Bleeding hot water radiators - Conflicting instructions

Could not get an answer to this on alt . hvac of all places:
There are many well-intentioned articles on how to bleed your basic hot water radiator heating network.
Most recommend bleeding when system is *relatively* cool(is off or hasn't fired in a while).
Where they differ most is the starting point. Some suggest moving from radiators closest to boiler(1st floor) to the farthest(IE 2nd flr). This site - http://www.ehow.com/how_6382979_do-air-out-heating-pipes_.html suggests the opposite!
Does it matter?
Also, I was told that after a good bleed job none of my radiators should ring like bells when knocked on with my fist. Some of mine do, even though they are evenly heated side-side and top-bottom. Does that indicate trapped air bubbles?
And how do I remedy those?
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On Sat, 19 Jan 2013 21:16:43 -0800 (PST), snipped-for-privacy@gmail.com wrote:

radiators closest to boiler(1st floor) to the farthest(IE 2nd flr).  This site - http://www.ehow.com/how_6382979_do-air-out-heating-pipes_.html  suggests the opposite!  

like bells when knocked on with my fist.  Some of mine do, even though they are evenly heated side-side and top-bottom.  Does that indicate trapped air bubbles?

I've had a couple 2 story houses with hot water radiators, and bled them numerous times. No zone control valves. All radiators are connected in a loop to the supply and return headers. What I would call a "basic" systems. One was natural circulation, the other had a circ pump. I've bled cold and hot. Best to do the bleed with the circ pump running, or hot enough to move the water with natural circulation. Trapped air doesn't care about heat, but water circulation aids in moving air to the highest point. When I've done uncirculated fills I always had to redo the bleeding later in the heating season. You want to at least fill and bleed the first level of radiators before you start the boiler to ensure return flow to the water jacket and pump. It goes like this on a fresh fill. Make sure the system is getting feed water. Open the highest rad vent. Use your judgement on watching it for water. I trusted an upstairs tenant to watch it for me once, and the result was stained walls. You don't have open to open the highest vent, but I found I got faster fills with it open. Up to you. Just don't leave it unattended. Test a radiator on the lowest level until it's full. Then do the rest on that level until all are full. Move to the second level and do the same. Then do a final recheck of all radiators, low to high. Sometimes a slug of air eludes you while you move from radiator to radiator. For bleeding a filled and running system, just start low, and move high. Never heard of the "tone" thing. Sound like voodoo. Cast iron isn't very consistent in producing tones. Not the best thermal conductor either, so it's always been easy for me to feel the difference in heat when there's water or air behind it. So if it's as hot at the top as the rest, there's no trapped air. If in doubt, just crack the bleeder to see. I have, and never got air when the top was hot.
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Thanks for the steps Vic.
I do have one radiator - the second floor bathroom's - that blows out one to two seconds of air before bleeding water, two days after a process similar to yours. I'll bleed em again in three weeks, same 1.5sec hiss of air followed by water. Other radiators up & down piss nothing but water.
Always has for as long as I've occupied the house, before and after a circulator was added as part of a boiler replacement 11 yrs ago.
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On Jan 20, 6:56am, snipped-for-privacy@gmail.com wrote:

It's not actually air. It is hydrogen gas left over from the corrosion going on in your system. http://robuild.co.uk/Corrosion-plumbing.htm
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The air scoop might be it- leave it alone (unsnug) and watch it, and if no more water shoots out, that may solve your problem (it solved mine, although my baseboard radiators don't have bleeder valves).
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On Sat, 19 Jan 2013 21:16:43 -0800 (PST), snipped-for-privacy@gmail.com wrote:

Those guys are "professionals" and don't want to be bothered by the great unwashed. Biggest bunch of a-holes around

radiators closest to boiler(1st floor) to the farthest(IE 2nd flr). This site - http://www.ehow.com/how_6382979_do-air-out-heating-pipes_.html suggests the opposite!

I'd do it both ways. And then I'd go back in a week and do it again. Air can get trapped in places you'd not expect. Check for evenness of heating when done.

like bells when knocked on with my fist. Some of mine do, even though they are evenly heated side-side and top-bottom. Does that indicate trapped air bubbles?

