Air Conditioner Size

The Air Conditioner Size calculator computes the number of BTUs needed to air condition a room with a window unit air conditioner based on the size of the room, number of occupants, sun exposure and use (kitchen or not).  The correct size of a window A/C unit is very important (see General Info below).

INSTRUCTIONS: Choose preferred units and enter the following:

• (L) This is the length of the room.
• (W) This is the width of the room.
• (H) This is the height of the room.
• (SE) This is the sun exposure.  Choices are Heavy Shade, Normal, Full Sun.
• (P) This is the number of people who regularly occupy the room.
• (K) This is whether the room is a kitchen or not.

A/C Unit BTUs: The calculator returns the hourly BTUs required to cool the space. BTUs from square feet

The Math / Science

According the reference article below, the BTU requirements to cool a room are:

• BTUs are a function of square footage (see Table).
• 10% added if the room is in direct (full) sun.
• 10% reduced if the room is heavily shaded
• add 600 BTUs for all regular occupants above a normal 2 occupants. 
• add 4,000 BTUs if the room is a kitchen.

General Information

It is important to choose the right size air conditioning unit for your room.  A/C units do two things to greatly contribute to your comfort.  First is to lower the temperature, but nearly as important, they remove humidity.  That's why you'll see water dripping from an A/C unit.  Lower humidity levels are much more comfortable in the summer and reduce the mustiness of furniture and materials in the room. 

• If your unit is too small, it will not keep up with the cooling demand, and your room will stay too warm in the hottest part of the day.
• If your unit is too big, it will cool the room too quickly and not remove the humidity.  You will have a cold and clammy room.  

Reference

• Energystar.gov article on "Room Air Conditioner"