Room Is Hot With New Window AC Running – 10 Helpful Cooling Tips




How do I cool down my room? My 300 square foot room is still warm when running my new window air conditioner. The new 5000 BTU AC runs for hours but the room is still hot. The temperature is 90°F outside and the AC is set to 75°F but the room is still 80°F degrees after running 8 hours. I live in an older home that has no air duct vents so I do not have a central AC unit. There is a large empty attic directly above my room. What can cause my bedroom to stay warm while running a window AC?

Room is hot with new window ACRoom is hot with new window AC, room does not cool down



Why Is My Room Hot With A New Window AC?

A hot room is not where anyone wants to be. Installing and running a window air conditioner or aircon can help. In certain situations your window AC may not cool down your room as desired. There are certain reasons why the AC cannot cool the room to your desired temperature. See below for reasons and tips to help cool down your room…

NOTE: If your bedroom is 300 square feet and you have a 5000 BTU Window AC, the AC will struggle to fully cool the room. For a room with the square footage of 300, you should have AT LEAST a 7000 BTU AC unit. A small AC in a large room will cause it to run constantly.

Check to confirm the window AC has the BTU’s needed for the size of your room. If the window AC is not powerful enough for the size of the room, it will struggle to cool the room. High ceilings and large windows can also, in combination with a smaller window AC, cause difficult cooling situations. See the BTU chart below!

AC BTU Calculator ChartHow Many BTUs Do I Need To Cool My Room? – AC BTU Chart



Please Note: This guide is for a new window AC that is not cooling the room. This guide shows how to fix a problem within your home knowing the window AC is in working condition. If you are having issues with an older window AC, please see the helpful guide here to fix your AC.

How To Cool Down A Room With Window AC

  • Is the door to your room open? Close it.
  • Large windows? Use window shades to reduce the sunlight coming into the room.
  • Is your AC on the highest FAN setting? Turn the AC on HIGH FAN.
  • Do you have the AC Thermostat set to the lowest setting? Set to the coldest temp.
  • Is the FRESH AIR INTAKE open? Close it to allow the cooler room air to circulate.
  • Check to be sure the AC is correctly installed in the window. Reinstall if issue is found.
  • Inspect the seal around the AC unit. Seal up any areas that allow warm air to enter.
  • Do you have high ceilings? Be sure to choose a higher BTU AC if initially buying your AC.
  • Poor Insulation? This can cause an excessively hot room, use the appropriate size BTU AC.
  • Is there an attic above your room? It may not be insulated correctly and heating up the room.

10 Reasons Why A Window AC Does Not Cool Your Room

  1. If the door to your room is wide open, the window AC will not cool down the room.
    The AC cannot cool the room down to the desired temperature if the door to your room is open. Shut the door and let the AC run for a few hours to get the room to a cooler temperature.
  2. If the AC is on a LOW FAN setting, it may not be able to properly cool the room.
    Turn the AC to the highest fan setting. If the AC is set to a low setting, it may not be enough to cool your room. Let the AC run on the highest fan setting for a few hours to cool your room.
  3. If the AC thermostat is not turned to the coldest temp, it may not cool the room down.
    Be sure the AC thermostat is turned to the coldest setting or temperature. If the room is quite large and the thermostat is set to medium or low, it may not get cold enough to cool the room.
  4. An open FRESH AIR INTAKE located on the AC can cause it to not cool the room.
    Shut the fresh air intake on your AC to let the room air circulate instead of bringing in outside air.
  5. An incorrectly installed window AC can cause your room to not cool down.
    A window AC needs to be installed correctly for it to run efficiently. If the AC is not placed properly in the window, the AC may not be able to cool the room. Read the manual and follow the directions for proper installation.
  6. If the room has windows without shade facing the sun, this can cause the AC to not cool.
    A room with sun coming in is extremely difficult to cool with a window AC. Cover the windows with sun shades if they are not already covered. Use a solar film on the windows to keep heat radiating in to a minimum. This will help keep the room darker and therefore help the AC unit to cool the room.
  7. The window AC may not be sealed as needed into the window which causes cooling issues.
    Window air conditioners come with a certain type of seal that goes around it to seal out the warm outside air. If the seal is missing, improperly installed, or damaged, the AC cannot cool. Inspect the seal around the AC to be sure it is installed correctly.
  8. High ceilings in your room can make it difficult to cool the room in terms of BTU’s.
    A high ceiling can cause the window AC to have to work overtime. If the AC is not the proper BTU’s and or hot air is trapped high in the ceiling, you will have cooling issues. Turn on the ceiling fan to help mix the air. Check to see if the BTU’s on the AC is high enough to cool down a room with a high ceiling.
  9. A poorly insulated room facing the sun during the hottest time of the day.
    A room facing the sun with poor insulation will get very hot in the summer. A window AC may have a hard time cooling down a room with so much heat radiating into it. This can be fixed by getting a window AC with higher BTU’s. You may also want to look into adding a higher grade insulation into the ceiling or walls.
  10. A hot attic above your room can make it more difficult for your AC to cool down the room.
    A hot attic can make the room so hot the AC is not able to cool it down. If the attic is accessible, you can see if it has proper insulation. If not, R-19 pink fiberglass insulation can be installed for heat protection between the hot attic and the ceiling of your room. You can also try getting a higher BTU AC unit.


