ℹ️ Schedule 80 required for systems exceeding 160 PSI or 250°F — consult project specifications
ASHRAE Velocity Guidelines
ApplicationRangeNote
Small Bore (≤ 2")1 – 4 FPSMax 4 FPS per ASHRAE
Medium Bore (2½" – 4")2 – 6 FPSTypical commercial range
Large Bore (6"+)4 – 10 FPSMax 10 FPS, erosion limit
Source: ASHRAE Handbook of Fundamentals, Chapter 22
Pressure Drop Guidelines
General Design Range1 – 4 ft w.g. / 100 ft
Typical Design Target2.5 ft w.g. / 100 ft
High Pressure (> 160 PSI)Sch 80 required per code
Source: ASHRAE Handbook of Fundamentals, Chapter 22
Standard Material by Size
Type L Copper — ½" to 2"
Standard small bore hydronic. Lead-free solder or press fittings. ASTM B88.
Sch 40 Black Steel — 2½" to 12"
Standard large bore hydronic mains. Grooved or welded connections. ASTM A53.
Sch 80 — High Pressure Systems
Required for systems exceeding 160 PSI or 250°F. Consult project specifications.
Glycol Selection Guide
0%Interior systems, no freeze risk
20%Mild climates, light freeze protection
30%Most common commercial — down to ~0°F
40%Cold climates — down to ~-10°F
50%Extreme cold / outdoor equipment
Propylene glycol — lower toxicity, preferred for most commercial HVAC