To supply a building with just the right heating or cooling temperature, proper hvac sizing is necessary. An HVAC that is sized too small is not capable of providing the residence with the desired temperature. As for an HVAC that is too big for a structure, temperature swings or short cycling may occur. The unit would run on short intervals, turning on and off, wearing out the system faster. In sizing an HVAC unit, prepare to do some measuring and calculations.
Know the square footage of the room you want to heat or cool. Measure the length and width of the area and multiply the two to get the square footage. For buildings involving more than one room, measure the square footage of each room and sum up all the resulting square footage together.
For CFM or cubic feet minute requirement, a building generally has 1 CFM per square foot. However, for areas with several windows installed, it is 2 CFM per square foot. So, if the building has a total square footage of 2,000, it equates to having 2,000 CFM.
Convert the total CFM into tons, 400 CFM=1 ton, to calculate the cooling load. If the building needs 2,000 CFM, divide it by 400 to achieve the 5 ton unit size of an air conditioner.
The heating load of an HVAC is calculated by multiplying the square footage and BTU or British thermal unit per square foot. The BTUs per square foot differ in area types. Places with warmer weather make use of 25-30 BTUs per square foot. For those with colder climates, it is 30-40 BTUs per square foot.
Have a certified HVAC contractor re-check the calculations and make the needed HVAC resizing to ensure that the unit size is accurate before the purchase.