Ruud Air Conditioner sizing guide in Greater Vancouver
Two houses on the same Burnaby street, same footprint, same year. One needs meaningfully less cooling capacity than the other because it faces north, kept its mature trees, and had the attic topped up. Square footage told you nothing useful about either.
The habit in this trade is to read the old nameplate and order the same number. That is how oversizing gets copied forward through three generations of equipment in the same house, along with the original guess that started it.
Cooling is different from heating in the Lower Mainland. Our design cooling loads run modest compared with most of Canada, our summers are dry rather than muggy, and a lot of homes here were never built with cooling in mind at all. That combination makes oversizing both easy to do and unusually punishing. HeatLand has been sizing and installing here since 1999.
Capacity is a rate, not a size
A tonne of cooling is a rate of heat removal, roughly twelve thousand BTU per hour. Sizing an air conditioner means matching that rate to how fast heat enters your house on a hot afternoon, so the equipment runs long and steady rather than blasting and stopping.
Heat gets in four ways and a load calculation counts each separately. Conduction through walls, ceilings and floors, driven by insulation levels and the temperature difference. Solar gain through glass, which depends enormously on which direction the window faces, whether it is shaded, and what the glazing is. Infiltration, meaning outdoor air leaking in through the building envelope, which in older Vancouver housing stock is often the largest single line item. And internal gains from people, cooking, lighting and the growing pile of electronics in a modern home.
Sensible load is the part that changes air temperature. Latent load is the part that removes moisture. The ratio between them determines whether a system feels comfortable or merely cold and clammy, and it varies by climate. Coastal BC summers carry less latent load than Ontario or the Prairies.
That is the number the equipment gets matched to. Not floor area, not the number of bedrooms, not the size of the furnace already sitting in the basement, which was sized for a completely different job in a completely different season.
Why the old unit’s tonnage is the wrong starting point
The existing nameplate tells you what someone installed. It does not tell you whether it was ever correct, and it does not account for anything that has changed since.
Plenty has changed in most homes. New windows, attic insulation top-ups, a finished basement that added conditioned area, a wall removed, a heat pump added, LED lighting replacing incandescent, blower door sealing done during a renovation. Each shifts the load, most of them downward. A house that genuinely needed a certain capacity in 2004 frequently needs less now.
The original number was often a guess in the first place. Rules of thumb based on square footage per tonne have circulated in this trade for decades and they systematically overshoot in mild climates, because they were built around hotter, more humid design conditions.
There is also survivorship reasoning at work. Homeowners rarely complain that a system is too large. They complain that a room is warm, and the reflexive fix is more tonnage, which makes the underlying distribution problem worse while appearing to address it.
Use the old nameplate as one data point, alongside how the house actually performed. Were there rooms that never cooled? Did the system run in short bursts? Did it feel cold but damp? Those observations are worth more than the number stamped on the cabinet.
What a load calculation actually measures
A proper Manual J is a room-by-room exercise, and it takes a technician a real hour or two in the house rather than a glance from the driveway.
The inputs collected: exterior wall construction and insulation level, attic or roof assembly and its insulation depth, floor assembly over crawlspace, basement or slab, and whether the basement is conditioned. Every window gets measured for area, orientation, glazing type, whether it has low-e coating, and what shades it, including neighbouring buildings and mature trees. Doors count separately. Ceiling heights matter, and vaulted ceilings change the picture.
Air tightness gets estimated from construction era and observed condition, or measured directly if a blower door test has been done. Occupancy, appliance loads and any unusual internal gain such as a home office full of equipment or a south-facing sunroom get added.
Duct location is an input too. Ducts running through an unconditioned attic or a vented crawlspace pick up heat and leak air, and that penalty belongs in the calculation rather than being ignored.
The output is a total load and a per-room load. The per-room numbers are the ones that determine airflow to each register, which is what actually makes bedrooms comfortable. A whole-house total with no room breakdown is half a calculation and it will not catch the upstairs bedroom that has been hot for fifteen years.
Lower Mainland design conditions and why loads run low here
Equipment is not sized for the hottest hour ever recorded. It is sized to a design temperature that a location exceeds only a small percentage of hours in a typical season, and Metro Vancouver’s cooling design condition is mild by Canadian standards. Chase the record heat instead and you buy a system that is wrong for the other ninety-nine percent of the summer.
Our climate has specific consequences. Low summer humidity relative to central and eastern Canada means the latent portion of the load is smaller, so equipment selected on sensible capacity alone can still dehumidify adequately, provided it runs long enough. Long overnight cooling means a well-shaded home coasts through the morning on stored coolness if you let it.
