A home office is a small room with a surprising amount of heat in it. The room itself might only need 2,000 to 3,000 BTU by the 20 BTU per square foot rule, but a desktop PC under load pulls 200 to 500 watts and two monitors add another 60 to 100. Every watt becomes 3.41 BTU per hour of heat that the air conditioner has to remove. A serious workstation or gaming rig can add 1,500 BTU on its own; a laptop and a single monitor add a few hundred.
The table below is computed for one occupant. To account for equipment, add roughly 300 BTU for a laptop setup, 1,000 BTU for a typical desktop with two monitors, and 1,500 to 2,000 BTU for a high-end workstation, printer, and networking gear. In practice this is why a 5,000 BTU window unit, which covers a bedroom of the same size easily, can feel marginal in a 150 sq ft office during a summer afternoon.
Offices are also occupied during the hottest part of the day, unlike bedrooms. If the window faces south or west and you work 1 to 5 p.m., use the 'very sunny' setting even if the room looks shaded in the morning.
Cooling BTU by home office size
Baseline: average sun, average insulation, moderate climate, 8 ft ceiling, 1 person.
| Floor area | Best case | Baseline | Worst case | Unit to buy |
|---|---|---|---|---|
| 80 sq ft | 1,300 | 1,600 | 2,000 | 5,000 BTU |
| 100 sq ft | 1,600 | 2,000 | 2,500 | 5,000 BTU |
| 120 sq ft | 1,900 | 2,400 | 3,000 | 5,000 BTU |
| 150 sq ft | 2,400 | 3,000 | 3,800 | 5,000 BTU |
| 200 sq ft | 3,200 | 4,000 | 5,100 | 5,000 BTU |
| 250 sq ft | 4,100 | 5,000 | 6,300 | 5,000 BTU |
Best case = good insulation and heavy shade; worst case = poor insulation and full sun.
Home office-specific advice
Add your equipment load in watts × 3.4
Look at the power supply ratings or use a plug-in meter. 300 W of computers is 1,020 BTU/hr. Add that to the calculator's result before choosing a unit.
Choose a unit that is quiet on low fan
You will be on video calls next to this machine. Under 50 dB on low is a good target; inverter units and U-shaped window units are quietest.
Consider a portable if the window is your only light
Offices often have one window. If blocking it with a window unit is unacceptable, a portable AC with a slim window plate works, but remember to use its SACC rating (usually 60–70% of the headline BTU).
Common questions
Is 5,000 BTU enough for a home office?
For offices up to about 120 sq ft with a laptop, yes. For a 150 sq ft office with a desktop PC and two monitors on a sunny side of the house, 6,000 BTU is a safer fit.
How much heat does a computer add to a room?
Roughly its power draw in watts times 3.41. A 400 W gaming PC plus 80 W of monitors is about 1,640 BTU per hour, about the same as adding three extra people to the room.