I've got a 3-zone baseboard/fin-tube hot water system in my house and
hear the water flowing when it circulates. From reading some other
internet-advice, it appears that I need to bleed the air from the
I've found the valves for the loops and understand that I need to bleed
from the highest point. However, I still have a couple of questions...
1. Some reading indicates that I should bleed when the water is
circulating, other places mention that you should not do it at this
time...the theory being the air settles at the highest point and
therefore you can release more when the water is not circulating.
Which is the better option, or is it a personal preference?
2. If the air is removed, how does the water enter the system. Is the
bell-looking device a control valve? I can reach this object, but it
is in a location where I cannot read the text on it. Is there another
valve that controls input flow and/or some type of auto-fill mechanism
that would allow water to come in when the necessary?
I bleed my radiators when it is running from each radiator. You have a
pressure gauge on your boiler you should rely on as autofill valves are
not always perfect. Also filling should be done on a cold boiler not
hot. If you bleed with the unit off and cold nothing may happen , or
little compared to when it is hot and under higher pressure. I have
found my autofill to over fill by 3lb.
On Thu, 3 Mar 2005 08:34:06 -0600, email@example.com (m Ransley)
It sounds like the original poster is talking about a hot water
circulating system as opposed to the steam heating system that you
appear to be discussing. Although there are similarities, hot water
and steam system heating are different. For one thing, most hot
water circulating radiators are not furnished with air blead valves.
They have two connections (and input and an output for the circulating
hot water- Steam radiators generally have one pipe connection to the
steam supply - the water condenses down the the same pipe) The hot
water system designer is supposed to supply a blead valve at the
highest point in the the system. Automatic air blead valves are also
The incoming feed water, to a varying degree will have disolved gases
in it (mostly air, which is about 78% Nitrogen). The air can impede
the flow of hot water to certain parts of the system and thus, the
radiators will be cold if it is not removed.
If you've got a lot of air in the pipes, there is nothing wrong with
bleeding it while the system is off (circulating pumps, not working).
However, to truly purge the most possible air out of the system, you
have to do it when the pumps are running. Presumably, you have an
auto-fill valve somewhere to supply fresh water to make up for any
lost volume. There should also be an expansion tank somewhere on the
system to keep the pressure uniform as the hot water expands.
Beachcomber, I am talking hot water. Ive never seen a large cast iron
radiator without an Air Bleed, or you can`t ever get the air
out....Maybe you are refering to baseboard.
You dont bleed steam manualy, the steam vents do that automaticly by
On Thu, 3 Mar 2005 10:52:16 -0600, firstname.lastname@example.org (m Ransley)
I don't know how to say this politely, but you don't know what you are
talking about. Perhaps this website will help educate you.
They are DIFFERENT Systems. The Steam Heat System is the older of the
two. STEAM HEAT VS. HOT WATER (HYDRONIC) CIRCULATING HEAT. THEY
USE DIFFERENT TYPES OF BOILERS. AGAIN CHECK OUT THE WEBSITE ABOVE
Steam Heat = Big cast iron radiators= one entry pipe with a shut off
for the steam. Air bleed with a manual or automatic valve. Operates
at high temperatures.
Hot Water Heat - radiators have an inlet and and outlet pipe. No air
bleeds on the radiator. What you call "baseboard" . Operates at
Medium temperatures (below boiling water).
Sorry beachcomber. You dont know what you are takling about. I have a
house with HW heat 20 large cast iron rads and ALL have air bleeds, Yes
2 pipe, so how do you think the air is removed? Answer by bleading at
the top of the radiator. Im not speaking of baseboard as I said, but
some do have air bleads on them.
I also own apt buildings with one pipe steam, I use Gordon and Dole
vents, Do your research and learn.
This is a hot-water boiler with fin-tube distribution in the living
space along the baseboards (I'm not familiar with steam systems...but
what I here traversing the pipe is water running when the system is
Interesting. I occasionally hear water flowing in my rads but I'm not
sure it's correlated with air build up. Perhaps it is.
The bell-shaped thing is probably the automatic pressure-regulating
inlet, and there should be a backflow preventer nearby or integrated
into the auto inlet.
There should be a manual feed valve just before (upstream of) the auto
inlet. Locate it and see if you can determine whether it's open or
closed. If you're lucky it'll be a ball valve and you can see the
handle position a mile away (inline with the pipe is open, right-angle
to it is closed, on any that you'd expect to find in consumer use in
North America). If it's a round handle you'll have to turn it to see
where it's at; it will of course be seized with years of disuse. The
auto inlets are known to fail (they can stick open or closed) so many
people with them will keep the manual valve normally shut and refill
the boiler manually when they bleed the rads. Keeping it shut also
limits the flood that would result from a leak; with the valve open,
water will flow forever until someone turns it off.
Prior to bleeding, find your boiler's pressure gauge and see what it
says. Lacking any better data, presume that's the correct pressure for
your system. Of course it'll be higher when the system is hot than when
(Nobody on the newsgroup can tell you what yours should be; but if you
post what yours is, someone will tell you that it's too high or too
low. If the gauge is calibrated in feet of head, it should be slightly
greater than the height of your highest rad -- or the attic expansion
tank, if you have such a thing -- relative to the boiler.)
Bleed the highest rad in the system until water appears, then close the
bleed valve and go look at the boiler gauge. Assuming it's down by a
measurable amount, open the manual feed valve and bring it back up to
what it was, then close the manual valve. (If no water ever emerged
when you did the bleeding, even though the air quit hissing, then the
system pressure was too low to fill the higher rads, or you've got a
block somewhere.) Then go over all the other rads, working downwards
through the house.
Works for me. The biggest things that can go wrong are probably the
manual inlet valve seizing open or closed, the auto inlet sticking
closed, the bleed valves breaking off in your hand, or a leak
developing as you disturb some long-neglected component. All of these
are in the category of "it if breaks, it needed fixing anyway" but it's
still a crisis when it actually happens and it's a big job to fix, so
pick a time when a spell of mild weather is expected.
If the system is new to you I'd suggest finding a local outfit that
has deep expertise in hydronic systems and having them come in, maybe
as a pre-season check next fall, to give the system a once-over and
show you how filling and bleeding should work, and getting a
recommendation for correct pressure. Otherwise, bleeding and refilling
should be pretty routine, though ideally not needed frequently.
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