Which formula corresponds to 1 gpm per 1,000 BTUH input?

Which formula corresponds to 1 gpm per 1,000 BTUH input?

• A. 1 gpm for each 100,000 BTUH input
• B. 1 gpm for each 10,000 BTUH input
• C. 1 gpm for each 1,000 BTUH input
• D. 10 gpm for each 10,000 BTUH input

Answer: (C)

Understanding how water flow translates to heating output helps you size and interpret gas heating equipment. The basic relationship is BTUH = GPM × ΔT × 500, where BTUH is the heat input, GPM is gallons per minute of water flow, and ΔT is the temperature rise the water experiences as it passes through the unit. If you consider a typical small temperature rise across a heater, about 2°F, the equation becomes BTUH ≈ GPM × (2) × 500 = GPM × 1000. That means, under that common operating condition, adding one gallon per minute of water flow adds roughly 1,000 BTUH of heat output. So the rule “one gallon per minute for each 1,000 BTUH input” is the practical way to relate flow to input for many gas-fired hydronic scenarios. The other options would imply much larger or smaller BTUH for the same flow without changing the actual ΔT, which isn’t the standard quick-approximation used in this context.

Understanding how water flow translates to heating output helps you size and interpret gas heating equipment. The basic relationship is BTUH = GPM × ΔT × 500, where BTUH is the heat input, GPM is gallons per minute of water flow, and ΔT is the temperature rise the water experiences as it passes through the unit.

If you consider a typical small temperature rise across a heater, about 2°F, the equation becomes BTUH ≈ GPM × (2) × 500 = GPM × 1000. That means, under that common operating condition, adding one gallon per minute of water flow adds roughly 1,000 BTUH of heat output. So the rule “one gallon per minute for each 1,000 BTUH input” is the practical way to relate flow to input for many gas-fired hydronic scenarios.

The other options would imply much larger or smaller BTUH for the same flow without changing the actual ΔT, which isn’t the standard quick-approximation used in this context.