Skimmer or Overflow Channel – Which System for Whom?
The choice between a skimmer and an overflow channel is made early in the planning stage and determines the construction effort, water quality and follow-up costs over the entire service life. This article compares both systems objectively – with an honest breakdown of the extra and follow-up costs.
How Both Systems Work
With the skimmer system, the water level sits about 10 to 15 cm below the pool edge. Skimmers set into the pool wall draw off the near-surface water through a hinged flap (weir) and feed it to the filter system. An integrated collection basket retains coarse debris. As a rough planning figure, one skimmer per around 25 m² of water surface is often assumed; the connection is usually made with OD d50 (DN40). On the suction side, the system has a simple design, is cost-effective and remains easy to manage even when retrofitted.
With the overflow channel, the pool is filled to the brim: the water flows over the surrounding pool edge into a channel and from there into a balance tank. A distinction is made between the deck-level design, in which the water level finishes flush with the surrounding paving, and the raised channel, in which the edge protrudes slightly. Here the water is fed in mostly through floor inlet nozzles, so that fresh water is displaced from the bottom upwards. The channel pipework is generously dimensioned, often OD d63 (DN50) or larger.
Surface Cleaning Compared
Surface cleaning is the key technical difference. The skimmer draws off the water at isolated points in a few places. This creates a directed flow, and on the leeward or opposite side, dead zones can form in which pollen, leaves, sunscreen and greasy films collect. The effect is also heavily wind-dependent – if the wind drives the dirt away from the skimmer, the cleaning performance drops.
The overflow channel draws off the surface all around and evenly. Exactly where most of the dirt collects – in the topmost layer of water – it is removed across the whole area. The result is a very even flow through the pool without pronounced dead zones and, as a rule, a visibly cleaner water surface. For heavily used or prestige pools, this is the decisive advantage.
- Skimmer: localized extraction, directed flow, wind-dependent, possible dead zones.
- Overflow channel: all-around extraction, even flow, very good surface cleaning.
Balance Tank and Water Level Control
The inherent need for a balance tank (surge tank) is the core issue with the overflow system. Because the pool stands filled to the brim, there is no buffer for water displacement in the pool itself: when bathers get in, the displaced volume flows over the channel into the tank; when they leave the pool, the tank feeds the missing water back in. The tank must therefore be able to hold at least the displacement of the maximum expected number of people plus the channel and pipework volume and a reserve. It takes up space in the plant room and is a component in its own right.
The water level control differs markedly as a result. With the overflow system, level sensors in the balance tank take over control: via a make-up water valve, they regulate the fresh water supply, protect the pump against dry running and report faults. This is convenient, but more technically demanding and comes with more sensor technology. With the skimmer pool, the water level only has to be kept within the catch range of the skimmer flap – this is achieved with a simple level controller with a float valve or by refilling manually. If the level drops too far, the skimmer draws air; if it is too high, it cleans the surface less effectively.
Extra and Follow-up Costs Honestly Considered
The overflow channel is noticeably more expensive to buy and to run – you should factor this in soberly before making a decision. On the construction cost side, there is the channel body, the cover grating, the balance tank, a larger circulation pump, considerably more pipework and the level control. On the follow-up cost side, it is above all the larger, constantly wetted water surface that has an effect: it evaporates more, which means more make-up water, more heating energy and more chemicals. On top of this come cleaning the tank and the greater susceptibility to faults caused by the additional technology.
| Criterion | Skimmer | Overflow channel |
|---|---|---|
| Construction costs | low | high (channel, grating, tank, control) |
| Pipework/pump | compact, smaller pump | more extensive, larger pump |
| Evaporation | lower | higher (brim-full, larger surface) |
| Water/heating/chemical demand | lower | higher |
| Technical complexity | low | high |
| Retrofittability | good | hardly, usually only new build |
The exact amounts depend on the pool size, region and design and should always be calculated on a project-specific basis. As an order of magnitude, however, the following reliably applies: an overflow pool costs a multiple of pure skimmer technology, both to build and in ongoing operation.
Maintenance Effort in Operation
The maintenance effort follows the complexity. With the skimmer, the routine is essentially limited to regularly emptying the collection basket, occasionally checking the skimmer flap and replacing wear parts. The effort is low and can also be managed well by owners who look after the pool themselves.
With the overflow channel, several additional points are added: the channel and cover grating have to be kept clean, the balance tank tends towards germ and algae growth under unfavourable conditions and therefore needs regular cleaning, and the level sensors have to be checked and calibrated from time to time. Every additional component is at the same time a potential source of faults. If you value low maintenance effort, you are better off with the skimmer system.
- Skimmer: empty the basket, check the flap, replace wear parts.
- Overflow channel: clean the channel and grating, service the tank, check and calibrate the sensors.
Which System Suits Whom?
The skimmer system is the standard for most private pools. It is inexpensive, technically simple, easy to retrofit and completely sufficient for small to medium-sized pools. If you plan on a budget, build the pool yourself or aim for low operating and maintenance effort, you are making the right choice with it.
The overflow channel plays to its strengths with prestige, large or heavily used pools where the highest water quality, a calm, brim-full look or an infinity edge is desired. However, it requires sufficient space for the balance tank, an appropriate construction budget and the willingness to bear the higher follow-up costs permanently. Somewhat simpler in terms of shell construction is the raised channel: it is likewise a fully-fledged overflow system with all-around extraction, a balance tank and floor inflow, and achieves the same even surface cleaning. The lower effort relates above all to the paving and shell construction – a deck-level, precisely levelled paving is not needed – but not to the balance tank or pump; the follow-up costs are therefore at a similar level to the deck-level design. Because an overflow channel can hardly be retrofitted in practice, the choice of system should be agreed with the specialist company as early as the planning phase.
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 |
|---|---|---|---|---|
| Balance tank (surge water tank) | – | – | – | Only for the overflow system; size the volume for bather displacement, channel and pipework volume plus a reserve. |
| Overflow channel with cover grating | – | – | – | Running around the pool edge; level-deck or raised design. |
| Level control with make-up valve | – | – | – | Level probes and automatic fresh-water make-up; for a skimmer a simple level controller is sufficient. |
| Skimmer | – | – | – | Wall built-in part with flap and collection basket; the standard solution for private pools. |
FAQ
Is an overflow channel more hygienic than a skimmer?
On balance, yes, because it draws off the surface all around and evenly and avoids dead zones. With properly designed skimmer technology, however, the water quality in a private pool is likewise perfectly fine.
Can I install an overflow channel retrospectively?
As a rule, not economically. A brim-full water level, an all-around channel and a balance tank intervene deeply in the pool construction and can usually only be implemented with a new build. The skimmer, by contrast, is easy to retrofit.
How many skimmers does my pool need?
As a rough planning figure, one skimmer per around 25 m² of water surface is often assumed. The exact number depends on the pool shape, circulation capacity and wind direction and should be designed on a project-specific basis.
Does an overflow channel consume more water and energy?
Yes. The brim-full, constantly wetted and usually larger surface evaporates more, which means more make-up water, heating energy and chemicals. This is a significant part of the follow-up costs.
Does a skimmer pool also need a balance tank?
No. Because the water level is below the pool edge, the pool itself buffers the water displacement of the bathers. A separate balance tank is only needed with the overflow system.
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.
