Cooling a volume of air in a home depends on several factors, including the current temperature and humidity level in the home, the insulation and sealing of the home, the outdoor temperature and humidity, and the location and orientation of the building.
General Rule of Thumb
A Ton of HVAC system is designed to cool approximately 400-600 square feet of living space. If your home is 400 square feet, a ton of system will effectively cool your home. In Arizona, a ton would be enough for 300-400 square feet if glazing load is low & facing North-South direction, the walls are R-19, Ceiling is R-38, and ceiling height is 8-10 feet.
Homeowner should consider additional tonnage if the space is going to be used for social gathering or have high internal load due to computers, speakers, amplifiers, etc..
How much temperature drop can a Ton of system provide in 400sqft home?
Depending on the above-mentioned general rule of thumb, the amount of temperature drop will vary. Typically, on an ideal living space – R-19 Walls, R-38 Ceiling, 8 feet Ceiling height, Double Pane Low-e windows facing North South Direction, a Ton of system can drop a temperature by 1-2 degrees Fahrenheit per hour. So, if the initial temperature of the space is 77 degrees Fahrenheit, a Ton of system will bring down the temperature to 75-76 degrees Fahrenheit within an hour.
Load calculation is important
For areas like Arizona and high humidity during summer, it is vital to run the load calculation for homes that are masonry, bricks, ceiling height 10 feet, high glazing, or high internal load. This is due to under-performance of the system when temperature goes above 115 degrees Fahrenheit in dry weather region, and the system is unable to meet the latent load in high humid region.