How do I find and seal duct leaks?

Duct leaks are a common source of energy waste in Ottawa homes — a leaky duct system can reduce your heating and cooling efficiency by 20-30%, meaning you're paying to heat or cool your attic or crawlspace instead of your living areas.

Finding Duct Leaks

The easiest way to spot leaks yourself is to run your furnace or air handler and feel along accessible ductwork with your hand. You're looking for air blowing out at joints, seams, and connections — especially where sections of duct meet or where branches split off the main trunk. Visible signs include disconnected sections, gaps at joints, or duct tape that has dried out and pulled away (ironically, standard duct tape fails quickly in HVAC applications). You may also notice rooms that are consistently harder to heat or cool, or higher-than-expected energy bills.

Sealing Duct Leaks Yourself

For accessible ductwork in your basement or mechanical room, this is one of the few HVAC tasks a handy homeowner can tackle safely. The right product is mastic sealant — a thick, paste-like compound you brush on with a paintbrush or gloved hand over joints and seams. For larger gaps, embed fiberglass mesh tape into the wet mastic before it dries. UL 181-rated foil tape is also acceptable for metal ducts. Avoid standard hardware store duct tape — it dries out and fails within a few years.

Ottawa-Specific Context

Ottawa's climate makes duct sealing particularly worthwhile. With heating seasons running roughly October through April, even moderate duct leakage adds up significantly on your gas bill. If your ducts run through an unheated garage, attic, or crawlspace, sealing and insulating those sections should be a priority. Enbridge and Hydro Ottawa sometimes offer rebates tied to home energy audits — a certified energy advisor can perform a blower door test combined with duct pressurization testing to precisely measure your leakage rate, which is far more accurate than a manual inspection.

When to Call a Professional

If your ductwork is in hard-to-reach areas, if you suspect significant leakage throughout the system, or if you're seeing major comfort or efficiency problems, professional duct sealing or duct cleaning is the better route. Technicians can also identify if ducts are improperly sized or if there are design issues causing the problem. If you notice any issues near your furnace's heat exchanger or flue connections, stop and call a professional immediately — those areas involve combustion gases and are not DIY territory.

For a whole-home duct assessment or professional sealing, Ottawa HVAC Pro can inspect your system and give you an honest picture of where your losses are. Request a quote and we'll take a look.