On 13/01/2017 15:22, John Rumm wrote:
On 13/01/2017 12:45, mechanic wrote:

The balanced flue connects to the outside world? How does that
ensure under-pressure?

The fan sucks air out of the case. The case then draws its from the
flue. The fact that air is flowing via the flue into the case means the
case must be at lower than atmospheric pressure.

Combustion air is being pulled into the pre-mix burner (which is
adjacent to the fan) rather than pushed from a fan at the entry point of
the flue like on older designs.


What about older non-fan-assisted room-sealed boilers with balanced
flues? The airflow is presumably just down to convection. Do they have
negative case pressure?

There must surely be a pressure gradient within the case - with the
bottom being below atmospheric pressure in order to draw fresh air in,
and with the top being above atmospheric pressure in order to expel the
products of combustion?
--
Cheers,
Roger
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