'Manual J load calculations' is how air conditioning (AC) technicians refer to the determination of cooling (or heating) loads calculations. The calculation helps AC installers to know the size of the AC needed for a house. Below are some of the factors that feature in manual J load calculations.
Construction materials affect the interaction between the indoor and outdoor temperatures. Some materials allow heat to pass more freely than others. This determines how much the heat from outside will affect the indoor temperature during the summer. For example, heat passes more readily through aluminum compared to wood. Thus, an aluminum building would require more cooling than a wood building during the summer.
An AC cools the house by absorbing heat inside the house and dumping it outside. The more heat there is in the house, the more cooling the house needs. A big house holds more air (hence more heat) than a smaller house, which means the former requires more cooling.
Types of Windows and Doors
Windows and doors have different insulative values compared to the rest of the house. For one, windows and doors usually have different materials from the rest of the house. Secondly, windows and doors tend to have small air gaps along their perimeters. The number, sizes, and materials of the windows and doors are all factors of the calculations.
The standard ceiling height is 9 feet, but some ceilings can be as high as 12 feet or higher. The ceiling height is important since it determines the volume of air in the house. A high ceiling means more air that calls for more cooling, and the reverse is also true.
The orientation of the home refers to its positioning on the lot. The orientation determines how much sunlight (and hence heat) gets into the house and how much draft affects the house, among other things. Both sunlight and draft affect the needed cooling, which means orientation must feature in the calculations.
The manual J load calculation doesn't just focus on the house — it includes everything that can affect your home's temperature. For example, the local climate determines how hot your house is likely to get at any time of the year. Thus, the load calculations in Alaska cannot be the same as those of the Midwest regions.
The above list of factors is not exhaustive — anything that can affect cooling must be considered. Fortunately, you do not have to worry about the calculations because your AC installer will take care of them.