What Size AC Do I Need?

What Size AC Do I Need?

Are you on the fence about what size air conditioner you should get? Don’t want to make the mistake of buying a unit that’s too big or too small for your home? 

In this beginner’s guide, we’ll explore the factors you need to consider when selecting the right AC unit size.

CPI Plumbing and Heating has years of experience providing professional AC repair, installation, and maintenance to Mount Vernon, WA residents. 

If you need further assistance, please don’t hesitate to contact us at 360-822-9306.

Why Does AC Size Matter?

The size of your AC unit is important for several reasons. 

First, it directly influences your home’s comfort level. A properly sized AC keeps your home at the ideal temperature, warding off excessive heat or cold. 

Second, the size impacts your energy consumption and bills. Oversized or undersized ACs can lead to higher energy costs and potential damage to your unit.

When Your AC Is Too Small

Imagine your AC as a marathon runner, tasked with cooling your entire house. 

If it’s too small, it will struggle to keep up with the demand, like an undertrained runner facing a tough marathon. 

It will run continuously, leading to higher energy bills, inadequate cooling, and a shortened lifespan for the unit.

When Your AC Is Too Big

On the other hand, an oversized AC might seem like a great idea initially. 

You might think, “The bigger, the cooler!”

However, large AC cools quickly and then shuts off, leading to short-cycling, which causes fluctuating temperatures, increased energy consumption, and unnecessary wear on the unit.

So, an AC that’s too big isn’t exactly a great idea. 

Factors That Affect AC Size Requirements

Choosing the right AC size involves understanding a host of factors, including:

Room Size

The size of the room plays a significant role in determining the appropriate AC size. 

Larger rooms have more air to cool and require a more powerful AC.

In contrast, smaller rooms may become too cold with a larger AC. So, you’ll need a unit with a smaller cooling capacity.

Room Height

Room height impacts the volume of air that needs cooling. 

Taller rooms contain more air, and therefore require larger AC units. 

On the contrary, rooms with lower ceilings can be adequately cooled with smaller units. 

Note: For homes with high ceilings, remember that hot air rises, meaning a larger unit or a ceiling fan may be necessary to keep your home comfortable.


Insulation reduces the amount of heat exchange between your home’s interior and the outdoor environment. 

Well-insulated homes can maintain a stable temperature longer, reducing the need for continuous AC operation. 

Thus, a smaller AC might be sufficient. However, poor insulation can lead to frequent on-and-off cycles and higher energy demand, requiring a bigger AC.

Sun Exposure

Sunlight can significantly heat up your home. If a room gets a lot of sun exposure, it’ll need more cooling power to maintain a comfortable temperature.

For instance, a room with large, sun-facing windows might require a more powerful AC unit than a similar-sized room with less sun exposure.


If you live in hotter climates, such as Arizona or Texas, you will naturally need a larger AC unit. Cooler climates, such as those in the Pacific Northwest or New England, may not require as powerful an AC system.

Number of Residents

More people in your home mean more body heat and greater cooling demand. 

Additionally, human activities like cooking, showering, or operating appliances can generate heat. Hence, a larger family typically requires a larger AC.

Number of Windows and Doors

Homes with many windows and doors can experience more heat exchange, as these are potential weak spots for losing cool air and gaining heat. 

More windows and doors can therefore increase the demand for cooling, leading to the need for a larger AC unit.

Construction Materials

Some materials, like brick and concrete, absorb and retain more heat than others, such as wood or vinyl siding. 

If your home’s exterior can’t reflect or dissipate heat effectively, it might heat up faster, necessitating a larger AC. 

Similarly, your home’s interior materials can affect its ability to retain cool air.

Understanding these factors will help you to select an AC size that best suits your unique needs.

However, determining the right AC size isn’t a simple calculation. It’s always best to consult with an HVAC professional who can assess your home and provide an accurate recommendation.

