Homeowners tend to spend energy money in the wrong order. Windows and equipment are visible and expensive, so they get the attention. Air leakage and attic insulation are invisible and cheap, so they get skipped. The Department of Energy consistently finds that air sealing and insulation deliver the largest return per dollar in most American houses.
A professional audit with a blower door and an infrared camera is worth paying for, and many utilities subsidize one. But you can find most of the same problems yourself with an afternoon and about fifteen dollars of supplies.
What you need
A stick of incense or a lit candle, a bright flashlight, a tape measure, a step ladder, a notepad, and a phone camera. If you own an infrared thermometer, bring it. Do this on a cold or very hot day when the difference between inside and outside is large, because that is what makes leaks visible.
Step one: depressurize the house
Close all exterior doors and windows. Turn off any combustion appliance with a standing pilot, including a gas water heater and a furnace, so you do not backdraft flue gases. Then turn on every exhaust fan you have: kitchen range hood, bathroom fans, and the clothes dryer on air-fluff. The house is now at slightly negative pressure and pulling outside air in through every gap.
Step two: walk the perimeter with the smoke
Hold the lit incense a few inches from each of these and watch the smoke. Where it bends sharply or gets pulled sideways, you have found a leak. Mark each one with a note or a piece of tape.
- Window sashes and the joint between the window frame and the wall
- Exterior door frames, thresholds, and mail slots
- Electrical outlets and switch plates on exterior walls
- Where the plumbing and dryer vent penetrate the wall
- Recessed ceiling lights on the top floor
- The attic hatch or pull-down stair
- The rim joist in the basement, where the floor framing sits on the foundation
- Around the chimney chase and any duct chase
Two of these usually surprise people. Recessed lights on a top floor ceiling are holes straight into the attic, and older non-airtight housings leak badly. The attic hatch is often nothing but a sheet of plywood resting in a frame, with no weatherstripping and no insulation on top of it.
Step three: go into the attic
Take the flashlight and the tape measure and be careful to step only on joists. Measure the depth of the insulation. Loose fill or batt insulation in a modern cold-climate attic wants to be roughly fourteen to twenty inches deep depending on material and climate zone, and a great many houses have half of that. Look for spots where insulation has been pushed aside for storage or where someone worked on wiring and never put it back.
While you are there, look for gray or dark staining on the underside of the roof deck, which indicates a moisture problem, and check that bathroom fans vent to the outside rather than dumping humid air into the attic. That mistake is extremely common and it damages roofs.
Step four: check the ducts
If your ductwork runs through an unconditioned attic, crawlspace, or garage, run the system and feel along the seams and joints for air escaping. Duct leakage of twenty to thirty percent is common in older systems and it is money going directly outside. Seal joints with mastic or foil tape rated for the purpose. Cloth duct tape is the one thing that should never be used on ducts.
Step five: put it in priority order
Sort what you found by cost. Weatherstripping a door, caulking a window frame, adding foam gaskets behind outlet plates, and insulating and weatherstripping the attic hatch are afternoon jobs with hardware store materials. Air sealing attic penetrations and adding insulation is a few hundred to a couple thousand dollars and frequently the single highest return item in the house. Duct sealing is contractor work but not expensive. Windows and equipment come last, after the envelope is tight, because a new furnace heating a leaky house is still heating a leaky house.
Before you hire anyone
Check your utility's website for a subsidized or free energy audit and for rebates on insulation and air sealing. Many states run their own programs as well, and federal tax credits have applied to certain efficiency improvements in recent years. Confirm current eligibility before you buy, because a rebate can change which project makes sense first.
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