Cold plunge chillers: size, cost and what to look for

The chiller is the component that turns a tub of cold water into a cold plunge — water at your chosen temperature every day, no ice runs, no seasonal drift. It’s also the biggest single line on the equipment list after the tub itself, and the one where buyers most often get sold either too little machine or too much.

We don’t sell chillers. Here’s how to size one, what to pay, and what actually matters.

Sizing: horsepower against litres

A chiller is rated in horsepower (HP), and the honest sizing question is litres, target temperature, and where the tub lives:

Chiller	Tub volume	Right for
1/4 HP	up to ~300 L	small tubs, chest-freezer-scale volumes, 8–10°C targets
1/2 HP	up to ~500 L	the standard home barrel/tub, year-round UK use
1 HP	600–1,000 L	big tubs, sub-5°C targets, shared/frequent use
1.5 HP+	1,000 L+	bespoke pools and duty beyond domestic

Round up when: the tub sits outside in the sun, several people plunge daily, you chase sub-5°C, or the tub is poorly insulated. An undersized unit runs continuously, ages fast, and still loses a summer afternoon. (The temperatures worth chasing in the first place: how cold and how long.)

What chillers cost in 2026

• £500–£1,500 — the mainstream 1/4–1/2 HP class, usually with pump and basic filtration integrated. Where most home setups should land.
• £1,500–£3,000+ — 1 HP and up, and integrated units adding ozone or UV sanitation and app control. Worth it for big volumes and daily shared use.
• The budget route — aquarium-trade chillers can cool a small, well-insulated tub, but typically need a pump and filtration bought separately, which erodes the saving and multiplies the plumbing. The fuller DIY picture is in chest freezer ice baths — a different trade-off again.

Whether a chiller belongs in the budget at all is the chiller vs ice question — short version: start with ice, buy the chiller when regularity arrives.

Running cost: insulation is half the machine

A right-sized chiller cycles — it holds temperature rather than fighting for it, and a 1/2 HP unit on an insulated, covered 500 L tub adds a few tens of pounds a month used daily (the full per-session arithmetic is in cold plunge running costs).

The two multipliers owners control: a fitted insulated cover (evaporation is the main heat gain — an uncovered tub can double the duty cycle) and short, insulated hose runs. Cheap fixes, bigger effect than the next chiller size up.

The spec sheet, decoded

• Filtration: you want water turned over through a filter — the chiller loop usually provides it. No filtration means manual water management: maintenance and hygiene explains the regime either way, and chemicals what goes in the water.
• Ozone / UV: genuinely useful for keeping water fresh between changes on daily-use tubs; not a substitute for the maintenance basics.
• Flow rate and hose fittings: check the chiller’s fittings match your tub’s — adapters are the most common day-one annoyance.
• Noise: compressor cycling, akin to a quiet fridge — fine by a fence, less fine under a bedroom window.
• Power: standard 13 A plug for domestic sizes — no special circuit, unlike the sauna side of the garden. Outdoor sockets should be RCD-protected; the wider siting and electrics picture is in planning permission and electrics.

The whole-setup number

Chiller, tub, cover, siting and running costs together — the cold plunge cost calculator builds the realistic total for your setup in about a minute, and cold plunge pool cost breaks down where the money goes across the whole build.