Sealed System Expansion Vessel
Sizing & Selection

Sizes diaphragm, plain-steel and open vessels per the ASHRAE Handbook (HVAC Systems & Equipment) expansion-tank equations — with automatic gauge→absolute pressure conversion, glycol & pipe-expansion correction, and selection from standard manufacturer sizes.

System & Fluid

Step 01 – 03 · Vessel type, fluid & units

01Vessel Type

02Fluid

03Units

System Volume

Step 04 · Direct entry or kW estimate

04Method

Total System Volume

All coils, pipes, equipment & buffer tanks · litres

Temperatures

Step 05 · Operating range

05Highest Temp (t₂)

Hottest the vessel sees · °C

Lowest Temp (t₁)

Fill / coldest · °C

Pressures & Margin

Step 06 – 09 · Each pressure tagged gauge or absolute

06Operating (fill) Pressure

RPZ / make-up set point · kPa

07Relief Valve Set Point (P₂)

Maximum pressure · kPa

08Static Head Above Vessel

Water column to highest point · kPa

09Safety Margin

Spare acceptance capacity

Advanced — pre-charge, pipe expansion & atmospheric

Pre-charge Pressure

Pipe Expansion (−3αΔT)

Atmospheric Pressure

For gauge→absolute conversion · kPa

Awaiting Inputs

Enter system parameters and press Size Vessel to calculate the required expansion vessel volume and recommended standard size.

Sizing complete. Print or save as PDF — the layout reformats automatically for A4.

Notes. For internal use only — not for circulation. Valid for clean fresh water 1–99°C in HVAC systems. Pressures use gauge by default (atmospheric excluded); the tool converts to absolute for the acceptance term per ASHRAE. Pre-charge should equal the minimum (fill) pressure at the vessel. If static head exceeds 400 kPa, confirm the vessel pressure rating with the manufacturer. Glycol expansion is approximate — verify against the fluid supplier’s density data. Final selection is subject to engineering check and manufacturer confirmation.

TP Expansion Vessel Calculator V2 · ASHRAE Handbook (HVAC Systems & Equipment) method · © True Partners Consulting Engineers · Created by A. Karajibani

Sealed System Expansion VesselSizing & Selection

Sealed System Expansion Vessel
Sizing & Selection