Bleed on Supply or Return

Josh Schneider

I'm ashamed to be asking this question as I get ready to reassemble my parallel, direct-return hydronic system with a new boiler, mains, TRVs, and controls - a project that's taken me months. I'm just now noticing that the radiators were previously installed with bleed valves on either the supply or return side, more often on the supply (including on two connected loops of baseboard). I'd begun to assume all the bleeds were on the supply, and that this was correct. Now I'm convinced vents should always be on the return. My question is, Does it really matter? I'm also adding a scoop and vent at the new diaphragm expansion tank, in case that makes a difference. TIA for any advice.

Steamhead

Bleeds should be on the return

since the water flow moves the air that way.

Are you going to Pump Away when you reassemble that system? If you're not familiar, Dan has written a very good book on the subject- order it on the Books and More page of this site.

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Josh Schneider

So I should turn rads around

to place all the bleeds on the return, and repipe the vent elbows in the baseboard to be on the return side of each loop? I'm wondering why there was inconsitency in the first place, but it must be because some rads were removed in the past to work on the floors, and then replaced incorrectly. I assume the original plumbing, ca 1900, was done right, but who knows.

If it isn't absolutely critical to bleed on the return side, I'd rather not put the ugly side (ie, drips of paint over the original iron finish) of about half of the rads facing outward. I'd also like to avoid replumbing the baseboards. But if that's best, that's what I'll do. More comments please, thanks.

Yes, I am pumping away, with the old B&G 100 placed horizontally right after the feed/expansion/air purge assembly.

Dan Peel

bleeding

If you bleed only when the circulator is shut off the bleeder placement can be either end of your rad. Dan

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mellow

On A direct return piped boiler, the pipes to each radiator should have valves, right? This would make balancing much easier. I know the TRV's might be used this way but if you can shut off each radiator you can bleed everthing at the boiler. I don't know what you have for a system but power purging sounds better than bleeding radiators.

Josh Schneider

Getting more interesting

Thanks for the extra input. My system's going to have the TRVs (I've got 'em), as well as a little overkill mechanism on each loop -- a combo full-port ball valve (for shutoff and/or balancing) and purge/drain valve, which I have to put right above the Tees to the new return main, given the layout of the old system. I'm using an outdoor reset to control the boiler, so the pump will run constantly all winter. I've also got many automatic float vents for the rads, but haven't installed most of them yet. I don't know if they'll be more of a problem at this point, but I hope they'll just constantly let any accumulated air out of the system, all year round, circulator on or off. Does this make sense?

Mellowman, can you explain what you mean by power purging? I'm clueless. Thanks.

Josh Schneider

No need to explain power purging

I see what you're talking about. More comments on rad venting welcome, thanks.

john_24

autovents

id probably recommend a sprirovent or its equal at the boiler rather than auto vents at the rads. Ive seen the mess the autovents can make when installed in the livung area. just my opinion but auto vents in the attic on hydro air or rads in the living area are a leak waitin to happen.

John

Mike T., Swampeast MO

HOLD ON...

With standing iron WATER radiators it doesn't matter WHICH side the bleeder is on as long as it is at the TOP! They fill from the bottom up so it makes ZERO difference on which "side" the bleed valve is installed.

TRVs however DO CARE. If you install one on the return side and haven't oriented the flow direction you'll get noises--bang--bang--bang as the valve tries to close once the valve starts to be satisfied. Trace your lines carefully! With the valve wide open you won't be able to tell that there is a problem.

The "power purge" thing is for systems (or EXLUSIVE zones) using tubes for emitters, like radiant or baseboard. It's a way you can pipe the system such that you can fill everything from by the boiler without bleeding air in other places. It DOESN'T WORK with standing iron!!!

Since it sounds like you have a "mixed" system with standing iron and baseboard, ideally the baseboard will be on a separate loop that can be isolated and "power purged".

Josh Schneider

Already have scoop and float vent

Is a Spirovent that much better than an air scoop and vertical float vent above the expansion tank? I looked at one, but didn't think I wanted to spend the extra bucks. What auto vents have you had problems with? I've got Watts.

Josh Schneider

To MTMan

Hi, Mike. You gave me some advice earlier on, thanks. Well, I was going to make sure all the TRVs are on the supply, so that's not a prob. On some rads, and one loop of baseboard, the TRVs will be on the same side as the bleed valve, if I leave everything as is. That is, some bleeds will be on the supply. If that's okay, then good. As I said above, I'll have each loop able to be isolated using a ball shutoff and purge on the return, so I could power purge the baseboard alone each season. This sound right?

john_24

air scoop

air scoops work well but in my opinion they are nothing compared to a spirovent. I also havnt found a brand of auto air vent that wont leak eventually.

Just my opinion
john

Josh Schneider

Vents

Thanks for the info.

mellow

Power Purge- The best,fastest,chepest and most effective way to bleed any boiler. Dan's book Pumping Away realy explains this well. The boiler must be piped right to do this but it's worth it. Dan also recommends a spyrovent on his piping. I use them every time I pipe and they are well worth it. I realy wish everyone knew about him and his books. His book Pumping Away is the basics for anyone that dares to enter the BOILER ROOM.

