What Size Air Conditioner Do I Need in BC? (BTU Guide)

The Honest Answer Up Front

An air conditioner is sized in tons, and one ton is 12,000 BTU per hour of heat removal. Most detached Metro Vancouver homes land between 1.5 and 3.5 tons, townhomes and suites below that band, and large character homes with generous volumes and west glass sometimes above it. That band is context, not an answer, because the number that serves you comes from a room-by-room cooling load calculation run against your house as it stands, not from a chart applied to your floor area.

The regional context changed in 2021. When the heat dome killed more than 600 British Columbians, cooling stopped being a luxury in this province, and the sizing question stopped being hypothetical. But the instinct that followed, buying the biggest unit that fits the budget, is precisely backwards for a coastal climate: an oversized AC cools the air before it dries it, satisfies the thermostat in minutes, and leaves the house in that specific BC misery of cool and clammy at once. The correct response to hotter summers is a right-sized system plus the envelope and shade work that shrinks the load, and the cooling and AC page shows every system we size that way, with Manual J right-sizing on every quote, never oversized, never undersized.

An air conditioner earns its keep by running long enough to dehumidify. Size it for the one hottest afternoon and it will fail you on every other day of the year.

Tons and BTU, the Vocabulary

A BTU is the same unit the furnace conversation uses, one British Thermal Unit, the energy to raise a pound of water one degree Fahrenheit, and cooling is measured in BTU per hour of heat removed. The ton is the industry's shorthand: one ton equals 12,000 BTU per hour, a fossil of the ice-trade era when building cooling was literally measured in tons of melted ice. Residential central equipment runs from 1.5 to 5 tons in half-ton steps, 18,000 to 60,000 BTU per hour, and ductless heads come in smaller increments, commonly 9,000, 12,000 and 18,000 BTU per hour, which is why they size rooms rather than whole houses.

Two more numbers complete the vocabulary. SEER2, the efficiency rating now printed on the equipment label, tells you how many BTU of cooling each watt-hour of electricity buys under a standardized test, and higher is cheaper to run. The rating matters to sizing in one quiet way: a unit's rated capacity is stated at laboratory conditions, while its delivered capacity moves with indoor temperature, indoor humidity and the outdoor temperature of your actual afternoon. A proper selection reads the manufacturer's expanded performance data at real conditions, not the headline number on the brochure, and the same discipline governs our furnace and heat pump quotes.

The vocabulary explains the rest of this guide: a cooling load calculation produces a BTU-per-hour number for your house, tonnage is that number divided by 12,000, and the equipment is chosen so its delivered capacity at real conditions covers the load. Half-ton steps and ductless head sizes mean the final choice is always a rounding decision, and the honest direction to round in this climate is down, for reasons Chapter 7 makes painful.

The Square-Foot Folklore

The rule of thumb exists and every homeowner has met it: somewhere between 400 and 600 square feet per ton of cooling, or roughly 20 to 30 BTU per hour per square foot, with adjustments upward for hot climates and downward for mild ones. Multiply your floor area by a number from a band that wide and you can miss the real load by half in either direction, which is the difference between a system that dehumidifies properly and one that never runs long enough to try.

The folklore fails fastest exactly where Metro Vancouver housing lives. A 1,200 square foot top-floor corner condo in Burnaby with a wall of west glass can carry a bigger cooling load than a 2,000 square foot ground-oriented New Westminster house shaded by street trees, because solar gain through glass, not floor area, is the single largest driver of afternoon cooling loads in this region. Floor count matters as much as footprint, since upper floors collect the rising heat and the attic radiance. Ceiling heights change the volume. And the envelope era that dominates furnace sizing barely matters at all here, while the window quality and orientation that barely move heating math dominate the cooling math, which is why the same house can need a modest furnace and a disproportionate air conditioner.

Like the furnace version of the folklore, the square-foot rule has one legitimate use: sanity-checking a completed calculation. If the measured cooling load for your house lands wildly outside the band, something was measured wrong and the estimator re-runs it. Used that way it is a backstop. Used as the method it is how oversized condensers multiply, each one installed by a contractor who never asked which way your living room faces.

What Drives the Cooling Load

The cooling load is a different equation from the heating load, with different dominant terms, and knowing them makes you a sharper reader of any AC quote. In rough order of how much they move the number in this region:

Notice what the list implies: the cooling problems homeowners complain about, the upstairs that bakes, the west room that never recovers, the afternoon the whole system seems to surrender, are load-distribution problems as much as capacity problems. A whole-house tonnage number chosen without room-by-room data fixes none of them, and our heat dome preparedness guide covers the upstairs-five-degrees-warmer pattern and the envelope work that shaves it.

The Manual J Cooling Calculation

ACCA Manual J is the standardized room-by-room method, the same calculation family that sizes furnaces, and every cooling quote we write runs it. The cooling version measures your house against a design condition that represents the near-worst afternoon for your address, then produces a room-by-room breakdown that tells you both the tonnage the house needs and where the load concentrates. What happens on a proper estimate visit:

What BC Summers Actually Ask

The region's cooling season is short, concentrated and increasingly serious. For most of June through September, Metro Vancouver afternoons are warm rather than hot, evenings cool quickly, and overnight lows let houses shed the day's gain if the windows are managed well. The heat dome pattern is different: sustained daytime highs in the high 30s and beyond with nights that barely recover, the profile that killed more than 600 British Columbians in 2021 and turned air conditioning from luxury into survival equipment for seniors, infants and respiratory-sensitive households.

