Choose indoors if you have a ground floor room with a solid floor, good ventilation and somewhere to drain several hundred litres of water. Choose outdoors if you have a level, solid base, an RCD protected outdoor socket fitted by a registered electrician and a plunge rated for the weather. Both work well; the right answer depends on your floor, your power supply and how you will drain it.
This guide is part of our cold plunge setup and care hub.
Space and footprint
Start with a tape measure. You need room for the tub itself, space to step in and out safely, and clearance around any chiller so it can draw in and expel air. A plunge with an external chiller also needs a sensible hose run between the two.
- Allow a clear, non-slip area beside the tub to stand and dry off.
- Leave access to the filter housing and control panel.
- Keep the chiller's vents clear of walls, fences and planting.
Measure the route in as well. Doorways, tight corners, side gates and steps are often the real limit. We cover this in detail in Where to Put a Cold Plunge at Home.
Weight and floors
One litre of water weighs about one kilogram, so a filled plunge with a person in it can easily reach several hundred kilograms on a small footprint. A ground floor concrete slab or a properly built patio is usually the simplest base. Suspended timber floors, upper floors, balconies and decking need more thought, and for those you should ask a structural engineer before installing.
Drainage
At some point you will need to empty the tub. Work out in advance where several hundred litres will go.
- Indoors: a utility room, garage or plant room with a floor drain is ideal. Otherwise, plan a hose route to a sink, shower or outside gully, and check whether your plunge has a drain valve or needs a pump.
- Outdoors: draining is usually easier, but avoid flooding lawns and beds. If you use a chemical sanitiser, do not drain into ponds, streams or surface water drains that lead to watercourses; ask your water company if you are unsure where a drain leads.
Humidity and ventilation indoors
An indoor plunge adds moisture to the room, especially if your model has a heating mode and you run it warm. The chiller also releases heat into the space it sits in. Over time, poor ventilation can lead to condensation, damp and mould.
- Choose a room with an extractor fan or a window you can open.
- Keep the cover on between sessions to reduce evaporation.
- Use water resistant flooring around the tub and protect nearby walls from splashes.
- Avoid tight cupboards or small unventilated rooms for the chiller.
Indoor plunges do have real advantages: they are shielded from sun, leaves and frost, they are easier to use in the dark and cold, and they collect less garden debris.
Outdoor considerations
- Sun: direct sunlight warms the water and makes the chiller work harder. Shade helps.
- Debris: trees and hedges drop leaves, pollen and insects. A fitted cover is essential outside.
- Frost: check your plunge's minimum operating temperature and plan for freezing nights. See Using a Cold Plunge in a UK Winter.
- Power: outdoor sockets should be weatherproof and RCD protected, and new outdoor wiring should be done by a registered electrician. Our guide to cold plunge electrical requirements in the UK explains what to ask for.
- Privacy and access: think about overlooking neighbours and a safe, well lit path from the house.
IP ratings explained: IPX4 vs IPX5
If a plunge is sold for outdoor use, you will usually see an IP rating. IP stands for Ingress Protection and the codes come from the international standard IEC 60529. The first digit refers to protection against solid objects and dust; the second refers to water. An X in place of the first digit means it has not been rated for solids, not that it has zero protection.
| Rating | Water protection | How it is tested |
|---|---|---|
| IPX4 | Splashing water from any direction | Water sprayed from an oscillating tube or spray nozzle over the enclosure from all angles |
| IPX5 | Water jets from any direction | A jet from a 6.3mm nozzle at about 12.5 litres per minute, from roughly 2.5 to 3 metres away |
In plain terms, IPX4 covers rain and splashes, while IPX5 also covers a direct jet of water, such as driving rain or a hose. Three points are worth knowing:
- Neither rating means the equipment can be submerged. Immersion is covered by different ratings.
- The rating applies to the equipment's enclosure. It does not make an unsuitable socket or extension lead safe outdoors.
- Even rated equipment lasts longer when it is sheltered from standing water and pooled rain.
For reference, the ThermoX Elite and ThermoX Pro are rated IPX5 and the ThermoX Core is rated IPX4. All three are designed for indoor or outdoor use.
Quick decision guide
| Factor | Indoors suits you if | Outdoors suits you if |
|---|---|---|
| Floor | You have a ground floor slab or an engineer has approved the floor | You have a level patio or slab, or can lay one |
| Drainage | There is a floor drain or a short hose route | There is a suitable gully or drain nearby |
| Ventilation | The room has an extractor or opening window | Not a concern |
| Power | A suitable socket is within reach of the plug | A weatherproof, RCD protected outdoor socket is in place or can be fitted |
| Year round use | You want shelter from weather and darkness | You are happy to use a cover and plan for frost |
A quick safety note
Speak to your GP before cold plunging if you have a heart condition, high or low blood pressure, are pregnant or have any other medical condition. Never plunge after drinking alcohol, and avoid plunging alone. The RNLI warns that cold water shock is real: water below 15°C can trigger gasping and a sharp rise in heart rate and blood pressure. Start warmer and shorter.
Frequently asked questions
Can a cold plunge go indoors?
Yes, if the floor can take the filled weight, the room is well ventilated and you have a way to drain the water. A ground floor concrete slab is usually the simplest option. For upper floors or suspended timber floors, ask a structural engineer first.
What is the difference between IPX4 and IPX5?
Both come from the international standard IEC 60529. IPX4 means protection against splashing water from any direction. IPX5 means protection against water jets from any direction, tested with a 6.3mm nozzle. Neither means the equipment can be submerged.
What does the X in IPX4 mean?
The X replaces the first digit, which covers protection against solid objects and dust. It means the product has not been rated for solids, not that it has no protection.
Do I need a special socket for an outdoor cold plunge?
Outdoor sockets should be weatherproof and RCD protected. Any new outdoor socket or circuit should be installed by a registered electrician, and you should avoid extension leads for a permanent setup.