Never heard of that, but it may work.
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If he does it one way and then immediately does it the other way, he'll know if it matters or not. If no more air comes out the second time, then he knows doing it the first time got all the air out. Next time he bleeds he can start in the other direction and repeat the process. If he gets no additional air both times, then it doesn't matter. And if he does, he'll know which way works better.
I would think going from closest to the boiler, moving up floors, would be the preferred way. But it may not make much difference either. The question is if the air tends to remain trapped in the radiator, as opposed to easily moving from one to the next.

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On Sunday, January 20, 2013 9:32:52 AM UTC-5, snipped-for-privacy@optonline.net wrote:

Really appreciate it, guys!
Still, the issue is the hisser in the bathroom on 2nd floor. It's a narrow, taller unit behind the old claw tub. The whole system is bled to the point where I haven't hissed air out of any radiators except that one.
Is it possible that bathroom unit is at a particular "hot spot" where system air likes to congregate? It never hisses more than 2 seconds before water shoots out, so maybe I'm just over thinking.
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On Sunday, January 20, 2013 9:54:16 AM UTC-5, snipped-for-privacy@gmail.com wrote:

"Haven't hiss air out of any radiators except that one - IN TWO YEARS"(correction)
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Is there a tank in the radiator that fills with air, before the air fills the radiator itself? Because unless that's actually full of air (no water left in it) then there's probably no air in the radiator itself and it's not that big an issue as it's designed to keep air out of the radiator. So you wouldn't need to bleed that often. Just enough to keep that from completely filling with air (empty of water).
I'd bleed when cold because any minor benefit (if any) of bleeding hot is more than counterbalanced by the annoyance/danger of burning yourself.
As far as the order? If you're bleeding when cold there's nothing circulating so it probably makes no difference.
Modern systems have a small valve in the basement that releases any trapped air so there's no need to bleed them (my house doesn't have a bleed valve in the baseboard radiators)- don't know if it's possible to install that in an older system (or whether it'd be worth the expense).
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On Sunday, January 20, 2013 10:03:47 AM UTC-5, snipped-for-privacy@brainchampagne.com wrote:

_______________________
Nope. Plain boring York units from the late '20s:
http://www.centerforsocialinclusion.org/wp-content/uploads/2012/12/Household_radiator.jpg No special tanks or other features. Bleeds with classic http://compare.ebay.com/like/350633453538?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar key.
As far as a global bleeder valve in the basement, wouldn't know where that is. Home had new Burnham V8 installed 11 years ago along with circ.
The bathroom rad does get hot, for sure, so I think a 1 and a half second hiss from one radiator after monthly bleeding a houseful is no big deal.
Yes, I do bleed cold(or lukewarm!) and I start in the kitchen(closest run from boiler), work my way around the 1st floor, then upstairs.
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Bleeder valve would be a small can with a small nipple sticking up, if you google it you'll find all sorts of pictures. In my house there was air in the system because somebody screwed the nipple back down so it wouldn't let air out. Took about four or five plumbers before one guy said "Here's your problem" after a bunch of earlier ones kept telling me to empty and refill the system, that there was no way to bleed it.
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On Sunday, January 20, 2013 10:50:12 AM UTC-5, snipped-for-privacy@brainchampagne.com wrote:

Help!!! https://www.google.com/search?q=home+heating+bleeder+valve&hl=en&tbo=d&rls=com.microsoft:en-us:IE-Address&rlz=1I7ADFA_en&source=lnms&tbm=isch&sa=X&ei=ghL8ULKkF4T68QShkoGoDA&ved=0CAoQ_AUoAA&biw=1600&bih=733 !
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On Jan 20, 5:16am, snipped-for-privacy@gmail.com wrote:

All a load of bollocks. You can bleed them in any order. Hot or cold. Whether or not they ring like bells is neither here nor there. You may have to repeat the exercise twice if air gets moved around during the operation
If you have to do this more than once a year, you may have a corrosion/ galvanic action problem. Your system needs to be dosed up with a chemical to prevent this. Very important. Especially with the newer systems that may have aluminium/stainless steel components.
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