open vented copper cylinders
Also known as Indirect Single Feed
cylinders and/or Self-Priming (i.e. Primatic) Cylinders. In this
type of system (not fully compliant with current Part L) both the
heating and hot stored water are fed from the same header tank.
There are various proprietary methods
of achieving this, but all utilise an air lock within the cylinder
which prevents the heating circuit water and the domestic hot water
from coming into contact with each other.