Your furnace turns on. Air comes out of the registers. Everything seems fine. But in new build homes across Milton, Oakville, and the GTA, HVAC problems are one of the most frequently found deficiencies during professional PDI inspections — and one of the most commonly missed by buyers doing the walkthrough on their own.
Here's what goes wrong, what to check, and why this matters for your comfort and your wallet.
The Most Common HVAC Issues in New Builds
Disconnected or partially connected ductwork. In the rush to finish a home, duct connections sometimes get missed — especially in areas that aren't visible, like above ceilings, inside soffits, or in crawlspaces. The result: a register that looks fine but delivers little or no conditioned air to the room.
Missing or unopened balancing dampers. Dampers are adjustable plates inside ductwork that control airflow distribution between rooms. In many new builds, the dampers are either not installed or are left in the closed position from when the ductwork was pressure-tested. This means some rooms get too much airflow while others get almost none.
Improperly connected thermostat wiring. Smart thermostats and multi-zone systems require correct wiring to function. I've found thermostats in new builds that appear to work — the display turns on, you can set a temperature — but the HVAC system doesn't actually respond correctly because the control wiring is miswired or incomplete.
Missing return air pathways. Bedrooms with closed doors need a way for air to return to the HVAC system. This is typically accomplished through undercut doors, transfer grilles, or dedicated return ducts. In new builds, I frequently find bedrooms with insufficient return air pathways — leading to pressure imbalances that make rooms uncomfortable and reduce system efficiency.
Why buyers miss this: Most PDI walkthroughs happen in spring or fall, when temperatures are moderate. You won't notice that your second-floor bedroom isn't getting enough heating until January — or enough cooling until August. By then, you've signed off months ago.
A professional inspection checks every room, every register, every system →
What I Check During a New Build HVAC Inspection
I test airflow at every single register in the home — not just a couple of them. I check that the furnace and air conditioning unit are properly installed and operational. I verify that the thermostat is correctly wired and responding. I inspect accessible ductwork for connections, damage, and proper sealing. And I check for return air in every room that has a supply register.
This is where construction experience makes a real difference. Having spent years working alongside HVAC contractors on jobsites, I know how these systems are installed, where connections get missed, and what an undersized or unbalanced system looks like before it becomes a comfort problem.
What It Costs If Missed
Fixing a disconnected duct run after the home is finished can cost $500–$2,000 depending on accessibility. If the duct is above a finished ceiling, drywall needs to be opened and patched — adding to the cost and disruption. Rebalancing an entire HVAC system runs $300–$800. Rewiring a thermostat is $150–$400.
All of these are items the builder should fix at their expense — if they're caught before you sign the PDI form.