Direct answer
A garden sauna heats air — dry heat, or a brief burst of steam if you add water to the stones. A hot tub heats a body of water you sit in. That is the split. One is usually a quieter, more intense heat you switch on for a session. The other is a social soak that typically holds temperature all day.
There is no health winner on this page. Heat in air and heat in water have different research lines. Neither replaces a walk, a night’s sleep, or the care your GP already named. People with heart disease, blood-pressure problems, or who are pregnant should get individual advice before either. NHS-style wording still reproduced on GP sites: consider avoiding sauna and jacuzzi, especially in the first 12 weeks of pregnancy. Alcohol does not belong in either.
Planning is not “generally fine.” An outdoor sauna on an English house may fall under Class E permitted development if the building, the plot and the siting all fit. Sometimes it needs a planning application. Sometimes those rights have already been taken away. That conversation lives on planning permission for an outdoor sauna. It is not legal advice.
If you are shopping the water side, the due-diligence page is the spa pool buying guide. Comfort in warm water is not a treatment.
Key facts
- Heat medium: sauna = hot air (optional löyly); hot tub = warm-water immersion. Different jobs. Not the same session.
- Social vs quiet: a hot tub is easier conversation. A sauna can be social, but the heat often makes it quieter.
- Upkeep: a hot tub is water chemistry — pH, sanitiser, filters, water changes. A sauna is timber. No spa-pool chemistry.
- Energy pattern: a sauna is usually heat-on-demand. A hot tub often holds water temperature 24/7. That is a pattern, not a pounds-per-year figure. Running-cost method, if it ever exists, belongs on how much an outdoor sauna costs.
- Electrics: both may need a dedicated circuit. Garden work in a dwelling in England sits under Approved Document P. A competent person designs, installs, inspects, tests and certifies. See what electrical supply an outdoor sauna needs.
- Planning: Class E sometimes, on an English house, if every limit is met. Not PD-by-default. Not “most standard installations.” Ask the local planning authority.
- Health: no winner. Heat is a load in both cases. Pregnancy, heart, blood pressure: GP first. This page is not medical advice.
At a glance
| Outdoor sauna | Hot tub / spa pool | |
|---|---|---|
| Heat medium | Hot air; optional water on stones | Warm water you sit in |
| How it feels | Quiet, intense heat; you sweat | Buoyancy; easier to talk |
| Typical use | Heat when you want a session | Often left holding temperature |
| Upkeep | Timber cleaning; no water chemistry | pH, sanitiser, filters, water changes |
| Running cost on this page | No invented kWh or £/year | No invented kWh or £/year |
| Electrics | Dedicated circuit; Doc P in England | Dedicated circuit; Doc P in England |
| Planning (England house) | Class E sometimes; not PD-by-default | Site-specific; ask the LPA |
| Health claim | None. No winner. | None. No winner. |
Heat medium: air or water
The primary difference is the medium.
A traditional outdoor sauna is a hot room. The heater warms the air and the timber. If the heater manual permits it, a ladle of water on the stones gives a short burst of humidity — löyly. You sit. You sweat. You leave. The heat is around you, not a bath you are in.
A hot tub is warm-water immersion. You sit in the water. Buoyancy takes some load off the joints while you are in it. Hydrostatic pressure is a real physical fact of sitting in water. It is not a treatment, and it is not a reason to call a domestic spa “hydrotherapy” unless an evidence and regulatory basis actually supports that word. The spa pool buying guide is where we refuse that slide.
Both can feel wonderful after a long day. Feeling wonderful is not a clinical outcome. We will not pick a winner by citing a heart-failure sauna paper, and we will not pick one by implying that buoyancy is medicine.
Social versus quiet
Hot tubs are easier conversation. Several people can sit in warm water and talk without the heat closing the room down. That is why they get used as a social garden seat.
Saunas can be social too — a family, a couple, friends who already like heat. The intense air temperature often makes the room quieter. People sit. They do not hold forth. If what you want is a party in the garden, a sauna is usually the wrong picture. If what you want is a still half-hour, a hot tub can feel like too much chatter.
