How Much Does Air Sealing Actually Save? A Room-by-Room Leak Guide

Air leakage accounts for roughly 25-40% of the energy a typical home uses for heating and cooling, according to figures published by ENERGY STAR and the Department of Energy. That's a bigger single category than most people expect — bigger than what a lot of homeowners assume is "just the furnace being old."

Where leaks actually rank, by typical impact

Not all leaks are equal. Building science research consistently points to the same top offenders, largely because of the "stack effect" — warm air rises and escapes through the attic, pulling cold outside air in through the basement or crawlspace to replace it, like a slow chimney running through your whole house.

What sealing these leaks actually saves

EPA's modeling — built on the DOE-2 simulation engine and validated against field data from building science contractors — estimates that a knowledgeable homeowner or contractor can typically achieve about a 25% reduction in total air infiltration through targeted sealing. Combined with attic, crawlspace, and rim joist insulation, EPA estimates this saves an average of 15% on heating and cooling costs, or about 11% on total home energy costs — with the ceiling higher in older, leakier homes and lower in newer, tighter construction.

Air sealing before insulation, not after

A common and costly mistake: adding attic insulation without air sealing first. Insulation slows heat conduction — moving through solid material — but does very little to stop air infiltration — air physically moving through gaps. Blowing loose-fill insulation over unsealed bypasses buries the leaks under a layer of material that makes them far more expensive to find and fix later, while doing little to actually stop the airflow. Sealing always comes first.

DIY vs. professional sealing

Reasonable DIY projects: caulking around window and door trim, foam gaskets behind outlet and switch plates, weatherstripping on exterior doors, sealing the attic hatch with foam tape, and a chimney balloon for an unused fireplace flue.

Better left to a professional: attic bypass sealing around chimney chases and recessed lighting (often requires fire-rated materials and working safely on trusses), rim joist sealing in a finished basement (may require accessing behind drywall), and anything requiring a blower door test to actually verify the work — which is the only reliable way to confirm how much you improved, versus guessing.

FAQ

Can a house be sealed too tightly? Yes — homes tighter than roughly 3 ACH50 need mechanical ventilation (an ERV or HRV) to maintain healthy indoor air quality, since natural infiltration is no longer providing enough fresh air exchange. This is a real consideration for deep energy-retrofit projects, less of a concern for typical sealing work on an older leaky home.

How do I know if my home needs a blower door test, or if I can just seal the obvious gaps myself? DIY sealing of obvious gaps (door weatherstripping, outlet gaskets, visible window gaps) is reasonable as a first step regardless. A blower door test becomes valuable when you want to prioritize spending on a leaky older home, verify that professional work was actually effective, or determine whether the home is tight enough to need mechanical ventilation.

Does air sealing help with cooling costs too, or just heating? Both — the same leaks that let warm air escape in winter let cool, conditioned air escape in summer (and let hot, humid outside air in), so the ~25-40% air-leakage energy share applies to both heating and cooling seasons.

See how air sealing changes your numbers with our Home Energy Savings Calculator. Found an error? See our Corrections Policy.