Air Quality & Ductwork Questions, Answered

Professional duct cleaning for a typical GTA house costs $300 to $700, depending on home size, number of vents, and system accessibility.

Every 3 to 5 years is a reasonable interval for most GTA homes — duct cleaning is not an annual service, despite what telemarketers suggest.

Most Toronto homes with forced-air heating drop to 15–25% relative humidity in January — well below the healthy 30–40% winter range.

A forced-air house gets dusty when the return side of the system pulls in dust faster than the filter can catch it.

Duct cleaning helps allergies when the ducts are genuinely contaminated: visible dust build-up, mould after a leak, pest debris or renovation dust.

Most of the time a furnace humidifier stops working because the water panel is crusted with minerals, the solenoid valve is not opening, or the bypass damper was left in the summer position.

If your house was built in the last decade, you likely have an HRV already — Ontario's Building Code requires mechanical ventilation in new houses, and since the 2017 SB-12 energy-efficiency update most builders meet it with an HRV.

Condensation forms on windows in winter when indoor air holds more moisture than the cold glass can keep as vapour, so it condenses on the coldest surface in the room.

UV lights in HVAC systems work for one job: a UV-C lamp aimed at the evaporator coil and drain pan stops mould and biofilm from growing there, which prevents the musty smell and coil fouling of humid summers.

Yes.

Work from the room back to the furnace: open the register fully, find the balancing damper on that branch in the basement and open it, then check the run for crushed flex duct, a disconnected boot or too many elbows.

Vents whistle when air is forced through an opening that is too small for it.

No — closing vents in unused rooms does not save energy in a forced-air system and often costs it.

Dryer vent cleaning typically costs $100–$200 when added to a duct cleaning visit.

No air coming out of your vents means one of two things: the blower is not turning, or it is turning and the air is blocked.

A furnace humidifier leaking water has one of three causes: a blocked drain or scaled water panel overflowing the tray, a solenoid valve stuck open and feeding water with the furnace off, or a leak on the supply side at the saddle valve or feed tube.

Yes, run your AC during wildfire smoke.

The signs of a blocked dryer vent are loads that need two cycles, a dryer top and laundry room that get hot, a burning-lint smell, and an outside vent flap that barely opens while the dryer runs.

Weak airflow from your vents is caused by a restriction or by a blower that is not moving enough air.

You know there is mould in your air ducts when three things line up: a musty smell that appears only while the fan runs, visible fuzzy or slimy growth on registers, the coil or the drain pan, and a moisture source to feed it.

An HRV freezes up when its defrost cycle fails or cannot keep pace.

A basement is humid in summer because warm, moist outdoor air cools against foundation walls and a slab that stay near ground temperature, and cooler air holds less water, so relative humidity jumps.

Vents smell like sewage when sewer gas gets into the return air, most often from a basement floor drain whose trap has dried out beside the furnace, or from a condensate line piped into a drain with no trap.

An HRV gets loud when something interferes with its fans or its airflow: worn motor bearings grind or squeal, ice or debris on a fan wheel thumps, a core put back wrong after cleaning rattles, a failing defrost damper clicks, and clogged filters or outdoor hoods whistle.

Yes, run your HRV in summer, but on low or an intermittent setting such as 20 minutes on and 40 off, and turn the dehumidistat on the wall control to OFF.

Set a basement dehumidifier to 45–50% relative humidity in summer.

Condensation forms on ducts when the metal is colder than the dew point of the air around it.