How do I stop condensation dripping from my air conditioning ductwork in a humid Toronto summer?

Condensation dripping from air conditioning ducts is extremely common in Toronto's humid summers and indicates insufficient duct insulation. When cold supply air (typically 12-15°C) flows through ducts in warm, humid spaces like basements, attics, or crawlspaces, moisture in the air condenses on the cold duct surface and drips onto ceilings, floors, and belongings below.

The primary solution is proper duct insulation with a minimum R-8 duct wrap around all supply ducts in unconditioned spaces. Toronto's summer humidity levels regularly push the humidex above 40, creating perfect conditions for condensation on any cold surface. Supply ducts carrying air-conditioned air are essentially giant cold-water pipes running through your home — without adequate insulation, they will sweat profusely during humid weather.

Check your existing duct insulation first. Many GTA homes have inadequate insulation (R-4 or less) or damaged insulation with gaps, tears, or compression. The insulation must completely wrap the duct with no gaps, and the vapour barrier (usually foil facing) must face outward to prevent moisture penetration. Pay special attention to duct joints, fittings, and connections where insulation is often missing or poorly sealed.

Common problem areas in GTA homes include basement ductwork near foundation walls (where humidity is highest), ductwork in unfinished basements with poor ventilation, and any ducts running through crawlspaces or attached garages. Older homes in Toronto, Scarborough, and Etobicoke often have galvanized steel ducts with minimal or deteriorated insulation that needs complete replacement.

Immediate steps you can take: Ensure your basement has adequate ventilation and consider running a dehumidifier during peak summer humidity. Check that all supply registers are open — closing registers increases pressure in the duct system and can worsen condensation by making the remaining ducts even colder. Clean or replace your furnace filter, as restricted airflow makes the air conditioning coil work harder and produces colder supply air.

Professional solutions include re-insulating all supply ductwork with R-8 duct wrap, sealing duct joints with mastic to prevent air leakage, and potentially installing a whole-home dehumidifier integrated with your HVAC system. Some contractors also recommend upgrading to insulated flex duct or duct board for problem areas, though proper insulation of existing metal ductwork is usually more cost-effective.

Don't ignore this problem — condensation dripping from ducts causes water damage to ceilings, promotes mould growth on duct exteriors and surrounding materials, and wastes significant energy as your air conditioning system works harder to overcome heat gain through uninsulated ducts. In Toronto's climate, properly insulated ductwork isn't optional for air-conditioned homes.

Professional duct insulation typically costs $1,500-$4,000 for a whole-house upgrade, but the energy savings and comfort improvement make it one of the most cost-effective HVAC improvements you can make. Need help finding a ductwork contractor experienced with condensation issues? Toronto Ductwork can match you with local professionals who understand GTA climate challenges.