air in baseboard - over and over


  #1  
Old 01-14-03, 01:36 PM
jthompvt
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Question air in baseboard - over and over

I live in northern Vermont in an old (1850's) two story brick house with basement. The house has a c. 1970's oil boiler with hot water baseboard heat. We've lived in it for a little over a year. The heat has two zones - one for the first floor and one for the second floor. Each has a separate thermostat, and a Taco circulating pump off a manifold on the boiler.

Last heating season came and went without a hitch. This season, we keep getting air in the baseboard - sounds like someone flushing a toilet on the second floor when the circulator comes on. A plumber/heating specialist came out, and bled the air out, and explained to me that we SHOULD have about 30 pounds of pressure in the system - made sense to me, since the upper level circuit is about 16' above the furnace, x 2 = approximate pressure...I calculate a little higher, actually... anyway, he got us set up, and left, telling us we'd be fine. I asked what would have caused the air in the lines, and he never gave me a clear answer. Friends had told me in cryptic terms that the air vent needed to be changed, since they only last a few years. I have an amtrol tank above the furnace suspended from the air separation chamber, which in turn has the vent mounted on top of it between our beams. The plumber told me directly that it was working fine, and not the cause of the air.

Since then, we keep having to purge the air about once a week. Very loud, very noisy gurgling, lots of air in the baseboard. AND the pressure in the system seems to keep migrating down to the 12 pound range, despite being jacked up to 20 or more. This takes overnight or maybe two days to drop. Our Amtrol tank is a 12 pound design tank. Is this a coincidence?

Could this man be wrong? Is a tired vent the cause of my problem? If so, in order to change this, do I need to drop the system pressure to nil? Or can I simply unscrew one and screw in the new without reducing the pressure?

Lastly, the circulator pump for the first floor runs continuously. The thermostat (old Honeywell round type for both zones) does not seem to work very well. If it is cold, you can crank it, and do not hear the baseboard "pinging" as you would expect... Are these issues related?

I'd appreciate anyone's help. I'm getting worn out from carrying all those buckets up from the basement each week!
 
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Old 01-14-03, 02:02 PM
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hot water

Need more info here I think.First is the auto water fill turned on?
You say you bleed the boiler. Did you bleed all of the baseboards at the baseboards????????How about the first floor you say no heat there. That psi sounds high to me. The psi there should be what it takes to get water out of the very top baseboard or bleeder and thats all. Buckets from the basement????? You have to bleed the air out from the top Not down in the basement. Dont you think you should get some one in that can show you all about the boiler ED
 
  #3  
Old 01-14-03, 02:36 PM
brickeyee
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A 16 foot high column of water exerts about 7 PSI. If the highest spot of the highest radiotor is inly 16 feet, tyou should be at about 10-12 psi. 30 psi would support a height of 69 feet. The relief valve on your system should be at 30 psi. It sounds like the system has a lot of air and is overfilled to boot.
 
  #4  
Old 01-14-03, 03:48 PM
jthompvt
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We have bled the baseboards at their valves. Never got anything out of them but water. I mispoke when I said we bled the boiler. Each branch of the system has a shutoff valve on the return side of a hose bibb type valve. The plumber cranked the system to get the boiler to full pressure, then shut off each line at the valve near the bibb, and opened the bibb into a bucket. After some water would come lots of air. When all the air was purged, we'd shut off the drain valve and reopen the line. We did that at four locations (all the drains in the basement.)

The only bleed valves that exist on the baseboards are on "dead ends" where the line feeds a run of baseboard and then returns back to the loop. There are only 3 in the house - two on the first floor, one on the second - despite having 16 runs of baseboard total... I thought naturally that we'd bleed the air at these valves. When I took the covers off, only found three....

I didn't mean to say that we have no heat on the first floor - we do, but the thermostat doesn't seem to control it very well. It's never warmer than the thermostat, seems to be near temp most of the time, however if you turn it up, it takes a long time for the ambient temp to catch up...compared to the second floor where the baseboards are audibly working right away.

