Hydronic Flow – BTU to GPM Calculator
Convert hydronic load and water temperature difference into design flow, or check the capacity carried by a known GPM.
Required flow
10 GPM
Metric flow
0.631 L/s
Load in kW
29.31 kW
Capacity at known GPM
100 MBH
The factor 500 is a quick water-system approximation. Use actual density and specific heat for glycol or high-accuracy final calculations.
Turn the calculation into a complete design workflow
Use the free result as a quick engineering check, then continue into MEPFlow for connected system design, sizing and project calculations.
How the Hydronic Flow – BTU to GPM Calculator Works
For quick water-system design, the familiar hydronic relationship uses a rounded factor of 500, derived from water density, specific heat and 60 minutes per hour. Divide the design load by 500 × ΔT to estimate GPM.
The 500 factor is convenient but approximate because water density and specific heat vary with temperature. It is appropriate for preliminary sizing and quick checks; detailed calculations for glycol or unusual temperatures should use actual fluid properties.
The calculator also reports the equivalent metric flow and thermal load so the same result can be carried into pump and pipe-sizing workflows.
Calculation basis
Q ≈ 500 × GPM × ΔT
When to Use This Calculator
- Boiler loop flow
- Chilled-water flow
- Heat-pump hydronic flow
- Coil and terminal-unit flow checks
Engineering Checks Before Final Design
- The 500 factor is a water approximation.
- Glycol mixtures require fluid-property correction.
- Use equipment manufacturer minimum/maximum flow limits.
Frequently Asked Questions
What is the formula for BTU to GPM?
For a quick water-system estimate, GPM = BTU/hr ÷ (500 × ΔT in °F).
Why do hydronic designers use 500?
It combines the approximate weight and specific heat of water with 60 minutes per hour.
What happens if I increase delta-T?
For the same load, a larger delta-T reduces the required flow rate.
Can I use 500 for glycol?
Not for precise final sizing. Glycol changes density and specific heat, so use actual fluid properties for final calculations.
Engineering References
MEPFlow uses public engineering references to document the calculation basis. Always verify the final design against the standard, code edition and manufacturer data applicable to your project.