HVAC BTU Sizing Chart
Room AC by square footage, central AC tonnage by home size, and furnace BTU by climate zone — one printable page
An oversized system short-cycles, never dehumidifies, and wears out early; an undersized one runs forever and never catches up. Both waste money. This chart gives you the rule-of-thumb starting numbers HVAC pros use — room air conditioner BTU by area, central AC tonnage by home size and climate, and furnace output by climate zone — plus the adjustments that move the answer. Use it to sanity-check any quote before you buy.
Room Air Conditioner (Cooling BTU)
| Room Size | Cooling BTU |
|---|---|
| 100-150 sq ft | 5,000 BTU |
| 150-250 sq ft | 6,000 BTU |
| 250-300 sq ft | 7,000 BTU |
| 300-350 sq ft | 8,000 BTU |
| 350-400 sq ft | 9,000 BTU |
| 400-450 sq ft | 10,000 BTU |
| 450-550 sq ft | 12,000 BTU |
| 550-700 sq ft | 14,000 BTU |
| 700-1,000 sq ft | 18,000 BTU |
| 1,000-1,200 sq ft | 21,000 BTU |
| 1,200-1,400 sq ft | 23,000 BTU |
Based on the EPA Energy Star room AC guidance (~20 BTU per sq ft). Adjust with the table below for sun, ceilings, and occupancy.
Central AC Tonnage by Home Size
1 ton = 12,000 BTU. Mild climates need roughly 1 ton per 600 sq ft; hot climates closer to 1 ton per 450 sq ft.
| Conditioned Area | Mild Climate |
|---|---|
| 600 sq ft | 1 - 1.5 ton |
| 900 sq ft | 1.5 - 2 ton |
| 1,200 sq ft | 2 - 2.5 ton |
| 1,500 sq ft | 2.5 - 3 ton |
| 1,800 sq ft | 3 - 3.5 ton |
| 2,100 sq ft | 3.5 - 4 ton |
| 2,400 sq ft | 4 - 4.5 ton |
Furnace Sizing by Climate Zone
Furnace output BTU = conditioned square footage x the zone factor. Then divide by furnace efficiency (AFUE) for input rating — a 96% furnace delivers 96% of its rated input as heat.
| Climate Zone | BTU / sq ft |
|---|---|
| Zone 1 - Hot South | 30-35 BTU |
| Zone 2 - Warm | 35-40 BTU |
| Zone 3 - Moderate | 40-45 BTU |
| Zone 4 - Cold | 45-50 BTU |
| Zone 5 - Very Cold | 50-60 BTU |
Adjustments (Add or Subtract)
| Condition | Adjustment |
|---|---|
| Very sunny / west-facing room | +10% |
| Heavily shaded room | -10% |
| Kitchen | +4,000 BTU |
| Each occupant over 2 | +600 BTU |
| High ceilings (over 8 ft) | +10-20% |
| Poor insulation / old windows | +10-20% |
Quick Sizing Estimator
Cooling: BTU = area x 20, then apply adjustments, then tons = BTU / 12,000. Heating: BTU = area x zone factor. Round to the nearest standard unit size.