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### What Size AC Do I Need? How to Get the Right Measurements

Originally posted on http://www.designair.co/blog/what-size-ac-do-i-need-how-to-get-the-right-measurements/

Nearly 100 million homes in the United States have air conditioning.  Each one of these homes had a professional installation company determine the ideal size unit for the home.

You must install the right-sized unit so that it can effectively and efficiently cool your home. So if you’re thinking about installing a new AC unit in your home, the first question you should ask yourself is, what size AC do I need?

We’ve created this quick guide to help you figure out the ideal sized unit for your home.

## What Size AC Do I Need?

The first step is to determine what tonnage you’ll need. There are two methods for figuring this out, manual J calculation and the square footage measurement method.

### Manual J Calculation

This is a complicated calculation that is best left to the professionals in the HVAC industry. They’ll take into account several factors to determine the right-sized unit for your home.

• Climate zone
• Ductwork
• Square footage
• Heat generating appliances
• Number of people using the space
• Quality and amount of insulation

Two homes that are the same size could vary as much as 25% in their needs. This is because of the position of the homes to the sun and the number of windows they have.

### Square Footage Measurement

The second method will give you a rough estimate of BTUs by looking at the square footage of the home. A BTU is a British Thermal Unit. It’s the amount of heat that’s needed to raise 1 pound of water 1 degree Fahrenheit.

Once you have a rough estimate for the size you need, you can start looking for your unit. You may not find the exact size that you need. If this is the case, go with the next size up.

Having a little bit of extra power isn’t a bad thing. You’ll be able to be confident that your new unit will be effective on even the hottest of days.  Going with a unit that is too small will force it to overwork on the hottest days.

## What If You Go Too Big?

Bigger isn’t always better when it comes to HVAC units. If you choose a unit that is way bigger than you need, then you end up with a clammy house. The large unit won’t run long enough to dehumidify the air.

You’ll also end up with your unit not lasting the full intended lifetime. This is because the unit will turn on and off more often. This is called short cycling.

All of that extra size will also translate to increased costs for you. A bigger unit means more time and effort to install.