How BTU Impacts Heat Pump Performance

Daikin FIT heat pump outdoor unit

What Size Heat Pump Btu Do I Need for My Home?

A heat pump is a cost-effective and energy-efficient way to heat or cool your home. Unlike traditional systems that modify the temperature in your home by heating or cooling the surrounding air, a heat pump transfers heat. When you want your home to stay warm, the heat pump transfers heat from the outdoor unit to the indoor unit, and when you want your home to cool down, the heat pump transfers heat from the indoor unit to the outdoor unit. This thermal energy transfer is measured in British Thermal Units, or Btu. In order to choose a heat pump that is sized correctly to your living space, you first need to understand how heat pump Btu is measured and how Btu impacts heat pump performance. Heat pump capacity is measured in “tons of refrigeration,” and one ton is the equivalent of 12,000 Btu. A two-ton heat pump has 24,000 Btu of cooling capacity. Heating capacity will be in the range of 24,000 Btu, but it’s important to understand that the name-plate capacity on a unit refers to cooling only.

Why do you need to think about something as technical as heat pump Btu when choosing your unit? You want to size your heat pump appropriately in order to heat or cool your living space using the least amount of electricity possible. 

What if My Heat Pump is Too Big or Too Small? 

Problems arise when heat pump Btu isn’t matched to the area the heat pump is trying to heat or cool. 

Here’s what happens when you choose a heat pump that is too big: it reaches your desired temperature very quickly, and then shuts off. While that might sound effective if you are familiar with oil or electric heat, it can lead to problems with a heat pump. 

When the temperature begins to drop, the heat pump turns on again and bumps up the temperature sharply before shutting off. This on/off pattern is called “short cycling.” Short Cycling stresses the motor and shortens the lifespan of your heat pump because it always requires the system to run at its peak. Additionally, the heat pump will have difficulty maintaining a set temperature because it is constantly turning on and off. 

A properly sized Daikin heat pump will remain on pretty much always, but using much less energy than cycling going from Full to Empty. Think of it like cruise control for your car. You ramp up quickly to speed on the highway, but then your RPMs level out and you end up using a lot less gas. 

A short cycling system will struggle to provide the comfort and energy savings expected by a properly sized heat pump.

Another problem with an oversized heat pump is that defrost mode may not engage during winter months. For a heat pump’s outdoor unit to engage the defrost mode, it must run continuously for approximately 15 minutes. This may not be possible if the heat pump only runs for a couple of minutes at a time and then shuts off again due to being oversized. Ice buildup on the outdoor unit’s coil can potentially lead to permanent damage if not addressed. 

During the summer months, this short on/off cycle prevents the heat pump from running long enough to dehumidify the home, which creates mugginess and discomfort. 

Conversely, when a heat pump is undersized, the system runs constantly at full throttle to achieve your desired temperature. In the winter, the constant running of the heat pump at max capacity, and perpetual attempt to reach a set temperature, triggers the defrost mode more than needed. 

In both scenarios, when a heat pump is too big or too small for the space it is operating in, the heat pump uses a lot of electricity to reach a desired indoor temperature. The heat pump never gets a chance to do what the system does best, which is to switch into a sort of “coast” mode where it maintains a set temperature without having to run at its peak. This is where energy and cost savings are introduced. 

Discover how the new Daikin FIT’s inverter technology prevents temperature fluctuations and keeps indoor temperature consistent. 

Heat Pump Sizing Guide by Square Footage 

Below is a general guide to ductless heat pump units and room size. Other key factors you need to take into consideration include: heat loss and heat gain from the location of windows and also the layout of your home. You may have a certain square footage in a room, but if that room opens into a long hallway, has vaulted ceilings, etc., that could alter your heating or cooling needs for that room. Proper sizing should be done by a certified HVAC technician like your local Daikin dealer

  • 9,000 Btu: 250 sq ft – 450 sq ft
  • 12,000 Btu: 400 sq ft – 750 sq ft
  • 15,000 Btu: 700 sq ft – 1000 sq ft
  • 18,000 Btu: 800 sq ft – 1200 sq ft

Understanding heat pump Btu is vital to choosing the right heat pump for your space. If you want to take advantage of the cost and energy savings a heat pump can provide, enlist the help of an HVAC expert to weigh all of the factors that go into selecting the correct heat pump size for your needs. 

Find your nearest certified Daikin dealer to book your heat pump installation or service.