Seal air leaks before you add insulation

Seal the leaks first and insulate second. DOE's Energy Saver guide (2022) says that by sealing uncontrolled air leaks you can save 10%–20% on your heating and cooling bills. Owners start in the attic; renters start at doors, windows and outlets. Finding leaks takes a piece of paper and an incense stick or smoke pen, and the sealing materials are a small buy. The one condition: in a home with a gas or oil furnace, water heater or dryer, read what to check before sealing around gas appliances first.

Air moves through insulation, so the seal goes in first

DOE's 2022 guide gives the order: start by sealing air leaks, and after you complete air sealing, check whether you need to add insulation. ENERGY STAR's attic air sealing page shows why: dirty insulation is evidence that air is moving through it. ENERGY STAR's opportunity chart is blunt. Always do attic air sealing before adding insulation.

Together, the two jobs can provide up to a 10% savings on your annual energy bills, says ENERGY STAR's seal and insulate page. That figure covers sealing plus insulation and the whole bill; DOE's 10%–20% covers sealing alone and only heating and cooling. After sealing, attic insulation levels by climate zone set how much to add.

The biggest leaks hide in the attic and basement

Drafts show at windows and doors, but EPA's do-it-yourself sealing guide (2016) says the most significant air leaks in most homes are hidden in the attic and basement. ENERGY STAR's opportunity chart, effort chart and attic air sealing page rank the places and rate doing the work yourself; $ is under $100 and $$$$$ over $2,000.

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Renters work the bottom row. DOE's 2022 guide tells renters to use its tips and to encourage the landlord to follow them too.

Find the leaks with smoke and paper

On a windy day, DOE's 2022 guide says to carefully hold a lit incense stick or a smoke pen next to windows, doors, electrical boxes, plumbing fixtures, outlets, ceiling fixtures and attic hatches. Smoke that travels horizontally marks a leak. The same guide says to look for gaps, improperly applied caulk and weatherstripping, and doors and windows that don't close tightly. ENERGY STAR's window and door trim page adds a paper test: close the window on a piece of paper, and if it moves back and forth easily, thicker weatherstripping can make the window tighter.

Caulk what stays still, weatherstrip what moves

ENERGY STAR's attic air sealing page sizes the materials: caulk for holes of 1/4 inch or less, expanding spray foam for gaps of 1/4 inch to 3 inches. DOE's 2022 guide lists where they go. Weatherstrip doors and windows. Caulk and seal where plumbing, ducting or wiring comes through walls, floors and ceilings. Install foam gaskets behind outlet and switch plates. Check that fireplace dampers close properly; for a flue not in use, DOE suggests an inflatable chimney balloon, which deflates within seconds of contact with heat. A gas fireplace goes to a licensed gas fitter instead.

The attic hatch takes self-sticking weatherstrip and a piece of fiberglass or rigid foam insulation on its back, per EPA's DIY guide. Weatherstrip, outlet gaskets and a chimney balloon suit a renter. Standard caulk and foam are permanent, so in a rental they wait for the landlord's OK. Rented windows have removable fixes in the renter's window guide.

What sealing is worth on an average heating and cooling bill

Example, with published figures and one assumption. EIA's RECS 2020 table CE3.6 puts a single-family detached home's average 2020 spending at $625 for space heating and $350 for air conditioning, each per household using that end use. Adding the two for a home that uses both is the example's assumption: $625 + $350 = $975 a year. With DOE's 10%–20% from the 2022 guide, 10% of $975 is $97.50 a year and 20% is $195, in 2020 dollars. DOE's range is for sealing uncontrolled air leaks, not one drafty door; ENERGY STAR says door, window and wall leaks usually have the least impact on energy use.

Hiring out the attic costs more. ENERGY STAR's attic air sealing page rates a contractor at $$$ and 1 to 2 days. If cost is the barrier, free weatherization covers who qualifies.

Fuel-burning appliances, flues and old wiring go to a trade

Sealing can, in some cases, cause naturally venting combustion appliances to back-draft gases into the home, says ENERGY STAR's attic air sealing page, which suggests testing oil and gas appliances before and after sealing. EPA's DIY guide says to have your heating and cooling technician check a gas- or oil-fired furnace, water heater and dryer for proper venting; that is an HVAC contractor's job.

Three attic spots go to a trade. Around a furnace or water heater flue or a chimney, the same attic page calls for metal flashing and heat-resistant caulk, never spray foam; have an HVAC contractor seal it. The page says knob and tube wiring from before 1930 can be a fire hazard in contact with insulation; call a licensed electrician. Vermiculite insulation may contain asbestos, so leave it undisturbed until an approved lab has tested it, and hire a licensed asbestos abatement contractor if it must come out.