Josh Schneider

Pumping away and power purging

Since I'm pretty late in the game, I might not be checking out Dan's book just now. I have looked at another of his books (mostly radiant flooring) and read lots of what he says on this site. My Siegenthaler book has been my resource, and so I have my feed going into a tee on the supply right by the boiler, which itself attaches to the expansion tank and air purge (right now, a scoop and float vent - could be a spirovent). The pump comes right after that. This is pumping away, as I understand it. Does Pumping Away's design differ from that?

mellow

To mister HOLD ON

Question- If copper is in A loop the water will push the air through. If steel is in a loop it will push the air through. So if the piping is right, why do you say it don't it work? It works great on ALL, yes I mean ALL my JOBS.

Mike T., Swampeast MO

Even though young, I use "old" terminology. Standing iron: the old-fashioned tall iron radiators--NOT iron baseboard.

The standing iron radiator systems don't work that way. The pipes aren't the problem, it's the radiators themselves.

If you have some way of bleeding two-pipe standing iron systems from the basement please share!

Josh Schneider

Your opinion

Mike, what's your opinion on a basic scoop and float vent versus a spirovent? What about auto vents on the rads or baseboard? Problem waiting to happen?

Mike T., Swampeast MO

Can't say. All the systems I've worked on either had no air separator or used the one built-in to the boiler. The built-in variety seem to work fine with the flow volume in this sort of system. The ones without seem to wind up with the air where it's supposed to be (the tank)--eventually. If using a plain tank, install a B&G air-trol fitting! Again, all the systems I've worked on still use their original plain tank.

Absolutely no experience with auto air vents either. I've seen their literature and how used, but can't really comment. Sorry.

mellow

very old radiators

Yes you have to bleed very old and very large radiators. I would pipe so you could get most of the air out of a hose and not a coin vent. This would the best way Right? The radiation was never sugested but everything you can do helps. I have had some radiators that you can't reach get heat and work great from the B room. Not looking for a fight just some ideas. thanks good luck.

Mike T., Swampeast MO

Certainly not looking for fight

I was "shouting" because I didn't want him to turn his standing iron radiators around just to put the bleed valve on the return side when it makes absolutely no difference!

Thought earlier that he was talking about standing iron, but he also mentioned baseboard. Then with the comment about "exposing the paint drips on the back" I KNEW for certain.

Josh Schneider

Sorry for the confusion

Yep, you're right, I'm talking old, old, old American Radiator Company, standing units. Only one room has fin-tubed baseboard. I'm still thinking about the merits of a Spirovent and auto vents on the rads. Adding to my embarassment, which started this whole thread, I just realized that the float vents I have must be mounted vertically. I wondered when I got them a while back, but now it just hit me. I know disc-type auto vents are prone to some leakage, and I've heard some float vents will mount horizontally, so I'll be looking around.

Thanks for all the help, and I won't be turning around any rads!

Mike T., Swampeast MO

Josh

How you will purge the air from your baseboards is going to depend on how everything else is piped. The best advice I can give is "think like water".

I just hooked up my radiant shower floor. Because of the way it ran into the mud base the supply lines had to loop up and down to make their way in... NOT the "good" way for purging the air in a hydronic heating system, but the "only" way I could design that didn't penetrate the membrane in the floor itself.

Ball valve and plain air bleed on both supply and return. Filled with both valves closed, then opened one valve and bled from the OTHER side. Then closed the first valve, opened the other and bled again from the opposite side. There WAS an "air slog" in this second venting by the way.

Ran circulator only for about 24 hours and bled again. Water only--no air. I just hope it stays that way and I don't have to use my first automatic air vent!

Josh Schneider

Purging baseboards

Well, I guess I'll have to study this matter a bit. As it is, I think I'll do a little doctoring and add vent elbows at the return end of each fin-tube segment (there are two segments, piped on one loop, so sharing one supply and one return). There'll be one of those combo ball balancing/shutoff/purge/drain valves on the return end (in the basement), and a TRV on the supply, just before the pipe does a 180 and the fins begin. If I shut off all other circuits, I should be able to try power purging of the baseboard circuit. Otherwise, the Spirovent sounds more and more attractive. I'd like air extraction to be as automatic as possible.

Thanks again for your help.

Josh

Tony_8

that's it

and trade in those float vents for a Spirovent. You won't need 'em with a Spiro in place. It ain't called a air resorber for nothin' !

Josh Schneider

Built-in air separator?

Never heard of this. My new Viessmann Vitogas doesn't have one, that much I can say. I'm using a diaphragm expansion tank, and I think that's not what you mean by "plain." That's why I'm talking about a scoop and float vent or a Spirovent. This make sense?

Josh Schneider

Might be sold

Everyone talks up these Spirovents, so I'm looking into one tomorrow. Home Despot'll probably even take back the scoop if I clean off the pipe compound. Two of the float vents can go on my baseboard loops, though.

Josh Schneider

Off Topic - Flow Check

This is off topic in this thread, but one more question. With TRVs, new mains, one pump (always on during heating season), and an outdoor reset, do I need a flow check valve for any reason. Seems to me I don't, but any other thoughts? Thanks.

Tony_8

what for ? (nm)

Josh Schneider

I assume that means no

Thanks

Tony_8

correct