Asked 1000 times before but: Purging air from Baseboard?

[HeadRusch]

I've read online how to shut down the system and purge the air from the individual baseboard units in each room...but frankly I've got a lot of those units......and when I last had my plumber in here he said I could just open up one of the values on the return near the Boiler and drain the water out...he said drain until you no longer hear the "spurts" of air coming out, and its just water. Then turn the furnace back on and let it fill itself up again....and rebuild its pressure.

Ok...its worked fine every time over the past few years...except for this time.

For some reason now I think its another zone, because draining some water from my system resulted in a drop in waterpressure (temporarily) but no air seemed to bleed out...this was from the return spigot I usually use.

I've got two other red knobs that are on the return line...a little less convenient for me to reach to, but they're doable..I just have to be careful not to totally scald myself.

As I understand it, the object is to:

1) Shut off the furnace 2) Let the water cool a few hours so I dont burn myself on any blistering hot water (I'll wear gloves just in case). 3) Close the valve swich for that zone (located after the drain spigot on the way to the main return line) so that any water coming out will definately come out of the spigot and not continue on through the rest of the return system, back into the furnace. 4) Open the spigot with either a drain hose or a bucket underneath and drain out the water, or at least a majority of the water until one hears the spurts of air disappear.

Now here's my question: If you drain out the water this way, don't you need the furance ON to provide more water AS the air is being bled out? Or does the automatic refill/leveling of the furnace happen independent of the furnace actually being on or off (ie: turning the furnace "on" really just means turning the heat and electrical relays for the zones on).

I'm kinda confused....and wouldn't mind paying to have my plumber come and show me whats what, but I'd rather not waste his time if I dont have to.

Now my question is this: With the furnace off as I drain off this zone,

[Mark Monson]

You have the right plan.

You turn off the boiler to get the pump to shut off and all the zone valves to open. The water pressure for the purge comes from the compressed air in the expansion tank. The lost water will slowly refill from the Pressure Reducing Valve whether the boiler is on or off.

MM

[HeadRusch]

Ok, here's a followup question:

If I drain a bunch of water out of that pipe, and I then return the system to operational and turn the furance back on, wont the pipe just fill up with air again?

I would think I'd need to let that zone run with the furnace on (pump running) to "Push out" the rest of the air....or again am I relying on the pressure in the accumulator tank to handle that task..

[Gary Slusser]

"HeadRusch" wrote

Just a few thoughts of mine..... If you drain water out of a pipe, air has to enter the pipe/system to allow water out. Otherwise the water will not run out. So if that's the basis of your question.... why do that instead of venting the air out of the pipe? That's what's usually done.

It sounds to me as if you have a fair amount of air in one zone and it isn't being flushed out to be vented. That air is compressible and seems t obe preventing pressure buildup in the system. These type things usually happen when we short cut procedures. You/he didn't want to spend the time to vent each vent, so for years it's been done this way, now it's time to pay up.... usually, there's only one way to do something right and it's specific to the plumbing system with the problem.

Gary Quality Water Associates

Gary Slusser's Bulletin Board

[HeadRusch]

Ok, looks like I need to shut down the furnace and bite the bullet this weekend....venting from the baseboard radiators.

[Mark Monson]

No. You were right the first time. If you have a purge tee on your return you should use it. It is standard procedure to purge hot water baseboard loops to get the air out. You don't need to bleed all the baseboard units.

There are several reason why you could have air in that loop. What is the pressure in the system? How many stories is your building? Is the boiler in the basement? Do you have an air control system or air elimination ( bladder tank) system?

MM

[HeadRusch]

I've got 4 zones on my furnace. Of the 4 zones, I can actually see 3 physical purge spigots, with shut-off values just after them for isolating the "circuits" from the main return pipe. All of them find their way to the main return pipe.

