Whether you still enjoy your swim spa after three years is not decided by the number of jets or the horsepower rating. It is decided by the principle used to create the current — jets, a propeller in a duct, or a paddle wheel. Each produces a stream of a different width, a different depth and a different “hardness”, and you will notice exactly that within your first ten minutes in the water.
This article compares all three technologies from the point of view of the swimmer, the price, the noise and the servicing. Choosing size, equipment and installation in general is covered in a separate article, How to choose a swim spa, and counter-current units for conventional pools in Swim jets and counter-current units for pools.
Why the type of current matters more than the number of jets
Marketing materials like to quote “4 swim jets” or a “5.5 HP pump”. Neither figure tells you what it will actually be like to swim in. A swimmer does not perceive individual jets — they perceive the volume of water flowing towards them each minute, and how that flow is arranged.
A more useful quantity is flow rate. Manufacturers state it in gallons per minute (GPM) or litres per minute. The differences between principles are an order of magnitude apart: jetted systems sit in the low thousands of litres per minute, propeller systems in the tens of thousands, and paddle wheels higher still. PDC Spas quote 690 GPM (roughly 2,600 l/min) for their jetted Summit range, while the propeller-driven TruSwim range is quoted at up to 5,000 GPM (about 18,900 l/min). SwimEx quote up to 25,000 GPM for their paddle wheel, roughly 94,600 l/min.
The second thing the jet count does not tell you is whether air is present. Jetted systems draw air in as standard — this makes the stream look powerful and gives it a hissing sound, but the bubbles reduce water density, worsen visibility and can make side breathing awkward. Propeller and paddle wheel systems work with clean water and no air.
Three swim spa current principles
1. Jetted current
The most widespread and the cheapest solution. One to three powerful pumps drive water through two to six large jets in the end wall. The jets are usually adjustable; on better models they tilt up and down and side to side, so you can “line up” the stream to match your swimming position.
The advantages are price, simplicity and service availability — the pump is a standard pool component and a replacement jet costs only a few tens of euros. The drawback is the character of the current: it is narrower, shallower and harder, concentrated into two or three “columns”. Turbulence and side eddies form behind the jet and push the swimmer towards the wall. Control is often stepped only (low/high), or via a variable-frequency drive on more expensive models.
Who it suits: the recreational swimmer who wants 15–20 minutes of movement rather than training, and anyone who will mainly use the current as a massage feature for the back and legs.
2. Propeller / propulsion current
A propeller sits in a duct in the swim spa’s equipment bay (one or two propellers side by side), drawing water from the rear and pushing it forward through a large opening or grille. The result is a wide, flat and smooth column of water with no entrained air — the swimmer “lies” in a laminar current instead of fighting it.
Control is usually continuous in small increments, and on some systems in speed units. Hydropool, for example, quote continuous adjustment of 0–11 km/h (roughly 0–3 m/s) and a flow rate of over 1,400 GPM for their V-Twin technology. Master Spas use the name Wave Propulsion for this category — a motor drives a propeller and no air is added to the water.
There are three drawbacks: price (the gap against a comparably sized jetted model commonly runs into tens of thousands of euros), a closed service ecosystem (the propeller, shaft and seals are proprietary parts from a specific manufacturer, not universal pool equipment) and the weight of the unit. Noise, on the other hand, is usually lower than with a jetted solution at comparable “resistance”.
3. Paddle wheel
The premium and least common category, found mainly in rehabilitation and sports pools (typically SwimEx). A large paddle wheel at the rear of the pool drives water forward again through ducts beneath the floor, creating a “wall of water” across the full width of the pool, up to 76 cm deep according to the manufacturer.
The practical consequence: the current is the same on the centre line and at the edge, it does not push the swimmer sideways, and it also works for walking in water, running on the spot, water aerobics or whole-body rehabilitation — which is why this type is used in clinics and sports centres. You pay the highest purchase price for it, and accept one compromise: the current cannot be aimed. Unlike jets and propellers, it simply flows across the whole width.
Comparison table: jets vs propeller vs paddle wheel
| Parameter | Jetted | Propulsion | Paddle wheel |
|---|---|---|---|
| Stream width | narrow, 2–3 columns | wide, continuous | full pool width |
| Stream depth | shallow, near the surface | medium to large | greatest (up to ~76 cm) |
| Air in the stream | yes (bubbles, hiss) | no | no |
| Character | turbulent, “hard” | smooth, laminar | smooth, river-like |
| Control | stepped to continuous | continuous, fine | continuous, fine |
| Aimability | yes (tilting jets) | partly | no |
| Typical flow rate | low thousands of l/min | tens of thousands of l/min | highest in the category |
| Purchase price | lowest | high | highest |
| Servicing | standard pool parts | proprietary, via the manufacturer | proprietary, specialist |
| Noise | higher (pumps + air) | lower | low, but a deeper tone |
Which parameters can genuinely be compared
Do not compare horsepower or jet counts. Ask about four things that make physical sense:
- Flow rate (l/min or GPM) — the only figure that directly describes how much water is flowing towards you. It must be quoted for the whole system, not for a single jet.
- Stream width and depth — ideally in centimetres. A wide stream forgives an imprecise position; a narrow one forces you to swim exactly on the centre line.
- Range and fineness of control — how many steps, or continuous? The difference between “level 3 is too little, level 4 and I cannot keep up” and fine continuous adjustment is decisive for long-term use.
- Speed in m/s or pace per 100 m — take care, this is where most of the marketing lives.
On that last point: the speed of the current is not the same as your swimming speed. Water slows down near the walls and the floor, part of the energy dissipates into eddies, and a value measured 30 cm from the outlet will differ from the value two metres away, where the swimmer actually lies. If a manufacturer quotes “up to 3 m/s”, ask where and how it was measured. Without a methodology, the figure cannot be compared.