Sizing has to live between those two realities. A unit sized for the heat dome afternoon, the one-in-five-years event, would be badly oversized for the ordinary summer and the shoulder seasons around it, short cycling through cool-but-clammy evenings. A unit sized only for the ordinary afternoon will run continuously through a heat dome and hold a degree or two above setpoint in the worst rooms, which is uncomfortable and survivable, and which is the trade almost every building scientist recommends. The middle path is right-sizing for the realistic design afternoon plus the envelope and shade work that shaves the peak, blackout habits on west glass, attic insulation that cuts the radiance, and the ventilation routine that flushes overnight coolness.

Humidity is the regional signature that the folklore ignores. Coastal air carries moisture that a properly sized unit wrings out on the cooling coil during long runtimes, which is why dehumidification is a sizing outcome, not a feature you can buy separately. The cities we serve from Vancouver, Burnaby and New Westminster through Surrey, Langley, Delta and Richmond out to Coquitlam, Port Coquitlam, Maple Ridge, Abbotsford and North Vancouver all share the pattern, with the Fraser Valley's warmer afternoons pulling design conditions up a notch.

Ductless Head Sizes by Room

Ductless mini-splits size rooms instead of houses, and the head sizes come in increments that map onto familiar rooms: a 9,000 BTU head covers a typical bedroom or den, a 12,000 head covers a standard living room or master suite, and an 18,000 head covers an open main floor or a sun-struck great room. The same room-by-room calculation governs the choice, with the west-glass and top-floor terms doing the heavy lifting, and head placement working with the room's airflow rather than against it.

Single-zone ductless installs run $3,800 to $5,500, and multi-zone ductless systems, two to five heads on one outdoor condenser with independent room control, run $9,500 to $16,000 driven by head count, floor-plan spread and panel capacity. Multi-zone is the natural answer for homes without ductwork: baseboard-heated East Vancouver houses, top-floor suites where the whole floor bakes, and laneway homes where one condenser serves a compact plan. Ductless heat pump versions, single zones at $4,500 to $8,500, add the heating season to the same head count, which is where the CleanBC conversation starts. Our ductless versus central guide walks the fork in detail.

One ductless-specific sizing note: heads are often deliberately sized a step small for the room they serve, because an inverter head running continuously at partial output dehumidifies better, holds temperature steadier and runs quieter than a bigger head cycling on and off. That is the same rounding-down logic from the whole-house chapters, applied one room at a time, and it is why the head-count conversation always starts with the load map rather than the head brochure.

Ductwork, Blower and Coil Matching

A central air conditioner is two components, the outdoor condenser and the indoor evaporator coil, matched to each other and to the furnace blower that pushes air across the coil. The match is not optional: the coil has to pair with the condenser's tonnage, the blower has to move the airflow that tonnage expects, and the ductwork has to present low enough static pressure for the air to actually arrive in the upstairs west room. An AC quote that never looked inside the ducts is a quote that skipped half the system.

In practice, our quotes for the region's 1980s-2000s subdivisions are dominated by straight swaps: a matched coil and condenser onto a sound furnace and existing ductwork, after a static-pressure check confirms the ducts can carry the airflow, at central AC installs of $3,800 to $6,500. Where ductwork is undersized or the house has no ducts at all, ductless is usually the honest answer rather than duct surgery, and the two paths are priced side by side so the comparison is real. Attic-located ducts get inspected and sealed where they leak, because every gap bleeds the cooling the equipment paid to make.

Maintenance keeps the match honest over the years: coil cleaning, refrigerant verification, electrical tightening and the performance test that catches a slow capacity fade before it becomes a heat-dome failure. AC repairs run $180 to $450 with the $89 diagnostic credited, maintenance visits run $149 to $250, and after-hours emergency calls carry a $150 flat premium, disclosed upfront, with 24/7 live dispatch through heat waves. Capacitors, fan motors and contactors are the parts that fail most in this climate, and they ride in the vans.

AC Versus Heat Pump: The Same Math, Different Decision

Here is the point that saves the most money in this entire guide: the cooling side of the calculation is identical for an air conditioner and a heat pump. Same rooms, same windows, same afternoon, same tonnage. What changes is that a heat pump must also cover the heating load at your city's design temperature, and in this region the heating load usually governs the equipment choice, which is why a heat pump selected properly often ends up with more cooling capacity than the AC-only calculation called for, and why the inverter class spends its life modulating rather than cycling.

The decision framework is therefore sequential. Run the load calculation once. Look at the heating number and the cooling number together. Then choose the equipment: an AC plus your existing furnace where the furnace is sound, a heat pump conversion where the furnace is aging or absent, or dual fuel where a heat pump carries the mild bulk of winter and the furnace waits for the outflow nights. Cold-climate heat pumps hold rated capacity to -25 C, cover both seasons from one outdoor unit, and carry the incentive stack: combined CleanBC Better Homes, BC Hydro, FortisBC and municipal top-ups can reach $16,000 for qualifying cold-climate heat pumps in 2026, and we complete the paperwork. The heat pump page carries that path, and our Vancouver AC repair work keeps either choice honest for the decade after.

The honest footnote for the AC-only path: buy the efficiency tier your runtime justifies. A high-SEER2 unit that short cycles never visits its efficient operating band, and a right-sized standard tier that runs long steady afternoons can deliver better real-world economics than a premium badge sized badly. Efficiency is downstream of sizing, always, which is the thesis of every chapter in this guide.