Microclimates within the region are real. Inland Fraser Valley communities see hotter afternoons than the North Shore or homes near the water. Elevation and tree cover shift things again. A calculation done for a Maple Ridge home does not transfer to a West Vancouver one.
Older housing stock matters more than climate in many cases. A 1950s bungalow with original windows and minimal wall insulation carries a high infiltration and conduction load regardless of how mild the outdoor design temperature is. That is why two homes with identical square footage in the same municipality can land a full capacity step apart.
What oversizing does to comfort and equipment
An oversized air conditioner satisfies the thermostat quickly and shuts off. That sounds efficient. It is the opposite.
The coil needs several minutes of continuous operation before it is cold enough to strip meaningful moisture from the air. Short cycles never reach that point, so the house hits temperature while still feeling damp and heavy. Occupants respond by lowering the setpoint, which produces cold, clammy air and higher operating cost at once.
Short cycling also punishes hardware. Every compressor start draws far more current than steady running and generates the most wear, so a unit that starts four times an hour ages considerably faster than one that runs in longer blocks. Contactors pit sooner. Capacitors work harder.
Distribution suffers too. Short runs never move enough air to reach the far bedrooms, which is exactly the complaint that prompted the oversizing in the first place. The upstairs stays hot while the main floor overshoots, and the temperature swing between cycles grows wider and more noticeable.
Undersizing has its own failure mode, running continuously on the hottest afternoons and never quite reaching setpoint, but in this region it is far less common and far less damaging. A slightly undersized system that runs long is generally more comfortable than a clearly oversized one that runs in bursts. Correct sizing beats both, which is the entire point of doing the calculation.
Matching the Ruud condenser to the indoor coil and blower
The condenser outside is one half of a matched pair. The indoor coil and the blower moving air across it are the other half, and the system performs as the combination, not as the nameplate outdoors.
Certified performance for a matched system is published as an AHRI listing tying a specific outdoor model to a specific indoor coil and air handler or furnace combination. Efficiency is expressed under the SEER2 rating system for cooling. Look up the AHRI listing or the manufacturer’s spec sheet for your exact proposed combination rather than trusting a figure quoted for the outdoor unit alone, because a mismatched pair does not deliver the rated performance and may not qualify for utility program paperwork.
This matters practically when a homeowner replaces only the outdoor condenser and keeps an older indoor coil. The coil may be a different capacity, designed for a different refrigerant, or have a metering device that does not suit the new unit. The result is a system that cools, badly, and leaks money for a decade.
Blower capability sets the ceiling. A variable-speed blower can hold correct airflow across a wider range of duct static pressure than a single-speed one, which changes what is achievable in a house with marginal ductwork.
Ask to see the proposed match written down before you sign anything. HeatLand puts it in the estimate.
Ductwork and airflow: the constraint that overrides tonnage
Roughly four hundred cubic feet per minute of airflow per tonne is the working target for cooling. If the duct system cannot move that air, additional capacity is stranded and the coil runs cold enough to freeze.
Most Lower Mainland homes with ducts had them installed for heating only. Heating airflow requirements are lower, supply registers were placed under windows for warm air distribution, and returns are frequently a single large grille in a hallway. Convert that system to cooling and you find undersized trunks, long flexible runs crushed behind storage in the crawlspace, and nowhere near enough return path.
Static pressure is the measurement that reveals this, taken across the air handler with a manometer. High static means the blower is fighting the duct system, and no amount of outdoor tonnage fixes it. Common causes: a filter grille far too small for the airflow, closed or blocked registers, undersized returns, and flex duct with sags and sharp bends.
Before anyone quotes capacity, the ducts should be inspected and measured. Sometimes the honest answer is duct modification alongside equipment, and sometimes it is a ductless or multi-zone approach for a house where reworking the ducts is impractical, which describes a fair number of older homes and finished basements here.
A smaller correctly matched system on good ductwork outperforms a larger one on bad ductwork every summer.
Strata rules, electrical, permits and placement
Where the condenser can physically go often narrows the selection before capacity does. Townhouse and low-rise strata properties across Metro Vancouver commonly restrict outdoor unit placement, require council approval and an alteration agreement, and specify sound limits. Municipal noise bylaws add their own limits, measured at the property line, and they are usually stricter overnight.