I thought the formula for boiler pressure was 2x the height between the boiler and the highest run of baseboard...is that not true? The plumber said the boiler should have "at least 20, maybe 25 pounds of pressure to function..."

The automatic fill valve does not seem to work automatically. When we purge the air at the drains in the basement (as Joe Plumber told us to do it,) we open the valve to maintain some pressure. i.e. stem straight up.) Otherwise no water enters the system and the pressure ends up down at about 4 pounds. I thought this valve should be automatic, and the little stem on top was for manual fill mode...am I wrong?
 
  #5  
Old 01-14-03, 05:32 PM
brickeyee
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You are using 'flush' bleeding. The problem is that the new water you are introducing contains disolved air. This air comes out of solution upon heating anfd accumulates at high points in the system and can block water flow.
A correctly installed baseboard system should have a bleed valve at every 90 degree elbow that feeds a section of baseboard.
One atmosphere (15 psi) converts to a water column about 32 feet high. So a 16 foot high system would be about 7.5 psi. The pressure in the system at the boiler when the system is cold should only be a few PSI above this pressure. The pressure will go up as the heated water expands into the expansion tank. The safety vavles is 30 PSI. If you approach this limit it will start to open.
I would get a heating person in instead of a plumber and have him advise you on how to operate the system. Joe Plumber is not a very good heating person.
 
  #6  
Old 01-14-03, 05:48 PM
bigjohn
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I'm afraid I too have to disagree with joe plumber. 12lbs. will take care of a 3 story house, so with the highest baseboard 16 feet above the boiler, 12 lbs. is plenty. Perhaps you're trying to remember that 1 psi = 2.31 feet? So it would be 16 feet/2.31 per ft. = 6.92 which rounds off to 7psi. Are you sure the distance from the boiler water level to the second floor baseboards is 16 feet? Remember, the second story baseboards are at the floor level and the boiler water level is probably 3 to 4 feet off the floor in the basement. If the ceiling height on the first floor is 10 feet, then I suppose 16 feet would be about right. The stem on top of the pressure reducing valve, is it threaded with a stop nut? If so, that is the pressure adjusting stem. These valves usually have a u-shaped bail rod on the side [kind of like the bail rod on a fishing reel] that you lift up for manual fill. These valves, out of the box, are set for 12 lbs. [there is a 45# model but it's not for your applcation] As the other gentleman said, the relief valve on the boiler should blow off at 30 lbs. I think you are leaking water somewhere and air is getting in at the leak as water is going out. A tired vent isn't the problem because you shouldn't be getting air all the time. What happens is vents DO get clogged and need replacing. Now, I'm going to be as tactful as I can, but I need you to put on your thinking cap. If you unthread a vent from a PRESSURIZED pipe, what do think will happen? That's right, the water will come roaring out under pressure and you'll be scalded with 180 degree water. Concerning the poor heating on the first floor, I think that getting the air situation squared away should come first, then start looking into other problems. As a homeowner with a hydronic system, you'll covet this website- www.bellgossett.com
 
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Old 01-14-03, 08:56 PM
jthompvt
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Thanks, bigjohn. My common sense DID tell me that a closed system under pressure should not be opened...hence I have done nothing with the vent....

What history of this house I do know...it sat vacant for about 20 years. A gentleman bought it two owners ago, and attempted to restore it into a bed and breakfast. He hired locals to do the work moonlighting. They used a lot of "experienced" equipment, and did pretty much "shlock" work for him. Everyone in town tells us of the workers pitching their beer bottles out the back windows and than burying them in the landscaping...

I digress... the piping installation in the basement is horrible - a rats nest. Gravity pipes run uphill, the piping around the boiler is such a mess that you cannot effectively reach the aquastats to work on them. When "Joe Plumber" arrived to flush it the first time, he turned the corner and stopped in his tracks, muttering "Oh my god!" when he first saw it. Hence, I can understand perfectly WHY there are no (or at least not enough) proper vents ON the baseboards.) He has recommended that we replace the boiler, which we plan to do after the season is over. We may opt to have ALL of the piping redone to correct this mess, but I was not anxious to have the house torn up to that degree.

