How to properly size an air conditioner for a very sunny room

air-conditioning

I'm trying to size a window air conditioner for a room, but having trouble deciding if the usual guidelines are a good fit.

The room in question is about 230 sq. feet, and does not have full 8 foot ceilings, as part of the room is formed by the gable roof. Based on this I would pick a 6000 BTU unit. However, the room is also roofline with black asphalt shingles, east/west/southern exposure, the long dimension of the space being southern exposure with 2 south-facing skylights. There's no natural shading, and the room is also above an uncooled garage space. I typically see a 10% fudge factor recommended for "sunny rooms", but don't have a clear idea of what constitutes a "sunny room". Would this heat load significantly exceed that factor, and by how much?

Best Answer

This page from Energy Star gives some good basic guidelines.

If the room is heavily shaded, reduce capacity by 10 percent.

If the room is very sunny, increase capacity by 10 percent.

If more than two people regularly occupy the room, add 600 BTUs for each additional person.

If the unit is used in a kitchen, increase capacity by 4,000 BTUs.

Consider where you install the unit. If you are mounting an air conditioner near the corner of a room, look for a unit that can send the airflow in the right direction.

I'd say your room fits the "very sunny" definition.

Related Solutions

Is the window air conditioner cooling properly

According to this, the Frigidaire FAS182H2A1 is an 18000 BTU device.
http://www.appliancepartsnationwide.com/FAS182H2A1/53279.htm

That's pretty powerful if working properly. The government suggests 8000 BTU for 325 SF.

http://www.energystar.gov/index.cfm?c=roomac.pr_properly_sized

Check your outside coils too and clean if needed. If that is not a problem it could be something internal. Some examples:

partial clog in your expansion valve.
low freon level

If cleaning the outside coils doesn't work, I do not expect repair to be practical. You can buy a new 10,000 BTU unit from Home Depot for $300. It would be reasonable to ask the owner to pay for it.

What size air conditioner for a ~230 square foot room with 10 foot ceilings

The EPA has room size to BTU chart with some caveats for certain situations:

https://www.energystar.gov/index.cfm?c=roomac.pr_properly_sized

  Room size            A/C size
  ---------------     ------------
  100 up to   150 ->  5,000 BTU/hr
  150 up to   250 ->  6,000 BTU/hr
  250 up to   300 ->  7,000 BTU/hr
  300 up to   350 ->  8,000 BTU/hr
  350 up to   400 ->  9,000 BTU/hr
  400 up to   450 -> 10,000 BTU/hr
  450 up to   550 -> 12,000 BTU/hr
  550 up to   700 -> 14,000 BTU/hr
  700 up to 1,000 -> 18,000 BTU/hr
1,000 up to 1,200 -> 21,000 BTU/hr
1,200 up to 1,400 -> 23,000 BTU/hr
1,400 up to 1,500 -> 24,000 BTU/hr
1,500 up to 2,000 -> 30,000 BTU/hr
2,000 up to 2,500 -> 34,000 BTU/hr
Make any adjustments for the following circumstances:

If the room is heavily shaded, reduce capacity by 10 percent.

If the room is very sunny, increase capacity by 10 percent.

If more than two people regularly occupy the room, add 600 BTUs for each additional person.

If the unit is used in a kitchen, increase capacity by 4,000 BTUs.

Consider where you install the unit. If you are mounting an air conditioner near the corner of a room, look for a unit that can send
the airflow in the right direction.

If you fall into any of those special situations, that may help you with sizing. Otherwise, since you're between sizes of available units, unless your climate is particularly mild, I'd go up a size to allow a bit extra cooling capacity for hot days.

Best Answer

Related Solutions

Is the window air conditioner cooling properly

What size air conditioner for a ~230 square foot room with 10 foot ceilings

Related Topic