Two seats, 1.6 metres of water, and the temperature problem nobody mentions

Why a long tub needs two return lines

Cold water is denser than warm water, so in a long tub it pools at the bottom near the inlet and will not travel to the far end on its own. We measured it in Cikarang on a 1.9-metre test tub: with a single inlet and a suction on the same side, the seat nearest the nozzle and the seat furthest from it differed by 0.8 degrees after two hours of holding. With inlets at both ends and diagonally opposed suction, the difference falls below 0.2 degrees, which is finer than the chiller's own holding accuracy and therefore not perceptible.

The circulation pump goes up to 9,000 litres an hour on a 900-litre tub, so the whole contents turn over ten times each hour. The nozzles are angled 30 degrees downward so the stream does not hit the back of somebody already sitting down — a small detail that becomes important around minute two in 4-degree water.

Two bodies are a real heat load

An adult in 4-degree water gives off somewhere between 350 and 700 watts depending on body mass and how long they stay in. Two people for four minutes is roughly 0.15 kWh of heat, small against the daily load but visible as a 0.4-degree rise that has to be pulled back down. If the tub sees six paired sessions a day, body heat becomes a genuine line in the calculation, and our answer is a larger pump and a bigger heat exchanger rather than a bigger compressor.

Facing seats, and the geometry behind them

The seats face each other rather than sitting side by side, because two adults shoulder to shoulder in a 96-centimetre tub both end up leaning away. Facing, the knee-to-knee distance is 62 centimetres, and a seat height of 42 centimetres puts the waterline just below the collarbone for anyone between 165 and 185 centimetres tall. Outside that range we move the seat up or down by three centimetres at no extra cost, and we will set the two seats to different heights for a couple with a large height difference. Tell us at survey; we set the mould, not the tub.

Before you order: do you really need 900 litres?

Look at the second row. If you and your partner immerse one after the other rather than together, a single 500-litre tub gives you the same experience for about Rp 130,000 less every month and a shell price roughly fifteen million lower. We raise it early because about half the people who ask about a two-seater do not need one. Compare a 500 to 600-litre terrazzo ice bath first, or run both volumes through the chiller calculator.

Price, and which shell to put it in

The two-seater runs Rp 68-108 million for the body, with cast terrazzo at the lower end and electropolished 316 stainless at the top. The 4 HP chiller is added separately at Rp 105 million, and if the same tub will also be run warm, the heating and cooling version starts at Rp 56 million. Component-level pricing is on the pricing page.

Filling, draining, and what the water costs

Nine hundred litres take about 75 minutes from a household tap running at 12 litres a minute, and drain through a two-inch valve in 11 minutes. With ozone and two users a day the water is changed every four to six weeks: nine changes a year, about 8,100 litres, which on domestic water tariffs in Java and Bali is under Rp 60,000 annually. Water cost is never the issue. What you feel is re-chilling the fresh fill, roughly 6.3 kWh each time.

That is why every two-seater gets a drain valve at the lowest point and a permanent fill line with a float valve. Filling 900 litres by babysitting a garden hose for an hour and a quarter is a job people do twice and then stop doing, and a tub whose water is rarely changed becomes a tub nobody uses. In a rental villa we connect that fill line to the controller so changes are scheduled and logged, exactly as on a commercial ice bath.