To find out what size heat pump you are going to need, take the size of your house and your climate zone into consideration. In general, you are going to need around 30 BTUs of heating output for every square foot of space.
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Why is it important to invest in a properly sized unit and what factors you should pay attention to, in order to make the best possible decision? Here is everything that you need to know.
Related: The Most Efficient Way to Use a Heat Pump
How Do HVAC Experts Size Heat Pumps?
In North America, HVAC experts follow the Manual J and Manual S procedure to size a heating or cooling unit. These manuals are recommended by the ACCA (Air Conditioning Contractor’s Association of America).
Manual S, for example, is used to select the right equipment for proper airflow in a given house. It focuses on the ductwork, the thermostats, air handlers, and so on.
Manual J, in its turn, is used by the professionals to determine the heating and cooling load of the unit based on the house’s features and some other factors:
- The outdoor and indoor temperatures throughout the year
- Relative humidity
- The orientation of the house’s windows and doors
- Floor area
- Number of occupants
- Number of bedrooms
- Total heat loss
- Total heat gain, etc.
Fun fact: according to Manual S, the heat pump shouldn’t be sized to provide all the heat required by a home. Ideally, the heating loads should be met between 80% and 90%.
In Canada, the cooling and heating loads are determined by another sizing method – CSA-F280-M90.
How much does a Manual J and Manual S audit cost?
The price will depend on the company and your location. If you are lucky, the audit will be provided by the government for free.
Some HVAC companies offer such an audit for free as well, if you are buying a heat pump from them.
In all the other cases, such a procedure will cost you anywhere between $100 and $300.
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With the help of all the factors listed above, the professional will be able to choose the perfect system for your house for maximum efficiency.
But is there an easier way to find out what size heat pump you need?
What Size Heat Pump Do I Need?
Fortunately, there are a few simplified formulas that you can use to determine what size heat pump is the best fit for your house.
However, do bear in mind that the tips mentioned below will give you only a benchmark to work against. Those are only rough estimates and the numbers can differ from one house to another.
When talking about the size of a heat pump, experts don’t mean the size of the actual unit. The ‘size’ of a heat pump is referred to its heating and cooling output.
The most important factor that you should consider when choosing a heat pump is the size of your actual house.
For every square foot of living space, you are going to need about 30 BTUs of heating output.
This general rule can be applied to houses with a standard ceiling height – 8 feet. If your ceilings are higher, you are going to need a more powerful heat pump.
But what about your climate zone?
The seasonal outdoor temperatures should certainly be taken into consideration when choosing a heating or cooling system.
If you live in the cold north, feel free to add up to 40% to the total output.
If you live in the hot south, then reduce the total output by up to 30%.
What size heat pump do I need for a 2000 sq ft home?
You can use the simple 30 BTUs per square foot rule to get an idea of the size of the heat pump you are going to need.
That would be:
2.000 square feet x 30 BTUs = 60.000 BTUs
The great news is that this rule works for all types of heat pumps. Whether you decide to go for an air-source or a ground-source unit, you can certainly use this simple trick.
Heat Pump Sizing Charts
If you are not used to British Thermal Units, you can easily convert the BTUs into something more familiar:
1 ton = 12.000 BTUs
1 kW = 3412 BTUs
By square footage:
| House Size | The Approximate Heat Pump Size |
| 300 square feet | 9.000 BTUs |
| 750 square feet | 22.500 BTUs |
| 1.000 square feet | 30.000 BTUs |
| 2.500 square feet | 75.000 BTUs |
Size in BTUs and tons:
| BTUs | Heat Pump’s Tonnage |
| Up to 18.000 | 1.5 tons |
| 18.000 – 24.000 | 2 |
| 24.000 – 30.000 | 2.5 |
| 30.000 – 36.000 | 3 |
| 36.000 – 42.000 | 3.5 |
| 42.000 – 48.000 | 4 |
| 48.000 – 60.000 | 5 |
Size by the ton for different climates:
| Heat Pump’s Tonnage | Square Footage (hot climate; Zone 1, 2) | Square Footage (warm climate; Zone 3) | Square Footage (moderate climate; Zone 4, 5) |
| 1.5 tons | 600 – 800 square feet | 700 – 1.000 | 800 – 1.100 |
| 2 | 800 – 1.000 | 1.000 – 1.200 | 1.100 – 1.500 |
| 2.5 | 1.000 – 1.300 | 1.200 – 1.500 | 1.500 – 1.800 |
| 3.5 | 1.600 – 1.800 | 1.800 – 2.000 | 2.000 – 2.500 |
| 4 | 1.800 – 2.000 | 2.000 – 2.400 | 2.500 – 3.000 |
| 5 | 2.000 – 3.000 | 2.700 – 3.000 | 3.300 – 3.700 |
Other Heat Pump Factors to Consider
The size of the heat pump is an important, but not the only factor that you should consider when choosing a new unit.
Tip: remember that paying a higher upfront cost is practically always worth it when it comes to heat pumps. Highly efficient models will help you save a small fortune during their lifetime.
Energy efficiency ratings (SEER and HSPF)
SEER is the Seasonal Energy Efficiency Rating and it indicates the total amount of cooling (the lowest SEER rating allowed in the US for a heat pump is 13).
HSPF is the Heating Seasonal Performance Factor and it measures the system’s heating efficiency.
In general, the higher the rating, the more efficient the unit.
The type of the blower motor
You’ll find single-speed, two-speed, and multi-speed units available on the market today.
A variable-speed motor may use up to 75% less power than a single-speed motor.
The type of the compressor
You’ll get to choose between a single-stage, a two-stage compressor, and a variable-speed unit.
A single-stage compressor always operates at 100% capacity. A two-stage compressor, in its turn, has a low-capacity mode which is about 70% in the majority of the units.
Related: Why Heat Pump Compressor Is Not Turning On
Variable-capacity heat pumps can easily change their capacity from around 40% to 100% (the increments are less than 1%).
The location of the unit
The placement of the unit is not a feature of the actual heat pump, but it is definitely something that you would have to consider.
For example, you can purposely locate the indoor unit across the doorway to allow the heat pump to cool or heat your house more efficiently.
Is It Better to Oversize or Undersize a Heat Pump?
Does it even matter, if your heat pump is too big or too small for your house?
Yes, it does.
If you fail to get the size right, the unit won’t be able to work efficiently and might even break down.
If the heat pump is way too small for your house, the system will always be working extremely hard to try and meet the temperature demands. In the end, the unit won’t be able to heat or cool the space well enough, but your energy bills are going to skyrocket.
Moreover, the system’s components will wear down much faster or the whole unit would simply overheat and get damaged.
A heat pump that is too big will produce too much energy. This will lead to short cycling which is extremely stressful for the motor.
The homeowner will also be suffering from uncomfortable temperature changes throughout the day and ineffective control of indoor humidity which will result either in mold growth or the presence of static electricity.
If, for some reason, you would have to choose between an undersized and an oversized unit, better choose an undersized heat pump.
Even though such a unit would require more time to change the temperature, it won’t be as loud and will, all-in-all, last a bit longer.
With that being said, going for a properly sized heat pump is incredibly important, if you want to take advantage of all the benefits that these heating and cooling systems have to offer.