Air Sealing Your Home: Find Leaks, Seal Them and Stay Safe

Air sealing is one of the cheapest ways to make a home more comfortable and lower heating and cooling bills. The U.S. Department of Energy (DOE) calls it one of the most cost-effective upgrades you can make. This guide shows where homes really leak, how to find leaks, what you can seal yourself, and the safety checks that keep a tighter home healthy.

Why does air sealing matter?

Air leaks let heated or cooled air escape and pull outside air in, so your heating and cooling equipment works harder. ENERGY STAR says that if you added up all the leaks, holes and gaps in a typical home’s envelope, it would equal having a window open every day of the year. Sealing them improves comfort and cuts waste.

DOE explains it with a simple picture. Insulation is like a sweater: it keeps you warm, but wind blows right through it. Air sealing is the windbreaker. Without it, even a well-insulated house can feel drafty, with cold floors, hot upstairs rooms and uneven temperatures.

The U.S. Environmental Protection Agency (EPA) estimates homeowners can save an average of 15% on heating and cooling costs, or 11% of total energy costs, by air sealing and adding insulation in attics, floors over crawl spaces and basements (ENERGY STAR, accessed October 2026). Leaks also carry moisture into walls and attics, where DOE notes it can warp wood and lead to mold.

Where do homes leak the most?

The most noticeable drafts are around windows and doors, but the biggest leaks are usually hidden. DOE identifies at least 19 key air sealing areas in a typical house. The attic floor and the basement or crawl space are usually the top targets, because warm air rises out through the top of the house and pulls cold air in at the bottom.

This “stack effect” means a hole in your attic floor matters more than a similar-sized gap in a middle-floor wall. Here are common leak spots and what fixes them, based on DOE and ENERGY STAR guidance:

Don’t forget the ducts

If your ducts run through an attic, crawl space or garage, leaks there waste air you already paid to heat or cool. ENERGY STAR says about 20% to 30% of the air moving through a typical duct system is lost to leaks, holes and poorly connected ducts. Seal reachable joints with mastic or metal tape, not cloth duct tape, which ENERGY STAR says is not long-lasting.

How can you find air leaks yourself?

You can find many leaks on a cool, windy day with simple tests. ENERGY STAR suggests holding a lit incense stick near likely leak spots and watching for smoke that wavers or gets pulled in or out, feeling for cool air with a damp hand, and looking for daylight around door and window edges.

Try these checks:

1. Smoke test: Close windows and doors, turn on bathroom and kitchen exhaust fans to pull air through leaks, then move a lit incense stick slowly along window trim, outlets, baseboards, attic hatches and plumbing holes.
2. Damp hand test: Wet your hand and run it along the same spots. Leaks feel cool.
3. Paper test: Close a door or window on a sheet of paper. If you can pull it out without tearing it, the seal is weak.
4. Light test: At night, shine a flashlight from one side of a door while someone watches from the other. Light means a gap.
5. Attic check: Look for dark, dirty patches on attic insulation. Dust filtering through the insulation marks where air flows up from the house.

These checks find the obvious leaks. DOE notes that the DIY approach will not catch small, hard-to-find leaks, especially in attics where they are buried under insulation.

What does a blower door test show?

A blower door test measures how leaky your whole house is and helps find hidden leaks. An auditor uses it with an infrared camera to see where outside air is coming in. Testing before and after sealing shows how much the work actually helped and whether the home needs added ventilation.

DOE points to two nationally recognized certifications for home energy professionals: the Building Performance Institute (BPI) Building Analyst and the Residential Energy Services Network (RESNET) Home Energy Rating System (HERS) Rater. A blower door test is usually part of a full professional home energy audit, and many utilities subsidize audits.

How do you seal air leaks yourself?

Start with the biggest, easiest-to-reach leaks, then work down to small gaps. Match the material to the gap: caulk for narrow, still cracks, spray foam for wider holes, and weatherstripping for parts that move, like doors and window sashes. Expect most DIY air sealing to cost little in materials.

Choose the right material

• Caulk: for gaps of 1/4 inch or less. Acrylic latex is easy to clean up and paintable; silicone handles moisture well. ENERGY STAR says to clean the crack first and smooth the bead with a finger or tool.
• Backer rod: a foam rope pressed into wider cracks before caulking. Press it slightly below the surface, but don’t force it so hard that it bends a window or door frame.
• Expanding spray foam: ENERGY STAR recommends it for gaps from 1/4 inch to 3 inches. For gaps around windows and doors, use a non-expanding foam made for windows and doors so it doesn’t bow the frame.
• Weatherstripping: DOE lists tension seals, felt, reinforced foam, rubber tape, door sweeps, metal gaskets and bulb or fin seals. Pick a type that fits the gap and compresses when the door or window is closed.
• High-temperature caulk and metal flashing: the only correct choice around hot flues and chimneys.
• Rigid foam or foil board: to cover large openings like dropped soffits in the attic.

