Updated July 2026 · by Murugan Vellaichamy
A unit of cooling rate, not weight: one ton = 12,000 BTU/hr (≈3.517 kW), historically the cooling from melting a ton of ice over a day. See the converter.
How many times a space’s full air volume leaks in and out per hour through the building envelope; higher ACH means a bigger infiltration load.
The US industry standard that defines how SEER2, EER2 and HSPF2 are measured for residential AC and heat-pump equipment.
India’s Bureau of Energy Efficiency 1–5 star label for room ACs, based on ISEER. See the star rating guide.
A British Thermal Unit is the heat needed to raise one pound of water by 1°F. Cooling capacity is quoted in BTU per hour.
Cubic feet per minute of air moved by the system — roughly 400 CFM per ton in residential cooling.
The pump that compresses refrigerant gas and drives the refrigeration cycle; the most expensive component to replace.
The outdoor coil that rejects heat from the refrigerant to outside air.
The ratio of useful heat moved to electrical energy consumed; a heat pump with COP 3 delivers 3 units of heat per unit of electricity.
The temperature drop across the indoor coil between return and supply air; about 8–11 °C (15–20 °F) is normal.
Efficiency measured at a single hot operating point (95°F outdoor), reflecting peak-day performance.
The indoor coil where cold refrigerant absorbs heat from room air.
Heating Seasonal Performance Factor (2023 test) — the seasonal heating efficiency of a heat pump.
A compressor that modulates its speed to match the load instead of cycling fully on and off; steadier temperatures and better efficiency. See inverter vs non-inverter.
Indian Seasonal Energy Efficiency Ratio — the BEE metric behind India’s star ratings, tested across 24–43 °C.
The energy needed to remove moisture from the air (dehumidification), as opposed to lowering temperature. See humidity & comfort.
ACCA residential standards: Manual J calculates the load, Manual S selects equipment, Manual D designs the ducts. See Manual J explained.
Minimum Circuit Ampacity and Maximum Overcurrent Protection — the nameplate figures that set wire and breaker sizing for an AC.
Refrigerants: R-410A is being phased out for lower global-warming R-32 and R-454B in new US equipment from 2025 (India already uses R-32).
R-value measures insulation’s resistance to heat flow (higher is better); U-factor is its reciprocal for a whole assembly like a window (lower is better).
The valve that lets a heat pump swap refrigerant flow to heat in winter and cool in summer.
Seasonally Adjusted Cooling Capacity — the honest rating for a portable AC, typically 50–60% of the box BTU. See the portable calculator.
The energy needed to change air temperature, as opposed to latent (moisture) load.
Seasonal Energy Efficiency Ratio — average cooling efficiency over a season; SEER2 is the tougher post-2023 US test. See SEER vs SEER2.
The fraction of solar heat a window lets through, from 0 to 1; lower blocks more sun.
The share of a system’s cooling that goes to lowering temperature versus removing moisture (sensible ÷ total).
When an oversized AC cools so fast it shuts off within minutes, hurting dehumidification and wearing the compressor. See the oversizing guide.
Total External Static Pressure — the resistance the blower pushes against (ducts, filter, coil); high values choke airflow.
How far liquid refrigerant is cooled below its condensing temperature; a key charging target on TXV systems.
How far refrigerant gas is warmed above its boiling point leaving the coil; monitored to protect the compressor.
A metering device that varies refrigerant flow to hold correct superheat across changing conditions.
Using motorised dampers and multiple thermostats to direct cooling only to the areas that need it.
Related: how your AC works · our methodology · all guides · FAQ.