Tons = GPM × ΔT × 500 × Cf / 12,000Where:
· GPM = flow rate in gallons per minute
· ΔT = supply/return temperature difference (°F)
· 500 = 8.34 lb/gal × 60 min/hr × 1 BTU/lb·°F
· Cf = fluid correction factor (1.0 for water)
· 12,000 = BTU/hr per ton
Typical ΔT: CHW = 10–12°F | HHW = 20–40°F | Condenser = 10°F
This hydronic capacity calculator ties together flow rate, cooling or heating load, and the supply-to-return temperature difference (ΔT) using the standard water-side heat equation. Pick which quantity to solve for — GPM, tons, or ΔT — enter the other two, choose the fluid, and the tool returns the answer along with the equivalent load in BTU/hr.
It is the quick check engineers use to size pumps and coils: how much flow a chiller or boiler needs, how many tons a measured flow and ΔT represent, or what temperature difference a given flow will produce. A fluid selector applies a correction factor so glycol systems return slightly higher flow for the same load.
| Load | Q (BTU/hr) = 500 · Cf · GPM · ΔT |
| Tons | Tons = GPM · ΔT · 500 · Cf ÷ 12,000 |
| GPM | GPM = Tons × 12,000 ÷ (500 · Cf · ΔT) |
| ΔT | ΔT = Tons × 12,000 ÷ (500 · Cf · GPM) |
This is the standard hydronic heat-transfer relation (ASHRAE Fundamentals). The constant 500 = 60 min/hr × 8.34 lb/gal × 1.0 BTU/lb·°F for water; 12,000 BTU/hr = 1 ton of refrigeration. The fluid correction factor Cf adjusts the 500 for the lower specific heat of glycol (≈0.97 for 25% ethylene glycol, ≈0.93 for 50%), so antifreeze systems require slightly more flow for the same load.