What is Air Sealing & Why Does It Matter?

Air sealing means finding and closing gaps, cracks, and holes in your home's exterior envelope. These openings let conditioned air escape and outside air infiltrate, forcing your HVAC to work harder.

The Problem: Your Home is Leaky

The average American home has enough air leaks to equal leaving a window open 24/7. These leaks:

• Waste 25-40% of heating/cooling energy
• Create uncomfortable drafts and cold spots
• Allow dust, pollen, and pollution inside
• Let moisture in, causing mold and rot
• Make insulation less effective

Key insight: Air sealing should ALWAYS be done before adding insulation. Insulation slows heat transfer but does nothing to stop air flow. Sealing first gives 2-3× better results.

Where to Find Air Leaks

Air leaks occur at every penetration through your home's envelope. Here are the biggest culprits, ranked by typical air loss:

Attic Access & Top Plates (30%)

The attic hatch and gaps where walls meet the attic floor are the biggest leaks. Warm air rises and escapes here constantly.

Plumbing & Wiring Penetrations (20%)

Every pipe, wire, and duct that passes through floors, ceilings, and walls creates gaps. Bathrooms and kitchens are worst.

Windows & Doors (15%)

Gaps around frames, worn weatherstripping, and poor seals let air flow around (not through) windows and doors.

Recessed Lights & Ceiling Fixtures (10%)

Non-IC rated can lights are basically holes to the attic. Each one can leak 10+ cubic feet of air per minute.

Outlets, Switches & Other (25%)

Electrical boxes, fireplace dampers, dryer vents, exhaust fans, baseboards, and foundation cracks make up the rest.

How to Find Air Leaks

Method 1: Visual Inspection

Walk through your home looking for obvious gaps:

• Daylight visible around doors/windows
• Gaps where pipes/wires enter walls
• Cracks in caulk around windows
• Missing weatherstripping on doors
• Gaps at baseboards (especially exterior walls)

Method 2: The Hand Test

On a cold/windy day, hold your hand near suspected leak areas. You'll feel cold air moving in. Check:

• Window and door frames
• Electrical outlets on exterior walls
• Attic hatch edges
• Where walls meet floors/ceilings

Method 3: Incense Stick Test

Light an incense stick and hold it near suspected leaks. Watch the smoke:

• Smoke wavers/blows: Air leak present
• Smoke rises straight: No significant leak

Best done on a windy day or with blower door test running (depressurizes house to exaggerate leaks).

Method 4: Professional Blower Door Test

For $200-400, an energy auditor will:

• Mount a powerful fan in your door
• Depressurize your home by 50 pascals
• Measure total air leakage (ACH50 rating)
• Use thermal camera to find exact leak locations
• Provide prioritized repair list

Worth it if you want precision. Many utilities offer free/subsidized audits!

Air Sealing Materials & Costs

Your Air Sealing Toolkit

Caulk (Silicone or Latex)

For gaps under 1/4 inch - windows, baseboards, trim

$4-8/tube

Expanding Foam (Great Stuff)

For gaps 1/4 to 3 inches - pipes, wires, large cracks

$6-12/can

Weatherstripping

For doors and windows - adhesive foam or V-strip

$5-15/roll

Door Sweeps

For bottom of exterior doors

$8-20/each

Outlet Gaskets

Foam pads behind outlet/switch covers

$5-10/pack

Attic Hatch Cover

Insulated cover with weatherstripping

$30-80

Caulk Gun

Reusable, one-time purchase

$8-15

Total Materials Cost

For complete house air sealing

$75-200

Air Sealing: Room by Room Guide

🏠 Attic (Start Here - Biggest Impact)

1. Seal attic hatch: Add weatherstripping around edges, install insulated cover on top
2. Seal top plates: Foam or caulk gap where interior walls meet attic floor
3. Seal pipe/wire penetrations: Foam around every pipe, wire, and duct that enters attic
4. Seal recessed lights: Install IC-rated covers or replace with airtight LED fixtures
5. Seal chimney chase: Use metal flashing and high-temp caulk (never foam near chimney!)
6. Seal duct boots: Mastic or foil tape where ducts connect to registers

🪟 Windows & Doors

1. Caulk exterior trim: Fill gaps between frame and siding outside
2. Replace weatherstripping: Remove old, apply new adhesive foam or V-strip
3. Install door sweeps: Attach to bottom of exterior doors
4. Add window film: Shrink-wrap plastic for single-pane windows (winter only)
5. Check lock operation: Locks pull sash tight against weatherstripping

🏚️ Basement & Crawlspace

1. Seal rim joist: Foam between floor joists where they meet foundation wall
2. Seal pipe/wire penetrations: Foam around all utilities entering from outside
3. Seal basement windows: Caulk frames, add weatherstripping if operable
4. Seal floor drains: Add water-trap cover if dry (allows sewer gas in)
5. Seal crawlspace access: Weatherstrip door or hatch cover

🛋️ Living Spaces

1. Install outlet gaskets: Foam pads behind all exterior wall outlets/switches
2. Caulk baseboards: Run bead along bottom where baseboard meets floor
3. Seal fireplace: Close damper, add chimney balloon when not in use
4. Seal dryer vent: Check exterior flap closes fully, replace if stuck open
5. Seal bath/kitchen fans: Add backdraft dampers if missing