A BTU is the basic measurement used for rating how much energy it takes to produce heat. It’s used in determining the efficiency of air conditioning equipment, furnaces, and any appliances that heat—such as water heaters, ovens, and fireplaces.

A BTU, short for British Thermal Unit, is a standardized measurement of energy. Technically, 1 BTU is roughly equal to the amount of energy required to raise 1 pound of water 1 degree F.

In North America, the BTU is used to describe both the heat content of fuels and the power of heating and cooling appliances such as furnaces, air conditioners, water heaters, stoves, fireplaces, and barbecues. When used as this type of measurement, the term “BTU” actually refers to BTUs per hour (BTU/h).

When buying a heating or cooling appliance, be sure you understand whether the stated BTU capacity refers to the unit’s input or output. An input BTU refers to the fuel used; an output BTU measures the heat (or cooling) created.

SEER stands for Seasonal Energy Efficiency Ratio. Air conditioner units with high SEER ratings use less electricity to get your home to a comfortable temperature, reducing your energy or gas bill.

Mathematically speaking, a unit’s SEER rating is calculated by dividing the annual cooling output (measured in BTUs) by the total electric energy input (measured in kilowatt-hours)—in other words, dividing the amount of cool air the a/c generates by the number of kilowatts it takes to generate it.

The relationship between SEER ratings and efficiency doesn’t necessarily mean that you choose an a/c unit with the highest SEER rating you can find. There are other factors that may determine what SEER rating is best-suited for your home and overall HVAC system.

First, it’s important to note that a SEER rating signifies the maximum efficiency a particular unit can reach. It doesn’t mean that the unit will operate at that efficiency all of the time or even some of the time. For example, a top-of-the-line 20 SEER unit that’s far too large for the house it’s cooling is unlikely to ever perform at a higher rating than a more appropriately-sized unit, even one with a lower SEER rating. Knowing how the geography and climate of your area impact efficiency can ensure you don’t overpay for a higher SEER rating than you need.

You’ll also want to consider variables like your budget, your home size, how often your a/c is running, and how much time you spend at home. All of these factors can affect the necessary efficiency of the unit you choose.

If you are looking for a new air conditioner, it can be intimidating to review all the different options out there. One of the first things, and perhaps the most important, is to identify what size air conditioner you should get to meet your home’s cooling needs. Efficiency is often top of mind, but just as important is making sure you get the right sized system that will also work effectively.

There are a variety of reasons you want to make sure to find the appropriately-sized air conditioner:
Keeping the suitable humidity – Air conditioners not only aide in keeping your indoor temps cool, but it also works to lessen humidity. If your system is too big, probabilities are it will meet the desired temperature too fast to address the humidity levels.

Maintaining energy bills – While a system that is too small might keep up with cooling your house, you are forcing it to work more frequently or possibly constantly. This isn’t going to help your energy bills. You may have saved on initial costs for the equipment, but it won’t offer savings moving forward.

Allowing proper cycling – If you select a system that is too big for your house, it will quickly cool down your house and shut off, not allowing your air conditioner to run through the proper cycling. This can also impact your energy bills, because your air conditioner will be turning on and off constantly.