How long does it take for an AC to cool a room? 5 expert-approved tips to boost performance

HVAC pros detail when you can expect your AC to cool you down and how to speed the process up

We answer 'how long does it take for an AC to cool a room?' Here is a white rectangular AC unit with a black vent, mounted onto a light purple wall
(Image credit: Getty Images / geargodz)

Sweating it out and wondering when exactly your AC is going to pump sweet cool air around your room? Don't panic.

I've asked HVAC experts about the time it takes small, medium, and large sized rooms to be cooled down by AC, quizzed them on which factors can impact this and their top tips for speeding up the process. Proper insulation and placement are both key parts and they have plenty more advice.

If you've already learned how to cool down a room and are putting your AC to work, it won't be long before your place feels fresh and fabulous.

How long does it take for an AC to cool a room?

A close-up of a white ceiling corner with a rectangular white air condioning unit on the wall and white curtains underneath it

(Image credit: Getty Images / bee32)

Al Fouz, HVAC expert at ABACO Air Services says, “For a small room that's 150 square feet in size, a 5,000 BTU window AC unit should lower the temperature by 10-15 degrees Fahrenheit within 30-45 minutes."

BTU stands for British Thermal Unit and is a measurement for how much energy it takes an appliance to remove heat from the air inside a building. Bigger spaces need AC units with bigger BTU ratings to remain efficient and cool the air in a reasonable time frame.

It's also good to know the BTU to look for when choosing an AC unit for your space. The same way you wouldn't put a Ferrari engine on a pedal bike, you don't need an AC unit with enormous BTU for a small room but the higher the BTU, the quicker it will cool.

Al continues, "Medium-sized rooms of 200-500 sq. ft. will take 45-60 minutes for a portable or central AC unit rated around 10,000-18,000 BTU to achieve similar cooling."

“Larger spaces, open floor plans, or vaulted ceilings often require units of 20,000 BTU or more and can take two hours or longer to reach the target temperature,” he adds.

What factors affect how long it takes AC to cool down a room?

A hand wearing a brown jumper and with purple fingernails pressing the button of a white thermostat with a gray screen, on a beige wallpapered wall

(Image credit: Getty Images / Maryna Terletska)

There are numerous things that could affect how long it takes AC to cool down your room. Our experts recommend looking through these before worrying if yours is taking too long.

1. Type of AC

The type of AC that you have is one of the biggest factors for how long it takes for it to cool down a house. Josh Mitchell, HVAC expert and owner of Air Conditioner Lab explains what these are.

  • Window AC: These units generally cool a room quicker since they are more powerful and directly expel warm air outside.
  • Portable AC: This might take slightly longer than window units due to less efficiency in air exchange.
  • Central AC: While it may take longer initially to feel cool air (it often takes 15 to 30 minutes to start feeling a difference), central systems are more effective at keeping a consistent temperature across multiple rooms or larger spaces.

2. Starting temperature

If there's a big difference between the outdoor and indoor temperatures, the AC may take longer to cool the room.

“For example, if it's 95 degrees outside and you want your room at 75 degrees, it will take longer than if it's 85 degrees outside,” Josh says.

3. Insulation

For those who live in older homes, you might find that your insulation is insufficient.

“Ensure that the room is well insulated — this can significantly reduce cooling time by keeping the cold air in and the hot air out,” Josh says.

Make sure to seal gaps around windows, such as by using sealant (the GE Siliconized Acrylic Sealant from Walmart is a bestseller and is paint ready in 30 minutes), so air from the outside doesn’t easily get inside.

4. BTU rating

Al says the most important factor is matching the AC unit’s BTU rating to the specific room size for maximum efficiency. 

“Oversizing wastes energy, while undersizing won’t effectively cool the space. For the fastest cooling, choose the highest BTU unit your budget allows,” he adds.

For small rooms, Josh recommends the LG LW5016 Window Air Conditioner available on Amazon, saying it’s incredibly efficient for quick cooling in small spaces.

5. AC maintenance

Just like making the most out of a fan, making sure your AC is squeaky clean is important for the best breeze possible. 

“To maintain optimal performance, keep the AC's filters clean and ensure the unit is serviced regularly,” Josh says.

To do this, simply dust the filter with a cloth (the HOMEXCEL Microfiber Cleaning Cloths on Amazon are some of our favorite cleaning supplies), clean it with warm water and mild soap, and let it dry before using again.

Useful cooling buys

Whether you're looking for a renter-friendly AC or a new fan, our top-rated picks from trusted retailers will help keep you cool.

The prices below were correct at the time of publishing this article. 

Once you've found out how long it takes for an AC to cool down a room, you can relax knowing that soon enough your place will be a chilled place to hang out.

Struggling to beat the heat at night? Learning whether you should have the AC on at night or not will also come in useful.

Eve Smallman
Content Editor

Hi there! I’m a content editor at Real Homes. I've been a lifestyle journalist for over five years, previously working as an editor across regional magazines. Before this, I graduated from Nottingham Trent University a degree in journalism, along with an NCTJ gold diploma. I love running, decorating my rented Victorian home, and discovering new cheeses. For Real Homes, I specialize in interior design, trends and finding the best viral buys.