Room BTU Calculator

Cooling capacity is rated in BTU per hour, and the quickest honest way to size a single room is the ENERGY STAR rule of thumb: start at about `20` BTU/hr for every square foot of floor. A `340` square-foot bedroom therefore lands near `6,800` BTU/hr, which is why room air conditioners cluster around the `6,000`–`8,000` BTU marks.

Four adjustments from the same ENERGY STAR chart tune that base number. A heavily shaded room drops `10%`; a very sunny room adds `10%`. Once more than two people use the room regularly, add `600` BTU/hr per extra person. And because a kitchen dumps stove and oven heat into the air, add a flat `4,000` BTU/hr when you are sizing one. The calculator applies whichever boxes you check and shows the running total.

Heating is sized separately because it depends on your winter climate, not just floor area. We multiply the room area by a climate factor — roughly `30` BTU/hr per square foot in the Deep South, `40` in the middle of the country, and `50` up north — to give a companion heating estimate. Both numbers are planning figures: a Manual J load calculation by an HVAC professional accounts for insulation, windows, and air leakage that a per-square-foot rule cannot.