Inlet Nozzles: Number, Position and Flow Direction
The inlet nozzles distribute the treated water throughout the pool – and thus determine whether the circulation actually reaches everywhere. Number, mounting height and orientation are part of the hydraulic design, not just cosmetics.
Why Inlet Nozzles Determine Water Quality
The inlet nozzles – also called return or inflow nozzles – carry the water, which has been cleaned in the filter circuit, disinfected and (depending on the system) heated, back into the pool. They determine whether this treated flow reaches the entire body of pool water or only part of it.
A circulation rate that is sufficient on paper is of little use if the water is practically standing still in certain areas. Suspended matter collects there, disinfection works less effectively, and preferred zones for algae and biofilm develop. The number, mounting height and orientation of the nozzles are therefore not a minor detail but rank equally with the pump and filter as part of the hydraulic design.
Determining the Right Number of Inlet Nozzles
The relevant sizing figure is not the pool volume alone but the circulation flow rate delivered by the pump and filter. Each nozzle can cleanly deliver a flow rate of roughly 4 to 6 m³/h without the jet becoming too hard or producing disturbing noise. This guide figure gives the number of nozzles.
Rule of thumb: divide the circulation flow rate by around 5 m³/h and round up. Several nozzles each with a lower throughput distribute the water more evenly than a few with high throughput – especially in long or angular pools.
| Pool volume | Circulation flow rate (guide value) | Recommended number of nozzles |
|---|---|---|
| up to 20 m³ | approx. 6–8 m³/h | 1–2 nozzles |
| 20–40 m³ | approx. 8–12 m³/h | 2 nozzles |
| 40–60 m³ | approx. 12–16 m³/h | 2–3 nozzles |
| 60–80 m³ | approx. 16–20 m³/h | 3–4 nozzles |
The values are guide figures for private pools. Public pools are subject to their own sets of regulations with considerably stricter requirements; there, a professional engineering design of the inflow is required.
Mounting Height and Orientation of the Nozzles
Wall inlet nozzles are usually set roughly 20 to 40 cm below the water level. If they sit too high, they draw in air when the water is choppy and the jet loses its effect; if they sit too low, the surface stays still and the skimmer works less effectively.
Ball nozzles with an adjustable insert have proven their worth: they allow the jet direction to be fine-tuned by hand after filling. A slight downward tilt also sets the deeper water layers in motion, while part of the flow pushes the surface towards the skimmer.
For a ring flow, the nozzles are aimed not head-on at the centre of the pool but tangentially along the wall. This creates a circulating movement that carries the water right into the corners instead of merely damming it up against the opposite wall.
Recognising and Avoiding Dead Zones
Dead zones are areas where the water is barely moved. Typical candidates are pool corners, steps and benches, the area behind a built-in ladder and – with only one nozzle – the corner furthest from the inlet.
- distribute several nozzles across the wall instead of a single central nozzle
- direct at least one flow specifically towards the critical corners
- route the ring flow so that it passes by steps and recesses
Whether the design works out can easily be checked after commissioning: a few light suspended particles or some leaves on the surface show where the water travels and where it comes to rest.
Flow Direction by Pool Shape
How to arrange the nozzles sensibly depends heavily on the pool shape and the position of the skimmer. The following overview shows proven basic patterns.
| Pool shape | Nozzle arrangement | Flow pattern |
|---|---|---|
| Rectangle, skimmer on the short side | Nozzles on the opposite short side | Longitudinal flow towards the skimmer |
| Rectangle, skimmer on the long side | Nozzles on the opposite long wall, slightly angled | Ring flow along the walls |
| Round pool | 1–2 nozzles tangential to the wall | Circulating ring flow |
| L-shape or kidney shape | At least one nozzle per leg, aimed into the extension | Avoids a dead zone in the side arm |
If a counter-current unit or main drain is planned, they influence the flow pattern additionally; such fittings should be planned in from the outset.
Interaction with the Skimmer and Pipework
The skimmer and inlet nozzles form a pair: the skimmer draws water off the surface, and the nozzles have to guide the surface towards it. The nozzles are therefore arranged as far as possible opposite or laterally offset from the skimmer, so that the ring flow reliably drives leaves and grease to the skimmer opening. If the nozzle and skimmer sit directly next to each other and flow in the same direction, a hydraulic short circuit occurs – the fresh water is immediately drawn off again.
On the pipework side, the return line in the private sector usually runs in d50 (DN40); with several nozzles, the water is distributed from a main line – often d63 (DN50) from the filter, then reduced – to the individual runs. A ball valve on each run makes it possible to balance the flow between the nozzles if one zone is noticeably less strongly supplied.
Safety and electrical matters such as the equipotential bonding of metallic built-in parts belong in the hands of a qualified electrical contractor. For public pools, the inflow is part of a design to standards that should be handled by a professional planner.
Bill of materials
Example – please verify with a specialist. Parts and quantities depend on the installation; sizes shown are examples.
| Component | Size | Art. No. | KLN No. | Qty |
|---|---|---|---|---|
| Inlet nozzle / wall return fitting | – | – | – | An adjustable ball nozzle allows fine adjustment of the jet direction after filling |
| Skimmer | – | – | – | Its position determines the alignment of the nozzles; arrange opposite or laterally offset |
FAQ
How many inlet nozzles does my pool need?
As a guide value, roughly one nozzle per 4–6 m³/h of circulation flow rate. A 40 m³ pool with around 10 m³/h thus usually ends up with two nozzles.
How far below the water level should the nozzles sit?
Around 20 to 40 cm below the surface is usual. This keeps the surface moving without the nozzle drawing in air when the water is choppy.
Should the nozzles point towards the skimmer or away from it?
They should guide the surface flow towards the skimmer. So arrange them opposite or laterally offset and aim them tangentially to the wall.
Why does dirt settle in a corner even though the pump is running?
There is a dead zone there. An additional nozzle, or one aimed differently so that it flows into the corner, usually fixes this.
Can I change the jet direction later?
Yes, with adjustable ball nozzles – the insert can be readjusted by hand after filling.
This guide provides general technical orientation and does not replace professional planning. Safety-, electrical- and permit-relevant work must be carried out by qualified specialists.
