HVAC
BTU Rule of Thumb
Quick HVAC load estimate from square footage. Rule-of-thumb only — not a Manual J replacement.
Safety/code-sensitive estimate. This calculator is not a substitute for licensed professional review, applicable code requirements, manufacturer instructions, field verification, permits, or inspections. Do not rely on this result as the sole basis for work that could affect life safety, fire safety, electrical safety, structural safety, public safety, property damage, code compliance, or required licensure.
Formula: BTU = Area × BTU per sq ft