Amtrol expansion tank size

You can put multiple tanks together if you still have the #30

Yes. There is a big jump in physical  size when you jump two sizes.  Don't beat yourself up, like Hot Rod said, gang up two of them.  When in doubt, I go the next size up - it will never hurt.  You might want to dial down the aqaustat a few notches - you shouldn't be popping the relief valve even at the top end.  Mad Dog

Yeah, why build a 7 gallon tank for that small acceptance?

The EX-15 tanks should work for you.  Something else is going on.  Some pictures would help. 

So, the radiator circuit is pumping water toward the x-tank and the BB circuit is pumping away from the x-tank. Pumping away is good for pressure stability; pumping toward is bad.

Did you get a lot of water coming out of the air eliminator when you changed out the x-tanks? I would remove the x-tank and make sure that there's no buildup of corrosion inside the bottom of that air eliminator.

It looks as though the previous owner added the BB. And it looks as though the installer took the easy route as both heating loops should come off the copper main after the air eliminator.

Do you have a home warranty plan that you got when you purchased the house? Or any recourse with the previous owner to fix something that is a problem now?

So I did call amtrol as I ran into this same issue, hopefully someone finds this useful. I need about 4.5gal of expansion in my system it currently has an EX-30 on it, and I'm gonna need to goto EX-90 as the 60 won't cut it.

TLDR EX-60 is for 3 story houses and EX-30 is good for 1-2 story houses.

The person at Amtrol said it is not a typo but the EX-60 is good for higher pressure systems whereas the EX-30 is good for lower pressure systems that need similar acceptance volumes. He said low is 10-12 PSI, and 15 or more would be high. He also said they used to have something between the 60 and 90 but it didn't sell well so they don't make it anymore.

So to breakdown what he meant and why the EX-60 would be good for a higher pressure systems I'll my own system as a data point. My system needs to be at 16psi, 30ft of rise +3psi for the inducer pump. I need 4.5-5gal of expansion volume but assume I only needed 2gal which is in the acceptance range of what both the EX-30 and EX-60 can do.

So using ideal gas P1*V1=P2*V2 we can estimate the system pressure at both cold P1 and hot P2.

P2 = 16psi*V1/V2

For the EX-30 V1=4.4gal V2=4.4-2=2.4gal so P2 = 29.33 psi which is really darn close to the pressure relief valve setting on a residential unit. Now imagine if you needed just a bit more expansion, it'll still expand into the tank but you'll exceed the 30psi limit, and have leaking.

For the EX-60 V1=6.7gal, and V2=6.7-2=4.7gal so P2 = 22.8psi which is well within the limits of a residential boiler unit.

Now if I only needed my system at 12psi cold, then with the EX-30 my pressure is only 22psi which also works fine.

So to sum it up if you have a 3 story house and you only need a couple gallons of expansion use the EX-60 if you have 2 stories or less and the same expansion needs use the EX-30.

I considered ganging up two 30's but it seems like a pain, it'd require redoing plumbing vs just installing the bigger tank in the same spot. It also seems like more of a maintenance headache to make sure they are both charged to the right pressure.

I recall reading on one of Dan's books that there were some old systems with no expansion tank.

The top floor radiators were not completely bled of air. These were the expansion chambers.

You lost some expansion area by bleeding the upper rads. That may have made the difference.

Speaking as a novice homeowner;

Your home probably had a hand fired coal boiler that used the radiators as part of the compression system by maintaining an air charge in the radiators.

I agree with Alan from California Radiant that the previous owner added the baseboard.

Your boiler needs a lot of work, the near boiler piping should be stripped back to the boiler and replaced with black iron pipe and the proper sized piping and the circulator layout should be installed to pump away from the boiler. You need a separate low water cut off switch.

I am not sure if the pressure relief valve should be plumbed the way it is with a circulator pumping water by it into the boiler.

The boiler needs to be examined more closely to see why there is rust above the burner mounting plate. You may very well have a bad flange gasket that is leaking exhaust gas and causing corrosion.

A steel compression tank with a gauge glass would be ideal for your system as it would have 10 or more gallons of water to maintain the point of no pressure change and a much larger air cushion of 5 gallons of air or more. You could pipe it from the vent tapping in the air scoop to the tank at a longer distance away allowing for a more gradual slope to the airtrol valve under the tank but only if the tapping in the air scoop is 1/2".

You could reuse your air scoop to divert the air bubbles into the steel compression tank with an amtrol valve very easily if the tapping is large enough.

I would not add a second amtrol tank in the short term UNLESS you supported the two tanks by using a Tee'd connection with longer pipe nipples that were secured to the adjacent piping to hold them up using pipe strapping.

I would suggest that you invest in three of Mr. Holohans excellent books on hot water heating which are "CLASSIC HYDRONICS", "PUMPING AWAY" and "HOW COME" from the heating help bookstore as they would be the books you need to solve your boiler and heating issues.

@leonz said: Your boiler needs a lot of work, the near boiler piping should be stripped back to the boiler and replaced with black iron pipe and the proper sized piping and the circulator layout should be installed to pump away from the boiler. You need a separate low water cut off switch.

The three points listed therein Not actually needed. As a seasoned professional I have connected many Hot Water boilers with copper. I wouldn't do a steam boiler in copper, but a water boiler is always done in copper inless someone wants to build a specific manifold with some strength to support several circulator pumps or other specific assemblies. I have often started the first fitting out of a water boiler with a copper by male adaptor.

A circulator pumping away from the expansion tank that is located on the supply pipe is also not a necessity. I have worked on 50 year old boilers where the expansion tank of any type was connected directly to a return pipe and the circulator. Others where the circulator was installed on the return pipe. Some of them were put on the return by the manufacturer and pre-wired. And finally the LWCO that may be built into that Aqustat Relay is all that is needed to pass inspection. I was never a fan of that Hydrostat/Beckett control but it was a correct way to do the job.

And the fact that this original post was from December of 2022 makes me wonder where this new found interest is coming from? I am sure that @ryan242 has moved on to more important stuff by now like adding dish soap to the boiler water, or operating 2 circulators with one thermostat.