6 Factors That Determine What Size Air Conditioner You Need

It may sound counterintuitive, but cooling down your living space isn’t just a matter of finding the largest or most powerful air conditioner available. While an undersized AC will struggle to effectively cool off a large room, an oversized AC will work too well, bringing down the temperature before it reduces the humidity.

Finding that sweet spot between just powerful enough and too powerful is largely dependent on square footage, but several other factors are relevant as well. 

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Why Getting the AC Size Wrong Costs You More Than You Think

Incorrectly matching your AC tonnage to your home’s cooling requirements can affect your finances as much as your personal comfort. An air conditioner that is too small will have a hard time bringing the room’s temperature down to your desired level. On especially hot and humid days, it may need to run nonstop, even then failing to make the room cool enough. Running so frequently will draw more electricity, driving up your energy bills.

An air conditioner that is too powerful is no better. A high-capacity unit will bring down the temperature of a small room too quickly, shutting off before it can remove moisture from the air. This leaves the room feeling cold and damp, more like a dank basement than a comfortable living space. It also results in short cycling, as the unit turns on and off in rapid succession. Because the compressor and motor command a surge of power upon startup, short cycling consumes much more energy than is otherwise typical of an air conditioner.

Finally, constantly running or short cycling your air conditioner increases the amount of wear and tear on the appliance, driving up your HVAC maintenance costs because of more frequent or more costly breakdowns and malfunctions.

The 6 Factors That Determine What Size AC You Need

Room size is relevant, but it isn’t the only thing to consider when determining what kind of output you need from your air conditioner. Here’s what you should keep in mind.

• Square footage. Larger rooms require more powerful air conditioners. A 20 BTU per square foot ratio is a good rule of thumb, but treat that as a starting point and adjust higher or lower based on other factors.
• Climate. Homes that are otherwise comparable in size will need greater cooling capacity if located in an area with hot and humid weather.
• Ceiling height. Room height and air volume are directly correlated. Rooms with higher ceilings have a larger volume of air that needs to be cooled, and they need more powerful air conditioners accordingly.
• Amount of sunlight. The intensity of sunlight in a room drives cooling needs as well. Rooms that get a lot of sun, especially from skylights or windows that face west or south (in the Northern Hemisphere),usually need a stronger AC. Conversely, heavy shade cover means you can get away with a less powerful unit.
• Insulation. Insulation isn’t just a winter concern. In the summer, insulation keeps air conditioned air from escaping. If your home isn’t well insulated or has drafty doors and windows, you may need a slightly stronger air conditioner to compensate.
• Types of appliances. If a room has large, heat-generating appliances, the cooling unit may need to work a little harder. This is particularly relevant to kitchens, as the oven, stove, fridge, and dishwasher boost the temperature and humidity in their immediate vicinity. A room with a washer and dryer nearby may likewise benefit from stronger AC.
• Number of people. People generate heat. If you have a large family or frequently use a space in your home for social gatherings, you might consider a slight upgrade in your AC’s cooling capacity.

How to Calculate the Right AC Size for Your Home

Several factors may impact your home’s cooling needs, but you can often determine the right size AC for your home with little more than a tape measure and some casual observations.

1. First measure the length and width of the space you want to cool and multiply those measurements to get the square footage.
2. Multiply your space’s square footage by 20 BTUs to arrive at a baseline approximation of your cooling needs. For example, a space that’s 400 square feet could use an AC with 8,000 BTUs.
3. Begin to adjust your baseline based on the layout and features of your living space as outlined above. If you have a 10- or 12-foot ceiling, boost your BTU target by 10%. Scale appropriately if your ceilings are greater than 12 feet.
4. Assess your insulation and amount of sunlight. If your living space is drafty and gets a lot of afternoon sun, add 10% to 15% to your BTU target. Subtract the same amount if your home is very well insulated or has abundant shade.
5. If there are more than two adults in your home, add around 600 BTUs for each additional person.
6. If you’re calculating your cooling capacity for a kitchen, add 4,000 BTUs to offset the heat and humidity generated during cooking.

If necessary, you can also contact a professional for a more precise assessment of your home’s cooling needs. An expert can also help you understand which air conditioning systems are compatible with your existing home HVAC system.

Common AC Sizing Mistakes Homeowners Make and How to Avoid Them

As you shop for the appropriately sized AC for your home, be mindful of the pitfalls many homeowners encounter.

• Getting an AC that’s too large. Many homeowners assume that you might as well purchase a more powerful AC to be safe, but there is such a thing as too powerful. An oversized AC is prone to short cycling and will leave a home feeling cool but clammy.
• Neglecting insulation and air leaks. Poor insulation and drafts work against an air conditioner’s cooling action. If cool air is easily escaping the home, the AC has to be more powerful to compensate.
• Ignoring ceiling height. If you consider square footage alone, you might underestimate your cooling needs. High ceilings need to be accounted for because of the greater volume of air in the room. 

Increasing Your AC’s Longevity

Correctly sizing your AC for your living space is key to getting your money’s worth. An AC that is too weak or too powerful is liable to break down more quickly. But don’t discount other strategies to get the most out of your HVAC equipment. Home warranty protection, for instance, can ensure that any malfunctions are remedied quickly, before they have the chance to cause additional damage. Learn more about Liberty Home Guard’s top-rated coverage by calling (866)-983-0940.