Marilyn & Bob wrote:
"Heathcliff" wrote in message
oups.com...

On Feb 6, 11:20 pm, "Marilyn & Bob" wrote:

We have a four story plus cellar 1840's 2 family house with a hydronic
heating system with large radiators that was probably installed in the
1920's. The gas boiler is about 20 years old. The system has both a
conventional expansion tank (that has not been emptied in years) and a
Filltrol diaphragm expansion tank in series.

Every place I looked on the web (including the Filltrol site) says that
the
system pressure should be set at 12 psi when cold and should be 20 psi
when
hot and circulating. That is exactly where it is, but the radiators on
the
4th floor seem to have some air left in them. When bled, water does not
come out of the valve and the top of the radiators are not very hot (the
bottom halves are).

Should the pressure be higher in a 4 story house that in a shorter one?
And
if so what should it be? And how do I adjust it? The Filltrol manual
does
not give instructions other than to say that it is adjusted via the
intake
air valve and should be adjusted when the tank is empty.

So (if I really do need to increase the pressure) do I add air (and how
much) or remove air from the Filltrol expansion tank. And do I have to
completely drain the system to do it? Or just let out a few gallons of
water? Or not concern myself with letting any water out.

A link to a good website will suffice. As I said, my Google search was
unproductive.
--
Peace,
BobJ



You do not say whether you are getting enough heat in the top floor.


The 4th floor is occupied by our tenants. They tend not to complain, but
did alert us to the radiator problem at the beginning of the winter when it
was not cold. I did note an electric space heater in a room when I last bled
their radiators. In any case, I would want it to work right.


If the rooms up there are comfortable, then there is nothing wrong
with having the radiators half full, and if I were you I would not
touch it. If you need more heat up there then first try bleeding air
from the radiators.


I have bled the radiators twice this winter. In both cases only air came
out few a few seconds. Water never came out of these radiators no matter
how long the valve was left open.


The system should have an inlet valve that adds
water automatically when the pressure drops below 12 psi. -- H


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.


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

Jim