Help needed - constant air in hydronic loop in 1950s house.

ptz3233

Hi all, thanks for your time.
About a year ago I bought a fixer-upper 1950s house in the northeast.
I have cast iron rads in the 1st and 2nd floors, and copper with fin baseboard in the basement.

1st and 2nd floors are on one loop, basement is on another. I've only ever turned the basement loop on twice, to test.

When I was fixing up the house, I had a plumber replace the original 1950s boiler with a new one.
Ever since moving in, I have not been able to eradicate the noise of gurgling and bubbling in the pipes.
It gets way worse as it gets colder and the boiler works harder.
I have bled every radiator many many times, I only ever get a clear stream of water. Even after bleeding multiple gallons at a time, the air persists.

I have also purged the loop with the purge outlet the plumber installed.
One thing I noticed is that the system seems to be running in reverse, have old style monoflo tees under the rads in the basement, and according to the marking on those tees, the water direction is wrong. I'm not sure wether this is an issue or not, the system has no problem heating the house, it can just get very loud with all the gurgling.


My circ pump is on the return under both of the zone valves, and above the pump and below the zone valves is an automatic air vent. The cap is screwed on loosely. I suspect the placement of this air vent may be allowing it to suck in air when the pump runs hard, but I cant confirm this. I have closed the cap on that and let the boiler sit with the pump and heat off to see if I could get the air to rise to the top floor but still see a clear stream of water. The only thing that could be a clue is that the water seems "fizzy" when bleeding at the top floor bathroom rad, it seems this rad receives the most pressure.

I'm wary to keep bleeding and purging, as I know the older the water the better, and new water could start corroding the old cast iron rads, and introduce its own microbubbles.

Any help would be appreciated - this noise is driving me absolutely crazy (Im sure some of you can relate)

EdTheHeaterMan

The new boiler's near boiler piping is at fault, I'm sure. send pictures of the boiler piping from several angles so we can see how the pipes enter and leave the boiler.

Mono-flo in reverse may add to the problem

This publication will be helpful in describing your problem to the installing contractor.

read page 9, Zoning with circulators (First a Word on "Pumping Away")
https://documentlibrary.xylemappliedwater.com/wp-content/blogs.dir/22/files/2020/01/FH-Z100B-BG-Zoning-Made-Easy-2.pdf

For future help with problem-solving, see if you have any pictures of the old system, maybe from an inspection when you purchased the home. This will help in proving the boiler was installed incorrectly. the old system may have had an air removal or air management device in the system

ptz3233

EdTheHeaterMan said:

The new boiler's near boiler piping is at fault, I'm sure. send pictures of the boiler piping from several angles so we can see how the pipes enter and leave the boiler.

Mono-flo in reverse may add to the problem

This publication will be helpful in describing your problem to the installing contractor.

read page 9, Zoning with circulators (First a Word on "Pumping Away")
https://documentlibrary.xylemappliedwater.com/wp-content/blogs.dir/22/files/2020/01/FH-Z100B-BG-Zoning-Made-Easy-2.pdf

For future help with problem-solving, see if you have any pictures of the old system, maybe from an inspection when you purchased the home. This will help in proving the boiler was installed incorrectly. the old system may have had an air removal or air management device in the system

EdTheHeaterMan, Thanks for your reply. I have attached many pictures of the piping around the boiler, and a picture of one of my monoflo tees. Reading that brochure definitely makes it seem like the circ should be on the supply. I do wonder if thats the "full" problem however.

Canucker

Your air vent pictured in the second last pic is almost useless in that position. It would be a good spot to connect the expansion tank though. Currently there is no reason for the air to travel up that pipe to the vent

ptz3233

Canucker said:

Your air vent pictured in the second last pic is almost useless in that position. It would be a good spot to connect the expansion tank though. Currently there is no reason for the air to travel up that pipe to the vent

Thanks for your reply - where do you think a better place for the air vent would be? Im guessing on the supply side

I was able to find a picture of the old boiler, it does not seem to be clear enough to tell what is really going on however.

