Sizing A Heat Pump: Heat Pump Load Calculations

Many homes in the San Francisco Bay Area use a heat pump to provide energy-efficient heating and air-conditioning. A heat pump functions as typical central air conditioner in the summer; in the winter, the refrigeration cycle reverses itself to pump heat from the outdoors into your home. Instead of using combustion fuel, heat pumps use electricity and refrigerant to transfer heat from outside to inside.

When shopping for a new heat pump, the first thing you should do is determine what type of heat pump you want and how big it needs to be to provide ample heating and cooling to your home. If you’re unsure what you need, here are some tips to size a heat pump for your home’s particular needs.

Oversized Units

Consider the costs of an oversized heat pump. Not only are larger units more expensive to install and operate, they can also cause many comfort problems.

Short cycling (when unit turns on and off frequently) normally occurs when an HVAC system has been oversized for your home. An oversized heat pump that cycles on and off frequently wears down much faster, resulting in an increased electric bill and unnecessary wear on the unit. It’s not good for your home, heat pump, or wallet.

For optimum comfort and efficiency, you want your heat pump running at a steady pace rather than blasting your home with too much conditioned air all at once.

Undersized Units

Undersized heat pumps aren’t large enough to properly condition your indoor air. They end up running constantly, resulting in similar issues to oversized units. Undersized units will run up your energy bill and present ever-present problems.

Improperly sized heat pumps result in:

  • Not performing to their rated efficiency
  • Reduced performance (as much as 30%)
  • Decline in comfort
  • Insufficient dehumidification
  • Dust and energy loss from duct leaks
  • Poor air distribution
  • Unwanted stress on unit
  • Higher energy bills
  • More heating and air conditioning repairs
  • Reduced lifespan
  • Potentially voided manufacturer warranty

Hiring the right HVAC company to perform your heat pump load calculations is essential for getting the most return on your investment.

How to Properly Size a Heat Pump

To correctly size a heat pump, the first step is to perform a load calculation. Basically, take the total volume of the rooms being heated (in cubic meters) and then determine the number of BTUs needed based on size, space, insulation, and more. Heat pump load calculations should only be performed by qualified HVAC contractors.

Some HVAC installers simply replace your heat pump with a similarly sized one, assuming the first unit was properly sized in the first place. Even if it were properly sized, changes to your home could necessitate a larger or smaller unit.

What’s included in a Manual J inspection?

Manual J is the ACCA (Air Conditioning Contractors of America Association) certified requirements for proper HVAC load calculations. In order to properly size a heat pump unit, Manual J provides instructions for measuring ventilation and insulation levels, air duct tightness, the size of your home, and much more.

Only after completing a Manual J inspection should your technician choose the HVAC capacity you need.

Once a professional technician has taken everything into account, they can determine the number of kW (converted to BTUs) needed to heat or cool that particular room.

Professional Sizing

The reason it is so important to call a professional is that certain things, like poorly insulated windows, cracks in the foundation, leaks in the ducts and other issues can have an impact on the overall sizing.

Additionally, the type of heat pump you choose must be effective when connected to your existing air handler and ductwork. Service Champions can make these measurements and ensure the right sized device is selected.


  • Before installing a new heat pump, improve your home’s insulation. This may allow you to save some money upfront and over the long-term with a smaller unit.
  • Sign up for a home maintenance plan. Twice a year, Service Champions will provide a full HVAC cleaning and tune-up, providing you with reliable and energy-efficient heating and air-conditioning.

If you’re unsure about anything related to HVAC sizing and selecting a new heat pump for your Northern California home, contact Service Champions for an evaluation. We will perform a full load calculation and present you with options for a new heat pump based on our inspection.

Contact Service Champions for friendly Diamond Certified HVAC technicians in the East Bay and South Bay areas.

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