How To Correctly Install A Window Air Conditioning Unit

Is The Window Air Conditioner Working Properly?

Your AC may not be working properly. Let the AC run for 15 minutes then test the temperature of the room vs the temperature coming out of AC vents. If the difference is less than 16 degrees the AC may be faulty. This will tell you if the AC is operational or needs maintenance. Consult the AC manual if you find an issue.

An AC turning on for a few minutes and then off again for a few minutes is called short cycling, this can cause the room to be warm. Turn the AC unit off for 10 minutes, then turn the AC back on and observe AC function.

Check the window AC air filter. Clean the filter and reinstall. A clogged air filter can cause the AC to not cool.

Which AC Do I Need For My Room Size Square Footage?

Room Size: 150 SF = BTU Recommended: 5000 BTU’s
Room Size: 250 SF = BTU Recommended: 6000 BTU’s
Room Size: 300 SF = BTU Recommended: 7000 BTU’s
Room Size: 350 SF = BTU Recommended: 8000 BTU’s
Room Size: 400 SF = BTU Recommended: 9000 BTU’s
Room Size: 450 SF = BTU Recommended: 10000 BTU’s
Room Size: 550 SF = BTU Recommended: 12000 BTU’s
Room Size: 700 SF = BTU Recommended: 14000 BTU’s
Room Size: 1000 SF = BTU Recommended: 18000 BTU’s
Room Size: 1200 SF = BTU Recommended: 21000 BTU’s
Room Size: 1400 SF = BTU Recommended: 23000 BTU’s
Room Size: 1600 SF = BTU Recommended: 25000 BTU’s
Room Size: 1900 SF = BTU Recommended: 28000 BTU’s
Room Size: 2700 SF = BTU Recommended: 36000 BTU’s

What Is A BTU In Air Conditioning?

BTU is a unit of heat. BTU is an acronym for BRITISH THERMAL UNIT. This form of measurement measures energy. 1 BTU is the energy amount needed to increase the temp of a pound of water by 1° degree Fahrenheit.



Need help with your window AC? Let us know how we can help by leaving your air conditioning issue in the comments below. Please leave the model number of your A/C so we can help you with your cooling issues.

ALLEN VETTER - DIY Repair Assistant
Allen is a Home Maintenance/Appliance tech and the author/creator of this website. He has 33 years of experience troubleshooting and repairing all types of machinery. Contact here



More "Do It Yourself" DIY Tips, Tricks, Ideas, Repair:



1 thought on “Room Is Hot With New Window AC Running – 10 Helpful Cooling Tips”

Leave a Comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.



Scroll to Top