Canucker

@ptz3233 they make scoops for vertical pipes and yes, it should be on a spot where the hottest water passes through it. This is an example
https://www.caleffi.com/usa/en-us/catalogue/discalr-air-separators-vertical-or-horizontal-pipes-brass-551705a

SuperTech

Looking at your boiler pictures,  it reminds me of the way I found the boiler piping in my home done. The boiler has a 1-1/4" supply that runs down the middle of the house to a wye, then it splits off to 1" copper pipes that feed the cast iron baseboards in a reverse return setup. Two 1" pipes return to the boiler.  
I was quite surprised to find out that the venturi tees were facing the wrong direction. I'm thinking that it was a split loop monoflo design that may have been changed to two pipe reverse return at some point. When that happened or when the guys installed the current boiler they may have changed the supply direction.  

Now its primary secondary, I've tried circulating both ways, it doesn't matter. The venturis cause a pressure drop and flow either way. 

Ironman

Get rid of the auto vent: it's worthless in that place. Connect the expansion tank to the Tee above the pump where the vent now is. It can mount in any position. Set the fill valve and the air pressure on the tank to 15 psi. You have to do the tank air pressure with no water pressure on it. When you have it disconnected would be a good time.

You could put a vertical MBR (air separator) on the supply out of the boiler if you wish, but it's really not necessary since any air that it doesn't catch on the first pass will go to the top of the cast ion rad's and have to bled manually. Standing CI rad's are the best air separator ever invented.

Do these things and your problem will be gone.

EBEBRATT-Ed

The mono flow tee you took the picture of. Which way is the water flow in the main? With the arrow or against it? Also the branch pipe coming off that mono flow tee is it connected to the radiator supply or return?

BTW I have seen mono flow tees with arrows pointing in both directions. One arrow used if you mounted the tee on the radiator supply pipe and the other when it is used on the return

ptz3233

EBEBRATT-Ed said:

The mono flow tee you took the picture of. Which way is the water flow in the main? With the arrow or against it? Also the branch pipe coming off that mono flow tee is it connected to the radiator supply or return?

BTW I have seen mono flow tees with arrows pointing in both directions. One arrow used if you mounted the tee on the radiator supply pipe and the other when it is used on the return

The arrow is going opposite the direction of flow, and it seems the tee is connected to the return of the rad.

I have actually seemed to have success with purging the system completely and running it both while keeping the autovent closed. This may confirm my suspicion that it was sucking air into the system in the position it's in.

Moving the expansion tank will probably be the next thing I try, this may have to wait for the spring though. A wise man has told me that if the house is warm then don't go taking apart the boiler in the winter...

MaxMercy

ptz3233 said:

A wise man has told me that if the house is warm then don't go taking apart the boiler in the winter...

Amazing how things that are so obviously logical, like not taking apart a working boiler in the winter or not jumping out of a good airplane etc. get ignored..

EBEBRATT-Ed

@ptz3233
agree with not disturbing things in the winter if you don't have to.

Did someone reverse the supply and return connections at the boiler??

ptz3233

EBEBRATT-Ed said:

@ptz3233
agree with not disturbing things in the winter if you don't have to.

Did someone reverse the supply and return connections at the boiler??

It looks like that was the case, I'm guessing my plumber did that. But it could've been a plumber before I owned the house who had it that way on the old boiler too.
To see the direction of the tees I had to scratch off a few layers of old paint.

From what I remember before I started working on the house, the boiler was original, and looks like a second loop was added when the basement was finished, and there was a circ per loop.

hot_rod

Yes it is quite possible to pull air into an auto vent, lock down the cap or remove that Amtrol vent.

EdTheHeaterMan

On a monoflo tee, the preferred connection is to put the tee on the return of the radiator (or emitter) and make the water flow in the direction of the arrow.

The opposite will also work. place the tee on the supply and make the water flow in the opposite direction.

