Can a Heat Pump Be Too Big for a House?


I’ve been learning about the size of heat pumps, and I wondered whether a heat pump could be too big for a house. So, I did some research, and here’s what I found. Let’s explore whether a heat pump can be too big for a house?

An oversized heat pump will cycle quickly, causing harm to the motor. Heat pumps that are too big for your home lose efficiency and are more expensive to operate. HVAC professionals use the Model J calculation to discover what size heat pump your home needs. 

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There are a few issues that happen if your heat pump is too big for your house. And I also wondered about the nitty-gritty of getting the right sized heat pump. 

So, read on where I’ll explain what happens when your heat pump is too big and how to calculate what size heat pump you need.

Is an Oversized Heat Pump Bad?

There is a range of drawbacks to having an oversized heat pump:

  1. It reduces the life expectancy of your heat pump unit.
  2. You’ll have a higher electric bill.
  3. The heat pump unit will be louder.
  4. You can have indoor humidity issues.

1. Reduces the Life Expectancy of Your Unit

According to Unique Indoor Comfort, a leading HVAC company in Philadelphia, when your heat pump unit is too big for a house, it causes an issue known as short cycling. 

Short cycling is when it heats it or cools down much faster, which caused the heat pump to turn on and off frequently. Short cycling increases the wear and tear on the motor and other moving parts.

2. You’ll Have a Higher Electric Bill

When a heat pump heats a home slowly, the furnishings in your home warm up and trap the heat. Over time this heat gets released once the heat pump turns off. 

When your heat pump is too big, the heat pump will heat the room for a shorter time, and the furnishings in your home have less time to absorb heat. 

Your heat pump will have to heat the room more often because it cools down quicker.

3. You Will Have a Louder Unit

In the opinion of Sunshine Renewable Energy, a leading HVAC company in Canada, ductless heat pumps operate at about 17 to 26 decibels. Standard ducted heat pumps of 2-ton to 5-ton in size averages 40-60 decibels. Here’s a table that shows how loud familiar sounds:

NoiseVolume (decibels)
Ductless heat pump (1 ton)17 to 26
Standard heat pump (2-5 ton)40 to 60
Normal breathing10
Whispering20
Light rain40
Refrigerator hum40
Normal conversation60
Clothes washing machine70
City traffic (inside car)80
Motorcycle95
Data provided by Pulsarinstruments.com & Cdc.gov

Overall though, a bigger unit has a bigger fan, and a bigger fan is louder.

4. You Can Have Indoor Humidity Issues

A heat pump that is too large for your home can cause indoor humidity problems that can affect your home’s comfort. As a heat pump runs, it helps maintain an ideal indoor humidity level of around 55%. A heat pump that short cycles, doesn’t operate long enough to remove humidity from indoor air.

High humidity inside your home can lead to condensation problems on windows and cause your home to feel stuffy. In contrast, humidity levels that are too low, can feel very dry inside.

How Big Should Your Heat Pump Be?

HVAC specialists use a Manual J calculation to find the total BTUs your heat pump should be. The formula estimates the BTU size based on your home’s square footage, number of doors and windows, and ceiling height. 

Doing it the manual way is a long and lengthy process; however, it gives you the most accurate size heat.

Manual J Calculation Explained

The Manual J calculation is widely accepted as the best measurement for determining heat pump sizing. Manual J takes into consideration many factors other methods ignore.

The Manual J report will explain exactly how many British Thermal Units (BTUs) of heating and cooling your home needs. The data used to determine heat pump sizing comes from:

  • Heated square footage – this is the size of the heated living space.
  • Average ceiling height – ceiling height affects how much heating and cooling production is needed. The higher the ceilings means, the more heating and cooling output required. While this seems obvious, it is often an overlooked factor.
  • Climate zone you live in – climates zones based on historical temperature data.
  • Type, location, and ductwork condition – ductwork in basements, crawl spaces, and attics can cause heat loss. Ducts that are old and lack insulation also contribute to heat loss. Poor ductwork condition and location require larger heat pumps.
  • Number and style of windows – energy-efficient windows and older windows affect energy efficiency. Older windows that are not energy efficient will require a larger heat pump. Each window requires 1000 BTUs.
  • Number and style of exterior doors – like windows, each exterior door needs 1000 BTUs in the calculation.
  • Natural shade or sunlight – the calculation takes into account the amount of direct sunlight or natural shade.
  • Quality and amount of insulation – Houses will lower levels of insulation will experience more heat loss. The insulation R-value is determined by the type and thickness of the insulation. Older houses generally have low levels of insulation that affects heat pump performance.
  • The number of people using the home – the more people that live in a house, the more BTUs are needed. However, this has a minimal impact on BTUs. Each person living in a home needs about 100 BTUs.

