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Calculating the Peak Flow Rate Duty

To calculate the likely peak demand in a system, use the table below, which shows the actual flow requirements for each appliance, and the likely simultaneous demand in low usage applications, normal domestic situations and higher usage commercial systems.


Low frequency usage Care homes for elderly persons, offices
Domestic frequency usage Individual private residences, infant schools
Commercial frequency usage Hotels, student accommodation, apartments

By multiplying the number of appliances by the flow figure in the relevant column, a suggested design flow rate can be established. It is important to note that there are instances where a different column must be used for a particular appliance. A sports club, for example, may need all of the showers running at once, so the figure would be the actual flow requirement multipled by the number of showers installed.

Qty Appliance Actual Flow Requirement (l/s) Low Frequency Usage (l/s) Domestic Frequency Usage (l/s) Commercial Frequency Usage (l/s) Peak Flow Rate Design Duty
  Basin (H&C) 0.15 0.005 0.008 0.017  
  Sink (H&C) 0.20 0.010 0.020 0.040  
  Bath (H&C) 0.30 0.020 0.030 0.070  
  WC 0.1 0.005 0.010 0.020  
  Shower (std) 0.15 0.010 0.020 0.030  
  Shower (high flow) 0.50 0.040 0.065 0.030  
  Urinal 0.01 0.003 0.003 0.005  
  Bidet 0.08 0.002 0.003 0.004  
  Cleaners Sink (H&C) 0.30 0.003 0.005 0.006  
  Domestic Washing Machine 0.20 0.007 0.007 0.010  
  Commercial Washing Machine 0.30 0.020 0.030 0.060  
          Total (l/s)  

Important note: When calculating the pressure required, it is critical to allow for the static head and outlet pressure requirements in your calculations.

Once you have worked out the total peak flow rate design duty you can use this information to specify pumping products. If you need to specify a booster set you can use our helpful four step guide - click here.

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