Foul Pumping & Receiving-Chamber Calculator
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Foul Pumping & Receiving-Chamber Calculator
Size the emergency storage for a foul pumping station and check pump duty and start frequency. Built on UK Building Regulations (Approved Document H1, para 2.39 — 24-hour storage) with pump/sump cycling to BS EN 12056-4.
24-hour emergency storage
Approved Document H1 (2.39): the effluent receiving chamber should hold 24-hour inflow to cover a loss of service. Domestic inflow is taken as 150 litres per head per day; other buildings use their calculated daily water demand.
Pump duty & start frequency
Check the pump can clear the peak inflow and that the active (working) volume keeps motor starts within limits. Good-practice sizing to BS EN 12056-4 — in addition to the 24-hour emergency storage.
Reference & rules
The storage basis and the key rules for foul pumping installations.
| Users | Daily inflow | Min. storage |
|---|
Storage (2.39). Size the receiving chamber for 24-hour inflow to cover a service failure. Domestic = 150 L/head/day; other buildings = calculated daily water demand; pro-rata where only part of the flow is pumped.
When to pump (2.36). A pumping installation is needed where gravity drainage is impracticable, or to protect against flooding from surcharge in a downstream sewer.
Equipment (2.37–2.38). Packaged pumping units should conform to BS EN 12050; installations inside buildings are designed to BS EN 12056-4, and outside buildings to BS EN 752-6. Provide duty/standby pumps and a high-level alarm for resilience.
Pump cycling. The pump duty must exceed the peak inflow. Active volume between start/stop sets how often the motor starts: max starts/hour = 900 × Qp ÷ Va (Qp in l/s, Va in litres), worst case at inflow = half the pump rate.
This foul pump sizing calculator sizes the emergency storage for a foul pumping station and checks the pump duty and start frequency. It follows Approved Document H1 (paragraph 2.39, 24-hour storage) with pump and sump cycling to BS EN 12056-4. For the underlying guidance, see Approved Document H.
24-hour emergency storage
Approved Document H requires the receiving chamber to hold 24 hours of inflow, so a pump or power failure does not cause a backup into the building. Domestic inflow is taken as 150 litres per head per day; other buildings use their calculated daily demand. Enter the building type and population, or the daily demand, and the calculator returns the minimum 24-hour storage volume.
Pump duty and start frequency
A pump that is too large for the sump starts and stops too often and wears out; one too small struggles to clear the inflow. The calculator checks the pump duty against the sump volume and reports the start frequency, so you can choose a pump and sump that cycle within the manufacturer's limits.
Part-pumped systems
Where only part of the flow is pumped — a basement, say, with the rest draining by gravity — the storage is taken pro-rata to the pumped proportion. The calculator handles this so you do not over-size the chamber.
Further reading: foul, surface and combined sewers explained · drainage information needed for planning permission · Approved Document H.
Frequently asked questions
Either interpolate from the number of dwellings (Approved Document H Table 5) or sum the discharge units of the appliances (BS EN 12056-2). The calculator does both.
Match the pump duty to the sump volume. The calculator reports the start frequency so you can keep it within the pump's rated starts per hour.
That is the standard domestic figure in Approved Document H. Non-domestic buildings use their own calculated water demand instead.
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