Neither is a personality test we will sell you. It is how the two rooms actually behave.
Water chemistry versus timber
A hot tub is a small body of water you share. It needs regular chemistry: pH, sanitiser, filter cleaning, and periodic water changes. BISHTA publishes consumer factsheets on hot-tub and spa ownership. PWTAG publishes pool-water standards. HSE’s HSG282 is aimed at commercial operators and business-use domestic-type spas — do not copy its frequencies into a private-home routine as if they were the manufacturer’s instructions. Follow the model’s water-care documents.
That work does not stop because the water “looks clean.” It is an ongoing job. If you do not want that job, do not buy a hot tub as a low-maintenance ornament.
A sauna has no spa-pool chemistry. The interior timber needs occasional cleaning and the care the manufacturer named. That is a different kind of attention, not “no maintenance.” It is simply not water testing.
Two upkeep regimes. Pick the one you will actually do.
Heat-on-demand versus 24/7 hold
A sauna is usually heated when you want a session. You switch the heater on, wait until the room is in the range the manuals allow, sit, switch it off. Between sessions the room is a garden building, not a tank of warm water.
A hot tub typically holds water temperature so it is ready. That hold is continuous energy input, on top of filtration cycles. Insulation and a decent cover matter. They do not become a pounds-per-year promise without a measured method.
How much either costs to run depends on the exact model, insulation, how you use it, the weather, and your tariff. Wellness One does not publish a kWh or £/year figure on this page, because we do not have a measured method tied to a named tariff for a named sauna-versus-hot-tub pair.
The honest pattern is still useful: heat-on-demand versus 24/7 hold. Compare specific models, their insulation, and your intended use. For the sauna side of a quotation, see outdoor sauna cost in the UK.
Electrics: Dedicated circuit, Document P
Both products may need a dedicated electrical circuit. A household 13-amp kettle socket is the wrong starting point for an outdoor sauna heater, and it is often the wrong starting point for a hot tub too. The number that matters is the one in the signed equipment schedule and UK manual, applied to your property by a competent person.
Electrical work in a dwelling in England sits under Approved Document P. A suitably competent person should design, install, inspect, test and certify. The applicable rules and notification route must be checked for the nation and the property you actually own. Wellness One can tell you which heater or spa is on the quotation. We do not replace the electrician.
For the sauna supply conversation, see outdoor sauna electrical requirements. Do not size a circuit from this article.
Planning is not PD-by-default
An outdoor sauna on a house in England can fall under permitted development — Class E of the General Permitted Development Order — if the building, the plot and the siting all fit the limits. Eaves, overall height within 2 metres of a boundary, listed curtilage, conservation areas, Article 4 directions, and planning conditions can take you outside that class. Lifestyle is listed at 2504 mm. That is not a PD-by-default figure.
Hot tubs and spa pools have their own siting, weight, drainage and, where relevant, planning questions. They are not automatically “fine” because they are lower than a cabin.
This is not legal advice. Confirm with your local planning authority. If you want a piece of paper, that paper is a Lawful Development Certificate or a planning decision, not a Wellness One brochure.
The full outbuilding briefing is Do you need planning permission for an outdoor sauna in the UK?. This comparison will not retell Class E.
Space, base, and two different installs
Footprint is the brochure number. Access for delivery, maintenance, and — for a sauna — ventilation around the building are the numbers that actually bite. A hot tub also needs a base that can take the filled weight, and a way to drain and service it.
When you are planning the garden, measure the unit, the door swings, the route from the street, and the space a person needs to get in and out. Do not treat a photograph as a site survey.
Installation scope lives on the quotation: who builds the base, who runs the electrics, who commissions, what is excluded. A comparison article cannot fill those blanks.
