pressure issue with a newly installed boiler

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Guy in DC

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Thanks John. Could you please explain what you mean by "If you want to monitor pressure the point where the full valve, sep., and ex"?
 

John Gayewski

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Also, do you think that the expansion tank is large enough (extrol #30?)?
The way I size them is to figure thy system water volume. Your piping looks huge and is probably why your having trouble keeping the pressure down. That pump is probably oversized also which does contribute.

Do you know your systems volume?
 

Guy in DC

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I don't know exactly what the system volume could be. I assume based on large cast iron radiators, pipes, around 200 gallons.
Before replacing the boiler, the expansion tank was #15 (and I changed to #30) and it worked fine. The pressure was 12 psi when cold and ~20 psi when 170F.
 

Guy in DC

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John, one more question: In my house, the upper most radiator is 20 feet above the boiler, should the expansion tank be charged to 20ft x 0.433 = 8.66 psi and add around 5 psi so targeted around 14 psi?
 

John Gayewski

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If your system does have 200 gallon it that's a little over 5 gal of water increase in size as the system changes from 60to 170 degrees.

I don't know why your sytem as acting differently than before. The smaller expansion tank shouldve been too small. Something besides just the expansion tank must have changed.

Do you have a coil or indirect water heater?
 

Guy in DC

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Neither indirect or coil.

Before, the expansion tank was at the return size, if it is matter. the pump was directly mounted on the boiler supply.

For the the expansion tank: I can change from #30 to #60. However, I am confused about the maximum acceptance volume: https://www.amtrol.com/wp-content/uploads/2022/05/MC4400_04_22_Submittal_Data_Book-37.pdf

It is said that an EX-30 tank volume is 4.4G with max acceptance factor .57 so 2.5G; and an EX-60 is 6.7G with .4 so 2.7G, respectively. Does it mean that the EX-30 can accept the same volume as the EX-60? If so, why to install bigger if the smaller is almost the same?
 

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Neither indirect or coil.

Before, the expansion tank was at the return size, if it is matter. the pump was directly mounted on the boiler supply.

For the the expansion tank: I can change from #30 to #60. However, I am confused about the maximum acceptance volume: https://www.amtrol.com/wp-content/uploads/2022/05/MC4400_04_22_Submittal_Data_Book-37.pdf

It is said that an EX-30 tank volume is 4.4G with max acceptance factor .57 so 2.5G; and an EX-60 is 6.7G with .4 so 2.7G, respectively. Does it mean that the EX-30 can accept the same volume as the EX-60? If so, why to install bigger if the smaller is almost the same?
The reality is that more pressure is better for your system. The boiler itself, not so much, but it can handle plenty. The old setup probably had the suction side of your pump taking pressure off of the boiler. The new system delivers the full pressure of the pump to the system piping driving out air bubbles and moving them through to the seperater. This is good and makes the system service easier as it's not so hard to remove air.

I've not dug into the weeds on some of the finer points of expansion tanks, but maxing them out isn't good. If you need a 5gal. and the 4 isn't working then get the 6. I think your expansion tank will be more comfortable and last much longer if it's not being pushed to the max. This is just my opinion.
 

Fitter30

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200 gallons 120°f 60°to 180°. 6 gallons the increase in volume that why your pressure is going up. Since 200 gallons is a guess might want to up size it. Still have the old plain steel tank or a good guess of its size?
 

Guy in DC

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The reality is that more pressure is better for your system. The boiler itself, not so much, but it can handle plenty. The old setup probably had the suction side of your pump taking pressure off of the boiler. The new system delivers the full pressure of the pump to the system piping driving out air bubbles and moving them through to the seperater. This is good and makes the system service easier as it's not so hard to remove air.