Sound ratings are published per model by the manufacturer. If your unit sits three metres from a neighbour’s bedroom window, the quieter model is not a luxury, it is what gets the installation approved. Clearance requirements around the cabinet for airflow and service access are set by the manufacturer and must be respected, which rules out some tight side yards entirely.
Electrical is the other gate. Adding cooling means a dedicated circuit and breaker sized for the unit, plus a service disconnect within sight of it. Older panels in homes from the 1950s through 1970s frequently have no spare capacity, and a panel upgrade becomes part of the project. That gets found during a site visit, not from a photo.
Permits are municipal and vary across Vancouver, Surrey, Burnaby, Richmond and the Fraser Valley municipalities. Electrical permits are generally required, and mechanical permits depend on scope.
For CleanBC or FortisBC program paperwork, confirm current requirements with the program directly, since eligibility conditions change. HeatLand handles the load calculation, the duct assessment and a free written no-obligation estimate. Call (604) 330-3812.
Quick Checklist
- Ask for a room-by-room load calculation, not a square-footage estimate
- List every change since the last install: windows, insulation, finished basement, added rooms
- Note which rooms have never been comfortable and in which season
- Have the duct system inspected and static pressure measured before capacity is chosen
- Request the AHRI matched-system listing for the exact outdoor and indoor combination proposed
- Confirm the electrical panel has capacity for a dedicated circuit and disconnect
- Check strata bylaws and municipal noise limits before choosing a placement
- Get the recommended capacity, the matched components and the permit scope in writing
| Sizing input | Why it matters in this region | Where the number comes from |
|---|---|---|
| Window area and orientation | Solar gain is often the single largest summer load on west-facing rooms | Measured on site, per room, with shading noted |
| Insulation levels | Older Lower Mainland stock varies enormously house to house | Observed in attic and crawlspace, or from renovation records |
| Air leakage | Infiltration dominates the load in pre-1980 homes | Estimated by construction era, or measured by blower door |
| Design temperature | Sizing to record heat rather than design condition causes oversizing | Regional cooling design data for your municipality |
| Duct capacity and static pressure | Airflow limits usable capacity regardless of tonnage | Manometer reading at the air handler plus a duct inspection |
| Indoor coil and blower match | Performance and rated efficiency apply to the pair, not the condenser alone | AHRI listing or manufacturer spec sheet for that combination |
Frequently Asked Questions
How many square feet does one tonne of cooling cover?
There is no reliable answer, and that is the point. Two homes of identical area in the same municipality can differ by a full capacity step depending on window orientation, insulation, air leakage, ceiling height and shading. Square-footage rules of thumb were built around hotter, more humid climates and systematically oversize equipment in coastal BC. A room-by-room load calculation is the only defensible method.
Can I just replace my old AC with the same tonnage?
Only if you can confirm the old size was correct and nothing has changed. New windows, attic insulation, a finished basement, LED lighting and renovation air sealing all shift the load, usually downward. Many existing systems were oversized from the start. Treat the old nameplate as one data point and have the load recalculated, particularly if any room never cooled properly.
What happens if my air conditioner is too big?
It reaches the thermostat setting fast and shuts off before the coil has run long enough to remove moisture, so the house feels cold and damp. Occupants drop the setpoint, which costs more and feels worse. Frequent starts wear the compressor, contactor and capacitor faster than steady operation, and short runs never push enough air to reach distant bedrooms.
Does my ductwork affect what size unit I can install?
Yes, and it often decides the outcome. Cooling needs substantially more airflow than heating, and most older ducted homes here were designed for heating only, with undersized returns and restricted trunks. If the ducts cannot move roughly four hundred CFM per tonne, extra capacity is wasted and the coil can freeze. Static pressure should be measured before capacity is selected.
Do I need strata approval or a permit for an outdoor unit?
In a strata, almost always. Councils typically require an alteration agreement, approve placement, and apply sound limits, on top of municipal noise bylaws measured at the property line. Electrical permits are generally required for the dedicated circuit and disconnect, and mechanical permit requirements vary by municipality. Confirm strata rules early, because placement constraints can change which model is workable.
Reviewed by the HeatLand Heating & Cooling team — licensed, insured, TSBC-certified HVAC contractor serving Metro Vancouver & the Fraser Valley since 1999. Error codes, specifications, pricing and rebate programs vary by model and change over time; confirm details against your unit’s own manual, a written quote, and the manufacturer or CleanBC/FortisBC. If you smell gas or your CO alarm sounds, leave the home and call the gas utility and a licensed technician from outside.