Better insulating glass (Low-E, argon, warm-edge spacer) |
| You feel chilly sitting near the window even at 70°F | Radiant heat loss to a cold surface | Same as above |
| Whistling on windy days | Gap under pressure, usually a failed seal or unsquare sash | Adjust, re-seal, or replace |
That second and third row catch a lot of people. Your body loses heat toward any cold surface it can “see,” so a 40°F pane in a 70°F room makes you feel cold even in perfectly still air. No amount of caulk will change that. It is a glass problem.
The real causes of drafty windows
Worn weatherstripping
The strip of foam, felt, vinyl, or fin that compresses when the sash closes. It flattens, dries out, and stops springing back. On double hung windows this usually shows up at the meeting rail in the middle, where the two sashes overlap. It is the single most common cause and one of the cheapest to fix.
Cracked or missing caulk at the frame joint
Caulk seals the gap between the window frame and the surrounding wall. Indiana runs through dozens of freeze and thaw cycles every winter, and that movement shrinks caulk, pulls it off the substrate, and opens hairline splits. A 1/16 inch crack running the full perimeter of a window is not a small hole once you add it up.
Empty space behind the interior trim
This is the one nobody sees. Between the window frame and the framed opening in your wall there is a gap of roughly 1/4 to 1/2 inch. It is supposed to be filled with low-expansion foam or packed insulation and covered by a continuous air seal. On older homes it is often stuffed loosely with fiberglass, which stops nothing, or left completely empty. Air comes through the wall cavity, around the frame, and out from behind your trim. The window itself can be fine.
You can confirm this by pulling one piece of interior casing loose and looking. If you ever replace the unit, this is also the practical difference between a full frame and a pocket replacement, since only one of the two gives an installer access to that cavity.
Warped, rotted, or racked frames
Wood absorbs moisture, swells, dries, and eventually does not return to the shape it started in. Homes settle too, and a frame that is even slightly out of square no longer lets the sash seat evenly against its stops. Vinyl and aluminum can distort as well, especially cheaper vinyl on a south or west wall. Once the frame geometry is off, weatherstripping cannot bridge the gap.
A quick check: close and lock the window, then slide a dollar bill into the seam and pull. If it slides out with no resistance at several points along the sash, you have a fit problem, not a material problem.
Loose hardware and locks that aren’t doing their job
On most windows, the lock is not just a security device. It pulls the sashes together and compresses the weatherstripping. A worn cam lock, a stripped screw in the keeper, or a lock that turns but never tightens leaves the sash sitting loose in the opening. Casement and awning windows have the same issue through their crank and roto operator. When they are working, casement and awning units actually seal tighter than sliders because closing them wedges the sash against a compression gasket rather than sliding past a brush seal.
Single-pane or old clear double-pane glass
Glass conducts. A single pane has essentially no insulating value, and a clear double-pane from the 1980s or 1990s has no Low-E coating and no gas fill. These windows can be perfectly sealed and still make a room uncomfortable, for the downdraft and radiant reasons above. The U.S. Department of Energy estimates that heat gain and heat loss through windows account for 25% to 30% of residential heating and cooling energy use.
A failed insulated glass seal (the foggy one)
Worth clearing up, because the internet gets this wrong constantly. When the seal on an insulated glass unit fails, moisture gets between the panes and the argon escapes. You see haze, streaks, or a permanent smudge you cannot wipe off. That window has lost insulating performance and will feel colder. It is not leaking outdoor air into your room, though, because the sealed cavity is not connected to your living space. Fogged glass is a thermal failure, not an infiltration failure. Check your paperwork before paying for anything, since glass seal coverage is one of the more commonly honored parts of a window warranty.
Poor original installation
A window installed out of level, shimmed at the wrong points, over-fastened so the frame bows, or set without proper flashing will leak from day one. This is why a brand new window can feel drafty. It is also the reason install quality matters more than brand for comfort, and why a company that sends a trained crew rather than whoever is available that week tends to produce fewer callbacks.
Your windows may not even be the main problem
This is the part most articles skip. Air leakage is a whole-house behavior, not a window behavior. Here is how the Department of Energy breaks down where air actually escapes in an average home, as published by Purdue Extension:
| Leak location | Share of total air leakage |
| Floors, walls, and ceilings | 31% |
| Ducts | 15% |
| Fireplace | 14% |
| Plumbing penetrations | 13% |
| Doors | 11% |
| Windows | 10% |
| Fans and vents | 4% |
| Electrical outlets | 2% |
Then add the stack effect. Warm air rises and pushes out through leaks near the top of your house, mostly at the attic plane. That escaping air has to be replaced, so the house pulls cold outdoor air in through every low opening it can find: rim joists, basement penetrations, outlet boxes, and yes, your first-floor windows. In that situation the window is the symptom. Seal the attic and the “drafty” window often calms down.