I've not dug into the weeds on some of the finer points of expansion tanks, but maxing them out isn't good. If you need a 5gal. and the 4 isn't working then get the 6. I think your expansion tank will be more comfortable and last much longer if it's not being pushed to the max. This is just my opinion.
Thanks John. I will go for a slightly larger tank allowing more space when expands. I've just called Amtrak and the tech calculated the proper tank - they recommend EX90.
You mentioned -
"more pressure is better for your system"
Would it hurt the system and the pipes if the pressure is continuously high (meaning around 25 psi). Coming from a medical field, high pressure is a silent killer :)
 

Guy in DC

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200 gallons 120°f 60°to 180°. 6 gallons the increase in volume that why your pressure is going up. Since 200 gallons is a guess might want to up size it. Still have the old plain steel tank or a good guess of its size?
Thank Fitter30. Previously I had EX-15 2G and it worked fine. However, as John suggested, it was a different configuration and the pump was smaller.
 

Fitter30

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Doesn't make sense the installed tank is 2.7 gallons larger than the 2 gallon tank you stated. What size was the old boiler? Was it the original to the house or 80 years old probably converted from oil. There is no way that a 2 gallon ex tank was in the old system. They never made them back.then and on one would of removed the old tank in mounted in the rafters.
 
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Guy in DC

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Doesn't make sense the installed tank is 2.7 gallons larger than the 2 gallon tank you stated. What size was the old boiler? Was it the original to the house or 80 years old probably converted from oil. There is no way that a 2 gallon ex tank was in the old system. They never made them back.then and on one would of removed the old tank in mounted in the rafters.
It was a 2G tank. The previous boiler (with pictures are in this post
https://terrylove.com/forums/index....r-system-plumber-in-washington-dc-area.85119/
I think that the boiler was max 150-160K BTU. It was installed in the house early 90.
The new one is smaller X-205 Burnham.
 

Guy in DC

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John Gayewski

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I am looking at the old boiler: the tank and the pump were installed in a return pipe. Does it make a difference for the size of the expansion tank?
The beginning of that post says the relief valve opened previously so it seems like this was a problem before.

The pump being on the return piping would lower the dynamic pressure on the boiler, static pressure would be the same based on elevation in the system.

Your expansion tank WAS replaced prior to the 2 gal one you had more recently. The original one was probably big and in the rafters.
 

Fitter30

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Doesn't matter if pump is before or after boiler because the pump is a circulator just moves water around rather than like a well pump that takes a few pounds of pressure and raises it 50 to 100's of lbs. There is no problem if the pressure is a few lbs high. Boiler relief valve with blow off at 30lbs.
Heres a chart for working and bursting pressure for black pipe.
 

John Gayewski

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Doesn't matter if pump is before or after boiler because the pump is a circulator just moves water around rather than like a well pump that takes a few pounds of pressure and raises it 50 to 100's of lbs. There is no problem if the pressure is a few lbs high. Boiler relief valve with blow off at 30lbs.
Heres a chart for working and bursting pressure for black pipe.
It does matter. These pumps do create some pressure just not as much as a well pump. If you throw a baseball against a wall there is no pressure pushing the ball becuse it in the air. Velocity makes the pressure. The suction side of the pump will be negative pressure, if the suction side of the pump is on the boiler, the boiler will be at a lower pressure than the rest of the system.

The expansion tank negates the pressure change created by the pump, this is why we pump away from the ex tank, the pressure cannot change there so the system stays at higher pressure driving air out of the system rather than pulling on a bubble and making it bigger, we push it and make it smaller.
 

Guy in DC

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The beginning of that post says the relief valve opened previously so it seems like this was a problem before.

The pump being on the return piping would lower the dynamic pressure on the boiler, static pressure would be the same based on elevation in the system.

Your expansion tank WAS replaced prior to the 2 gal one you had more recently. The original one was probably big and in the rafters.
John, if you refer to the pressure relief valve opening I described in the old post, it was a different issue: the autofill valve was broken.

Would you advise to change the extension tank for a larger then?

Also, someone told me that the entire system was not properly vented so I might have some air inside, which induces pressure variation? Would it be a problem and if so how to fix it?
 
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