How can I reduce drafts and heat loss around windows and exterior doors?

Quick answer

Reduce drafts and heat loss by sealing air leaks with weatherstripping, door sweeps, and high-quality caulk; filling larger gaps with low-expansion spray foam; adjusting thresholds and hinges for a tight fit; and adding storm windows/doors or window film and insulated shades for extra thermal performance.

Why this works

Most heat loss around windows and exterior doors comes from uncontrolled air leakage through gaps, cracks, and poor compression at seals. Air sealing stops cold air from entering and warm air from escaping, which improves comfort and lowers energy bills. You’ll feel the difference immediately, especially on windy days.

Find the leaks first (5–15 minutes per opening)

• Smoke test: Close windows/doors and switch off HVAC. Hold an incense stick or a thin strip of tissue near suspect areas. If the smoke/tissue wavers or gets pulled in, you’ve found a leak.
• Light test: At night, have someone shine a flashlight from outside. Light shining through reveals gaps.
• Dollar-bill test (doors): Close the door on a dollar bill. If it slides out easily anywhere around the perimeter, you need more compression.

Tools and materials

• Hand tools: Utility knife, tape measure, screwdriver/driver bits, pry bar (to remove interior casing), miter shears or tin snips (for V-strip), caulk gun
• Sealing products:
  • Interior/exterior caulk: 100% silicone (windows), polyurethane, or high-quality acrylic latex with silicone
  • Low-expansion spray foam labeled “for windows & doors”
  • Backer rod (foam) for gaps 1/4–1/2 inch
  • Weatherstripping: adhesive foam, silicone bulb, EPDM, spring bronze/V-strip, or magnetic (steel doors)
  • Door sweep: silicone/rubber fin or brush; or an automatic door bottom for premium fit
  • Adjustable threshold (if present) or replaceable bulb gasket
• Cleaning: Denatured alcohol or mild cleaner, rags
• Optional: Window shrink-film kit, rope caulk, storm window/door kits, insulated cellular shades
• Safety: Cut-resistant gloves, eye protection, mask for spray foam/old dust

Recommended specs

Gaps: 1/16"–1/8" = caulk; 1/8"–3/8" = backer rod + caulk; 1/4"–3/4" (hidden frame gap) = low-expansion foam
Backer rod: size 25–50% larger than gap
Caulk beads: ~1/8"–3/16"; tool to concave profile
Door reveal: even 1/8" around; sweep clearance to threshold ~1/16"
Weatherstrip compression: light contact all around; no bowing of door/window

Step-by-step: Windows (30–60 minutes each)

1. Clean and prep: Wipe interior and exterior perimeters. Remove loose, cracked caulk. If comfortable, pop interior casing off with a thin pry bar to access the frame-to-stud gap.
2. Seal the big hidden gap: Lightly mist with water (helps foam cure). Apply low-expansion foam around the frame. Don’t overfill—foam grows. After curing, trim flush with a utility knife.
3. Caulk the interior trim: Use backer rod where needed, then run a smooth caulk bead along the trim-to-wall and trim-to-frame joints. Tool the bead.
4. Caulk exterior: Use paintable polyurethane or exterior-grade silicone along the window frame-to-siding joint. Do not block weep holes on window frames.
5. Weatherstrip moving parts:
   • Double-hungs: Add V-strip or silicone bulb along the meeting rails and side jambs if factory seals are worn.
   • Casements/awnings: Replace compression gaskets if flattened or cracked.
6. Extras for tough winters: Apply clear shrink-film on the interior (15–20 minutes). It’s a cheap, high-impact fix for drafty windows.

Time/cost: $10–25 in materials per window (caulk, foam, small weatherstrip); shrink film kits run $8–12 per window.

Step-by-step: Exterior doors (45–90 minutes)

1. Inspect and adjust: Tighten hinges. If the latch side isn’t pulling tight, adjust the strike plate or shim the top hinge slightly to improve reveal and compression.
2. Replace perimeter weatherstripping: Choose a system that matches your jamb:
   • Kerf-in bulb seals (most newer doors): Pull out the old, press in new
   • Surface-mount V-strip or silicone bulb for older jambs
   • Magnetic weatherstrip for steel doors provides excellent seal
3. Install or upgrade the door sweep: Choose a fin-style rubber/silicone sweep for smooth thresholds; brush sweeps work well over uneven surfaces. Set the sweep so it just kisses the threshold across the entire width.
4. Adjust/replace threshold: If it’s adjustable, turn the screws to raise until the sweep seals evenly without dragging. Replace worn threshold gaskets.
5. Caulk and foam: Seal the interior and exterior trim joints. If the interior casing comes off, foam the frame-to-stud gap as with windows.

Time/cost: $20–60 per door (weatherstrip + sweep + caulk). An adjustable threshold adds $30–80 if replacement is needed.

Tips for best results

• Work in mild weather (40–90°F) so caulk adheres and cures well.
• Clean surfaces and let them dry before applying adhesives or caulk.
• Tool caulk with a wet finger or caulk tool for a neat, long-lasting joint.
• For very irregular gaps, spring bronze or V-strip adapts better than foam tapes.
• Layer solutions: air seal first, then consider thermal upgrades like cellular shades or storms.

Common mistakes to avoid

• Over-foaming window/door frames (can bow them). Always use low-expansion foam and light passes.
• Using interior-only caulk outdoors, or cheap painter’s caulk in high-movement joints.
• Blocking window weep holes or siding drainage paths with caulk.
• Installing a sweep too low so the door drags, wearing the seal quickly.
• Skipping backer rod on wide joints, which leads to premature caulk failure.

Safety

• Wear eye protection and gloves while foaming or cutting old caulk.
• Homes built before 1978 may have lead paint. Avoid sanding; use safe removal methods or consult a certified pro.
• Ventilate when using solvent-based products. Keep ignition sources away from expanding foam.
• After major air sealing, verify combustion appliances vent properly; keep CO detectors functional.

Supplemental upgrades

• Insulated cellular shades or tight-fitting curtains reduce heat loss at night.
• Interior or exterior storm windows/doors add a significant performance boost without full replacement.
• Outlet/switch gaskets on exterior walls can help in rooms that still feel drafty.

When to call a pro

• Persistent leaks despite new seals (door frame out of square or structural movement)
• Rot, water stains, or soft wood around frames
• Failed glass seals (fogged double panes)
• Historic windows needing specialized weatherstripping or sash repairs

With careful air sealing and a few adjustments, most homeowners can meaningfully cut drafts in a weekend and enjoy warmer rooms and lower bills all season.