HVAC

HVAC and air conditioning calculators

Capacity, units, energy and cost, with the workings on show.

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Most used

Air conditioner size calculatorA component estimate: you can see where every watt comes from.Cooling capacity calculatorWith the load per square metre visible, so you can adjust it.AC energy consumption calculatorCooling capacity and electricity used are not the same thing.Monthly AC costHours a day, days a month and your tariff: the summer bill.BTU to frigoriesFor comparing units advertised in different markets.EER calculatorCapacity over power input, in both scales: European and US.

How it is calculated

Three different questions

Almost everything people search about air conditioning is really three questions that are worth keeping apart:

  1. What capacity do I need. That depends on the room: floor area, ceiling height, insulation, sun, people and appliances. Measured in BTU/h, kW or tons.
  2. How much does it use. That depends on the electrical power the unit draws, which is not its cooling capacity. Measured in kWh.
  3. What does it cost. That depends on the energy use and your tariff.

The most common mistake

A 12,000 BTU/h unit does not consume 12,000 W. BTU/h measures the heat the unit can pull out of the room; the watts on your bill are a different quantity, and you can only work them out if you know the efficiency rating (EER or SEER) or the rated input power on the plate.

About accuracy

These calculators give guideline estimates and are honest about their limits. A professional heat-load calculation considers far more: the real build-up of walls and roof, thermal bridges, infiltration, humidity and hour-by-hour climate data.

HVAC calculators (14)

Air conditioner size calculatorCooling capacity calculatorFrigories to BTUBTU to frigoriesBTU to kWkW to BTUkW to frigoriesBTU per area calculatorAC energy consumption calculatorAC cost per hourMonthly AC costEER calculatorSEER calculatorAir changes per hour

HVAC guides

What size air conditioner do I need?It depends on far more than square footage, but there is a starting point.BTU per square foot for air conditioning30 to 40 BTU/h per square foot, with caveats that matter.BTU, tons and kW of cooling explainedOne ton is 12,000 BTU/h. Here is everything that follows from that.What size air conditioner for 200 square feet?Around 7,000 BTU, with caveats that can move the number.What size air conditioner for 300 square feet?Around 10,000 to 12,000 BTU for a typical living room.BTU vs frigories: what is the difference?They measure the same thing on different scales: 1 frigorie is 3.97 BTU.