Choosing the right size Wates Pressure Vessel for your hot water system is essential for achieving stable water pressure, managing thermal expansion, and ensuring long-term reliability. An undersized vessel can lead to excessive pump cycling and system strain, while an oversized one may cost more than necessary and take up valuable space.
This step-by-step guide will help you select the correct vessel size for your hot water application.

Step 1: Determine Your System’s Maximum and Minimum Operating Pressure
Start by identifying:

• Maximum system pressure (often the setting of the pressure relief valve)
• Minimum system pressure (the cut-in point for the pump)

These values are crucial for calculating the pressure range your vessel will operate within. For most hot water systems, typical ranges are 2–6 bar, but always confirm your specific system requirements.

Step 2: Identify the System Volume
Calculate the total water volume in your hot water system, including:

• Water heater or boiler capacity
• Pipework water volume
• Any storage tanks connected

Knowing the system volume ensures the vessel can handle thermal expansion without pressure spikes.

Step 3: Factor in Thermal Expansion
Hot water expands when heated. The amount of expansion depends on:

• Initial cold water temperature (e.g., 15°C)
• Maximum hot water temperature (e.g., 70°C)

Use the thermal expansion coefficient (around 2–4% of system volume for domestic hot water) to estimate how much space is needed to absorb this expansion.

Step 4: Select the Appropriate Vessel Type
Wates offers vertical and horizontal hot water pressure vessels in various sizes. Choose based on:

• Installation space availability
• Connection type and location
• Ease of maintenance access

Step 5: Use the Manufacturer’s Sizing Chart
Wates provides sizing charts and technical data to help match your calculated requirements with the correct vessel model. These charts factor in:

• Pre-charge pressure
• Maximum allowable working pressure
• Temperature rating

Always round up to the next available size to ensure safe operation.

Step 6: Set the Correct Pre-Charge Pressure
Once installed, adjust the vessel’s pre-charge pressure (with the system off and drained) to match the pump cut-in pressure, minus about 0.2–0.3 bar. This ensures optimal performance and maximum energy efficiency.

Step 7: Plan for Future Expansion
If your hot water demand is likely to increase (e.g., adding more bathrooms, hotel rooms, or industrial processes), choose a slightly larger capacity vessel to accommodate future needs without replacement.
Correctly sizing a Wates Pressure Vessel for hot water applications ensures consistent pressure, reduces energy consumption, and protects your system from damage. By following these steps — and consulting Wates’ technical data — you can make a smart, long-term investment in hot water system performance. For more info contact Wates UAE or call us at +971 4 2522966.