How to calculate the air conditioner size for a house

The key to finding the right air conditioner for your house lies in finding the right-sized unit to cool all your living spaces efficiently.

The hot summer season may be upon you and you may be thinking of ways to keep your household cool and comfortable in often uncomfortable, hot, and humid temperatures. Investing in an air conditioner could be the best move to make to ensure you make it through summer.

Getting an air conditioner, however, is not as simple as just walking into a store and asking for the unit you like. It takes careful consideration of the size and type of house you have.

Thus, you have to choose the right sized unit to be able to cool your space effectively.

Air conditioner size for a house

The most important factor to address when you are looking for the right air conditioner for cooling or heating your house is the size of the unit you need.

The sizing process can be quite tricky to understand, but simply put, the unit must have the cooling power or capacity to cool the size of your space efficiently.

Bigger might not always be better, and smaller might not always be cheaper. The air conditioner’s cooling capacity determines its size and you need to know how big your home space is to check what cooling capacity you need.

How to calculate the air conditioner size for a house

The cooling capacity of air conditioners is measured in British Thermal Units (BTU). This is what you need to pay attention to in terms of size.

In order to choose the right size, you need to know the size of your home in square feet. 20 BTUs are needed for every square foot.

For your entire home you need to measure the square feet of each room and add them all up to determine the number of square feet your home equates to.

It is important that you only measure and calculate the living spaces of rooms you intend to cool and not every single room such as the kitchen or bathrooms where the air conditioner is not used.

Once you have the total square footage of all the living spaces, multiply this by the number of BTUs per square foot and this will give you a general idea of the BTU size you need in an air conditioner.

Since different homes are built differently, it may be helpful to get the assistance of an air conditioning expert in this regard, as you also need to determine room heights and the number and size of windows you have in your living spaces.

This will require that you add some BTUs. It is worth noting that sun exposure also alters calculations.

BTU = square footage (length x width) x 20 (BTU per square foot)

Steps to calculate the air conditioner size that you need
Step What to do
1 Measure length and width of all living spaces
2 Add all measurements up to determine the total square footage
3 Multiply the total square footage by 20

How the Manual J Load calculation helps determine the exact AC size you need

You will need the help of a professional to find the right sized air conditioner for your home. A professional might mention the Manual J Load calculation, which is a calculation made by software that only HVAC professionals have access to.

This measurement helps you work out the exact AC size your house requires by determining the heating and cooling loads of a particular house or building.

This software can also calculate this in a fraction of the time it would take to calculate it manually.

The HVAC professional you hire will plug certain information about your home into the software to work out the exact AC size your home needs.

Why does the AC size matter?

The size of an air conditioner matters because choosing the correctly sized unit ensures that it runs a proper, full cycle and that your home stays cooler for longer.

If the air conditioner is too small, it will be running non-stop in an attempt to cool a space that is too large for it, while a bigger air conditioner will cool too quickly making it too cool and uncomfortable in the space.

Either way, the wrong sized unit will only rack up high electricity bills, from overworking or short cycling.

The best air conditioner types for cooling your entire home

Certain air conditioners are only suitable for cooling individual rooms, either big or small.

Other types of air conditioners, such as central units and mini-split units are capable of cooling multiple rooms at the same time, making them ideal for cooling all your spaces with ease.

They are not cheap, but they can be well worth the price when every living space in your home is cool enough to keep you comfortable no matter which room you occupy.

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