Why Does My Upstairs Get So Hot in Summer Even With the AC Running?

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Why the upstairs runs hotter

There is rarely a single cause. In most Metro Vancouver two-storey homes, a few things stack up at once during a warm stretch or heat wave:

• Heat rises. Warm air from the main floor drifts upward through the stairwell all day, so the second storey is fighting a constant supply of heat from below.
• Roof and attic heat. Sun beats on the roof and, if attic insulation is thin or ventilation is poor, that heat radiates straight down into upstairs bedrooms.
• Ductwork favours the main floor. In many homes the trunk lines were sized and balanced so the cool air reaches the living areas first, leaving weaker airflow at the upstairs registers.
• One thermostat, two floors. A single thermostat on the main floor shuts the system off once that floor is comfortable, before the upstairs ever catches up.
• Sun-facing windows. West and south bedrooms pick up a lot of afternoon solar heat that a central AC struggles to overcome.

What you can check and try yourself

Several of these are simple, no-cost adjustments worth trying before you call anyone:

• Change a dirty filter. A clogged filter chokes airflow to the whole home, and the farthest registers (usually upstairs) suffer first.
• Open upstairs registers fully and partially close a few main-floor ones. This pushes more cool air up where you need it.
• Set the fan to ON instead of AUTO during hot afternoons. Continuous circulation helps mix the cooler main-floor air with the warm upstairs air.
• Close blinds or curtains on sun-facing windows before the afternoon heat hits.
• Make sure upstairs supply and return vents are not blocked by furniture, rugs, or bedding.
• Run bathroom and kitchen exhaust fans only as long as needed, since they pull conditioned air out of the house.

If a small adjustment like balancing the registers noticeably narrows the gap, you were dealing with an airflow imbalance rather than an equipment problem.

Longer-term fixes that actually work

When simple tweaks are not enough, the problem is usually built into the home or the system. Options a contractor can look at include a proper duct balancing or a zoning system with dampers and a second thermostat so the upstairs cools independently. Improving attic insulation and ventilation is often the single most effective step in older Vancouver-area homes, since it stops the roof heat from loading the second storey in the first place. For rooms that never keep up, a ductless mini-split head can cool a specific bedroom or bonus room without touching the main ductwork.

It is also worth confirming the central system is actually sized and charged correctly. An AC that is undersized for the home, low on refrigerant, or short on airflow will always leave the hardest-to-reach spaces warm.

When to call CANRO

If you have balanced the registers, changed the filter, and the upstairs is still uncomfortably warm during normal summer weather, it is worth having it looked at properly. A technician can measure the airflow at each floor, check the refrigerant charge, and tell you honestly whether the fix is duct balancing, zoning, insulation, or added cooling. CANRO Heating & Cooling has served Metro Vancouver since 1999 and is Red Seal certified and fully insured. Call (604) 359-1081 or email info@canroheat.ca for a diagnostic visit and a free written quote, with no dollar figures guessed over the phone.

Frequently asked questions

Reviewed by the CANRO Heating & Cooling service team — July 07, 2026. Technical Safety BC gas licence LGA0043870 · boiler licence LBP0046450 · Red Seal certified · WorkSafeBC and liability insured · 4.9★ from 85+ Google reviews · serving Metro Vancouver since 1999 · (604) 359-1081.