Discover the factors affecting HVAC zoning system cost, energy savings, DIY options, and expert insights. Get informed about your home’s heating and cooling.
What Is BTU in AC?
Of all the numbers, facts, and figures, BTU is probably your most important AC factor to consider
Photo: KDP / Moment / Getty Images
Photo: KDP / Moment / Getty Images
Highlights
BTUs measure the energy output of your AC system.
It takes about 20 to 35 BTUs to cool each square foot of space.
Higher BTUs cool a room faster, but boost humidity and wear your unit down.
EERs measure the energy efficiency of an AC unit.
It costs $0.10 to $0.20 per BTU to have an AC unit installed.
Get quotes from up to 3 pros!
Enter a zip below and get matched to top-rated pros near you.
One of the key attributes of an air conditioning system is BTUs. While you know that BTUs have to do with power, it may not be clear exactly what the term refers to, and why it is relevant to the system you choose.
This guide breaks down what a BTU is, how many you need depending on the size of the space you want to cool, and how much you can expect to pay per BTU. With this information, you’ll be better able to choose the best AC unit for your home.
What Does BTU Mean?
BTU stands for British Thermal Unit, and its purpose is to serve as a unit of measurement that describes how much energy your air conditioning system uses per hour. More specifically, a BTU measures how much energy a unit needs to cool a pound of water by 1 degree Fahrenheit below the current temperature.
Why BTU Matters
BTU matters because too few BTUs mean your AC unit won't be powerful enough to cool the space, but too many BTUs will wear down your unit faster and make your room humid. As a result, it's important to strike a balance and figure out the right BTUs for your home.
BTU Cooling Calculator
Calculations are based on the average square footage of a bedroom, which is 132 square feet, and a 8-foot-tall ceiling. Calculations rounded to the nearest whole number.
| BTU Cooling Factor | Quantity |
|---|---|
| Square footage | 132 square feet |
| Ceiling height | 8 feet tall |
| Number of people in the room | 2 people |
| Type of room | Bedroom |
| Insulation condition | Average |
| Sun exposure | Average |
| Climate | Average |
| Suggested BTUs | 5,140 |
How to Calculate BTU Cooling
To calculate your BTU cooling needs, follow these steps:
Determine square footage and ceiling height: Measure the total square footage of the space and the ceiling height.
Account for room’s purpose: Determine the type of room and the average number of people typically inside of it.
Determine insulation, sun, and climate conditions: Consider the current status of your insulation, how much sunlight the area receives, and your home’s climate.
How to Determine the Proper AC Size and BTU
Generally, it takes about 20 to 35 BTUs to cool each square foot of space. For example, 5,000 to 6,000 BTUs is enough to cool 150 square feet, while you'll need 11,000 to 12,000 BTUs to cool 500 square feet. The higher the BTUs and the larger the space, the more efficient the system's cooling efficiency. A professional AC installer near you is the best person to help you navigate the BTUs you need for your home, but you can use this table to get started.
| Room or Home Size (sq. ft.) | BTUs |
|---|---|
| 100–250 | 5,000–6,000 |
| 250–350 | 7,000–8,000 |
| 350–450 | 8,000–10,000 |
| 450–550 | 12,000–18,000 |
| 550–750 | 14,000–20,000 |
| 750–1,000 | 18,000–25,000 |
| 1,000–1,200 | 21,000–24,000 |
| 1,200–1,800 | 24,000–36,000 |
| 1,800–2,400 | 36,000–48,000 |
| 2,400–3,000 | 48,000–60,000 |
Factors That Affect BTU Size
The following factors will have the biggest impact on the number of BTUs you should target:
Size of the space you intend to cool
Number of windows and floors in the home
Insulation and flooring type
Number of family members in the home
Size of your kitchen and how often you cook in it
Higher BTU Isn’t Always Better
Photo: Pramote Polyamate / Moment / Getty Images
Generally speaking, a higher BTU is not better for your AC system. That's because higher BTUs will make the room more humid. It will also put more wear and tear on the unit, requiring more maintenance and shortening its lifespan. The key to comfort is finding a balance: an AC armed with enough BTUs to get the job done, but not too many for the space you're cooling.
Will an Air Conditioner With a Higher BTU Cool My Room Faster?
Yes, an air conditioner with higher BTUs will be more powerful and will therefore cool your room faster. But as noted above, this comes with significant drawbacks, like higher humidity and greater wear on the AC system itself (not to mention higher energy bills).
BTU vs. EER
While the BTUs measure the amount of energy used, the EER notes the unit's energy efficiency, or how well your AC will cool down a room compared to power usage. You can calculate EER by dividing the BTU rating by how many watts the unit uses. It's a helpful measurement if you're trying to compare to AC systems. The higher the EER, the more efficient the system is.
How Much Does an AC System Cost per BTU?
The cost to install an AC system by BTUs is about $0.10 to $0.20 per BTU, with the price being on the lower end for larger, more powerful systems and on the higher end for smaller systems.
An AC unit with a capacity of 18,000 BTUs would cost about $2,500 to $4,500 to install, while a large 48,000-BTU system would cost $4,200 to $6,200 to install.
Frequently Asked Questions
The homeowners guide to heating and air conditioning services
From average costs to expert advice, get all the answers you need to get your job done.
The cost to replace ductwork in a crawl space depends on accessibility, size, and whether or not your crawl space requires additional work.
Your leaky ductwork may be hiking up your energy bills. We explore the cost of checking air ducts for leaks, which may be worth it for your home.
When deciding whether to repair or replace an AC unit consider the age of the unit, its overall performance, efficiency, and the cost of required repairs.
Wondering if you should buy an air purifier? Discover important air purifier pros and cons for your home, health, and budget.
If your window AC needs some TLC, learn who to hire to clean and repair window AC units. Check out what you can do as a DIYer and what’s best left to a pro.
Tell us about the job—we’ll find top pros.