Bought a resale house? How to check the ducts and when to clean them

You do not have to clean the ducts just because you bought a house. Check them first. If they are dirty, the best time to clean is after you get the keys and before the furniture arrives, because every register and the whole furnace room are clear. If you are also painting, refinishing floors or renovating, clean the ducts after that work, not before. This guide shows how to check the ducts yourself in ten minutes, what to ask the seller, and how to fit a cleaning around a closing date.

What you inherit with a resale house

A resale house comes with a duct system and no history. You do not know whether the previous owners had shedding pets, whether they renovated, how often the furnace filter was changed, or whether the ducts have ever been cleaned. In a house that sat empty before the sale, you also do not know what moved in.

None of that means the ducts are dirty. It means nobody has told you. The US Environmental Protection Agency recommends cleaning on "an as-needed basis" and notes that "a light amount of household dust in your air ducts is normal." So the first job is to look.

How to check the ducts in ten minutes

You can do this at the final walkthrough, or on the day you get the keys.

• Open one return and one supply. Lift a floor register or unscrew a return grille and look inside with your phone's flashlight. A light, even film is normal. Clumps, matted pet hair, drywall dust, screws, toys or droppings are not.
• Pull the furnace filter. Slide it out of its slot. A filter that is grey and furred, bowed, or missing tells you how the system was looked after.
• Run the blower. Set the thermostat fan to On and watch a supply register. A puff of dust at start-up means loose material in the supply runs.
• Smell the first minute of air. A musty smell points to moisture somewhere in the system. Our guide to musty smells from vents lists the causes.
• Look at the dryer vent outside. The flap should open freely when the dryer runs. Lint packed around it is a sign the run needs cleaning, and dryer lint is a fire risk in a way that duct dust is not. See why your dryer takes two cycles.

Leave the furnace cabinet itself closed. Opening the blower compartment is a job for a technician.

What to ask the seller

• When were the ducts last cleaned, and is there an invoice or photos?
• Were there pets in the house?
• Was any renovation done, and were the ducts cleaned afterwards?
• Has there been a water leak, a flood or a pest problem?

Also read the heating section of your home inspection report for what was actually examined. If it does not mention the inside of the ducts, nobody has looked there.

Why before move-in is the easiest time

Nothing about duct cleaning requires an empty house. It is simply easier in one.

• Every register is reachable. Each supply and return is cleaned individually, and in a furnished house a blocked one has to be dug out or it delays the job.
• The furnace room is clear. The technician needs to reach the furnace from the front and sides.
• There are no pets or children underfoot. The vacuum is loud and a door stays open for the hose.
• You start clean. Rugs, bedding and sofas go into a house that is no longer circulating someone else's dust.

If you have already moved in, the cleaning is still worth doing when the ducts need it. Expect to move some furniture off the registers first.

The right order if you are also doing work

Most buyers do something before moving in: painting, floor refinishing, a new kitchen. Dust from that work goes straight into the returns. Clean the ducts first and you will be cleaning them again. The order that works:

• All dusty work finished. Drywall, sanding, tile cutting, flooring and trim.
• Final clean of the rooms. So the crew is not pulling fresh dust back into the ducts from the floor.
• Duct cleaning. Trunks, branches, blower and furnace base.
• Move in.

Our guide to duct cleaning after a renovation or new build covers this in detail, including why a brand-new house is not a clean duct system either.

Fitting it around your closing date

You need access to the house, so the cleaning has to fall on or after the day you take possession, unless the seller agrees to let a contractor in earlier. The booking page shows open dates for the next three weeks, so once the closing date is firm you can pick the day you get the keys or the day after. A house takes about 1.5 hours. We work seven days a week from 6:00 AM to midnight, which helps when the movers are booked for the weekend.

Have a new furnace filter in the right size ready, and we install it at the end.

If you bought a condo

A suite has a fan coil or wall unit instead of a furnace, short duct runs, bathroom exhausts and a dryer vent. The check is the same: look into a vent and pull the filter if the unit has one. The cleaning takes about 45 minutes with portable equipment, and you may need to tell the concierge or property manager that a contractor is coming. Our condo duct cleaning guide covers what to ask the building.

What it costs

A house with one furnace is $399 under 2,000 sq ft, $449 from 2,001 to 3,000 sq ft and $499 from 3,001 to 4,000 sq ft, before HST. A second furnace adds $150. A condo suite is $449 flat for a single unit, with the dryer vent and one bathroom exhaust fan included. On a house the dryer vent is a $90 add-on, and it is the one most worth adding in a house you know nothing about. The price list has the rest, or get a quote online.

When to skip it

• You looked and found a light, even film with nothing loose.
• The seller has a recent invoice and photos from a proper cleaning, and nothing has been renovated since.
• The house is heated by a boiler and radiators and has no ducts. It may still have a dryer vent and bathroom exhaust fans worth doing.

If you are unsure, our technicians photograph the trunks and the blower compartment before any work starts. If there is nothing worth cleaning, we tell you then.

Frequently Asked Questions

Should I clean the ducts before moving into a house?

Check them first. If they are dirty, before move-in is the easiest time, because every register and the furnace room are clear. If the ducts hold only a light film of dust, you can skip it.

Can I have the ducts cleaned after I move in?

Yes. The work is the same. You will need to move furniture and rugs off the registers and clear space around the furnace.

How do I know if the previous owner cleaned the ducts?

Ask for the invoice and any photos. Without them, look inside a return and a supply with a flashlight and check the furnace filter. That tells you more than a verbal answer.

Should I clean the ducts before or after painting and floor refinishing?

After. Sanding and construction dust is drawn into the returns, so cleaning first means cleaning twice. Wait until the dusty work and the final clean of the rooms are finished.

Do the ducts in a brand-new house need cleaning?

Often, yes. Builders leave sawdust, drywall dust and offcuts in the trunk lines, and CMHC lists a newly built house as a reason to consider cleaning. Inspect, and clean if it is dirty.

How much does it cost to clean the ducts in a house I just bought?

$399 to $499 before HST for a house with one furnace, depending on its size. A second furnace adds $150, and a dryer vent cleaning is a $90 add-on.