BTU

BTU (British Thermal Unit) is the energy required to raise one pound of water by 1°F. In HVAC, equipment capacity is rated in BTUs per hour.

A typical Colorado home needs roughly 30-60 BTUs per square foot of heating — but altitude, insulation, window orientation, and air infiltration all shift the number. That’s why proper sizing requires a Manual J load calculation, not a rule-of-thumb.

Approximate BTU needs

• 1,500 sq ft Colorado home — 60,000-80,000 BTU furnace, 2 ton AC
• 2,500 sq ft Colorado home — 80,000-100,000 BTU furnace, 2.5-3 ton AC
• 3,500 sq ft Colorado home — 100,000-120,000 BTU furnace, 3-3.5 ton AC

For ACs, capacity is also expressed in tons — one ton = 12,000 BTU/hour. A 3-ton AC delivers 36,000 BTU/hour of cooling.

Related: Ton, CFM, Manual J.