Cold water that costs less to hold in the highlands

Why the highlands are cheap and the coast is not

Nairobi's altitude keeps nights cool all year. A shaded, insulated, lidded tub here spends most of the night losing almost nothing, so the compressor cycles rather than running and the monthly bill is modest.

Mombasa and Diani are the opposite: warm, humid and never really cooling. The same tub on the coast needs a larger unit, more insulation and more shade, and it will still cost more to run. We size and price the two completely differently.

Insulation and the lid come first

Closed-cell insulation in the wall cavity and under the base, and a fitted lid light enough to lift with one hand. Those two decide how hard the machine has to work, and almost everyone stops using a lid that is too heavy.

Shade is the third. Under a jacaranda or a pergola a tub behaves completely differently from one on an open terrace.

Basalt, timber or built in

A tub carved from a single block of Kenyan basalt is dense, dark and thermally massive — it holds temperature better than any clad tub and it looks like the country it is in. It is also heavy, so the structure gets checked first.

Oiled timber on a deck is the movable option. A built-in microcement basin is the commercial answer. All three need insulation, a drain, circulation, cartridge filtration and ozone or UV on anything shared.

In short

• Nairobi's cool nights make the highlands cheap for cold water; the coast is not
• Insulated shell and base, plus a lid people will actually lift
• 1 HP ≤260 l, 2 HP ≤570 l, 4 HP ≤1,200 l, stepped up for coast, sun or 4 °C
• Circulation, filtration and ozone or UV on anything more than one household uses