The head/pressure rule of thumb and why heated water needs expansion provision.
A useful plumbing rule of thumb: roughly 1 bar of pressure for every 10 metres of vertical head of water. More head above an outlet means more static pressure at it.
Water expands when heated, so closed hot-water systems need expansion provision (an expansion vessel or equivalent) to absorb the increase safely.
*Original revision guidance; the head/pressure value is an approximation for revision — confirm exact figures.*
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