Air Conditioner Guide: From Maintenance to Buying New Systems

Window air conditioner unit mounted directly in a window.
A window air conditioner unit mounts right on the window. (©tanvirshafi, Adobe Stock Photos)

Window Units

When choosing a window unit, the most important factor is the size of the room you wish to cool and the cooling power, measured in British thermal units, of the unit you choose.

Here’s a general guide for window air conditioners based on room size:

  • 12′ x 12′ room: 5,000 BTU unit
  • 16′ x 16′ room: 7,000 BTU unit
  • 20′ x 20′ room: 10,000 BTU unit
  • 24′ x 24′ room: 14,000 BTU unit

In addition to size, make sure the AC unit you buy:

  • Has an EER (Energy Efficiency Ratio) of 11 or higher
  • Carries the EnergyStar label
  • Has a low noise rating
  • Provides good airflow
  • Uses a permanent or reusable air filter
  • Has various speed settings

Portable, ventless air conditioner rolled up beside a bed with a spread hanging down and tassels touching the hardwood floor.
Portable air conditioning provides a zoned, efficient option for cooling small spaces. (©Axel Bueckert, Adobe Stock Photos)

Portable AC Units

A portable air conditioner is basically AC on wheels. It has an exhaust tube, which must be vented outside, to remove hot air from the room.

Portable AC systems don’t require permanent installation. In fact, they come with wheels so can move them from room to room. And most of them come with a window venting kit that allows you to prepare a window for the exhaust tube.

These systems accumulate moisture, and you’ll need to routinely drain them. This means emptying a reservoir on the unit or hooking up a drainage hose, if compatible with the unit.

Before purchasing a portable AC, consider its energy efficiency. Systems with dual hoses cool rooms faster than their single-hose counterparts.

Through-the-wall air conditioner unit, as seen in a luxury hotel room
Through-the-wall air conditioners (which are exactly what they sound like) are commonly found in hotel rooms, but you also can purchase them for the home. (DepositPhotos)

Through-the-Wall Units

You often see through-the-wall AC units in hotel rooms, but they’re also ideal for large open rooms, studio apartments or remodeled garages.

You can use through-the-wall units in rooms that aren’t connected to a central air conditioning system. They’re ideal for home additions and, really, wherever you want to add AC without running ductwork.

You can purchase these units with heating and cooling features, or just cooling features, and you must carefully choose where to install them.

You must install these units in exterior walls where there’s no plumbing or electrical wiring. In addition, you’ll need to install a sleeve or chassis that can support the weight of the air conditioner.

A mini-split ductless air conditioner is one type of through-the-wall system, but it’s not boxy and comes with a separate outdoor unit. Mini-split AC units are sleek, subtle and look good in any home.

Consider A Warranty

If you are worried about your air conditioning unit breaking down due to normal wear and tear, consider investing in a homeowner’s warranty.

A review team independent of Today’s Homeowner picked out the best homeowner warranty providers, though they also looked at smaller companies such as Fidelity National Home Warranty, Global Home USA Warranty, and A.B. May Home Warranty.

Further Information


  1. how do you install a window air conditioner in an above door transom. How should it be supported, insulated and waterproffed?

  2. Great information….any ideas on the brands of Air Conditions and Furnaces to buy? List the best then lesser, etc…Thank you and keep us informed on all issues regarding maintaining a home….

    Will Krohe.

  3. Great information. Having to buy a new central unit in San Antonio this year. The effeciency is most important to me. Want to keep it clean and green as long as we can

  4. A few other things to remember.
    The units seer rating may only be as good as the building its installed in.If the envelope is less than to be desired than the hi seer unit will not pay back as quickly as stated.It is as important to have the home checked for window,insulation and air infiltration.You may want to spend the money on insulation instead of the hier seer ,the cost offset could be the same or in most older homes better to insulate in the long run.
    John Cannamela

  5. Dear Danny,

    I was wonderding if it was a good idea to build a lean to to cover my a/c unit or build an actual cover that will cover that will cover the top, sides and front? I’ve looked on your website and am not able to find an answer to that question. Thank you for your help.

  6. I have seen a system advertised on the Wether Channel that dosen’t require duct work. Right now we are using 2 window air conditioners & they work fine, but, I also know they are now as cost effective as centeral air. We are also getting older & putting them in & taking them out every season can be back breaking. Please let me know how well these work & where I can find a dealer in my area. We live in St. Pau MN.

  7. Would window air-conditioners installed on its side instead of its designed upright position due to window space restrictions function properly or not?

  8. Dear Sir,
    I am setting up a motor home and wish to place a window wall air conditioner inside the bus, the rear of the unit would extend to the out side of the bus wall and the remainder or the unit would be in an inclosure with four inches on either side of the unit, is this exceptable for air flow to the unit or not, I am not sure if a unit needs to have air flow around it or only on the rear, any help would be appreciated.

  9. I have central A/C but its only one zone. Upstairs I have 3 bedrooms and its always warmer. I hate to waste the central air at night since I just need it to cool upstairs. I was thinking of getting a window air conditioner, but I don’t think it will cool one of the bedrooms because of where it is located. It can cool off 2. So that would mean I would have to get another small a/c for that 3rd bedroom. Would it be cost-effective to buy one average size a/c and one small a/c for night time only instead of runnning our central a/c? Plus I think it will cool it better since its a one zone and upstairs is always warmer then downstairs.

  10. Inquiring on the average cost to have my 18,000 btu Ramsond a/c wall unit cleaned (has some mold on the plate). I would appreciate knowing the cost I will be expecting to pay for this service.

  11. Summer is coming and I was thinking of installing air-conditioner at their homes. Thanks for sharing your information on air conditioning buying guide and maintenance. Specially the points mentioned in the article will help me cleaning it smoothly.

  12. Hi,
    I am from Kolkata.
    I want to buy an AC for my house. Based on the following criterias can someone please advice me which Brand (Hitachi, Samsung etc), Star (5 , 3) and Volume (Ton) should i buy considering economical, worth of money,electric consumption,quality and offcourse service etc ?

    1>Area of room (length*width*height): 3.2*3.8*3.01 (Meters) OR 10.49*12.46*9.9 (ft) – Top floor (1st)
    2>Usage probability: 5 months (Max) and 5.5 hours (Max) in a day — In a year.

    It will be a great help if i get comments as i am not much aware of the calculation of electric consumption and overall idea on Ac.

  13. This is so useful, thank you! My air conditioner is in need of repair probably due to overuse this summer. It is an older unit and it is about time anyways for a replacement. However, I am so glad that it lasted throughout the summer. I would really like to get another one that is long lasting. Which brand is known for being the most durable?

    • Hi, Valerie!
      We provide questions (we receive thousands each year) to Danny Lipford, America’s leading home improvement expert, on a weekly basis. We’re not able to answer every question due to the high volume of mail we receive, but we sure do our best.
      We encourage the community to help each other when they can. One fan may have the answer to another fan’s question, and we think that’s awesome. 🙂
      Thanks for visiting

  14. I recently read in a leading consumer magazine, the the portable type air conditioners are next to useless. Let the buyer beware. Just sayin!


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