My guess is the air vent at the location so close to the intel of the circulator pump will allow the pressure to get low enough for air to enter the vent. one point to consider is that every pressure change happens over time. the outlet of the pump increase in pressure and the inlet of the pump decrease in pressure happens immediately upon the start of the pump. It takes time to equalize throughout the system. Only a second or so, but it does take time. In that initial shock of the startup, the pressure may drop below 0 PSIg for that split second.

You can actually see this phenomenon can be witnessed if you have a gauge on the system. when the pump starts, you will see the gauge move past the operating pressure on startup, then quickly bounce back to the operating pressure

During the surge, air will be allowed to go into the system on every start-up of the pump thru the air vent. That air is then distributed throughout the piping and make the annoying noise you are experiencing. Get rid of the air vent. if you have bleeders on the radiators, let the air out at the radiator bleeder location.

This will add less air than trying to flush or purge the air out at the boiler.

EdTheHeaterMan

In looking at the old system, there was a path for air to leave the system and find its way to the expansion tank. see the parts indicated in the attached picture


There is another point of concern. The 1" zone valve will only allow about 4.5 to 5 gallons per minute (GPM) to flow in the 1" pipe. This is due to the restrictions to flow designed into the valve. When the system was zoned by circulators, the flow rate could be as much as 8 GPM. As long as your system does not require more than about 45,000 BTU of heating capacity in that zone, there will be no problem. If however, the zone requires 60,000 0r 70,000 BTUs on the cold days, you may notice a reduction in the ability to heat the zone, This will show up in the radiators furthest from the boiler supply pipe.

You may want to keep detailed records of the air noise and the temperature during the colder days (or nights, when it is colder) Get yourself an accurate thermometer and record the individual room temperatures and compare it to the thermostat set point. If it is consistently the correct temperature during the mild weather and the room temperatures begin to become noticeably cooler during the extreme temperatures, you will be wise to have these records. Record the outdoor temperature each time you record the indoor temperatures.

Other than the obvious design flaws, the job looks like he did a good job. Craftsmanship I would give him an A Design is would give him a C-. Reading the instructions I would give him an F

ptz3233

EdTheHeaterMan said:

In looking at the old system, there was a path for air to leave the system and find its way to the expansion tank. see the parts indicated in the attached picture


There is another point of concern. The 1" zone valve will only allow about 4.5 to 5 gallons per minute (GPM) to flow in the 1" pipe. This is due to the restrictions to flow designed into the valve. When the system was zoned by circulators, the flow rate could be as much as 8 GPM. As long as your system does not require more than about 45,000 BTU of heating capacity in that zone, there will be no problem. If however, the zone requires 60,000 0r 70,000 BTUs on the cold days, you may notice a reduction in the ability to heat the zone, This will show up in the radiators furthest from the boiler supply pipe.

You may want to keep detailed records of the air noise and the temperature during the colder days (or nights, when it is colder) Get yourself an accurate thermometer and record the individual room temperatures and compare it to the thermostat set point. If it is consistently the correct temperature during the mild weather and the room temperatures begin to become noticeably cooler during the extreme temperatures, you will be wise to have these records. Record the outdoor temperature each time you record the indoor temperatures.

Other than the obvious design flaws, the job looks like he did a good job. Craftsmanship I would give him an A Design is would give him a C-. Reading the instructions I would give him an F

Thanks for all your insight, this is starting to make more sense to me. I purchased a copy of Dan Halohans book to educate myself some more. I am still crossing my fingers because I have not heard any air since closing the air vent.

The true test will still be when the extreme cold comes in the next few months. This system was installed last year, but I was not living in the house at that time because of the renovations. It was kept at 55ish all last winter.

Im not hearing any air in the pipes but I have a feeling there still is some at the rads, I think the problem may be that because the system is in reverse the bleeders are on the supply side of the radiators, but that may not matter.

hot_rod

@EdTheHeaterMan zone valve restriction?
Most 3/4 and 1" ZVs are 7.5- 8 Cv.
The large the WR are 11- 13. That really should not reduce flow as long as the circ can overcome a 1 psi drop at 8 gpm?

