Jim,
See my response to Doug Miller.

"Speedy Jim" wrote in message
. net...
Marilyn & Bob wrote:

"Doug Miller" wrote in message
. net...

In article , Speedy Jim
wrote:

Marilyn & Bob wrote:

"Heathcliff" wrote in message
glegroups.com...

Yes, I understand this. My question is whether 12 psi cold pressure
(20 psi
hot with circulator pump on) is enough for a system with large
radiators
that are about 35 feet above the level of the boiler.

If you haven't actually measured, I think you should. This sounds a bit
low to
me, for rads on the top floor of an older 4-story building.

You need to measure from the bottom of the boiler to the top of the rad.

Consider also that older buildings frequently have 9- or even 10-foot
ceilings, and floor joists were often 2x10 true (instead of 2x10 nominal
= 1.5
x 9.25 true).

The 12 psi recommendation is based on having the boiler in the basement
of a
*two* story building, where the head probably won't exceed 20 feet. I
wouldn't
be at all surprised if the head in your building is closer to 40 feet
than it
is to 35.


Short answer: NO! Cold pressure must be enough to maintain
the head at 35 Feet.

Entirely correct (as is what follows) -- but incomplete.

The missing part is that 1 foot of head = 0.4335 psi. Thus 35 feet of
head is
a bit over 15 psi, and 40 feet of head is 17.3 psi.


Anytime the pressure drops (cold or hot)
below that required at the highest elevation, air *will* be sucked
into the system. On the next startup, that air will block flow
to the highest rads, even if pressure rises.

You may need more expansion tank capacity to reduce the swing
between cold and hot pressure.

In any case, you need higher system pressure.

Exactly.

--
Regards,
Doug Miller (alphageek at milmac dot com)

It's time to throw all their damned tea in the harbor again.


OK. It's about 36' to the bottom of the top radiator about 39' to the
top where the bleeder valve is. So about 17 psi. Now the question is
how do I get to that? We have a Filltrol diaphragm expansion tank and
standard expansion tank. I have not drained that standard tank in many
years. m Ransley suggested bleeding the radiator with the water cold (but
the circulator pump on), is that a place to start? I've always bled it
with the system on full blast.



Your boiler *may* have an automatic fill valve, like:
http://www.cashacme.com/cbl.php

If so, the regulator section is adjustable.

Drain the expansion tank first.
Get the pressure (cold) up where it should be and then bleed.

Jim