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| Formulae of Heat Supply and Heating Area | With an instantaneous water-heater devoid of accumulating calorifier the heat supply can be calculated as:
H = 4.19 v (q1 - q2) (2)
where
v = required volume flow (liter/s)
The heating area of a heat-transfer device can be calculated as:
A = 1000 H / k qm (3)
where
A = heating area (m2)
H = rate heating (kW)
k = overall heat transmission coefficient (W/m2K)
qm = logarithmic mean temperature difference (K)
Coefficient of heat transfer depends on construction and material of the calorifier.
The boiler
 Boiler with the fitted rating must be selected from producer catalogues where
Boiler rating = heating capacity of calorifier + safety margin (on average 10 - 20%)
Design pipe scheme and size pipes
The maximum volume flow through connection pipes to fittings and other gear is contingent on the maximum demand of each consumer or fitting.
The maximum volume flow through main pipes is determined by the maximum demand of the fittings and statistic demand based on the number and types of fittings and equipment supplied.
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