How to Check Air Ducts

If your HVAC system runs constantly but some rooms never seem comfortable, the problem might not be the equipment. It could be the ducts. Leaky ductwork can waste 20-30% of your conditioned air before it ever reaches the vents. That’s like throwing away a quarter of every dollar you spend on heating and cooling.

Why This Matters

Your ducts are the delivery system for heated and cooled air. When they leak:

• Conditioned air escapes into attics, crawlspaces, and walls
• Energy bills climb because the system runs longer
• Rooms stay uncomfortable no matter how you set the thermostat
• Dust and contaminants get pulled into the system from unconditioned spaces
• System lifespan shortens from the extra workload

Most duct problems are invisible from the living space. You have to go looking for them.

Where to Check

Not all ducts are accessible, but check what you can reach:

• Attic – Look for disconnected joints and crushed flex duct
• Basement or crawlspace – Check the main trunk lines and branch connections
• Garage – Often the forgotten zone with exposed ductwork
• Behind access panels – Where ducts connect to the air handler
• At register boots – Where ducts meet the floor or ceiling vents

What to Look For

Shine your flashlight along the duct runs and check for:

1. Disconnected sections – The most obvious and common problem
2. Visible gaps or holes – Even small gaps matter over time
3. Damaged or missing insulation – Causes condensation and energy loss
4. Crushed or kinked flex duct – Restricts airflow significantly
5. Dirty streaks around joints – Dust patterns reveal air leaks
6. Tape peeling off – Cloth duct tape dries out and fails

DIY Fixes

Some problems you can handle yourself:

• Reconnect separated joints – Push them back together and secure with screws or straps
• Seal small gaps – Use mastic sealant or UL-listed metal tape (foil tape)
• Avoid regular duct tape – It dries out and fails within a year or two
• Reattach loose insulation – Use insulation tape or mechanical fasteners

Warning Signs of Bigger Problems

If you notice these, the issue goes beyond simple duct checks:

• Excessive dust throughout the house
• Strong musty smell when the system runs
• Unexplained increase in allergy symptoms
• Hot or cold spots that won’t go away
• System runs constantly but can’t maintain temperature

These could indicate problems inside walls, under floors, or with the equipment itself.

DIY vs. Call a Pro

DIY: Visual inspection of accessible ducts and sealing small, obvious leaks with proper materials.

Call a pro: Full duct inspection with pressure testing, duct cleaning, major repairs, or adding new runs. If you suspect major leakage but can’t find it, a pro with diagnostic tools can pinpoint the problems. Find an HVAC contractor →

How Often to Check

• Quick visual check: Once a year, ideally before heating or cooling season
• Full inspection: Every 3-5 years or when upgrading HVAC equipment

The Bottom Line

You can’t fix what you can’t see. Take thirty minutes once a year to crawl around and look at your ducts. Finding one disconnected joint could save you hundreds on energy bills and finally make that back bedroom comfortable.