A simple order of work

1. Seal the attic first: plumbing and wiring holes, top plates, the hatch, and openings over soffits and kneewalls. Our attic insulation guide explains how this fits with adding insulation.
2. Seal the basement or crawl space rim joists and sill plate. ENERGY STAR says to seal the top and bottom of the inside of each rim joist cavity.
3. Seal holes where pipes, wires, the dryer vent and outdoor faucets pass through exterior walls.
4. Add foam gaskets behind outlet and switch covers on exterior walls.
5. Weatherstrip exterior doors and add door sweeps. Weatherstrip and caulk windows, or use plastic window film kits for the winter.
6. Seal reachable duct joints with mastic or metal tape.

ENERGY STAR estimates a DIY attic air sealing project takes 1 to 3 days and under $100 in materials. Windows themselves leak too: if yours are old and drafty, see our guide to energy-efficient windows and storm windows before deciding on replacement.

Can sealing make your home unsafe?

It can if you ignore ventilation and fuel-burning appliances. A tighter home holds in moisture and pollutants, and ENERGY STAR warns that sealing can cause naturally venting gas or oil water heaters and furnaces to backdraft exhaust gases, including carbon monoxide, into the house. Professional testing before and after sealing prevents this.

Combustion safety testing

DOE says that before sealing, it’s essential to know how much fresh air the house needs and how combustion appliances such as furnaces, water heaters, stoves and fireplaces get their air. ENERGY STAR recommends that a home performance contractor test oil- and gas-fired appliances before and after air sealing.

That testing is often called a combustion appliance zone (CAZ) test. The technician runs exhaust fans, the clothes dryer and the furnace blower together to create a “worst case” pressure in the room with the furnace or water heater. Then they check that exhaust still goes up the flue and measure carbon monoxide. If an appliance fails, it must be fixed before or alongside the sealing work.

Ventilation, carbon monoxide and radon

• Exhaust fans: make sure kitchen, bathroom and dryer vents go all the way outdoors, not into the attic.
• Mechanical ventilation: ENERGY STAR notes that a tight home may need added mechanical ventilation to keep indoor air safe. A blower door test tells your contractor whether you need it.
• Carbon monoxide alarms: EPA cites Consumer Product Safety Commission guidance to install CO alarms on each level of the home and outside sleeping areas. EPA also recommends having furnaces, flues and chimneys inspected and tuned up by a trained professional every year.
• Radon: EPA says all homes should be tested for radon. ENERGY STAR recommends testing after you reduce air leaks, and testing first in high-radon areas.

How much does air sealing save and cost?

DIY air sealing usually costs little, and EPA estimates that air sealing plus insulation saves an average of 15% on heating and cooling costs. Savings are larger in colder climates and leakier, older homes. Professional work costs more but finds hidden leaks, so get at least three written quotes that list the areas to be sealed.

In EPA’s modeling for the ENERGY STAR savings estimate, a 1970s or 1980s home with a 25% cut in air leakage plus added insulation saved about 16% of total energy costs in the coldest climate zone and about 5% in the warmest (ENERGY STAR methodology, accessed October 2026). Your results will depend on how leaky the house is now, your climate and your energy prices.

Help paying for it in 2026

• No federal tax credit for 2026 work: the 25C Energy Efficient Home Improvement Credit, which covered air sealing materials, does not apply to property placed in service after December 31, 2025. Work placed in service in 2025 may still be claimed on a 2025 return; confirm with a tax professional.
• State Home Energy Rebates: the HEEHR program has a statutory maximum of $1,600 for insulation, air sealing and ventilation for income-qualified households, and under DOE Program Notice 26-2 (effective May 29, 2026), households generally must address insulation and air sealing before getting appliance rebates. Only some states run these programs; see our state-by-state rebate guide.
• Utility programs: many utilities offer free or discounted audits and air sealing rebates.
• Free weatherization: DOE’s Weatherization Assistance Program serves income-eligible households, generally up to 200% of the federal poverty guidelines. Learn more in our guide to energy bill help and weatherization.

Bottom line

Air sealing is a low-cost, high-value fix. Focus on the attic floor and basement rim joists first, use caulk, foam and weatherstripping where each fits, and seal ducts with mastic or metal tape. If you burn gas, oil or propane at home, install CO alarms and have a professional test your appliances before and after sealing. Then add insulation on top of the sealed surfaces.