Who should speak to a GP first
Heat in air and heat in water both ask something of circulation and blood pressure. Speak to your GP before either if you have heart disease, arrhythmia, uncontrolled blood pressure, a recent heart attack or stroke, impaired heat sensation, take medicines that affect temperature or circulation, or you are unsure.
If you are pregnant, NHS-style advice still reproduced on GP sites is to consider avoiding sauna and jacuzzi, especially in the first 12 weeks. This page is not antenatal advice. Ask your midwife or GP.
Do not drink alcohol and then sit in heat, in air or in water.
Children are not small adults. Thermoregulation is different. A parent or guardian should obtain advice from the child’s clinician and the appliance manufacturer before use.
What we are not claiming
We are not claiming a health winner. We are not claiming that most standard installations do not require planning permission. We are not claiming Class E by default, and we are not offering legal advice. We are not publishing a kWh, £/year or £/session figure. We are not calling a domestic hot tub hydrotherapy or exercise. We are not offering this as medical advice.
FAQ
Is a sauna or hot tub better for your health?
Neither. Heat exposure and warm-water immersion have different research lines. Neither replaces exercise or healthcare. People with heart or blood-pressure conditions, or who are pregnant, should get individual clinical advice before use.
Which is cheaper to run — a sauna or a hot tub?
A sauna is usually heated when you use it. A hot tub often holds water temperature 24/7. That pattern matters. A pounds-per-year number needs a measured kWh method, a named tariff, and the actual models.
Do I need planning permission for a garden sauna or hot tub?
Sometimes. For an outdoor sauna on an English house, Class E may apply if every limit is met. It is not PD-by-default. Listed buildings, conservation areas, Article 4, height near a boundary, and the rest of the plot can change the answer. Ask the local planning authority. Read the planning guide. This is not legal advice.
Which is less maintenance?
Different jobs. A hot tub is water chemistry for as long as you own it. A sauna is timber care and no spa-pool chemistry. If you will not test water, do not buy a hot tub as the “easier” option.
Can I use a sauna or hot tub if I am pregnant?
NHS-style wording still reproduced on GP sites: consider avoiding sauna and jacuzzi, especially in the first 12 weeks of pregnancy. Ask your midwife or GP. This page is not medical advice.
Do I need a qualified electrician?
Yes. Both may need a dedicated circuit. Approved Document P is the framework for dwellings in England. A competent person designs, installs, inspects, tests and certifies. See the electrical guide for the sauna supply conversation.
Where do I go if I am buying a spa pool, not comparing it with a sauna?
The spa pool buying guide. Specification, water care, BISHTA / PWTAG / HSG282, quotation checklist. Comfort is not a treatment.
Sources
- The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2, Part 1, Class E. https://www.legislation.gov.uk/uksi/2015/596/schedule/2/part/1 — planning detail is owned by outdoor-sauna-planning-permission-uk.
- Ministry of Housing, Communities & Local Government. Permitted development rights for householders: technical guidance (England). https://www.gov.uk/government/publications/permitted-development-rights-for-householders-technical-guidance/permitted-development-rights-for-householders-technical-guidance
- GOV.UK. Electrical safety: Approved Document P. https://www.gov.uk/government/publications/electrical-safety-approved-document-p
- BISHTA. Consumer factsheets on hot-tub and spa ownership. https://www.bishta.co.uk/knowledge-hub/factsheets/
- PWTAG. Pool water standards. https://www.pwtag.org/standards/
- HSE. HSG282 — Control of legionella and other infectious agents in spa-pool systems. Primarily commercial / business-use. https://www.hse.gov.uk/pubns/books/hsg282.htm
- Collingwood Surgery. Is it safe to use a sauna or jacuzzi if I am pregnant? https://collingwoodsurgery.nhs.uk/collingwood/common-questions/pregnancyis-it-safe-to-use-a-sauna-or-jacuzzi-if-i-am-pregnant
Byline: Wellness One specialist team, Wellness One Healthstyle Ltd (Co. No. 14514433)
Last updated: 27 August 2026
This page is not medical advice and not legal advice.