An HVAC professional can provide this service for you. However, there are other options to allow you to do this yourself.

Online options do all the calculations, but you need to know a lot of information about your house ahead of time. 

One of the best options is an app called Cool Calc. It is approved by the Air Conditioning Contractors of America (ACCA). It’s free to use to do calculations, and you can also pay to get ACCA approved reports.  

Here’s a cool video that shows how Cool Calc works for doing a Manual J calculation:

Is an Oversized or Undersized Heat Pump Better?

Overall, an undersized heat pump is better than an oversized one. An undersized heat pump will take longer to change the temperature. But, the unit won’t be as loud and will last longer. An oversized heat pump will turn on and off more frequently, which will use more electricity.

The advantage of having an oversized heat pump is that it will change the space’s temperature quicker because of the bigger fan and capacity. 

However, because the heat pump gets the air to the right temperature before turning off so quickly, the furnishing and construction in your home haven’t had much time to absorb the heat. 

For example, if you have tiles or brick walls. These can store a lot of heat and release heat back into the room once your heat pump turns off.

With a correct sized heat pump, the temperature will increase slowly, and heat will have time to seep into all the nooks and crannies before the unit recognizes the temperature is warm or cool enough and shuts off. 

A correctly sized system causes the temperature to stay the same for a long time.

How Many Square Feet Does a Heat Pump Cover?

The most common size of heat pumps used in residential areas are:

BTUsHeated Square Footage
5,000100 – 150
6,000150 – 250
7,000250 – 300
8,000300 – 350
9,000350 – 400
10,000400 – 450
12,000450 – 500
14,000500 – 700
18,000700 – 1,000
21,0001,000 – 1,200
23,0001,200 – 1,400
24,0001,400 – 1,500
30,0001,500 – 2,000
34,0002,000 – 2,500
Data provided by TraneSunshine Renewal Energy.

 The 9,000 BTU size is ideal for small studio apartments. The next size, up 12,000 BTU, is ideal for larger studio apartments and 2 bedroom apartments.

A 15,000 BTU heat pump is around the size of a standard 3 bedroom home. However, heat pumps can be much larger than these. 

There is also a back of the envelope calculation you can use to figure out what size heat pump you will need in British Thermal Units (BTU). 

To do this, you need to calculate the area in square feet. Multiply each room’s length by its width. Add them all together to get the total area. Then to get BTUs, multiply the area by 25. 

Other factors also influence what size heat pump you need. These are:

  • The kind of floor: wood, tile, or carpet.
  • Whether residents be spending a lot of time indoors, for example, the elderly or small children.
  • Whether the house gets a lot of sunlight.
  • The climate of the region
  • The number of doors the rooms have
  • The number of windows and their size
  • Whether insulation has been installed, and what kind
  • How high the ceiling is

These factors can increase how many BTU’s you’ll want to have by around 20%. 

For example, if you have taller ceilings, over 9 feet tall (2.7 meters), you need to increase the BTU estimate by 20%, according to HVAC contractors MSPPlumbingHeatingAir.com.

Because it can be quite tricky to figure out the exact size heat pump you should get, it helps to hire a consultant.

In Conclusion

A heat pump can be too big for a house. Having a heat pump that is too big for a house has drawbacks. And you want to get the right size heat pump for your house. When a heat pump isn’t the right size for a house, it will use more electricity. 

It will also have to turn on and off more times, which causes more wear and tear on the unit. Compared to a correctly sized heat pump. You can calculate it roughly, but it’s better to consult a professional to ensure you get the right size for your climate and your home or office’s unique characteristics.

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.

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