The furnace is a Crane and it's original, so figure early 60's....so far the furnace has run just fine, no leaks, no issues, and while I'm sure I could get better efficiency if I replaced it, it seems to be doing the job. I haven't had it serviced however...wasn't sure if anyone even worked on equipment this old anymore.

When we first moved into the home we saw the pressure spiking as high as

40psi somteimes, which I quickly learned was a bad, bad thing. The pressure-relief valve was supposed to dump at 30.....it must have been rusted shut.

Problem was determined to be a bad accumulator (pressure regulator tank). That was replaced, a new pressure relief valve and offshoot pipe was added, and a new air-release value (the red-capped thing) was installed.

Now the pressure stays steady at around 12-14psi, never goes higher, and only goes lower if I drain hot water from the system (like when the pipes are doing the waterfall or boiling-water sounds and I figure there is air in there). It has stayed this way for 2 years. During the summer I physically shut off the furnace, the pressure dips down to about 8-10 psi......(perhaps this is my problem...standing water evaporating from the air-release valve??).

Typical New England colonial, 3 stories...basement (where the boiler is), first floor and 2nd floor. One zone in basement rec room, two zones on 1st floor (one zone for each "side" of home), and one zone for upstairs bedrooms.

I have a big grey tank that I call, thanks to those engineering classes in college, an Accumulator. SOme call it a pressure regulator. That sits underneath the main "out" pipe from the furnace, before it hits the zone control valves. Above that grey accumulator is a pipe fitting that is raised up, with a new air-relief valve on top of it....its a little cylinder with a red cap on top that I now have set to be very loose (the cap not the valve itself!).

The odd thing is that before, each year when I'd hear a little bit of waterfall or gurgling coming from the pipes, I could just hit one of the spigots....and the water would gush out...blurting with air....the pressure in the system would drop a bit, and I'd stop getting bursts of air...then it would be fine for the rest of the year. There is one "spigot" on the returns that is easy to access, so thats the one I'd use. Its particular to one of the zones.

But whats different *this* year is that when I use the same drain valve I have in the past, I get solid water...no air "pops". Hence I think the air may be more "congrugated" in one of the other pipes in the system, ie: one of the other zones. The only thing that *sucks* is that the spigots for those pipes are difficult to access....well, without burning myself on the other piping around them...I'll have to tread lightly.

For what its worth, I'd love to hear an answer to this....but I've decided to call in the pros. I'm having my Hot water heater replaced (its 16 years old) next week, and my plumber is going to drain and purge the system for me, and show me how to do the same thing myself if I need to again....I'll also have him make sure the air-release valve is functioning.

Could it be shutting off the furnace during the summer months?? Should I instead just drop the thermostats to below 50 instead of turning off the system?

[kenny b]

"The water pressure for the purge comes from the compressed air in the expansion tank."

And your the professional, where's Hot when you need him.

The purge is done with constant high pressure (street main pressure), in theory your making your loop a water line. Call a professional and let him instruct you to the proper method for your system. Systems may very slightly but the basics are the same.

kenny b

[Mark Monson]

Where is street main pressure going to come from? Unless you have a bypass, all make up has to come through the PRV. Not enough flow through the PRV to purge with. What happens is the push comes from the expansion tank and the PRV refills the expansion tank.

MM

Call a professional and

[kenny b]

Where is street main pressure going to come from? Unless you have a bypass,

Street main pressure will come from a bypass or a fast fill such as the B&G- FB-38. You really are a novice at this aren't you. You actually offer a heating service to the public, amazing! Would/could you actually give us some insight to your education in hydronics. Dan's column in PM mag won't cut it. The only reason I responded was due to the bogus info. your passing. kenny b

[Mark Monson]

Or not, which is more common in residential systems.

