Duct cleaning after a renovation or new build: the drywall dust risk

A renovation or a new build is the one time a duct system should be cleaned regardless of its age. Drywall sanding, cutting and framing put fine gypsum dust and sawdust into open ducts, and the furnace blower then spreads it through every room for months. The right time to book is after the final construction clean and before anyone moves in.

What construction leaves inside your ducts

During a build or a major renovation the duct system is usually the lowest open cavity in the house. Floor registers sit at foot level with the covers off, and the trunk lines in the basement ceiling are open at every branch until the drywallers close them in. Anything that falls, drifts or is swept toward a register ends up inside. On post-construction jobs across the GTA, our technicians regularly pull out:

• Drywall dust. The bulk of it. Sanding joint compound produces a fine, chalky gypsum powder that settles in a layer along the bottom of every supply run.
• Sawdust and wood shavings from framing, trim and flooring cuts.
• Insulation fragments, both fibreglass batts and loose-fill, blown in during the envelope work.
• Packaging: plastic wrap, cardboard, foam corners, fastener boxes and the paper backing from tile and flooring.
• Screws, nails, drywall anchors and drill shavings, which collect at elbows and at the bottom of vertical drops.
• Food wrappers, coffee cups and cigarette ends left by trades over several months on site.

Our pre-inspection photos are taken before anything is touched, and on a post-construction job they typically show a grey layer along the floor of the supply trunk. Those photos are emailed to you with the after shots so you can see exactly what came out.

Why fine gypsum dust is the worst case for a furnace

Ordinary household dust is mostly fabric fibre, skin, hair and pet dander. It is relatively coarse, and a good filter catches most of it. Drywall dust is different in three ways that matter to your equipment.

It is fine enough to pass a standard filter. A typical one-inch furnace filter is built for lint and hair, not for the powder that comes off a sanding sponge. A share of the gypsum goes straight through to the blower and the evaporator coil on every cycle.

It packs rather than tumbles. Because the particles are small and slightly abrasive, they wedge into the curved vanes of the blower wheel and into the fins of the air-conditioning coil. Once the blower vanes are caked, the wheel moves less air for the same motor effort. Once the coil fins are coated, heat transfer drops and the air conditioner runs longer to reach the thermostat setting. Both problems get worse the longer the dust sits, because summer humidity turns the coating on the coil into a damp paste that holds more dust.

It keeps coming back. A single dusting of the registers after the job does nothing for the layer inside the trunk. Every time the blower starts, air moving through the duct lifts a little more of that layer and carries it into the rooms. The fine grey film that keeps reappearing on furniture months after a basement finish is usually this.

The US Environmental Protection Agency gives the same advice from the other direction: during construction or renovation work that produces dust in your home, it recommends sealing off the supply and return registers and not running the HVAC system until the dust is cleaned up (EPA, Should You Have the Air Ducts in Your Home Cleaned?). In practice most GTA renovations run the furnace through the winter with the registers open, so a cleaning at the end is the fix for what already got in.

A brand-new home is not a clean duct system

Buyers of new builds in Vaughan, Markham and Milton often assume that new means clean. The ductwork is new, but it was installed early and sat open through every dusty stage of construction that followed: drywall, sanding, paint, flooring and trim. Builders do a final clean of the visible surfaces, and some run the furnace during the build to dry out the structure, which pulls that construction dust through the system. The result is a new furnace with a dusty blower and a supply trunk that has never been cleaned. The first owner inherits it.

The same applies to a resale home where the previous owner finished a basement or opened up a kitchen. If you can see drywall patches, assume the ducts below them took the dust.

When to schedule the cleaning

Timing matters more here than with a routine cleaning. The order that works:

1. All dusty trades finished. Drywall, sanding, tile cutting, flooring and trim are done. If one more sanding pass is coming, wait for it.
2. Final construction clean complete. The cleaners have vacuumed and wiped the rooms, so our crew is not pulling fresh dust back into the ducts from the floor.
3. Duct cleaning. With the trunks, branches, blower and furnace base done, the system is ready to run clean.
4. Move in. Furniture, rugs and bedding go into a home that is no longer circulating gypsum.

If you have already moved in, the cleaning is still worth doing, and the sooner the better, because every blower cycle redistributes a little more. For houses we need about 1.5 hours on site; a condo takes about 45 minutes. Our residential duct cleaning page describes what is included for a house, and the cost page sets out the pricing.

What we find and what we do about it

A post-construction job follows our standard 12-step house process, but the volume of debris changes how each step feels. Floor mats and corner guards go down first, because new floors and fresh paint are the things most likely to get scuffed. We photograph the inside of the trunks and the furnace before starting, seal every supply and return register, and connect the truck-mounted vacuum, which pulls up to 20,000 CFM, to the main trunks so the whole system is under negative pressure before anything is disturbed.

Each supply and return vent is then pressure-cleaned with compressed air toward the vacuum. On a renovation job this is where the screws, wrappers and insulation come out; anything the air will not move, the technician removes by hand from the register box. The main trunks get contact brushing plus suction plus compressed air, because packed gypsum does not lift with air alone. Then the furnace J-channel, the blower and the furnace base are cleaned, which is the step that deals with the dust that got past the filter. A Benefect botanical sanitizer is applied, every access point is resealed, and the after photos are taken and emailed to you.

Two practical notes for new builds and renovations:

• Change the filter the day we leave. The construction filter has done its job. Start fresh so the clean system stays that way.
• Have the dryer vent and bathroom exhausts done at the same time. New dryer vents often contain the same debris, and the renovation may have added or moved exhaust fans. These are $90 add-ons, and when you book two add-ons the third is free.

What it costs

We price by the size of the home, not per vent, so a dusty system does not cost more than a clean one of the same size. For a house with one furnace: under 2,000 sq ft $399; 2,001 to 3,000 sq ft $449; 3,001 to 4,000 sq ft $499; over 4,000 sq ft quoted by phone. Each extra furnace is $200, up to three. A condo is a flat $399 for a single unit or $599 for a double, and that includes the vents, the fan coil or wall unit, the bathroom exhaust fans and the dryer vent. All prices are in CAD before HST. The work is covered by our "love it or don't pay" guarantee.

We work across the GTA seven days a week, including the newer subdivisions in Vaughan, Markham and Milton. If your build or renovation is wrapping up, get a quote with your square footage and a target date, and we will fit the cleaning between the final clean and move-in.

Frequently Asked Questions

Should I clean the ducts in a brand-new house?

Yes. The ductwork was installed before drywall and sanding, and it sat open through the dustiest stages of the build. The builder's final clean covers the rooms, not the inside of the trunks or the furnace blower. A cleaning before move-in removes what construction left behind.

How soon after a renovation should the ducts be cleaned?

As soon as the dusty trades are finished and the final construction clean is done. Cleaning before that point risks pulling new dust into a system that was just cleaned. If you have already moved in, book it anyway; each blower cycle spreads more of what is in the trunk.

Can I just change the furnace filter instead?

A new filter protects the furnace going forward but does nothing about the dust already sitting in the supply trunks or packed into the blower wheel. Change the filter after the cleaning, not instead of it.

Does a renovation of one room mean the whole house needs cleaning?

Usually yes, because the ducts serving that room connect to the same trunk and the same furnace as every other room. Dust that entered through one register travels through the system. We clean the whole system in one visit; the price is set by home size, not by how much comes out.

Will the cleaning damage new floors or fresh paint?

Our crew puts down floor mats and corner guards before bringing in any hose, and the vacuum connection is made at the furnace, not through the finished rooms. The before-and-after photos cover the ducts, and our guarantee covers your satisfaction with the job.