What is the 20 BTU rule for air conditioners?

When choosing a new air conditioner for the home, one of the biggest considerations is knowing the size of unit you'll need. Thanks to the 20 BTU rule, this shouldn't be too much of a headache. The idea is that, generally, for every square foot of space you want to cool, you need 20 BTUs. It's pretty easy math. All you have to do is take your square footage and multiply it by 20. 

BTU, or British Thermal Unit, describes the amount of energy an AC produces. Specifically, the unit measures the power necessary to change a pound of water by one degree Fahrenheit — either higher or lower. In other words, it's the amount of air your machine can circulate in an hour. Naturally, the bigger your area, the more circulation is required.

However, while this is a great guideline, it's just that. To figure out the actual size of your AC unit, you have to calculate some other factors specific to your space, from ceiling height to climate. While perhaps frustrating, this whole process is necessary, as getting the right-sized AC unit can save you not only more headaches, but also money down the road.

Read more: 12 Ways To Cover Sliding Glass Doors That Aren't Curtains

The right AC size means more efficient cooling

While there are some big questions about picking the right AC unit for your home that you've likely already dealt with, your research isn't done yet until you figure out the right size. The 20 BTU rule is a start, but it's important to take time to actually calculate the correct number — for your specific space.

Having the right AC size is one of the useful tips to prolong the life of your HVAC system. Too small means your AC will constantly be running to try and meet your desired temperature. Despite working hard, it may never hit the goal. This will not only prevent you from being comfortable in your home, but it can actually increase your energy bill.

Getting one too big has its own problems as well. It will go through on and off cycles much more quickly than recommended, raising energy bills and wearing down your machine. These reasons are why sometimes it's better to choose a smaller, more affordable AC. Additionally, air conditioners not only cool down a space, but they also dehumidify rooms to make it feel cooler. However, if your AC doesn't stay on long enough, it won't be able to properly remove the humidity.

Of course, you'll still have to round a bit. Air conditioners tend to come in tons and half-tons; one ton is equal to 12,000 BTUs. Generally, for AC units that stay in place, the lowest you'll find is 5,000 BTUs, which will cover a space of around 150 square feet. However, if you have a smaller space than that, you can look at portable or window units. The main goal, though, is to get as close as possible to the BTUs you need.

Factors that will increase the BTUs you need

Although the 20 BTU rule is a good one to start with, there are times you may want to make some additional adjustments. After all, not every situation, or even room, is the same. For starters, if you live in a very hot and humid region, you may need to go higher.

In fact, the U.S. Department of Energy has broken down the United States into eight climate zones, with Alaska being its own sub-arctic zone (8). Based on which zone you live in, you may need more or fewer BTUs. For example, those who live in the lower part of Texas fall into zone 2; for this zone, it's recommended you get an AC with 30 to 40 BTU per square foot, rather than 20. This means that for a 1,000-square-foot home, you'd need somewhere between a 30,000- to 40,000-BTU central AC unit to effectively keep the house cool.

Other factors that influence the necessary size of your AC unit include how insulated your home is, the number of windows you have and the direction they face, and whether your house is in the shade at all. How many people live in your home also increases the required BTUs.

For example, for each person that lives in your home, you want to add another 500 to 600 BTUs. For the first one or two people, it might not matter much, but if you have four or five people living in a home, then you may need to think about upping your BTUs. Finally, keep in mind that appliances, electronics (like desktop computers), and areas that run hot (like kitchens) will also require more work from your air conditioner.

Enjoyed this article? Get expert home tips, DIY guides, and design inspiration by signing up to the House Digest newsletter and adding us as a preferred search source!

Read the original article on House Digest.