MM

[kenny b]

Somehow I feel like a conservative talking to a liberal. Keep going through life like you know it all already.

kenny b

[Mark Monson]

Kenny

I never said I knew it all. You said street pressure will come from a bypass or a fast fill PRV. That's all well and good if the house has a bypass or a fast fill PRV. But it's not going to help much with the majority of residential hot water heating systems that DON'T HAVE A BYPASS OR A FAST FILL PRV. In those cases, the purge pressure WILL COME FROM THE EXPANSION TANK, until the slow filling PRV refills the system.

Did you have anything else? I'm all ears waiting to learn something.

Warm regards,

Mark

[kenny b]

Obviously if the system is designed to be purged correctly it will have a way of inducing street main pressure for a constant flow. If not it should be corrected. You state the majority of residentual systems don't have a bypass or fast fill. True but they are not designed to be purged, only a series loop can be purged and it must have a constant swift flow to remove and purge all trapped air. You never asked if the fill valve had a fast fill lever or if a bypass was present, you went right to this is how its done. There's a little more to it then closing the purge valves and draining a bucket or two from each zone at the valves. If he dosen't understand the principle behind what he doing he shouldn't be attempting it and you shouldn't be encouraging him especially with false information. If he's willing to learn, teach him so he fully understands the principle behind what he going to do before he dose it. Mark I'm sorry for jumping on you but I've personally seen the outcome of makeshift work and it dangerous, almost cost a homeowner his life and he was just a bystander while the so called professional was at work. Poor guy caught the full force of the relief valve discharge at 200 degrees as he turned the corner. Not a pretty sight seeing the skin roll off his body.

kenny b

[Mark Monson]

OK. You make some good points. On a list like this people are constantly asking for DIY advice and I agree that many times the best thing to tell them is call a professional. Maybe this is one of those times. I definitely have a problem with telling a DIYfer to touch the bypass valve.

Mark

[Lori & Dean Wigmore]

After reading all the posts, it sounds like HeadRusch has a common diaphragm type expansion tank attached underneath a "boiler scoop" (simple air separator). The top of this boiler scoop will have an automatic air eliminator attached to it. It sounds like all the air is trapped on the higher floors. As the air is usually less dense than water, it will be trapped wherever the piping turns to go down. That is the point to bleed the air from. There is no need to drain water from the boiler, open bypass valves, or cool off the boiler. Just turn up the room thermostat and find the small vent at the end of the run of baseboard. The vent is usually a manually operated device (small coin or screwdriver) but may be a variation of an auto vent. Open the vent slightly and vent the air, using a small container to catch any water. If you can avoid introducing fresh water into the boiler system, eventually all the air will be gone, and you won't have to do it again. I do agree that the water pressure should be higher, though. Ideally there should be around 5 psi at the top floor. Pressure at the boiler can be figured out by taking the difference in elevation from the pressure gauge to the top radiator (in feet) and multiply by 0.434. Take that number and add 5 psi. Set the pressure reducing valve to obtain desired reading.

Dean

[Mark Monson]

First the guy says his plumber, who has been working on this system, told him how to purge a zone without opening a bypass or using a fast fill PRV, but the guy wants to know if the water will be made up without the boiler turned on. So I tell the guy that the PRV will refill the expansion tank slowly whether or not the boiler is on. Then Kenny jumps me for telling the guy he can purge without a fast-fill PRV or bypass like it was my idea. Then Dean, who is smart enough not to weigh in until the dust settles, comes in with a perfect post right on the money. LOL

MM

[HeadRusch]

That would be correct (re. my layout) Upon examining my system, it was determined that my air was probably becoming noticable because of my low system pressure. We introduced more water into the system, but the system pressure wouldn't rise above about 12psi.

We managed to get more water into the system, bringing the standing pressure up to 18psi. No more air bubbles. So far the system is holding at that pressure....it ups to about

22psi max when its running full out, but otherwise its behaving like normal again. no bubbles, no gurgles.

I'm just keeping an eye on the pressure......

[Ned Flanders]

BTW nobody has given the "correct" answer yet.

[Lori & Dean Wigmore]

That's what I love about this group - its both educational AND entertaining!

Dean