Another first from Dutypoint
ScubaTank® is now the UK’s first
EPD-Certified Booster Set
Continue to Dutypoint
How to size a cold-water break tank
The importance of BS EN 806-2 when calculating the size of a cold water break tank
BS EN 806-2 provides requirements and recommendations for installations inside buildings which come into contact with drinking water. This specification provides technical requirements to ensure that:
- Appropriate pressures and flow rates are achieved
- Water quality at the tap is not contaminated or affected by the local environment
- The system from mains connection to tap avoids waste and leakage
- The system is efficient, convenient, safe, reliable and has a reasonable working life
Please note that some of the guidance in this article is based on BS EN 806 Part 2. Any further recommendations are for guidance only and should always be checked by a qualified mechanical, public health or building services engineer, as the requirements of different projects can vary greatly. For example, if you require information about one piece tanks, see the BS 7491-3: 1992 or for sectional tanks, see the BS 7491-3: 1994 specifications.
Sizing a cold water break tank
When sizing a cold water break tank, there are 2 different considerations you need to take, the recommended storage for the building type and the expected peak flow rate.
1. Building type and use
The table shows the recommended minimum storage levels for each type of premises. The likely peak occupancy of the building should be considered when making this calculation. When sizing for a domestic building, a standard property should be sized as a hostel; storage of 90 litres per person is sufficient for most installations. High-end properties may require additional storage.
Table 1: BS EN806-2 Table 6, used for buildings with a specific usage
2. Timed storage
Secondly, the expected peak flow rate of the premises should be considered. The peak flow is calculated when sizing the booster set. In determining the peak flow rate, we must consider how much water storage must be provided to facilitate this flow rate. Dutypoint recommends that a minimum of 15 minutes storage, according to the peak flow rate of the booster set, should be provided in a booster set break tank within a commercial installation. For example, a booster set with a peak design flow rate of 1.1 litres/second or 66 litres/minute requires a break tank with a capacity of at least 990 litres.
Dutypoint recommends that a minimum of 15 minutes storage, according to the peak flow rate of the booster set, should be provided in a cold-water break tank.
Other factors to consider
Other factors such as the tank inlet flow rate and the usage patterns of the building should be taken into account; buildings with a poor rate of mains water supply will require greater storage. The siting of the break tank will also influence this. A tank on the ground floor of a building will fill at a higher rate than a tank on an upper floor or in the roof space. Siting a tank in the roof space of a building is likely to necessitate a larger storage volume, however a cold water storage tank should not be oversized as this could result in the stagnation of the stored water.
Flow rates for filling cold water storage tanks can vary depending on the amount of storage provided, the pressure available from the source or main and whether the supply is constant - where other information is unavailable, a maximum of four hours filling time may be assumed.
The following graph shows the minimum storage required for a range of booster set peak flow rates:
Graph 1 demonstrates the expected booster set flow rate in relation to 15 minutes of different litre storage
If you require more information about sizing a cold water break tank, get in touch with our team by calling us on