Which current you need for your level
A rough conversion: a pace of 3:00 min/100 m corresponds to a speed of about 0.55 m/s, 2:00 min/100 m to roughly 0.85 m/s and 1:25 min/100 m to approximately 1.2 m/s. A recreational swimmer therefore needs considerably less than a salesperson usually offers.
| Swimmer level | Real requirement | Recommended type | What to watch out for |
|---|---|---|---|
| Recreational (2–3× a week, 15–20 min) | slow to medium current, comfort | jetted | tilting jets, at least 3 power levels |
| Fitness (longer continuous swims, technique) | steady current with no bubbles, fine control | propulsion, exceptionally a top-end jetted system | stream width, so it does not push you towards the wall |
| Training (triathlon, open-water swimming) | high speed, repeatable intervals | propulsion or paddle wheel | measurable settings, longer shell (min. 5 m) |
| Rehabilitation, water walking, older users | wide current across the full width, low speeds | paddle wheel | easy entry, handrails, water temperature |
Accessories that decide how usable it is
Even the best current does not work without the small details that often never make it onto the price list:
- Swim tether — an elastic cord around your waist keeps you on the centre line. Practically essential with jetted systems, optional with wide currents. More detail in the article Swim spa as home fitness.
- A guide line or mirror on the floor — without a reference point a swimmer naturally drifts. A mirror also lets you check your stroke technique.
- Pace meter and timer — better control units let you set an interval (e.g. 4 × 4 minutes with a rest) and the system changes the speed by itself.
- Anchor points for resistance bands and a rowing kit — the current runs while you train your upper body against resistance.
Power consumption and noise of the current system
The current system is by far the most powerful appliance in a swim spa — motors commonly sit in the low single-digit kilowatts. The key point, though, is that it runs for short periods. Half an hour of swimming a day adds a few kWh, which is a smaller item than year-round water heating and temperature maintenance. A complete cost breakdown is in the article Swim spa running costs.
Two rules apply to noise. A jetted system makes a higher, hissing sound (air in the stream) and is audible outside the shell too — with terraced housing, sort this out in advance. Propulsion and paddle wheel systems are quieter, but have a deeper tone that travels more readily through the structure into floors and walls. In both cases resilient mounting and a heavy substrate help; the principles are the same as for other equipment, see Noise from pool equipment.
Servicing and service life of each type
A jetted system ages like any other pool equipment: the pump’s mechanical seal, bearings, worn jets. Parts are available and a general pool service engineer can handle the repair. That is the main, frequently underrated argument for this category.
A propulsion system has fewer moving parts, but the ones it has are specific: the shaft seal, the propeller mounting, control electronics with a variable-frequency drive. A repair means waiting for an original part and usually requires a brand service technician. Before buying, therefore, find out who services this model in your country and how available the parts are — with imported equipment that has no local representation, this tends to be the weak point.
The paddle wheel is the most robust in construction and turns at low revolutions, so it suffers the least mechanically. At the same time it is the least common, so the service network is the thinnest and any intervention the most expensive.
How to test a current system before you buy it
No catalogue or video replaces a wet test — swimming in the dealer’s test room. Bring your own swimsuit and goggles and do three things:
- Swim continuously for at least 8–10 minutes, not two. Fatigue changes your body position and the weaknesses of the current only show up afterwards.
- Try both the lowest and the highest setting and note whether there is a setting between them that genuinely suits you.
- Try breathing on both sides. This is exactly where a bubbly current shows itself — if you inhale water in the turbulence, no amount of power makes up for it.
The wet test procedure and other points worth checking with a dealer are covered in How to choose a swim spa. If you are still weighing up whether to go for a swim spa at all or rather a conventional pool, the comparison Swim spa vs pool will help.
Frequently asked questions
Is a jetted current enough for real swimming?
For swimming, yes; for training swims with technique work, probably not. A narrow, turbulent current forces you to correct your position constantly, so holding your stroke and side breathing is harder. For 15–20 minutes of movement a few times a week, though, a jetted solution is normally sufficient and it is the cheapest route to your own swim spa.
How many jets should a good current system have?
The number of jets tells you nothing in itself. Four jets fed by one weak pump give a weaker current than two jets with two strong ones. Ask about the total system flow rate in litres per minute and whether the jets tilt.
Can a swim spa current system be upgraded to a stronger one later?
With jetted systems it is sometimes possible to add a more powerful pump, but the pipework and manifolds in the shell set the limit — beyond a certain point only consumption and noise increase, not the pull of the current. Propulsion and paddle wheel systems are a structural part of the shell and cannot be swapped afterwards. The type of current is therefore a decision made once, for the whole service life.
Is a propulsion current really quieter?
Generally yes, at comparable water resistance, because it draws in no air and does not have to force water through narrow jets. It does produce a deeper tone, though, which travels more easily through the structure into the building’s floors and walls. Subjectively it is almost always quieter; the measured value in decibels may not be all that much lower.
How do I spot a marketing-inflated current speed figure?
By the missing methodology. A credible figure includes the measurement location (distance from the outlet, depth) and a range, not just a single maximum. If a manufacturer quotes only “up to X m/s” with no further context, treat it as an advertising number and rely on a wet test.
In conclusion
Put simply: you buy a jetted current for the price and service availability, a propulsion one for the quality of the current, and a paddle wheel for the width and rehabilitation use. The mistake easiest to avoid is buying power you will never use — or, conversely, saving money on the principle and finding a year later that you cannot really swim in it.
If you would like to browse the range of swim spas and hot tubs including data sheets and current system parameters, start in the hot tubs and swim spas category. And before you decide, go through the general buying guide as well — the size of the shell and the installation method affect the result just as strongly as the type of current itself.
