What Size Heat Pump Do I Need?

Whether you’re getting a heat pump system for a new home or upgrading your HVAC system to include an electric heat pump, correct sizing is critical to the success of the installation and your ongoing comfort. For proper sizing and installation, work with a trusted HVAC professional.

HVAC sizing is a process that HVAC contractors use to determine the appropriate heat pump and paired air handler or furnace combination you need to efficiently heat and cool your home. You need the right capacity to get the job done, without the system being oversized or undersized. 

Improper sizing causes long-term problems. Because a heat pump can last an average of 15 years, you (and your dealer) want to get the sizing right.

An oversized system causes short cycling or rapid cycling. The system turns on and off too frequently and may cool your house to the set temperature before it reduces the humidity sufficiently. This can result in you feeling cold and clammy. Frequent cycling also results in increased energy bills.

An HVAC system that’s too small for your home can result in excessive run times. The system may struggle to reach the set temperature. Long run times lead to higher heating and cooling bills.

If it’s time to replace an old or inefficient heat pump or replace a furnace and AC unit with an air-source heat pump system, don’t just assume that your current units are the right size for your home. Work with a trusted HVAC company in your area to calculate your home’s heating and cooling load to get you the Goldilocks system that’s just right for your home.  

HVAC technicians learn how to size an HVAC system accurately as part of their training. But not every HVAC contractor goes to the trouble of doing it right. That’s why industry estimates are that up to 90% of HVAC systems are improperly sized or improperly installed.

Correct sizing involves performing the Manual J calculation and can also involve a separate calculation for duct sizing.  Factors to consider include:

• Your climate zone 
• Your heating and cooling needs
• The age of your home
• The size of your home
• Your home’s layout
• Ceiling height
• Number, type, and efficiency of your windows and doors
• How much sun or shade your home gets
• The existing ductwork
• How well your home is insulated
• Other heat-generating appliances

Before an HVAC contractor comes to give you a quote on heat pump installation, you can estimate the proper size of the heat pump you need by using the square feet heat pump size calculator. 

This tons per square foot estimation is not as accurate as the Manual J load calculation but can give you an idea of the system capacity you need. Listen to the HVAC contractors who give you estimates on a new system. They’ve been working in the industry for years.

A ton refers to capacity rather than the weight of the unit. One ton equals 12,000 British Thermal Units (BTUs).

Heat pumps also come in half-ton sizes, including 2.5-ton and 3.5-ton heat pumps.

This SF/ton calculation has evolved over the years due to construction material and insulation requirements used today vs historically.  Thirty years ago, the rule of thumb was 500 SF/ton. More recently, this estimation would be 600 SF/ton for existing residential applications with different requirements for multi-family and commercial locations.   

However, with the updated insulating materials used in new construction, it may be closer to 1000 SF/ton for residential. The SF/ton may also need to be adjusted for your home if you’ve installed energy-efficient replacement windows and doors, made insulation upgrades, and more.

So if one HVAC contractor recommends one unit size and another recommends a larger capacity heat pump, ask them to show you their calculations to back up their recommendation.

Your HVAC ductwork plays an important role in your home's comfort as well. Hidden behind the walls or above the ceiling, this system of ducts and vents transports the heated or cooled air throughout your home.

In addition to performing the Manual J load calculation, your HVAC contractor should evaluate your existing ductwork. Does it need duct sealing? Does it need to be replaced with smaller ducts? Does it need to be replaced with larger ducts? They can perform an assessment including the Manual D calculation to help determine the answers. 

Before you schedule quotes for a new heat pump system, do some more homework. Check out our recommended reading list:

• Heat Pump Buying Checklist
• New Heat Pump Rebates
• How to Find the Best HVAC Service Near Me

Be sure to work with an HVAC company with a lot of experience in designing and installing heat pump systems. Go for a system that will qualify you for heat pump rebates and the $2,000 federal heat pump tax credit.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Kimberly Sexton, Senior Systems Engineer

Heat Pump Capacitor: What You Need to Know

How Long Do Heat Pumps Last?

How Do I Know If I Have a Heat Pump?

Heat Pump Reversing Valve Basics

Why Is My Heat Pump Not Turning On?

Why Is My Heat Pump Not Cooling?

Heat Pump Not Heating

Heat Pump Fan Not Spinning