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Heat Pump Sizes: What Size Heat Pump Do I Need?

heat pump sizes explained what size heat pump do i need

Any discussion about heating and cooling your home means talking about home energy efficiency. Up to 48 percent of home energy costs come from your HVAC system. One of the most crucial choices for energy efficiency and green heating is the size of your system. Heat pumps, as one of the most popular HVAC home systems, need to be sized correctly or you will find yourself with a host of problems, including high energy bills.

What is a Heat Pump?

A heat pump is a central heating and cooling system that uses refrigerant to move heat from one point to another. In winter, a heat pump transfers heat from the outside air (air source heat pump) or the ground (geothermal heat pump) into your home while in the summer it reverses that process to cool your home.

Heat pumps typically run on electricity and are extremely energy efficient. Local climate plays a big part in how efficient a heat pump is at warming or cooling your home. Heat pumps don’t fare well in an extremely hot or cold climate but do well in moderate climates like Portland where temperatures don’t go below freezing often.

Additional reading: Heat Pumps 101: How Does a Heat Pump Work?

Why are Heat Pumps Sized in Tons?

Let’s go over a short heat pump vocabulary lesson.

  • A ton is a measure of cooling with every 1 ton of cooling equal to 12,000 BTUs per hour. 
  • BTU stands for British Thermal Unit and is the amount of energy it takes to change the temperature of a pound of water by one degree Fahrenheit.

When looking at heat pump sizing, a ton is a measurement of the capacity of the system. It takes a little math to come up with how much a heat pump capacity is.

If a heat pump is 3 tons then it is equal to 36,000 BTU cooling power.

One rule of thumb in determining how many tons of cooling your heat pump will need is less than 1 ton per 500 square feet of space. However, that number can vary widely. Do not assume that because your neighbor has a 3-ton heat pump that you should too. Each home has varying factors that need to be assessed to find the right size for your particular home and comfort level. 

SEER and HSPF Ratings

You have seen them. Bright yellow energy labels on a heat pump tell you the SEER and HSPF ratings. But what are SEER and HSPF ratings?

What is a SEER Rating?

SEER stands for Seasonal Energy Efficiency Ratio and it measures a cooling unit’s effectiveness, taking into account seasonal fluctuations. The higher the number the more efficient a heat pump is at cooling a home during warm seasons. This is an educated estimate since the season and home factors can change energy consumption. Higher SEER ratings are typically more expensive units but are also more efficient.

What is an HSPF Rating?

An HSPF rating stands for Heating Seasonal Performance Factor and measures the heating efficiency of a unit. Like the SEER rating, this is an average standard based on a variety of conditions. The greater the rating the better the heat pump. When you look for efficiency ratings the higher the number the lower the energy consumption which is a win for your energy costs.

Additional reading: Heating & Cooling Efficiency Ratings Explained

Is it Better to Oversize or Undersize a Heat Pump?

In the summer, when heat and humidity start to climb, an oversized heat pump will get a room to the right level of coolness but will never switch to maintenance mode. Not only does this cause the heat pump to start and stop early, creating incomplete cycles, it also consumes a lot of energy.

It also will make your heat pump freeze up in winter and wear out quickly. To extend the life of your equipment it is important to have the right size heat pump for your home. 

Alternatively, an undersized heat pump will work at max capacity to keep the temperature at the right level. Eventually, your heat pump will not be able to keep up with the demands of the thermostat and you will find the comfort level in your home isn’t what you would like. 

One of the primary things to consider when sizing a heat pump is the load calculation. In the case of heat pumps, going bigger is not better.  If a heat pump is not sized properly something called “short cycling” occurs. Heat pumps go through a natural on and off cycle to maintain temperatures in your home. 

Heat pumps work a bit like bicycle gears. To get started they draw a lot of power to get the indoor temperature to the desired comfort level. Once the room is at the desired temperature, the heat pump goes into maintenance gear, using less energy to cycle on and off to keep everything just right. 

What Size Heat Pump Do I Need?

In order to answer the question about heat pump size there are a few things about your home that will need to be evaluated: 

  • House orientation
  • Size
  • Number of doors
  • Windows
  • Insulation 
  • Winter and summer conditions
  • Ductwork

Using Manual J procedures, professional Jacobs Heating & Air Conditioning experts can determine the right size heat pump system or the right size air conditioner for your home. They can find the balance point between heating and cooling your home with a heat pump system to reduce energy use, cost, and maintenance and keep you comfortable.

Additional reading:

How Jacobs Can Help

Finding the right size heat pump for your home is crucial to both your energy bills and your comfort. Jacobs Heating & Air Conditioning experts are here to guide you through the process of correctly sizing a heat pump for your home. Consultants will help evaluate your home to ensure your heat pump is long-lasting and will keep you comfortable in all seasons. Avoid extra costs and fewer repairs by scheduling a tune-up for your existing heating system before issues arise. Our maintenance plans keep your system running like clockwork without any stress or hassle. No matter what you need we’re always just a phone call away. You are welcome to review our statement on COVID-19 and how we’re taking precautions to protect you, our team, and our communities.

About the Author

Amanda Jacobs portrait

Amanda Jacobs, Internal Project Manager

Amanda Jacobs is an Internal Projects Manager and 3rd generation member of Jacobs Heating & Air Conditioning. She received her MBA from Seattle University and has worked for a leading HVAC training and consulting firm. When not talking HVAC on the Jacobs Blog, you can find her on the golf course or whipping up her famous vegan chili.