Any insight on why the circulator on the first floor loop ALWAYS is running?
 
  #8  
Old 01-14-03, 10:35 PM
bigjohn
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Ah- the plot thickens. The thermostat on the first floor probably operates a relay which in turn controls the circulator. So maybe the wiring is crossed up keeping the relay energized or the relay contacts may be stuck closed. I have a suggestion that I think will pay off for you. Go to www.nhraw.org and click on the Home Study Institute button on the left side of the home page. On the next page, click on the course list. Next page, scroll down and you'll find 2 courses on hydronic heating. The first is a basics course and the second is a design course. Now, you're supposed to be an industry worker, so you'll have to fudge some there. You'll see there are 2 prices. I've always used my local wholesaler as the member reference and so I pay member price. You might have to scout around your area to find a member company who'll sponsor you. Maybe some kind of gentleman's agreement that you'll buy the new boiler from them if they'll help you.. Or, just bite the bullet and pay the higher price. With all the courses I've taken, they've never contacted my employer. I don't know if they contact the wholesaler members. If you have the time to take both courses this Winter, you'll be ready next Summer to at least intelligently talk with a contractor about the design and installation of a new system. Check out the website and see what you think. The other suggestion I have is, if you're going to tear up the house to repipe, insulate, insulate, insulate the house as you go. I can't imagine what your heating bill must be like.
 
  #9  
Old 01-16-03, 10:10 AM
jthompvt
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Thanks bigjohn again. You've clarified many things for me. By the way, we're spending about $240 every 3 weeks or so for oil this year, keeping in mind our oil prices has gone up 25% in the past 6 weeks...

I thought that we would be introducing air in the "refill" water every time we purge the system using the drains in the basement. My lingering question is: When we get the air in the pipes, it SEEMS to appear in mass overnight. Not there Tuesday, wake up Wednesday and it sounds like the pipes are only 1/2 full of water there's so much noise. Does the increase in air mean that water is escaping the system somewhere between purgings? We have no evidence of leaks anywhere, but the pipes REALLY sound like there's only a trickle going through them.

AND - having the air separator chamber and vent above the furnace, I thought these would work to bleed out that air from the water each time it cycles through... I guess once it gets beyond the vent, up into the pipes, it's not coming down under its own force.... It's just that we NEVER had this problem last year, lived here ALL heating season, and this year is the PITS! Why such a difference?

Lastly, our son took up residence in a charming little attic bedroom. There is a radiator up there, but it is not connected to the rest of the system in the basement. The supply and return terminate in the basement. We have a third aquastat and circulator on the manifold for this purpose, but they were never connected together. Would this boiler be able to feed that third floor radiator? Obviously we'd air-test the pipe first to check integrity, and I assume now that a boiler pressure of only a few more pounds would get us there. Is that possible? Probably not recommended givent the other problems, but possible?

Bottom line I'm getting is that the system is the pits. I KNOW I want to replace the furnace - being early 70's, I assume I could just about double the efficiency going to an 80%+ unit. As I suspected, it appears that the entire piping system is the pits too. Of the 3 bleed valves at the baseboards, 2 of them are mounted on the bottom run of pipe - it elbows UP and reverses direction immediately above the bleeder. Even I know that if there's air at the end of that line, I'll never get to it from those valves!
 
  #10  
Old 01-16-03, 05:45 PM
bigjohn
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Well, the air is being released by the water as it heats up. If you don't add water and you shut off the makeup, what happens? Does the boiler pressure go lower and lower untilhe low water cutoff shuts off the burner? If so, you have to be losing water somehwere. How often are you adding water? The extra zone- I agree, you'll want to loop that run together and pressure test it first. Do you know how to solder copper piping? You might want to learn, otherwise the plumber will enjoy his new BMW. You should able to add the new zone. You need to take those correspondence courses. The fuel bill- ouch!
 
  #11  
Old 01-16-03, 07:36 PM
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Pumping away is the answer...

