The water in the boiler stays hot for many hours, however this depends on a number of factors:

a. Size of the boiler (water volume): the bigger it is, the longer the inertia to stay hot

b. Air temperature: the colder the air, the faster the loss of heat from the boiler and pipes

c. Initial water temperature: the hotter the water prior to cloudy moments or nights, the longer the availability of it

d. Thickness of the insulation: the thicker it is, the longer the water stays hot (our boilers have a 5cm thick polyurethane HD insulation with a thermal factor of XX); also the pipes must be insulated, both outside and inside the building

e. Usage: the more water you use the shorter the period it stays hot while the sun is out (cold water enters the boiler and as such cools down the existing hot water)

f. Insulation: the more insulated, the lower the heat loss