A heated wooden tub for the cool evenings: timber outside, a white liner inside, 37-39 °C

Cold tub, hot tub: the same timber, a different machine

The wooden plunge tub on the neighbouring page is this tub's cold twin: the same thermally modified staves, the same white liner, the same rule that nothing metal wraps the timber. The difference is the plant: the cold tub is cooled by a chiller sized by litres, this one is warmed by an electric heater sized by litres and by how fast the family wants it ready. It is a home product, and only that; a club or a hotel that wants warm water for a queue takes the hydromassage hot tub with its filtration turnover and its water log.

Why ash or cedar, and why the liner is white

Thermal modification cooks the sugars out of the timber, so ash and cedar staves take up far less water and move far less than raw wood through a monsoon and a dry April. Because the liner, not the timber, holds the water, the staves are cladding: they carry no load, need no hoops and can be re-oiled without draining the tub. The liner is white so that the water is seen to be clean, and smooth so that it can be wiped rather than scrubbed. A tub whose staves are the water barrier swells, weeps and blackens at the joints within a year in Goa.

Heating time, kilowatts and the cover

The arithmetic is litres x kelvin x 4.186 kJ, divided by 3,600; a 15 °C fill is an assumption for a Delhi January, so measure yours. The practical answer is a timer and the insulated cover: the heater starts in the afternoon, the cover stays on until the family steps in, and on a second evening the heater lifts a few degrees instead of twenty. A 6 kW heater runs on a single-phase supply; 9 kW needs three phases, which a farmhouse DB usually has and an apartment usually does not.

Wooden tub or acrylic shell

Where it earns its place: Delhi winters, Bengaluru evenings, the hills

Delhi's mean January minimum is about 7.5 °C (IMD, Safdarjung, 1991-2020); from November to February a farmhouse in Chattarpur uses a warm tub more than a cold one. Pune's January minimum is about 11.2 °C (IMD, 1981-2009), and the Sahyadri hills around Mulshi are cooler and wetter still, which is where the tub in the photograph stands. Bengaluru, at about 920 m, has evenings cool enough all year. In Goa and Mumbai the tub is a cool-season and monsoon-evening object, and the cold twin earns the summer.

Monsoon, sun and the timber

• Partial shade. Direct sun heats the deck and the staves; the cover protects the water, not the wood.
• Re-oil before the rains: one coat a year on thermally modified timber; the liner needs none.
• A deck or a stone plinth with a fall to a drain. A tub standing on soil makes a mud ring and a mosquito pond.
• Coastal plots: 316 fittings and a cover that fastens, because the monsoon wind lifts anything that does not.

Water and power at a farmhouse

Borewell water that scales a kettle scales a heater element faster, because the element runs for hours. A TDS and hardness test before the fill decides between a softener, an inhibitor and a mains fill; the filter and the UV stage run on the pump's timer whether anyone bathes or not. On an inverter, the pump and the controls run and the heater waits; the cover holds the evening's heat through a cut of an hour or two. On a generator set, the heater runs only if the set was sized for it. Residual-current protection and sockets outside the splash zone are your electrician's, to our layout.

Where it goes, and how it arrives

• Weight. 1,800 litres is 1.8 tonnes before the tub and six bathers; a terrace needs the slab check, a garden a level, firm base.
• The gate. The tub arrives whole on a pallet and passes a gate of about a metre; a narrower gate means a lift over the wall.
• The pair. A heated tub beside a farmhouse sauna on one deck is the private version of the suite; on a society podium the RWA asks about weight, the drain and the pump.