"Christian McArdle" wrote in message
t...
The pressure would be the same throughout the system if the whole thing
is
sealed. The pressure vessel is not actually replenishing or supplying
the

No, the pressure depends on the height at the point you measure it. The
static pressure will be higher at the ground, compared to the loft, quite
considerably.

pressure between these two positions. If the gauge is in the attic, do
you
pressurise to half a bar less than if it were at ground level?

Basically, yes. There are some parameters about the system that are
important to design in. This will help you determine vessel sizing and
pressurisation.

1. The boiler probably wants 1-1.5 bar cold pressure. (Check the manual!)

2. The boiler probably wants you to stay below 2 bar when hot. (Check the
manual!)

3. The amount the pressure goes up depends on the pressure vessel. You
need
a bigger one if running at 1.5 bar, to reduce the pressure rise to contain
it within 2 bar.

4. The hot pressure must be below 3 bar at all points in the system.

5. The hot pressure must be below 2 bar at the position on the pressure
relief valve.

6. The cold pressure should be above around 0.5 bar at all points in the
system.

7. 5m height equates to around 0.5 bar.

These requirements are very easy to achieve in a 2 storey house. If the
boiler is wall mounted on the ground floor and the pressure gauge in the
loft, you'll probably need to fill to around 0.6 bar (but no lower than
0.5
bar). However, there is nothing stopping you have the filling loop next to
the boiler, where it is more convenient and filling to 1 bar.

Christian.



Thanks for that. It all makes perfect sense - and is more or less what I
expected to be the case - but I have never previously seen it spelled out.

Incidentally, my current boiler is suitable for both vented and sealed
systems, and requires a static head in the range 1 - 30 metres - so there
seems to be plenty of scope.

Roger