Build no. 2 · the contrast circuit

A warm pool and a cold pool side by side: 38 °C, 4 °C, one plant room

The duo is the contrast ritual without a sauna: a 38 °C soaking pool beside a 4 °C plunge pool, tiled to match and fed from one plant room. Where a 90 °C cabin can feel like a lot at midday, this is the version people use at dawn, after yoga and after dinner.

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Warm sage-gold mosaic soaking pool and round lagoon-teal cold plunge pool side by side on a teak deck, each with a small display reading 38 and 4

Compositionwarm pool 36⁠-⁠40 °C beside a cold pool at 3⁠-⁠5 °C

Waterabout 1,100 L on each side

Heatingsmall electric heater on the warm side, sized for the pool and the cover

Coolingone 4 HP chiller on the cold side, out of sight

Plantone ventilated niche, shared filtration, two displays at the rim

RangeTHB 700k⁠-⁠1.25M

WarrantyTwo years, then a further year of assisted service visits

The routine, in the order guests actually do it

Rinse, five to eight minutes in the warm pool, one to three in the cold, a rest on the ledge, then round two. Nobody needs a manual for that, but the geometry has to cooperate: the two pools sit within three steps of each other, the walkway between them is slip-rated and drains away from both shells, and there is somewhere dry for the towel. People with heart conditions, high blood pressure or pregnancy should ask a doctor before any contrast routine; the layout does not change that advice.

The warm side is easy in Thailand; the cold side is the project

Bringing 1,100 litres from a 29 °C start to 38 °C takes about 11.5 kWh, roughly four hours on a 3 kW heater, and a covered pool then loses little to 30 °C air. Taking the other 1,100 litres from 29 °C down to 4 °C means removing about 32 kWh, then fighting sun and warm air all day. That is why most of a duo's budget and most of our engineering sit on the cold side, and why the warm pool is the cheaper half of the pair.

A sage-gold warm pool and a lagoon-teal cold pool separated by a narrow stone ledge, each with a small temperature display — Two mosaics, one ledge, two displays: 38 and 4, never a decimal point.

Two shells, one plant room

Two shells, one footprint. Masonry shells with matching coping, a stone ledge between them and underwater steps on both sides.
One technical niche. Heater, chiller, filter and pumps share a ventilated room or a louvre-screened niche, with the chiller's exhaust kept away from the heater's air.
Insulated common wall. The ledge between the pools is insulated, otherwise the warm side quietly feeds the cold side all afternoon.
Two displays, two digits. 38 and 4 on slim stands at the rims; nothing else on show.

Where a duo earns its keep

On a retreat it is the bridge between the yoga deck and the spa, as in the Koh Samui case note. On a villa terrace it replaces the sauna for owners who prefer soaking. In a hotel spa garden it gives couples a ritual to book at a fixed time. Add a glass sauna later and the circuit has all three temperatures; we leave the footprint and the electrical capacity ready for it.

Warm water needs a routine, not a miracle

Water at 38 °C is comfortable for people and for bacteria, so the pool gets proper filtration, UV or another sanitiser, a cover and a written routine: test, top up, backwash, drain on schedule. We hand over a one-page routine with the keys. If you run guests rather than family, ask your provincial public-health office which water standard applies; the hospitality page lists the questions.

Warm and cold pools at night with soft underwater lights, palms lit from below and a glass sauna glowing behind — At night the duo carries its own light: low underwater LEDs, no glare toward the neighbours.

A duo against two separate pools

Choice	What you get	Indicative range
Duo, built together	two shells, one plant room, matched tiling	THB 700k⁠-⁠1.25M
Cold pool only	one 1,100 L plunge pool, own chiller	THB 330⁠-⁠590k
Duo plus glass sauna	the full three-temperature circuit	add 380-540k for a 4-seat cabin

Building the two pools together saves a second excavation, a second plant niche and a second round of approvals. The budget ranges page breaks out the extras, and the configurator lets you add the sauna in one click.

Do we still need a sauna if we have a hot and cold pool?

No. Plenty of retreats and villas run the duo alone. A sauna adds dry heat and a place to sit in silence; the duo gives contrast with water at both ends. Many owners start with the duo and reserve space and power for a glass sauna.

Is 38 °C pleasant when the air is 33 °C?

At midday often not, which is why duos are used early, late and in the cool season in the north. The warm pool can run at 36 °C in the hot months and 38⁠-⁠40 °C in December and January, and the display shows what is set.

Can the warm pool use the chiller's waste heat?

In principle a chiller rejects heat that a warm pool could use. Whether it pays back depends on layout and hours of use, so we raise it as a design question in the 3D phase rather than as a promise.

How big is the footprint?

Two 1.2 m pools with a ledge between them fit inside about 3.4 x 1.6 m of deck, plus a plant niche of roughly 1 x 2 m within a few metres of the pools.

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