How to Determine What Size AC Unit I Need?

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How to Determine What Size AC Unit I Need?

AC Size in Kennewick, WA

One of the challenges of replacing your current air conditioner is getting a unit that’s properly sized for your property. While it may seem rather simple to calculate the right size for your system, there are several factors that experts consider. Discover why size does matter for your air conditioner and the various factors used to determine the correct size.

Why Does Size Matter?

Before digging into the factors around AC unit sizing, it’s important to understand why size matters. For air conditioners, when you talk about size, you’re talking about their cooling capacity. This is measured in British Thermal Units, also called BTUs, or in Tons, which is merely a different way of thinking about BTUs.

When a system is sized for a certain cooling capacity, this means the system’s refrigerant can absorb a specified amount of heat. It also means the system will circulate enough air for the unit to absorb the heat.

When the system is too small for the space, it causes longer cooling cycles than normal. Likewise, when the unit is too large, it causes it to freeze up and shut down prematurely, which is known as short cycling. In both cases, this drives up your utility costs and increases the wear on your equipment, leading to more repairs.

Calculating Your Service Area

The first step is calculating your serviceable area in square feet. The most accurate way to calculate this is to go room by room through your home. The rooms in most houses are square or rectangular, so you’ll simply multiply the length by the width.

When going to each room, look for either supply or return vents for your HVAC system. If the room has vents, be sure to include it in the calculation. Don’t forget to include closets, hallways, and stairwells. Be sure to check your basement, attic, and garage to see if there are vents, too. Even if you don’t want to heat or cool all those spaces all the time, you need to include them in your calculations to ensure the system can support them.

Once you have the area your system needs to serve, you must convert that into the BTUs needed. Your climate zone determines the number of BTUs needed per square foot serviced. Hermiston is in climate zone 5, which needs about 35 BTUs per square foot. If your house is 1,800 square feet, that translates into about 63,000 BTUs. Keep in mind that this only gives you an estimate of the BTUs needed. There are additional variables that may raise or lower the capacity you need for your system.

Home Construction Variables

Some of the largest variables affecting the size of your air conditioner are aspects of how your house is constructed. Consider your ceiling height, for instance. Vaulted ceilings mean there’s more air to condition for the same square footage.

Your windows are also a key factor, in terms of how many you have and their construction. The more windows you have, the more heat they may transfer into your home on sunny days or allow it to escape during cold weather.

Your insulation is also a key consideration. If your insulation isn’t sufficient, your house will transfer more heat in and out of your residence. Ideally, you want an insulation rating of R49 or better, which equates to at least 16 inches of blown-in fiberglass insulation. If you’re using cellulose insulation, you’ll need insulation that’s at least 15 inches thick.

Environmental and Occupant Considerations

Beyond your home’s construction, there are several other factors you’ll want to consider as well. First, your home’s exterior environment plays a major influence on your HVAC system. If your house is constantly in the shade, you may not need as much capacity. Conversely, if you have no shade, you may need a little more cooling capacity.

Next, think about how many people occupy your home regularly. This may not just be how many people live there, but how many people are in your house routinely. You may need more capacity if you run a business that has people come through it frequently, or if you entertain often.

People around Hermiston have turned to Bruce Mechanical to keep their homes comfortable for the last 20 years. Our team of expert technicians provides cooling and heating repair, maintenance, and installation, along with indoor air quality and fireplace services. Call us to schedule your new air conditioning system consultation with one of our expert installers today.