Drafty Windows in Winter: How to Find the Leak and Fix It Before You Replace Anything (NJ)

A window can feel drafty with no air coming through it at all. In winter the glass is usually the coldest surface in the room. The Efficient Windows Collaborative explains that when the gap between the glass temperature and the room gets too large, cold air forms near the window and drops to the floor.

A Lawrence Berkeley National Laboratory comfort study modeled this and found that for most residential-size windows the draft from a cold surface is typically small. Its authors suggest people often mistake the heat their body radiates toward a cold window for a draft, or are feeling real infiltration past poor weatherstripping. Weatherstripping cures the second problem, not the first, so test before you spend.

Air you can feel at the edges is a leak. A chill at the middle of the glass with still air is cold glass.

Use a windy day, or make wind. The Department of Energy's Building America Solution Center suggests closing every window and exterior door, opening the bathroom and laundry doors, and turning on all the exhaust fans so the house pulls outside air in through its leaks. Then move a tissue along every window edge. The DOE Energy Saver Guide adds a lit incense stick or smoke pen: if the smoke stream travels horizontally, you have found a leak. ENERGY STAR's paper test also works: close the window on a sheet of paper, and if it moves back and forth easily, the window could seal tighter. Keep any flame away from curtains.

Where the air shows up tells you the fix.

On a double-hung, the lock does more than keep the window shut. It draws the two meeting rails together against their seal. The Solution Center goes so far as to say that if a window has no lock, installing one will likely pull the sashes closer for a tighter seal. Lock it and rerun the paper test. If the lock turns but the rails still gap, the lock is worn or the keeper no longer lines up with it. Our hardware upgrades service covers that small repair.

The other mechanical cause is the balance, the spring-loaded part in the jamb that holds a double-hung sash where you leave it. When one fails, the sash creeps open, and a sash that will not stay shut will not stay sealed. Window balance and crank repair fixes that without replacing the window.

Original wood windows in older North Jersey houses use ropes and weights instead. The Solution Center lists three routes: restore them with new ropes or chains and cleaned pulleys, swap the weights for spring balances, or replace the window and seal and insulate the pockets. Historical sash restoration is the first route.

The Solution Center's rule is short: install weatherstripping in the framing of the parts that open, and use caulk on the seams in and around the trim.

On a double-hung, the Solution Center's weatherstrip table puts a tension seal, a V-shaped strip that springs open to bridge the gap, inside the track, and reinforced foam, vinyl or foam tape at the top and bottom of the sash. Felt is the weak choice: the table rates it least effective at stopping airflow and says to keep it away from moisture and friction. Tension seals can make a sash harder to move, so after installing any strip, check that it still closes fully and locks.

For the gap where the sashes meet, putty sealing cord goes in during fall and comes out in spring. Interlocking metal strips or silicone gaskets are the permanent versions. Casements and awnings close against a gasket, so look for one that is flattened or loose, and for a crank that no longer pulls the sash snug.

Caulk is for seams that do not move. Run it along a sash that is meant to open and you get a window that will not open and a bead that tears the first time it does. Behind interior trim, ENERGY STAR lists non-expanding foam made for windows and doors, caulk and backer rod. A Building America sheet adds that the foam must be low or no expansion so it does not bow the frame. ENERGY STAR suggests a professional when the trim is complicated or the house predates 1978.

If the leaks are many and small, or the glass is the problem, add a layer. The cheapest is heat-shrink plastic film: clear film on double-sided tape, tightened with a hair dryer. ENERGY STAR says it reduces drafts, helps the house feel warmer and cuts condensation moisture on the glass, and can eliminate air leaks around the window if it extends over the woodwork. It lasts one season, fixes no balance or rotted sill, and seals the sash shut while it is up.

For windows that still feel drafty after weatherizing, DOE suggests tight-fitting insulating shades, with curtains and shades closed at night and opened by day for the sun. The step up is a storm window: DOE says low-e exterior or interior storm windows can save 10% to 30% on heating and cooling costs, depending on the window already in the house. The Efficient Windows Collaborative puts the cut in heat loss at roughly one-third for a regular storm over a single-pane wood window and at least half with a low-e coating. In a thermal image published by the Solution Center, an interior storm panel read 50°F while the original glass beside it read about 0°F.

Two cautions. The room-side layer should be airtight, because the Solution Center warns that condensation can form between an interior storm and the original window if the storm leaks; our guide to winter window condensation covers what you may see. And repair the window first: cracked or rotting sills should be replaced before a storm goes in.

A bedroom window has to stay a way out. A sash sealed with film or caulk cannot be opened quickly, and the Solution Center's storm guidance says to match the opening style of the existing window for operability and egress. Use weatherstrip, not film or caulk, on bedroom windows meant for escape, and see our NJ bedroom egress window guide for what the rules require.

Freeing a painted-shut sash, planing an edge and sanding a sill all disturb paint, which in a pre-1978 house may contain lead. The EPA lists sanding, cutting and replacing windows among the activities that can create hazardous lead dust and chips.

The EPA says its Renovation, Repair and Painting Rule generally does not apply to homeowners working in their own homes, but it does apply if you rent out all or part of the house, which matters in a North Jersey two-family. The rule requires contractors working in pre-1978 homes to be lead-safe certified, and EPA recommends homeowners hire one, so ask whoever you hire for that certification. For your own work, EPA lists closing off the area with plastic sheeting, misting surfaces before sanding or scraping, a HEPA vacuum, a disposable N-100 respirator, and a heat gun kept under 1,100°F. If the sashes need real work, hand it off.

The Solution Center's interior storm guide calls peeling paint, cracks or rotten wood at the sills or trim often a sign of water intrusion, and says to plan on removing the trim to investigate. Its guides also say loose or water-damaged windows may need replacing, and that excessive deterioration or frame rot can mean full replacement. Glass fogged between the panes is a failed seal that no draft fix reaches.

If the room is still cold after these steps, compare what you found with our signs you need new windows. For a sash or hardware problem, window repair is where we start. If a lock adjustment and new weatherstrip fix it, that is the right outcome, and we will say so.

Every rule, test and figure above comes from these.