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Ask John HVAC Sizing Main Image

How Do I Choose the Right Size HVAC System for My Home?

John Turpin is our resident home service repair expert here at Service Direct. He’s got the knowledge and experience to help homeowners like you make sense of most home repair issues. And with Service Direct, we connect you with top-tier service professionals to help with any repairs needed.

Learn How to Pick the Right Size AC Unit for Your House

The main purpose of the air conditioner is to cool your home, making it more comfortable, especially during the hot season. But that might not happen if your unit doesn’t match the square footage of your home. It will cause your AC to struggle to keep the space cool, working extra hard and eventually breaking down.

This makes choosing the right HVAC system size crucial when deciding on a unit to buy or install. If not, you might not get the best results when it comes to comfort, performance, and energy efficiency.  That’s why we’re here to help you learn how to choose the right HVAC system for your house.

Ensure You Get The Right Size HVAC
Getting the right size HVAC us essential to keeping warm in the winter and cool in the summer.

Why Does Choosing the Right HVAC System Size Matter?

When choosing the right HVAC system, it’s highly important to consider the unit’s size. You see, if the HVAC system is too large, it’s more than likely that you’ll have to pay a lot to maintain it.

On the other hand, if it’s too small, your home will not be properly cooled or heated. It also means the unit works extra hard, which may lead to early breakdown. An improperly sized HVAC unit works inefficiently, running overtime to provide your desired room temperature.

As such, we strongly advise that you find the right sized central air conditioner for your home. With that said, let us give you an idea of what makes the best size based on your home’s square footage.

AC Ratings

There are two ways that air conditioners are usually rated—cooling capacity and energy efficiency.

1. Cooling Capacity

All air conditioners come with British Thermal Unit (BTU) and British Thermal Unit per hour (BTUh) ratings, which are units of measure for cooling capacity. BTU refers to the amount of energy necessary to raise the temperature of a pound of water by 1 degree Fahrenheit. Comparatively, BTUh is a measurement of the cooling ability of an AC per hour. It’s also known as “tons.” An air conditioner with one ton can remove 12,000 BTUs of heat every hour.

2. Energy Efficiency

One of the energy efficiency ratings of air conditioners is the SEER, which stands for Seasonal Energy Efficiency Ratio. SEER is the total cooling amount provided by the AC during the whole cooling season, divided by the total electrical energy the unit used. The higher the SEER rating of an air conditioner, the more energy efficient it is. If not SEER, the AC may have an Energy Star® certification instead, which means the unit uses at least 8% less energy than standard models.

Window Air Conditioners

If it’s for window air conditioners, keep in mind they mostly have a cooling capacity range of 5,000 to 12,500 BTUs. When determining the system size you need, you will need to compute the square footage of the room where you’ll be installing the window AC. Remember to include the square footage of the adjacent room without a door.

You’ll get the square footage by multiplying the room’s length by its width. Do this as well with the adjoining rooms that weren’t separated by a door. Once you get both numbers, add them up to get the total, which is the square footage that your window air conditioner will need to accommodate.

Central Air Conditioners

If you want to learn how to choose the right size of central AC unit, start by finding the square footage of your home. When you know, multiply the length of every room by its width then add them all together. After that, multiply the total square footage by 20. This should give you the number of BTUhs needed to cool your space.

Know Which HVAC Is Best For You
HVAC sizing is affected by a variety of factors including the amount of living space and unit type.

Other Factors That Influence the Right HVAC System Size

The main factor when choosing the right HVAC system is your home’s square footage. But others can impact the AC’s cooling efficiency. It’s good to know these variables, so you can be sure to pick truly the right HVAC system size.


Since AC units run far more than they usually do during summer months if you are in a warm climate, it’s a great idea to pick an AC unit with a higher SEER rating.

Home Exterior

Keep in mind that a home’s exterior, the type, and color of the material on them, can affect how much heat it absorbs or reflects. This can affect your choice of an HVAC system.

Shade and Sun Exposure

Homes facing north or east or have lots of shade are usually less exposed to sun, making them much cooler than south- or west-facing homes.


The insulation levels in your home play a significant role in maintaining indoor temperature stability. Well-insulated homes retain cooled or heated air better, reducing the HVAC system’s workload. Properly sealed windows and doors also prevent air leaks, enhancing energy efficiency.

Number of Occupants and Heat-Generating Appliances

The number of people living in the home and the presence of heat-generating appliances (e.g., ovens, computers, and electronics) can increase the indoor heat load, influencing the system’s sizing.

Our resident home repair guru, John Turpin, explains everything you need to know about sizing your new HVAC system, including some expert tips and tricks.

Home Layout and Design

The layout and design of your home can impact airflow and temperature distribution. Multi-story homes may require zoning or multiple HVAC units to maintain consistent comfort.

Ductwork Condition

If you have existing ductwork, ensure that it is appropriately sized and in good condition. Leaky or undersized ducts can lead to energy loss and inefficient cooling or heating.

Energy Efficiency Goals

Consider your energy efficiency goals when selecting an HVAC system size. A system that is too large for your needs may cycle on and off frequently, reducing efficiency and leading to higher energy bills.

Future Home Improvements

If you plan to make energy-efficient upgrades or renovations to your home, consider how these changes may affect your heating and cooling requirements in the future.

Professional Load Calculation

It’s essential to have a professional HVAC technician perform a load calculation to determine the exact heating and cooling needs of your home. Load calculations take into account all the factors mentioned above and provide a more accurate sizing recommendation.

Have Someone Calculate Your HVAC Requirements
An HVAC expert is best placed to ensure you install a system suited to your needs.

HVAC Sizing FAQs

Can I use the size of my existing HVAC system as a reference for choosing a new one?

The size of your existing HVAC system can provide some guidance. But, it’s important to reassess your home’s requirements before selecting a new system. Changes in home insulation, square footage, or other factors might have occurred since the installation of your current system. Conducting a proper load calculation or consulting with an HVAC professional will help determine the appropriate size for your new HVAC system.

Can I install a larger HVAC system to ensure better performance?

Installing a larger HVAC system than what is actually needed is not recommended. Oversized systems may result in inefficient operation, increased energy consumption, and potential comfort issues. It’s best to choose an HVAC system that matches the cooling and heating load of your home to ensure optimal performance and energy efficiency.

Is it possible to downsize an existing HVAC system?

It’s not a common practice to downsize an existing HVAC system. But if you have made significant energy efficiency improvements to your home or modified the layout, it may be worth consulting with an HVAC professional to assess whether downsizing is feasible. They can evaluate the load requirements and make appropriate recommendations based on your specific situation.

Hire a Local HVAC Pro

It’s important to understand how to choose the right size of HVAC system for your home. But even so, it’s the HVAC pros that will perform all the required calculations to ensure the unit’s maximum efficiency. When you’re ready, you can find the right local expert using the phone number or form on this page.

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