Hot water system - bleeding

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 system.
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?
Thank you, Dave
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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.
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On Thu, 3 Mar 2005 08:34:06 -0600, snipped-for-privacy@webtv.net (m Ransley) wrote:

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 available.
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
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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 closing .
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On Thu, 3 Mar 2005 10:52:16 -0600, snipped-for-privacy@webtv.net (m Ransley) wrote:

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.
http://www.heimer.com/information/heating_system.html#HotWater
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).
Beachcomber
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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.
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Beachcomber wrote:

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 circulating.
Dave
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tom snipped-for-privacy@yahoo.com wrote:

Interesting. I occasionally hear water flowing in my rads but I'm not sure it's correlated with air build up. Perhaps it is.

bleed
questions...
Dunno.
the
another
mechanism
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 it's cold.
(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.
Chip C Toronto
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"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."
The pressure reads 30psi.
Dave
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30 pounds on the gauge? Or is it on the relief?

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HeatMan wrote:

HeatMan, It is on the top of the unit on a gauge that has both the temp and the pressure.
Dave
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The way you were saying it made me think you were looking at the rating on the releif valve...

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