Definition — the refrigerant loop, one component at a time
A residential central AC has four core parts: the outdoor condenser (the noisy metal box beside your house), the indoor evaporator coil (usually sitting on top of your furnace), a metering device (a fixed orifice or a TXV), and a length of copper line-set connecting them. Refrigerant circulates continuously between the two coils.
Warm household air is pulled through the return grille by the furnace blower, passes over the cold evaporator coil (which is boiling refrigerant absorbing heat), and comes out through your supply vents 15–20 °F cooler. On the outdoor side, a compressor pressurizes the refrigerant and the condenser fan blows outside air over hot coils to dump that heat outside.
The condensate — moisture that pulls out of your indoor air as the coil chills it — drains through a small PVC line to a floor drain or condensate pump. In a GTA July that can be several litres a day, which is why a plugged condensate line is one of the most common summer service calls.
When to use it — matching capacity to your GTA home
A properly sized central AC is a 'run-time' machine — not a burst machine. The right unit runs for long, steady cycles and pulls humidity out of the air along with heat. That's why over-sized ACs feel clammy: they cool the thermostat quickly, shut off, and never dehumidify.
The right way to size cooling is a Manual J load calculation that accounts for your square footage, insulation, window orientation (east-west GTA lots gain more heat than north-south), and duct location. 'Rule of thumb per square foot' consistently oversizes ACs in Toronto and Scarborough homes.
- Modest 1,200–1,800 sq ft bungalow: usually 1.5–2 tons
- 1,800–2,400 sq ft two-storey (Scarborough / Ajax / Pickering): usually 2–2.5 tons
- 2,400–3,500 sq ft two-storey with three-piece bath and finished basement: usually 2.5–3.5 tons
- Above 3,500 sq ft or dedicated cooling for a bonus room over a garage: often a zoned or dual-system approach
Failure modes — the signs your AC needs help
Warm-air symptoms usually point to refrigerant issues (a leak that has to be located and repaired) or a frozen indoor coil (dirty filter, low airflow, or a metering-device problem). Loud grinding or a hard-start noise typically means a failing compressor or dry blower bearings. Water damage under the furnace means the condensate drain has plugged.
Short cycling — the AC clicks on and off in under 5 minutes — is often an over-sized unit, a thermostat problem, or a low-refrigerant safety trip. Ice on the outdoor unit in summer is always abnormal and almost always indicates a serious refrigerant issue.
Proof — how the industry measures cooling performance
SEER2 (Seasonal Energy Efficiency Ratio 2) is the current North American test standard for central AC. Higher SEER2 = more cooling per kWh across a typical season. Modern efficient equipment ranges roughly SEER2 15–20+, with variable-speed models leading the pack.
In Ontario, ENERGY STAR-certified equipment meets minimum SEER2 and cold-climate criteria set jointly by NRCan and the US EPA. Look for the ENERGY STAR mark and the equipment's EnerGuide rating when comparing quotes.
Action — how Metroheat sizes and installs
Before we quote a new central AC, we walk the home, measure supply and return duct dimensions, and use those numbers in a Manual J calculation. If your ducts can't move the air the new AC will need, we tell you — because the wrong duct system will leave your upstairs bedrooms hot no matter what condenser you buy.
Every install includes commissioning: refrigerant charge verified by superheat/subcool, static pressure measured across the coil, and a homeowner walkthrough of the thermostat and filter schedule. That is how you protect the manufacturer warranty and get the SEER2 you paid for.