Unless someone installed a 1 or 2 Cv zone valve, by mistake

ptz3233

Hi all,
i moved the expansion tank to the return above the pump as some forum members suggested. But now I have a concern about the pressure the boiler is running at. It seems that even when the water was cold the boiler pressure was about 20psi, which seems to be higher than what my PRV is labeled (15). And when I run it it seems to creep all the way up to about 30 but haven’t blown the PRV yet. The system is sure running quiet though which is nice. I wonder if the plumber who installed possibly raised the pressure on the PRV but I’m not sure as I never paid much attention to the pressure before messing with it myself. I am considering moving it back because I would hate to flood my basement, thoughts?

mattmia2

If the pressure rises that much between cold and hot your expansion tank needs some sort of attention(it may be where the air came from in the first place).

hot_rod

It could be the fill valve is creeping up, isolate it if you can.
Or the expansion tank is not pre-charged properly, undersized, or failed.

As far as air, either it has not been adequately purged to get it all out, or air is getting in somewhere.

mattmia2

Is it increasing from 20 to 30 with the boiler heating, or does it stay at 30 even after it cools?

ptz3233

mattmia2 said:

If the pressure rises that much between cold and hot your expansion tank needs some sort of attention(it may be where the air came from in the first place).

I would guess I started at 22ish when cold and made it up to 29 when it was at 180 (the boiler turns off at this temp). Although after running it at full call for heat for a while the pressure seems to have stabilized somewhere around 24. 

hot_rod

Do you need 22 psi? The static fill pressure is used to push water to the highest point in your building for a 2- 3 story building 12- 25 psi should be adequate.

If you fill to 22, then the expansion tank also needs to pre-charge to 22 psi.
Also higher operating pressure reduces the expansion tank ability to absorb the pressure increase as the boiler heats up.

ptz3233

hot_rod said:

Do you need 22 psi? The static fill pressure is used to push water to the highest point in your building for a 2- 3 story building 12- 25 psi should be adequate.

If you fill to 22, then the expansion tank also needs to pre-charge to 22 psi.
Also higher operating pressure reduces the expansion tank ability to absorb the pressure increase as the boiler heats up.

I have a 2 story house with boiler in basement, according to some rough calculations, I shouldn't need more than 15 psi. I think its possible the plumber raised the system pressure when he installed last year. There was a problem with one of the rads in the 2nd floor and he tried all sorts of things to get it going (turned out to be bad valve).
I have a hunch one of the things he tried was raising the pressure.

Im going to keep an eye on it tonight - then tomorrow when its warmer outside ill let it cool and see about adjusting that PRV.

I will note that since moving the tank, I have not heard any air noise since the initial start up - at this temp before it would sound like a thunderstorm is in my walls. I was able to go up to the upstairs rads and bleed - and air actually came out.

bburd

Expansion tank sizing is calculated from the total quantity of water in the system.

That small bladder type expansion tank looks rather small for a system with cast iron radiators, which hold a great deal more water than fin tube does. That could account for that wide pressure fluctuation, which is abnormal.

The old boiler had a ceiling mounted compression tank that appears to be of larger capacity.

HVACNUT

If the contractor piped the monoflo loop reverse of what it originally was, then that must be changed.
And since that must be done, they might as well use "pumping away" while they're at it. Maybe recommend Dan's book to them. 
What's the condition of the bleeders on the CI rads? If it wasnt done already, it might be a good time to replace them as well.

ptz3233

I lowered the feed valve pressure to around 13 psi, which seems to be what the expansion tank is charged to. Pressure still seems to jump around a bit but nowhere near 30 psi.

Thanks everyone for all the help. At one point I figured I was over my head working on this myself so I got a quote from a trusted contractor found on this site to repipe the boiler, and it became very clear to me that good work costs good money. It wasn't in the financials for me to do that at this time so these temporary fixes will get me through this heating season, and I will spend some time this summer making some other more risky changes.