What Size Air Conditioner for a Small vs Big House?

Air conditioners—like homes—come in many different shapes and sizes. Central air systems, which are tasked with heating, ventilating, and cooling the air across an entire home, are increasingly popular across North America for their ability to manage a home’s overall temperature. Those seeking an individual unit, however, will need to find a model that can function effectively to provide a quick and efficient cooling process without putting too much strain on the system.

This article looks at the importance of picking the right conditioning unit for your home size, no matter the number of bedrooms or floors. It’s not always easy to find the right size for you, so we’ll be covering everything you need to know about finding the right air conditioner.

Finding the Right Air Conditioner

Air conditioners are designed to function alongside most central air systems, but they can range greatly in size, power, efficiency, and most effective climate zone. Depending upon home size, you may also need to consider purchasing more than one air conditioning unit to make sure that no part of your HVAC system is overstrained.

We highly recommend consulting with an HVAC professional to make sure that your chosen unit will work for your central air system before committing to a purchase. Likewise, we would like to remind homeowners that air conditioning units can only handle cooling the air in the home. If you’d like heating as well, you will need to invest in a heat pump or furnace to get the job done.

Uncovering Your Climate Zone

Assuming you live in North America, the first step we recommend taking is determining your dwelling’s climate zone. The Department of Energy has created a clear guide of climate zones to assist homeowners and HVAC technicians alike. This guide can be used as a springboard for finding the right air conditioner for your home. You won’t be expected to know or memorize all of the country’s climate zones, but it is important that you keep in mind your specific zone for future reference.

Generally speaking, the higher the number of your climate zone, the less powerful of an air conditioner you will need. For example, if you live in Wisconsin and have a 1,000 square foot home, you won’t need as much cooling power as a 1,000 square foot home in Florida may need. We’ll come back to these zone numbers a little bit later on, but for now, keep in mind that you may be expected to go above and beyond with your purchase should your home fall in one of the more hot and humid climates.

The Issue of Occupancy

Leading experts point out that the number of people in your home will also have a considerable effect on your air conditioner’s ability to cool the home for two reasons. First, more people in the home means more body heat being generated. While the amount of heat you release may not seem like much, if you amplify that by three or four, it can put a significant strain on an air conditioning unit as it tries to adjust. Second, and perhaps more importantly, there is the natural issue of air loss. More inhabitants means more entrances into and exits from the home. The cool air loss, especially in the summer months, from opening and closing a door is quite significant. As a result, estimates covering how many people are in your home tend to account for both increased traffic as well as increased body heat.

Square Footage & Home Age

Of course, your home’s square footage is the most important factor to consider when buying a near air conditioner unit. The larger the home, the more powerful your unit needs to be, meaning the more BTUs you will need. BTUs, or British Thermal Units, are a measure of the energy and power of thermal heat. 1 BTU is the amount of power or energy needed to heat up one pound of water one degree at sea level.

You normally can see an air conditioner’s power in BTU per hour, but sometimes, this number is listed on an entirely different scale: tonnage. When it comes to air conditioner units, a ton is equal to the power, or heat, required to melt a ton of ice (literally) in a day. This is equal to 12,000 BTU per hour if you need to make quick conversions in your head.

So what does that mean for you? If you know the BTU rating of your air conditioner, you can know how powerful it is at cooling the home. You may be tempted to seek out the highest BTU air conditioner immediately to get the best cooling possible, but unfortunately, the air conditioner with the highest BTU is not always the best air conditioner for your home.

Most home air conditioners run on a single stage, which means they are either on or off. This all-or-nothing design, combined with a high BTU rating, may make your air conditioner unit too good at hitting the right temperature. Your unit would then shut entirely off, leaving your home to slowly heat up until the thermostat detects the change and turns the unit on once more. This might force your air conditioner to start and stop constantly and thus might wear it out more quickly over time.

That’s why you need to match the square footage of your home with the right air conditioner to balance out efficiency with power. If you’re looking for a quick and easy way to calculate just have many BTUs you need for your home, try out the following based on your zone:

Climate Zone (EPA)BTUs per sq ft (Cooling)
Zones 1/2 – Hot/Humid25 – 30
Zone 3 – Mixed Humid20 – 25
Zone 4 – Mixed/Dry, Mixed/Wet, Marine17 – 22
Zone 5 – Cold, Very Cold15 – 20

While square footage needs to be considered alongside the other metrics we’ve mentioned so far, there’s one last thing you need to consider: the age of your home. HVAC technologies have come a long way in the past few decades, so if your home is older it might be missing out on some of these advances. Older homes may also suffer from compromised or failing ductwork may leak air, which might cause your home to cool far slower than expected and result in less overall efficiency.

Whether your home is old or not, we highly recommend calling out a licensed professional to take a look at your central air system to make sure that nothing is leaking or compromised. This will help make sure that you give your new air conditioner unit the best possible chance to work efficiency and save you money.

Need Heating?

If you’re in need of both heating and cooling you are in luck because many of the same metrics and considerations we’ve mentioned here are just as applicable to furnaces and heat pumps. Of course, you’ll need to invert most of our tips here: for example, those in zones further north will need a more powerful furnace or heat pump than those further south.

In some cases, those in the southernmost states may not even need furnaces in the first place; instead, they might opt for electric, portable heaters. This is similar to those who may live in the very cold or even subarctic sections of North America, who may not get much use out of an air conditioner.

Climate Zone (EPA)BTUs per sq ft (Heating)
Zones 1/2 – Hot/Humid30 – 40
Zone 3 – Mixed Humid40 – 45
Zone 4 – Mixed/Dry, Mixed/Wet, Marine45 – 50
Zone 5 – Cold, Very Cold50 – 60

Overall, we do recommend considering a powerful furnace for more northern climates, but if you can take the time to find a good heat pump, you may be able to take care of both heating and cooling in one simple machine.

Final Thoughts

While we’ve mentioned all of the major considerations we think you should make, there’s no substituting the eye of an astute professional. We highly recommend getting a licensed HVAC technician to come out and personally inspect your home to help you uncover what your exact BTU needs would be. We hope that our breakdown here has nevertheless given you a path to understanding just what all goes into cooling your home. Make sure to choose carefully, as the most energy efficient air conditioner will help make sure you get through the summer season without an oversized power bill at the end of it.

Further Reading