We’ve featured many tips about staying cool during summer without the help of an air conditioner. What about when the heat or humidity is so brutal that there is no choice but to break out the big guns and use AC? Here are some tips from Apartment Therapy about how to use air conditioning in the most energy-efficient, cost-effective ways.

1. Use Window or Portable Units: if you’re not looking to cool your entire home, just using a portable unit to cool one area could use up to 50% less energy than a larger central air unit.
2. Close off Vents: close the vents in the lower portion of your home (the basement is traditionally coolest anyway). This will force the cool air up.
3. Rearrange Your Furniture: don’t let your furniture obstruct your cool air flow.
4. Try 78 Degrees: an air conditioner can run at optimal performance level at this temperature. This is a steady pace for it. Decreasing the temperature even 5 degrees lower than that can make your AC use up to 40% more energy.

For 6 more AC tips, head over to 10 Ways To Save Energy When Air Conditioning Is A Must.