You may have monoflo tees in the system. Air is a constant problem with them when not installed properly. First, the nipple preceding the air scoop must be horizontal, a minimum of 18" to work properly, the water pressure regulator is always on, no need to shut it off, if its set to 12PSI (this must match the air bladder tank charge) make sure to throw away the cap on the auto air vent, people tend to close them which defeats their purpose. Your solution is to move these circulator pumps from the return side to the supply side.
A much cheaper Idea is to read Dan Holohans book called Pumping Away.. it's great. I know what he'll say. If your trying to bleeding air, and don't get any, stop bleeding, it's not an air problem. I did this at a Museum that had these air problems for years, and moving the pumps cured the problem after all the engineers said it was several things. Moving the pumps increased the line pressure and forces any air back to the boiler to be scooped, and vented. We never had to bleed again. Pumping on the return side is a sign of poor engineering. Try it. You might have to run some BX to extend the wire, big deal.
His sight is heatinghelp.com don't loose heart!
 
  #12  
Old 01-19-03, 07:49 PM
jthompvt
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Episode IV - the quest for heat

Well - to follow up even further on our situation...after a night at 20 below zero, we blew two pipes in the heat system. I had inadvertantly left that zone shut off after draining it. My bad. A NEW plumber came out, and patched us up okay. He confirmed we do have a monoflow system with venturi valves to separate each zone. Stated that it is EXTREMELY difficult to bleed the air from this type of system, and that I don't have the air vents that we should have on each zone. He said we should have a vent on the return side of each baseboard, as the water will get turbulent there since it does not want to travel down. This all makes sense to me. He suggested that I get some copper and solder, and practice, as I have already been told.

He also said that our boiler is an old converted steam boiler. He ALSO stated that we need to run the boiler at about 18 pounds - like the first plumber - not the 12 that seems to make sense, and which seems to be the concensus on this site. When he finished patching us up and we got the pipe thawed out, he set the pressure to about 18 pounds. This with the boiler cold. A while later, while sitting with my family in the living room, we heard the rocket take off in the basement, which of course was the pressure releif valve opening, and issuing a bunch of steam and water. Seems we did not get all of the air out of the system after having the pipes open for repairs. I bled a great deal of air from the system. Anyhow, I assume he too was wrong, since his higher cold pressure exceeded 30# when the furnace was at full temp.

My goal is to correct the "monoflow" piping so that each zone flows in its own branch. Right now we have three rooms piped in series from one branch that parallels the main. I also want to install vents in the baseboards to bleed the system properly. AND add the third floor bedroom to the system...

I guess my question is how there can be so many opinions on this...he thought that maybe without seeing the system, that "generalizations" were not accurate...but then again his pressure appeared to be too high. I heard that every 90d elbow should have a vent - he states you only need them on the return side of each baseboard where the hot water is turning downward. Is this accurate?
 
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Old 01-20-03, 09:52 AM
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This whole thread is long and sad. I believe you have been told three times to set the system pressure at 12 psi and I'll make it 4. The math you were given is accurate and every recommendation you got here is valid an sensible. Except for throwing away the cap from the air vent. Keep it loose but handy. On the other hand. The people you are dealing with sound a little under-educated. I don't know how they can work in a climate like yours and not catch on eventually.

You should have a vent on a monoflo system everywhere the flow needs to defy gravity. And bleeding should be done with the circulator turned OFF. The suggestion about correct installation of an air scoop is often overlooked too. If you have a very large quantity of water in the system, you may need a larger or a second expansion tank. Purging the system is an effective way to remove very large quantities of air but won't get 100% of it. The best way to purge is with a short hose connected to the purge drain and submerged in a bucket so you can see when there is no more air with the water. Sight or sound can fool you. Keep posting us and maybe even start a new thread. We can help you to do whats right and avoid the nonsense of Joe Plumber and Co.
 
  #14  
Old 01-20-03, 08:28 PM
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Move the pumps

Try reading some of the stuff on heatinghelp.com and I think you'll find, moving the pumps to the supply will solve the pressure and air problems altogether. It'll cost some sweat & time. Where is your water supply line connected to anyway?
 
 

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