How to choose the right size air conditioner

Summer is coming. I know the robins are here and I saw a blackbird at  my friend’s house the other day. There is green poking through the nasty ‘lawn’ thingy in front of my condo. I moved bedrooms this winter and my current one faces west; that means I may need an air conditioner this summer. I like my sleeping area cool but don’t want to cool down the whole house just for one tiny room so now I have to decide what to get. So, here is how to choose the size of air conditioner for your space.
Start by calculating the square footage of the space to be cooled.  (I know we use meters, not feet, but no one seems to have told the air conditioning manufacturers). For example, if the room is 24 by 24,  the square footage is 576. You need an air conditioner that will cool a minimum of 576 square feet. 
The cooling capacity of an air conditioner is measured in British Thermal Units (BTUs). So are your bar-b-ques, by the way. The capacity required per square foot  varies from 30  for a small room down to 20 for a large, open-concept space. For example, a 200 square foot room requires 6,000 BTUs, which is 30 BTUs per square foot, but a 600 square foot room requires 14,000, which is 23 BTUs. 
If the room is a shaded, subtract 20% from the number of BTUs required, if it gets a lot of sunlight, add 20%. If the space has a kitchen, add 4000 BTUs, if more than two people use the room daily, add 600 BTUs for each person. 
Still with me?  Now if you decide to throw caution to the wind and just buy the biggest one you can carry home from the big-box store, consider that a unit that is too large for the space will cool too quickly, shut off frequently and not remove enough moisture from the air, resulting in freezing. Not good. One that is too small will run continuously and cost more to operate than the specs say. Read the box.
So, now that we are all totally confused, take heart and contact a professional. Not only will they be able to determine the size of air conditioner you need, they will advise you on the type of system— which is a whole other discussion.  Good luck. Check my website, connect to the newspaper archives, for references and more information.

Written by