Plunge Pool: Everything You Need to Know (Sizes, Costs, Safety and DIY)

Last updated: September 2026

Plunge pool? Yes please! A plunge pool is small enough to fit in an ordinary back garden, deep enough to cool off in properly, and if you heat it, you can use it for most of the year. It’s also a realistic DIY project if you’re willing to plan.

This is my overview of plunge pools: what they are, the sizes, the types, what they cost, safety, water care, using one as a cold plunge, and whether you can build your own. When you’re ready to build, my step-by-step DIY plunge pool guide takes it from there.

What is a plunge pool?

A plunge pool is a small pool built for cooling off, wading and relaxing. There’s no strict definition, but it’s usually deep enough to stand in with your shoulders under the water, and too short to swim lengths in. Many have built-in steps and a bench. Add a counter current swim jet and it becomes a mini exercise pool.

The names get muddled, so here’s how they compare:

Type	Typical size and depth	Typical water temperature	Used for
Plunge pool	3–6m (10–20ft) long, 1.2–1.5m (4–5ft) deep	Unheated to about 30°C (86°F)	Cooling off, wading, a swim jet if it’s long enough
Hot tub	2–3m (7–10ft) square, ~1m (40in) deep, with seats	37–40°C (98–104°F)	Hot soaking with jets
Cocktail pool or spool	Similar to a plunge pool, with benches, loungers and often jets	Pool temperature in summer, can be run hotter in winter	Socialising with a drink in hand
Cold plunge	Usually one person, 1–1.2m deep	Kept cold, often with a chiller	Short cold immersions

Still deciding? Read Hot tub vs plunge pool: which should you build in 2026? and What is a spool?

How big is a plunge pool?

Sizes vary a lot. Checkatrade describes UK plunge pools as anything from 1.5m x 1.5m up to about 1.5m x 5m, and 1m to 2.5m deep. Angi says US plunge pools are around 4 to 8ft deep. Most DIY plunge pools are 3–6m (10–20ft) long, with about 1.2–1.4m (4ft–4ft 6in) of water. That suits most adults for standing and cooling off.

When choosing a size, think about:

• How many people will use it at once.
• Steps and a bench, which take up floor space but make it far more usable.
• A swim jet. If you want one, the pool needs to be at least 4m (14ft) long, or the wave bounces back off the far wall. See swim jet considerations.
• Heating. Every extra cubic metre is another tonne of water to heat.

Types of plunge pool

Type	Pros	Cons
Concrete, block or ICF (built in place)	Any size or shape, tiled finish, very long-lasting, and the best option for DIY	The most work, and the structure has to be right
Fibreglass shell	Quick to install, smooth finish	Fixed sizes, usually needs crane access, and must be installed exactly to the maker’s spec
Vinyl liner	Lower upfront cost	The liner needs replacing over time and can be punctured
Above-ground or container	Little or no digging	On display in the garden, and the walls need to resist the full water pressure

Personally, I prefer in-ground. I like things as minimal as possible in the garden, and the idea of dropping into the ground rather than being on display for the neighbours.

How much does a plunge pool cost?

USA

Angi’s cost guide puts the average plunge pool at about $28,000, with most homeowners paying $10,000–$40,000. By material, Angi gives:

Material	Typical installed cost (Angi)
Vinyl	$10,000–$30,000
Fiberglass	$18,000–$55,000
Concrete	$20,000–$75,000

Angi also puts a pool heater at $1,800–$4,200 installed, and says labour is typically 25–50% of the total.

UK

Checkatrade’s cost guide puts a concrete in-ground plunge pool at £15,000–£25,000, plus £1,500–£4,500 labour, and a fibre or resin pool at £7,500–£16,000 plus labour. A heater adds £1,200–£2,600.

DIY

Building your own costs a fraction of that, because labour is such a big part of a pro build. I’m not going to give you a single DIY figure, because it depends so much on size, finish, heating and how much you hire in, and material prices keep moving. Price your own parts list before you start. That’s one of the things my plans give you.

Don’t forget the extras, whichever route you take: permits, excavation and spoil removal, the electrics, fencing, paving and a cover.

Where to put it

• Water in and out. You’ll lose water to evaporation and splashing, so you need a tap nearby, and somewhere sensible to drain it. An auto top-up is worth weighing up.
• The view. If you can face a view rather than a fence, do it.
• The control room. The pump, filter and heater need a dry, covered spot close to the pool.
• Power. Plan the cable route before you pour concrete across it.
• Services. Check for buried cables and pipes with LinesearchbeforeUdig in the UK or 811 in the USA.
• Sun and shelter. Sun helps warm the water, but it isn’t essential. Shelter from wind and overhanging trees matters more.

Permissions and safety

Planning and permits

In England, the Planning Portal says outdoor domestic pools often don’t need planning permission, because they can go in under permitted development. Check with your council if you’re in a listed building, a conservation area, a national park, green belt or other designated land. In the USA, an in-ground pool almost always needs a building permit, an electrical inspection and a compliant barrier. See Do I need a permit for my hot tub?

Barriers and covers

• USA: The CPSC’s barrier guidelines call for a barrier at least 48in high, no gaps a 4in sphere can pass through, and self-closing, self-latching gates that open away from the pool. Local codes vary.
• UK: No law requires a fence around a private pool, but RLSS UK recommends secure fencing at least 4ft high. It also points out that 86% of child drownings happen without adult supervision.

