The tank is insulated with 100mm of pink batts (fibreglass), surrounded
by 50mm thick polystyrene panels, and covered with 2 layers of black
plastic raincoat covers. It stays hot for at least 2 days.
Here's how we use the hot water. There are two independent hot
water systems which utilise the 800 litre tank:
1. There's a copper coil heat exchanger which provides all the
hot water for showers, kitchen, bath, etc.
2. And there's a central heating system which heats radiator
panels in the cottage.
Here's a diagram: