Honestly, most dealers guess what size heating and air conditioning equipment you need.
As a result, most existing equipment is too large. In the old days, the thought was, “the bigger, the better.” But big furnaces cycling constantly aren’t efficient, nor do they deliver even comfort. And big air conditioners cycling constantly are also inefficient, don’t remove moisture well, and don’t cool evenly. In fact, the newer high SEER (Seasonal Energy Efficiency Ratio) units are particularly bad at moisture removal in the first 7-8 minutes of operation.
The only way to really make sure you’re getting the right equipment is to have a trained professional survey the house. Your estimator should not just consider square footage of floor space, but also take into account walls, windows, doors, insulation, shade—anything that affects heat entering and leaving your house. You need all this information to make the right choice.
Want to figure it out for yourself? You can purchase an easy-to-use calculation package at hvac-calc.com. But it may be easier to find a contractor you trust.