Drains and electrics

Fit two main drains, teed together and at least 1m (3ft) apart, with anti-entrapment covers, so a single drain can’t trap someone underwater. See Installing a main drain. Leave the electrics to a qualified electrician. In the UK, pools come under BS 7671 Section 702, which only allows 12V SELV equipment in the water and requires supplementary bonding, and the work is notifiable under Part P. In the USA, NEC Article 680 covers GFCI protection and bonding.

Heating, or keeping it cold

A plunge pool holds several times the water of a hot tub. A 4m x 2.5m pool with 1.3m of water is around 13,000 litres (about 3,400 US gallons). A small 3kW spa heater would take about 50 hours to raise that by 10°C, even with no heat loss. So for year-round use, an air source heat pump is the sensible choice, and many can cool as well. See how to choose the right air source heat pump. Whatever you choose, a good insulated cover makes the biggest difference to running costs.

Using it as a cold plunge

Lots of people now build a plunge pool partly for cold water immersion. Unheated, an in-ground pool stays properly cold for much of the year in the UK and the northern USA. For consistent cold in summer, you’ll need a chiller or a heat pump that can cool. See how to build a DIY cold plunge pool.

Are plunge pools good for your health?

A lot of claims get made about cold plunges: better circulation, less muscle soreness, better mood and sleep, even weight loss. Plenty of people say they feel great afterwards. But the evidence for many of these claims is still limited, so I’d enjoy it for how it makes you feel rather than as a cure for anything.

What is well established is the risk. The US National Weather Service warns that cold shock can be as dangerous in water at 10–15°C (50–60°F) as at 2°C (35°F), with an involuntary gasp and a sudden spike in heart rate and blood pressure. So:

• Get in slowly, and keep it short.
• Never plunge alone, and never after alcohol.
• Talk to your doctor first if you have a heart condition or high blood pressure, or you’re pregnant.

If you heat it to hot tub temperatures, the CPSC says never go above 104°F (40°C).

Keeping the water balanced

A plunge pool needs the same water care as any pool: a filter, a sanitiser and balanced water. Test at least weekly, and more often in hot weather or after heavy use.

Parameter	Target	Notes
Free chlorine	At least 1ppm (2ppm if you use stabiliser). At least 3ppm if you run it hot	CDC guidance
Bromine (alternative)	4–6ppm	Gentler on skin, but sunlight breaks it down
pH	7.2–7.6	Within the CDC’s 7.0–7.8 range
Total alkalinity	80–120ppm	Buffers the pH
Calcium hardness	200–400ppm	Protects the grout and render in a tiled pool
Cyanuric acid (stabiliser)	30–50ppm, outdoor unheated pools only	Protects chlorine from sunlight. Don’t use it if you run the pool at hot tub temperatures

Adjust one thing at a time, alkalinity first, then pH, then sanitiser, and retest after each. If alkalinity or calcium gets too high, the only real fix is a partial drain and refill. My guide to balancing chemicals goes through each step.

Can I build my own plunge pool?

Yes, if you’re a reasonably confident DIYer and willing to plan properly. The method is the same as an in-ground hot tub: dig, lay a reinforced slab, build ICF or core-filled block walls, plumb it, waterproof it and tile it. The parts that need real care are the structure, which has to hold many tonnes of water without cracking, and the electrics, which you should leave to a qualified electrician. It’s perfectly normal to do most of it yourself and hire in a digger or a bricklayer for a few days.

My full DIY plunge pool build guide walks through every stage. For real examples, see Ben’s DIY concrete plunge pool and Roger’s dipping pool, and for smaller ideas, mini pool ideas.

Common mistakes

• Digging to the water depth, forgetting the slab, waterproofing and tiles underneath.
• No hydrostatic relief valve on a site with groundwater. See Why do I need a hydrostatic relief valve?
• A single main drain with no anti-entrapment protection.
• Expecting a small spa heater to heat a pool-sized volume.
• No barrier or cover around something deep enough to drown in.

Planning your own plunge pool?

My plunge pool / cocktail pool plans come in standard sizes from 10ft x 7ft and 12ft x 8ft up to 20ft x 10ft. Each one includes architectural drawings, plumbing layouts, steps and a lounger area, plus a build guide and videos, in imperial and metric. Want to swim? Add a counter current swim jet.

For something bespoke, draw it in the free Tub & Pool Designer Pro software, and I can turn it into architectural CAD and a 3D plumbing design.

FAQs

How deep is a plunge pool?

Usually 1.2–1.5m (4–5ft) of water, enough to stand with your shoulders under. Some are deeper.

How much does a plunge pool cost?

Professionally installed, Angi puts the US average at about $28,000, and Checkatrade puts a UK concrete in-ground plunge pool at £15,000–£25,000 plus labour. DIY is a fraction of that.

Do I need planning permission for a plunge pool in the UK?

Often not in England, under permitted development, but check if you’re in a listed building, a conservation area or on other designated land. The electrics are notifiable under Part P.

Can you swim in a plunge pool?

Not lengths. With a counter current swim jet and at least 4m (14ft) of length, you can swim on the spot.

Can a plunge pool be heated?

Yes. An air source heat pump is the most economical way, and a good cover makes a big difference.

Can I use a plunge pool as a cold plunge?

Yes. Leave it unheated or add a chiller. Get in slowly, keep it short and never plunge alone.

Thinking about a plunge pool? Ask me anything in the comments below. I read them all.

Cheers,
Andi

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Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi