HVAC Sizing 101 – How to determine the size of the HVAC system you need for your home

An HVAC system is a big investment on your part. We’re not just referring to the initial costs of purchasing and installing the equipment, but we’re also referring to the amount of money you’ll spend on energy bills over the years. Statistics say that you will spend more than $2,000 this year on energy bills alone. Your HVAC system accounts for almost half of the energy your home consumes in that time period. Your home, regardless of whether it is old or new, consumes a lot of energy. Whether you choose to upgrade your existing HVAC system or install a new one in your new home, here are some tips to follow to choose the right size system to ensure energy efficiency.

So what does one do to prevent their home from absorbing so much energy? First, understand that if your equipment is old, it’s time to replace it. Equipment that is 10 years old or older is extremely inefficient and should be replaced, preferably with an energy efficient (ie Energy Star qualified) model. When shopping for any type of HVAC equipment, it’s smart to go with an energy efficient model. It will save you a ton of money over the years.

You’re probably wondering, “So if I choose energy-efficient equipment, why does size matter?” It matters! Choosing the right size equipment (ie, the right heating/cooling output) directly affects your comfort, the efficiency of your HVAC system, and your operating and maintenance costs. You can see how important and underrated this topic is. In fact, it has been estimated that more than half of the HVAC industry does not correctly size their HVAC systems.

“Oversizing” tends to be the biggest mistake people make. When you oversize an HVAC system, it can affect several areas within the process. For example, the installation will be more expensive. Typically, large systems tend to cost more to operate, break down frequently, run inefficiently, and require more maintenance. Large air conditioners tend to shut down before they have had a chance to properly dehumidify the air. This results in a damp environment that can be prone to mold. Oversized ovens create uncomfortable temperature swings.

When your HVAC technician tries to size your system, they shouldn’t be reading a label or simple book standards. Instead, the calculation should be multivariable and include factors that are unique to your situation. For example, what is the weather like in your area? How many windows does it have and how big are they? How much insulation is there and what kind of insulation is it? How big is the house? Is the house two stories or one story? How much outside is sneaking in? How many occupants are there?

There are two industry standards that should be used to help determine the proper size for your system. These are “Manual J” and “Manual D”, created by Air Conditioning Contractors of America. Manual J, also called “Residential Load Calculation”, is primarily used to determine HVAC sizing calculations. A reputable HVAC company will tell you that they use Manual J to determine sizing. Manual D, also called “Residential Duct Layout,” is used to determine duct sizing. When looking for a company to help you install your new HVAC system, always be sure to ask whether or not they use the J & D Manual in their sizing and installation process.