HO sizing question on boiler expansion tank

[Deleted User]

My Extrol Model 30 bit the dust over the weekend.  It looks like it rusted through and developed a pinhole sized leak.

 

As I was looking up replacement pricing online, I came across some literature on Amtrol's website that leads me to believe the existing tank may have been undersized.  I was hoping to get your opinions/thoughts on the subject.



My boiler details:

Late 70's Hydrotherm R210B Hot Water boiler - 210K BTU Input, 168K BTU Output, 146K Net IBR, Extrol Model 30 Expansion tank



The literature that I found on Amtrol's site was a chart that showed expansion tank sizing based on boiler BTU.  According to the chart - my boiler should have a Model 90 or SX-30V tank (my boiler appears to be right in between the two if I am reading correctly).  The table can be found here:

<a href="http://amtrol.com/media/documents/extrol/MC2680EXTROLBrochurelow.pdf">http://amtrol.com/media/documents/extrol/MC2680EXTROLBrochurelow.pdf</a> (page 4).



My question is - did the installer put the wrong tank on last time (about 5 years ago when I bought the house) or is the Amtrol documentation a recommendation and other factors contribute to the selection of the Model 30?  When the tank was replaced, I recall the installer just getting a part number off of the tank and ording that.  I'm not sure he checked sizing vs just replacing what was there.  It has been hard to find good boiler pros in central Ohio...there aren't many residential boilers installed here. 

Now that I have to replace the tank - I want to be sure I have the correct part.  Thaks for the help.

lchmb

curious

Was there a water leak that caused the tank to rust out so fast? As far as tank size, if the system never over pressurized you should be ok. You can increase to an extrol 60 and not hurt anything. Have you also checked the P.R.V to make sure it's not frozen shut? I like to replace them both if one goes bad..

[Deleted User]

PRV is OK

The PRV is fine as far as I can tell.  Last winter I could manually open it with no issue.  In addition, there were 4-5 instances (that I know of) in which the boiler pressure hit 30 PSI and the PRV opened to release some pressure.  There were also several instances of my boiler pressure rising to 25-29 PSI when the PRV did not open.  Typically this happened when I was pushing the boiler hard (reheating the house after an extended power failure, or coming back from vacation and requesting a 5-6 degree temp increase).  I just assumed that the heavy load was causing the pressure to rise...now I'm wondering if the expansion tank is too small.

lchmb

could be

like I said, doesnt hurt to increase to an extrol 60. Think in your case I would. I just like to replace the P.R.V at the same time. It's a safety and for the cost pretty cheap to replace while you have pressure off the boiler...

kcopp

what do you....

have for radiation? Is it Cast iron rads or baseboard? Greater the volume of the system = larger diaphragm tank.

STEVE PAUL_3

Expansion tanks and Pressure relief valves

It sounds like the #30 tank is right on the edge of the high end for your system. If it were in my house, as others have advised, I would install a #60 tank and sleep well at night, it would be prudent to replace the 30 PSI Pressure relief valve at the same time. If the boiler  pressure is down to replace the tank, then replacing the valve will be simple.

The most likely reason your pressure went up to 29 PSI was because of the tank leak. The pressure relief valve should have started to weep at that pressure. 

As an aside, when I was teaching. I tried to avoid confusion when discussing  pressure relief valves, pressure reducing valves and pressure regulating valves. THEY ALL CAN BE CALLED PRV's. I just feel more comfortable (and accurate) calling them by name.

[Deleted User]

Cast Iron Rads

I have Cast Iron Rads...I'm in the process of counting the sections and sizing because I have no idea of the total volume

lchmb

I'm thinking

I think by your description you will be fine with the extrol 60...