Signs Your Air Ducts Are Leaking (and What It Costs You)

Leaking air ducts are one of the most common reasons Bay Area homeowners see high utility bills and rooms that never seem to reach the right temperature. If your HVAC system runs constantly but certain rooms stay stuffy or cold, there’s a good chance conditioned air is escaping before it reaches you.

What leaking ducts actually do to your home

When ducts leak, your system is blowing paid-for air into your attic, crawl space, or wall cavities instead of into your living areas. The equipment works harder, runs longer, and wears out faster. ENERGY STAR puts duct leakage in typical homes at 20 to 30 percent of total airflow, meaning up to a third of what your system produces never reaches the rooms it’s supposed to.

That shows up on your bill every month.

The most common symptoms

Rooms that won’t stay comfortable. Hot spots in summer, cold spots in winter, one bedroom always off from the rest of the house. If closing or opening registers doesn’t help, it’s often duct leakage rather than an equipment problem.

Bills that jumped without an obvious cause. A spike in PG&E charges that doesn’t match a change in weather or usage is worth investigating. Duct sealing is frequently the fix nobody thinks to look for first.

Excess dust on furniture and registers. Return-side leaks are particularly bad for this. When return ducts leak, they pull in unconditioned air, and if that air comes from an attic or crawl space, it brings dust, insulation particles, and whatever else is up there. If you’re wiping down the same surfaces every week, that’s a signal.

System running almost continuously. If your thermostat never reaches setpoint because too much air is lost in transit, the system just keeps running.

Visible damage you can see. Sometimes it’s obvious: disconnected flex duct in the attic, a joint that separated, tape that’s peeling off. A lot of duct connections were never sealed properly to begin with, especially in older Bay Area homes with original 1970s or 80s ductwork.

How we actually find leaks

The quick visual check is a starting point, but duct leakage isn’t always visible. The reliable method is a duct pressurization test. A technician seals off your supply and return registers, attaches a calibrated fan to the system, and pressurizes the ducts. Software measures exactly how much air escapes. That tells you both the total leakage rate and, combined with pressure measurements at individual sections, where the worst leaks are.

Thermal imaging cameras help with in-wall or in-ceiling runs where you can’t see anything directly. An infrared camera shows temperature differences that betray where conditioned air is escaping.

It takes a couple of hours done right. Anyone offering a “duct inspection” that’s just a flashlight in the attic isn’t giving you reliable data.

What you can check yourself

Take a look at any accessible ductwork in your attic or crawl space. If you see a connection that’s obviously pulled apart or tape that’s completely failed, you’ve found a contributor. Note where it is.

That said, even an obvious disconnection usually has a cause: poor original installation, vibration, support failure. Reattaching it without understanding why it separated puts you back in the same spot within a year. And anything near the air handler plenum, inside a finished wall, or requiring mastic sealant is not a homeowner repair. The plenum is under the most pressure; sealing it wrong changes airflow balance across your whole system.

The useful thing you can do: note what you saw and where, and tell the tech when they arrive. That saves diagnostic time.

California Title 24 also requires duct systems to meet leakage standards when HVAC equipment is replaced. If you’re due for a new system and you have an older duct network, a pressurization test upfront tells you whether you’re looking at just equipment or equipment plus duct work.

What it typically costs

Duct sealing costs vary depending on accessibility, system size, and the extent of leakage. Aeroseal (an aerosol-injection sealing method) runs higher than conventional mastic sealing but can reach leaks inside walls without cutting drywall. Manual mastic sealing is effective for accessible ductwork. Get a written quote that specifies the method and whether a post-seal blower test is included to verify the result.

I’m not going to give you a number here because a figure I cite today won’t match what’s accurate in your specific home. Any contractor who quotes over the phone without seeing the system is guessing.

Call us if you’re seeing this

If you’ve got more than one symptom above, or your utility bills have been climbing without explanation, get a proper duct leakage test. It’s a straightforward diagnostic, and you’ll have actual numbers instead of guessing.

Call us at (925) 999-4095. We’re available 7AM to 7PM, seven days a week. We’ll get you on the schedule fast, often same or next day when we can. We’ll do the pressurization test, show you what we find, and tell you straight what it would take to fix and whether it makes sense before anything else. No commitment to proceed.

Key takeaways

• ENERGY STAR puts duct leakage in typical homes at 20 to 30 percent of total airflow, so the air you pay to condition may never reach your rooms.
• Uneven temperatures, rising utility bills, and excess dust are the most common signs, not just noise or visible damage.
• A duct pressurization test is the only reliable way to quantify leakage; a visual inspection alone is not enough.
• Most duct repairs need a licensed technician. Improperly sealed connections change airflow balance across your whole system and can make the underlying problem worse.

Related questions

Written by Andrew Kuznetsov. Andrew is the founder and owner of Bay Area HVAC Service (ADRIUM Service Solutions). He holds a California Contractor License (CSLB #1136642), EPA 608 certification, and completed factory training at the Daikin/Goodman plant in Houston in 2025. He writes from direct field experience, not marketing copy.

Further reading

• Mitsubishi Hyper-Heat (H2i): How It Keeps Putting Out Heat When It Gets Cold in the Bay Area , Most people think heat pumps quit when it gets cold. Mitsubishi's Hyper-Heat (H2i) line is built to keep working as temperatures drop, which matters more here than folks expect, especially on cold mornings and up in the East Bay hills.
• Mitsubishi Mini-Split Blinking a Fault Light? What It Means and What to Do , A blinking light on your Mitsubishi indoor head is the system telling you something is wrong. Here is what the blink pattern means, the checks you can safely do yourself, and when to bring in a factory-trained tech.
• Why Your Mitsubishi Mini-Split Is Leaking Water Inside (and How to Fix It) , A Mitsubishi mini-split dripping water inside almost always comes down to condensate that can't drain. Here's what causes it, the safe checks you can do yourself, and when to call a tech.