How to Keep a Clean Home When Your AC Runs All Day

Your AC Is Working Hard — And Making a Mess

When Montreal gets into one of its long humid stretches, the air conditioner runs almost without stopping. That's great for comfort, but it creates a cleaning situation most people don't think about: constant air circulation means constant filtration, constant condensation, and a home that collects dust and mold risk in ways it simply doesn't during milder months. If you've noticed your surfaces getting dusty faster than usual, or a faint musty smell you can't locate, your AC system is likely part of the story.

Start With the Filter — Then Actually Look at It

The standard advice is to change or clean your AC filter every 30 days. In August in Montreal, when the unit is running 10 or more hours a day, that timeline is too relaxed. Pull the filter out and hold it up to the light. If you can't see light through it clearly, it needed cleaning a week ago.

• Window units: Slide the front panel off and rinse the foam filter under warm water. Let it dry fully before replacing it — a damp filter will grow mold faster than a dirty one.
• Central forced-air systems: Replace the disposable filter rather than cleaning it. Keep two spares on hand so there's no excuse to leave a clogged filter in place.
• Mini-splits (ductless units): These have washable filters on the indoor head unit. Wipe them down with a damp cloth every two weeks during heavy use.

A clean filter doesn't just improve air quality — it also means the unit doesn't have to work as hard, which keeps your electricity bill lower during peak billing months.

The Dust Pattern Will Tell You Where to Clean

With air moving constantly through a room, dust doesn't settle the way it does in winter. It lands on surfaces in the direct path of the airflow — the wall below a vent, the top of a bookshelf that's in line with the unit, the curtains nearest the window AC. Look for that directional pattern in your rooms and you'll know exactly where to focus.

Use a microfibre cloth slightly dampened with water on hard surfaces. A dry cloth in heavy summer dust just pushes particles back into the air where they'll recirculate. Wipe with the grain on wood surfaces and work from higher surfaces down so you're not re-dusting what you just cleaned.

Watch the Condensate Drain Pan on Window Units

Window AC units produce a significant amount of condensate — the water that drips from the front of the unit when it's working hard. Most of it drips outside, but some collects in a drain pan at the base of the unit inside your home. If that pan isn't draining freely, it becomes standing water, and standing water in a humid August apartment is a fast route to mold and a persistent sour smell.

Every two weeks, unplug the unit, slide it out slightly if you can, and check the pan. A few drops of white vinegar in standing water will slow bacterial growth. If you see any visible slime or discolouration on the pan itself, clean it with a solution of one part white vinegar to three parts water and a soft brush.

Don't Forget the Coils

The evaporator coils — the finned metal part at the back of the filter on a window unit — accumulate a fine layer of dust and sometimes mold spores over a summer. You don't need special products to clean them. A can of compressed air to loosen buildup, followed by a light spray of undiluted white vinegar and a gentle wipe with a soft brush, is enough for routine maintenance. Do this once at the start of August and once before you put the unit away in fall.

Manage Humidity Room by Room

Montreal in August is humid, and AC alone doesn't always bring indoor humidity to a comfortable level — especially in basement apartments or older homes without tight insulation. If you're seeing condensation on windows or walls, or if rooms feel clammy even with the AC on, a small portable dehumidifier running alongside your unit will protect surfaces, reduce dust mite activity, and make the space genuinely more comfortable rather than just cooler.

Empty and rinse the dehumidifier reservoir every day. It fills faster than you expect in high-humidity weeks, and a reservoir that sits full becomes another source of the musty smell you're trying to eliminate.

A Quick Weekly Routine for AC Season

• Check window unit filter every two weeks; clean if airflow looks restricted
• Wipe down surfaces in the direct path of AC vents with a damp microfibre cloth
• Inspect drain pan on window units and clear any standing water
• Empty and rinse dehumidifier reservoir daily during humid stretches
• Replace central system filters on a 30-day schedule — shorter if you have pets or do a lot of cooking

None of these tasks take more than a few minutes, but skipping them through a long Montreal summer adds up to a home that smells stale and surfaces that are harder to clean by the time fall arrives. Stay on top of it now and the end-of-season refresh becomes a lot less work.