An outdoor hot tub turns a terrace into a relaxation space for a fraction of the price of a built-in model. But you still need to choose the right structure and anticipate running costs, which is the item most buyers discover too late. Here are the criteria that genuinely matter.
Inflatable or semi-rigid: the real difference
An inflatable hot tub relies on a laminated PVC wall held by air pressure. Light, it stores in a cupboard out of season and can be moved by two people. In return the seating is soft, the wall deforms when you lean on it, and thermal insulation remains limited.
A semi-rigid hot tub keeps the easy installation of an inflatable but adds a supporting structure, often a shell or rigid panels. Seating is markedly more comfortable, it holds up better over time, and insulation is superior, which translates directly into heating savings.
If the hot tub stays in the same place all season, semi-rigid is the better choice. Inflatable retains the advantage for genuinely occasional use or frequent storage.
- Inflatable: light, storable, soft seating, limited insulation
- Semi-rigid: more comfortable, better insulated, more durable
- Fixed seasonal use: favour semi-rigid
Seating capacity, not to be overestimated
Stated capacities correspond to maximum occupancy, shoulder to shoulder. In practice, a hot tub advertised for six comfortably seats four adults who want to stretch their legs.
Think in terms of real use rather than theoretical peak. A six-seat model suits a family of four with occasional guests perfectly. Oversizing costs twice: at purchase, then every month heating a needlessly large volume of water.
Check the external diameter too, not just the number of seats: you need at least sixty centimetres of clearance all round to get in, get out and reach the equipment housing.
Consumption, the real cost of a hot tub
The main item is not filling but holding temperature. An outdoor hot tub loses heat continuously, and all the faster the greater the gap with ambient temperature.
Three levers make most of the difference. The insulating cover first: used systematically as soon as you get out, it sharply reduces losses, since most of the heat escapes through the surface. Then the insulating ground mat, which breaks the thermal bridge with the slab or decking. And finally the location, sheltered from the prevailing wind.
Holding a constant temperature generally costs less than letting it cool and bringing it all back up, since reheating is very demanding. With regular use, keep the hot tub warm rather than switching it off between sessions.
- Insulating cover closed as soon as you get out
- Insulating ground mat under the structure
- Location sheltered from the wind
- Temperature held rather than hot-cold cycles
Heating: power and time to temperature
Bringing an outdoor hot tub up to temperature is counted in hours, not minutes. Depending on the power of the unit, the volume and the temperature of the filling water, a first heat-up often takes a full day.
One technical point often goes unnoticed: on many models the heater and the air jets do not run at the same time, or activating the jets causes the temperature to drop. Plan to heat in advance rather than during use.
Finally, check the maximum attainable temperature, generally 40 °C, and whether programmable control is available so you can have the bath ready for a given time.
Air jets, water jets: what changes
Most inflatable and semi-rigid hot tubs work with air jets, or bubbles, generated by a blower. The result is an enveloping, diffuse effervescence, very pleasant for relaxation but without any localised massage effect.
Water jets, or hydrojets, propel pressurised water and target specific areas such as the back or the neck. They are reserved for more elaborate and more expensive models.
For family use oriented towards relaxation, a large number of air jets distributed around the whole perimeter is thoroughly satisfying. Only look for hydrojets if you want a genuine therapeutic massage effect.
Installation: base, power supply, clearance
The most underestimated point is loaded weight. Once filled and occupied, a six-seat hot tub can exceed a tonne and a half. A concrete slab, a tiled terrace on a slab, or a stabilised and perfectly level surface are essential. Timber decking on adjustable pedestals requires a load-bearing check.
The base must be level: even a slight slope distorts the structure and causes overflow on one side. No gravel or sharp stones beneath the ground mat.
On the electrical side, provide a dedicated socket protected by a 30 mA residual current device, with no extension lead or multi-way adaptor. If in any doubt about the outdoor installation, have it validated by an electrician: it is the one point where improvising is not an option.
- Perfectly level, load-bearing base, ideally a slab
- Loaded weight over a tonne for six seats
- Dedicated socket with 30 mA RCD, no extension lead
- Clearance of at least 60 cm all round
Day-to-day water care
Hot tub water is warm, agitated and heavily loaded relative to its volume: it degrades far faster than pool water. Bromine is generally preferred to chlorine, since it stays stable at high temperature and gives off less odour.
Check pH two to three times a week, aiming for 7.0 to 7.4 as with a pool. Rinse the filter cartridge every week and replace it regularly, since it works far harder than in a pool.
A quick shower before bathing considerably reduces the input of creams, cosmetics and residues, which are the main cause of foaming water and a clogged filter. Depending on how often you use it, allow a complete water change every four to eight weeks.
- Bromine rather than chlorine in warm water
- pH checked two to three times a week
- Cartridge rinsed every week
- Complete water change every 4 to 8 weeks
Using your hot tub out of season
An outdoor hot tub is very enjoyable in the shoulder seasons, when the temperature gap makes the bath all the more appealing. Consumption nonetheless climbs appreciably, and an insulating cover in good condition becomes essential.
In freezing conditions, vigilance is required: still water in the pipework of the equipment housing can freeze and damage the pump irreversibly. If you no longer use the hot tub in winter, complete draining and dry storage remains the safest course.
As with a tubular pool, dry the structure completely before folding and store it frost-free, away from rodents.
Frequently asked questions
What is the difference between an inflatable and a semi-rigid hot tub?
An inflatable hot tub is held by air pressure in a laminated PVC wall: it is light and storable, but its seating is soft and its insulation limited. A semi-rigid model adds a rigid supporting structure that markedly improves seating comfort, durability and thermal insulation, and therefore consumption. For an installation that stays in place all season, semi-rigid is the better choice.
How many people fit in a hot tub advertised for 6?
Stated capacities correspond to maximum occupancy shoulder to shoulder. A six-seat hot tub comfortably seats four adults wanting to stretch their legs. Size for real use: oversizing costs at purchase and then every month heating a needlessly large volume of water.
Does an outdoor hot tub use a lot of electricity?
The main item is holding temperature, not filling. Three levers sharply reduce the bill: using the insulating cover systematically as soon as you get out, laying an insulating ground mat under the structure, and siting the hot tub sheltered from the wind. With regular use, holding a constant temperature costs less than letting it cool and bringing it all back up.
What base do I need to install a hot tub?
A perfectly level, load-bearing surface, ideally a concrete slab or a tiled terrace on a slab. The loaded weight of a filled and occupied six-seat hot tub frequently exceeds a tonne and a half. Timber decking on adjustable pedestals needs a load-bearing check. Also provide a dedicated socket protected by a 30 mA RCD, with no extension lead.
Chlorine or bromine for a hot tub?
Bromine is generally preferred for a hot tub because it stays stable at high temperature and gives off less odour than chlorine, which breaks down quickly in warm water. Check pH two to three times a week aiming for 7.0 to 7.4, and rinse the cartridge weekly: it works much harder than in a pool.
How often should hot tub water be changed?
Allow a complete change every four to eight weeks depending on how often it is used and how many people bathe. Hot tub water is warm and heavily loaded relative to its volume, so it degrades far faster than pool water. A quick shower before each bath noticeably extends that interval.
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