When it comes to air conditioning, calculating BTUs is an essential part of determining the size of the unit. A BTU or British Thermal Unit is the measure of heat energy that comes from a thermal unit and an Imperial Gallon is 10 pounds in weight. Therefore, a BTU is 1/10 of an Imperial Gallon or one pound of water at sea level and a BTU will raise water temperature one degree Fahrenheit. However, in air-conditioning, we are not changing water temperature, but the temperature of the air. While the metric system has taken over most industries, BTUs in air conditioning remains the standard due to their significance in heating and cooling.
What does a BTU do?
Simply put, a BTU measurement shows how much energy an AC unit uses to remove heat from a space within an hour. This allows HVAC techs to determine what size HVAC units should be installed. When an HVAC tech determines BTU usage, they must account for many factors. Every BTU has a corresponding tonnage, which has nothing to do with weight but is in reference to a unit’s cooling capacity.
A ton of cooling known as refrigeration is the amount of heat it takes to melt a pound of ice in a 24-hour period. Furthermore, 12,000 BTUs is equal to one ton of cooling and there are guidelines for how many BTUs are needed for the square footage of a space. Also, heat in air conditioning is referring to energy and not temperature. Air conditioning systems simply move energy from one place to another.
| Square Fee | BTUs |
|---|---|
| 100-150 | 5,000 |
| 150-250 | 6,000 |
| 250-300 | 7,000 |
| 300-350 | 8,000 |
| 350-400 | 9,000 |
| 400-450 | 10,000 |
| 450-500 | 12,000 |
| 500-700 | 14,000 |
| 700-1,000 | 18,000 |
| 1,000-1,200 | 21,000 |
| 1,200-1,400 | 23,000 |
| 1,400-1,500 | 24,000 |
| 1,500-2,000 | 30,000 |
| 2,000-2,500 | 34,000 |
Here is a resource to quickly calculate the BTUs needed.
Conclusion
Many factors go into choosing an HVAC system and BTUs are just one factor in this calculation. It also helps in determining kilowatts which has a direct impact on energy costs. Equally important are room size, aspects of insulation, humidity levels, ceiling height, window size, and room occupancy. Being informed of all these factors make sure the perfect sized HVAC unit is installed to serve the cooling needs.