For expert calculations, feel free to contact CPI Plumbing and Heating at 360-822-9306 or leave us a message here

What is a SEER Rating?

The Seasonal Energy Efficiency Ratio, or SEER rating, is a measure of an AC unit’s energy efficiency. 

It calculates the total cooling output during a typical cooling season (in BTUs), divided by the total electrical energy input (in watt-hours).

The SEER rating helps you understand how much cool air the unit provides for the electricity it consumes. Higher SEER ratings indicate better energy efficiency.

What is a BTU Rating?

BTU, or British Thermal Unit, is a traditional unit of heat. It represents the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. 

A higher BTU rating means a stronger cooling capacity. Thus, larger rooms often require an AC unit with a higher BTU rating. 

Regardless, it’s essential not to go overboard, as an excessively high BTU rating can also lead to inefficiencies.

What is a Manual J Calculation?

A Manual J calculation, also known as a Residential Load Calculation, is a procedure HVAC professionals use to gauge the exact cooling (and heating) needs of a home. 

This industry-standard approach takes into account many factors, including insulation levels, window size and location, floor area, local climate, and more. 

Using these comprehensive calculations, HVAC professionals can make precise recommendations about the size of the AC unit your home needs.

So, What Size AC Do I Need?

Generally, you’ll need about 20 BTUs for each square foot of your living area. However, there’s no one-size-fits-all number for homeowners. 

Every home is unique and will require varying AC sizes. Nevertheless, here’s a quick chart that you can use in your search:

Room SizeCooling Capacity (BTUs)
200-300 sq ft6,000 BTU
400-500 sq ft10,000 BTU
500-600 sq ft12,000 BTU
600-700 sq ft14,000 BTU

For more accurate calculations, it’s best to contact a professional for assistance. Call CPI Plumbing and Heating today to book an appointment! 

Dial 360-822-9306 or leave us a message here

Tips to Find the Right AC Size for Your Home

Tip 1: Use an AC Sizing Calculator

Online AC sizing calculators provide a quick estimate of the AC size you might need based on a few input parameters, such as room size and insulation level. They’re handy tools for getting a basic understanding of your needs.

Tip 2: Professional Energy Audits and Calculations

HVAC technicians can perform detailed energy audits and Manual J calculations to determine your exact cooling requirements. This can be especially useful for complex homes with many rooms, high ceilings, or unusual layouts.

Tip 3: Consider Future Changes

If you plan to extend your home, add insulation, or make any changes that could affect heating or cooling demand, take these into account when selecting your AC size.

Professional Energy Audits and Calculations

While understanding the basics of AC sizing is important, selecting the perfect unit for your home can be complex. That’s where professional energy audits and calculations come in. 

These expert services offer a precise, scientific approach to determine your home’s unique cooling needs.

An energy audit is a comprehensive assessment of your home’s energy use. 

During an audit, the professional will evaluate various factors, such as the insulation in your walls and attic, the size and orientation of your windows, the construction materials used in your home, and even the number and behavior of the home’s residents. 

They’ll also take into account your geographical location, local weather patterns, and typical sun exposure. All these elements can greatly influence your home’s cooling demand.

Every home is unique, with its own set of factors and considerations. 

That’s why there isn’t a one-size-fits-all AC solution. Professional energy audits and Manual J calculations account for these nuances, offering you the best possible advice based on a deep understanding of your home’s specific needs.

We’re Here for You!

CPI Plumbing, Heating & Cooling is your trusted partner for all things HVAC. 

From advising on the perfect AC size for your home to performing professional energy audits and Manual J calculations—our team of certified experts is here to ensure your comfort is maximized and your energy costs are minimized.

But we don’t stop at installation. Our dedicated team is also on standby for any AC repair needs, ensuring your system runs smoothly and efficiently no matter the season. 

Regular maintenance is key to extending the life of your AC unit, and our comprehensive maintenance services make this task easy and worry-free.

Contact us today to learn more about our AC repair, replacement, and maintenance services.

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