Cooling load is not floor area
Floor area helps describe a house but does not determine cooling load by itself. Window area and orientation, insulation, roof exposure, infiltration, internal gains, shading and duct location all matter. Two Toronto houses of equal size can require different capacity. Oversizing may cool the thermostat zone quickly while upper rooms remain warm and indoor moisture stays high. Undersizing can cause excessive runtime during design weather, but long runtime on ordinary hot days is not automatically a fault. A load calculation gives the selection a transparent foundation and helps separate equipment capacity from distribution problems.
Matched components and ratings
Central AC performance is rated as a system: outdoor condensing unit, indoor coil, metering device and blower setup. Mixing components without an approved match can change capacity, efficiency, pressure and warranty status. The contractor should provide exact model numbers and the matched-system reference where applicable. Coil dimensions must fit the furnace or air handler without bypass leakage, and the drain pan orientation must suit the installation. If a future heat-pump conversion is likely, discuss whether today’s indoor components and controls support that path rather than creating another early replacement.
Refrigerant lines are part of the system
Line-set diameter, length, vertical lift, insulation and cleanliness affect oil return and refrigerant performance. Reusing existing lines may be reasonable only after confirming compatibility, condition and manufacturer requirements. Installation practices should keep moisture and debris out, use appropriate brazing and evacuation procedures, pressure-test the circuit and charge it according to equipment instructions. Kinked lines, poor insulation and concealed joints create future failures. The line route should also protect the piping from physical damage and allow service access at both units.
Airflow, filtration and noise
Required airflow must move through the real filter, coil and ducts at an acceptable static pressure. A dense filter installed for indoor-air concerns may reduce airflow if the cabinet and return system were not designed for it. High air velocity causes grille noise and may carry water off the coil. Low airflow can freeze the coil. Room balance matters as well: closed bedroom doors need return-air pathways, and upper floors may need balancing or duct correction. Commissioning should test the system with the filter and panels in their normal operating condition.
Drainage and commissioning
The evaporator removes water during humid weather. Primary drainage needs continuous slope or a correctly installed pump, trap where required, cleanout access and protection against property damage. Attic or finished-space installations need particular attention to overflow controls and secondary pans. Startup should document indoor and outdoor conditions, voltage, current, airflow or static pressure, temperature change, refrigerant charge method, drainage and thermostat operation. The homeowner should know filter size, service clearances and basic seasonal care. A cold supply register alone is not proof of a correct installation.