How Do I Size a Heat Pump for My Home?

Why Heat Pump Sizing Matters

Proper sizing is one of the most important parts of selecting a heat pump. A correctly sized system not only cools your home, it also removes moisture, and a home that holds low humidity feels much cooler at any thermostat setting. An oversized system will short cycle, meaning it turns on and off too frequently. Short cycling does not give the equipment the run time it needs to control humidity, it shortens the life of the system, and it raises operating cost through repeated on and off power surges. The goal is a system that is neither too large nor too small.

How To Pick the Right Size

Software Load Calculation

Running a sizing program with all of your construction data is by far the most accurate method, because it removes guesswork, opinion, and rules of thumb. Your system performs as the manufacturer intended, your power bills stay as low as possible, and your comfort is assured. Many municipalities require a software load calculation when permitting new construction, since no best guesses are allowed for a code correct installation. AC Direct provides a free sizing program with any equipment purchase.

Contractor Estimate

A local contractor can visit your home and evaluate the size needed. An experienced contractor may already know the right capacity from similar floor plans nearby. Contractors do not always agree, so ask what criteria each one used. If the evaluation relies only on square footage, there is no assurance the system will perform properly. A simplistic estimate often errs toward an oversized unit because that feels safer than undersizing. Ask good questions and expect clear, well thought out answers.

Read Your Existing Model Number

If you are replacing a system, the outdoor unit model number usually codes the BTU capacity. There are 12,000 BTU per ton, so a number such as 24 means 24,000 BTU, which divided by 12,000 equals 2 tons. Use the model number, not the serial number.