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Hydronic Pipe Sizing

Hazen-Williams · GPM · Friction Loss · Pump Head · Glycol Systems

When to use: Use for hydronic heating and chilled water piping systems — boilers, chillers, fan coils, radiant floors, and heat exchangers. Enter flow rate (GPM) and pipe run length to determine pipe size (keeping velocity ≤ 4 fps), friction loss (ft/100 ft), and total pump head. Supports glycol solutions for freeze protection. The 500 rule (BTU/hr = GPM × 500 × ΔT) is used to verify flow rate vs. capacity.

System Parameters
GPM
Chilled: 10–14°F, Hot: 20°F
°F ΔT
One-way length
ft
1.3–1.5 typical
(×)
Recommended Pipe Size
6"
Nominal Pipe Size
2.24 fps · 0.01 ft/100ft friction
System Summary
Pipe Size (max 4 fps)6"
Flow Velocity2.24 fps
Friction Loss0.01 ft/100 ft
Equivalent Length (w/ fittings)300 ft
Total System Head Loss0.0 ft (0.0 psi)
Estimated Pump BHP0.000 BHP
System Capacity (500 rule)200,000 BTU/hr (16.7 tons)
References
Hazen-Williams: hf = 10.67 × Q^1.852 / (C^1.852 × d^4.87)
500 Rule: BTU/hr = GPM × 500 × ΔT
Max velocity: 4 fps residential, 6 fps commercial
ASHRAE Hydronic Piping – System design guide
Add glycol factor (1.1–1.75×) to friction for antifreeze