Worth knowing: sealing air leaks and adding insulation typically saves 10% to 20% on home energy use, per DOE studies. That is usually cheaper per dollar of comfort than glass.
How to find your leak in about ten minutes
- Close and lock every window first. Half of reported drafts are an unlocked sash.
- Light a stick of incense on a cold, breezy day and move it slowly around the sash perimeter, the frame-to-wall joint, and the bottom of the trim. Smoke that bends or scatters marks the leak.
- Dollar bill test. Shut the window on a bill. If it pulls free without drag, the seal is not compressing there.
- Look for daylight around the frame with the lights off.
- Check the trim line specifically. Run your hand along the bottom edge of the interior casing. Cold air there points at the rough opening, not the window.
- Rattle the sash. Movement means worn jamb liners, a failed balance, or a frame that has gone out of square.
If you want the definitive version, a home energy assessment with a blower door test will pressure the whole house and rank every leak by size. Some Indiana utilities subsidize them.
Repair it or replace it?
| Cause | Repair first? | Realistic outcome |
| Worn weatherstripping | Yes | Often solves it completely |
| Cracked exterior caulk | Yes | Cheap, meaningful improvement |
| Loose lock or worn operator | Yes | Restores compression, quick fix |
| Empty gap behind trim | Yes, if trim is removable | Big improvement for low cost |
| Rotted or warped frame | No | Sealing cannot fix geometry |
| Fogged or failed glass seal | Glass unit or full window | Check warranty first |
| Single-pane glass | No | Comfort issue is the glass itself |
| Bad original installation | Usually no | Needs correct reinstallation |
Rough rule: if the window still opens, closes, and locks smoothly and the frame is sound, fix it. If the frame has moved or the glass is the issue, you are patching something that will keep failing. Our write-up on signs it’s time to replace rather than repair goes deeper on where that line sits.
If you replace: the number that actually controls drafts
Most people shop U-factor. U-factor measures conduction through the assembly, and it matters for heating bills, but it does not tell you how airtight the unit is. That is a separate rating.
- Air leakage (AL) is measured in cubic feet per minute per square foot of window area. ENERGY STAR requires 0.3 cfm/ft² or less on windows, sliding doors, and skylights. Premium units test at 0.1 or below. Budget vinyl often lands higher.
- U-factor for windows generally ranges from 0.10 to 0.60. ENERGY STAR recommends 0.22 or lower for northern climates. The windows we install reach as low as .17.
- Low-E coating, argon fill, and a warm-edge spacer are what keep the interior glass surface warm enough to stop the downdraft. Without those, the room will still feel cold near the window even with a perfect seal.
- ENERGY STAR climate zone matters. A window certified for the wrong zone is a common trick. Confirm the label matches the zone your address falls in.
EPA puts the average bill reduction from ENERGY STAR certified windows at about 12% nationwide compared with non-certified products. Comfort usually improves faster than the number suggests, because drafts and cold surfaces are what you actually feel.
If you are past the caulk-and-weatherstrip stage, our window replacement page covers the styles, glass packages, and install process we use across North Central Indiana.
Common questions
Why is my window drafty even when it’s closed and locked?
Usually flattened weatherstripping, a cracked caulk joint, or a frame that has shifted enough that the sash no longer seats evenly. If no air is moving at all, you are feeling cold glass rather than a leak.
Can new windows still feel drafty?
Yes, for two reasons. Either the install left the rough opening unsealed, or the draft was never coming from the window. Check the trim line and the rest of the house before blaming the unit.
Does plastic film or a draft snake help?
Film helps a little on single-pane glass by adding a dead air layer, and it does reduce the downdraft. Both are seasonal patches, not repairs.
Is a foggy window the same as a drafty window?
No. Fogging means the sealed glass unit failed. It costs you insulation value, but it does not let outside air into the room.
How cold should glass feel in an Indiana winter?
Cool to the touch is normal. Painfully cold, frost on the interior surface, or condensation running down onto the sill points to single-pane or failed glass.
Written by the team at The Window Shop Of North Indy, a local, owner-operated window and door replacement company serving Carmel, Fishers, Westfield, Noblesville, Zionsville, and the surrounding North Central Indiana communities. Questions about a specific window? Call (317) 689-0759 or email hello@windowshopindy.com.
