Larger Expansion Tank?

Doug_39

H/O with 14 hot water radiators piped reverse return on one zone with a 72 gallon indirect on the the other zone. Radiators circulate with a Taco 007 and the indirect with a Taco 010. All's well but for this: during cold weather, long runs cause the PSI to max out at 30+ (where the gauge runs out) and during coldest weather, we can end up with a puddle under the relief pipe. Current expansion tank is Amtrol Extrol 30.....perhaps undersized for the system? Unfortunately, sizing up will require relocation of the E.T., so tech. can't just screw in another to see if it solves the problem. So, before we go to the trouble.....any thoughts?

kevin coppinger_4

how many btu...

is the system...amtrol has a pretty handy chart in their catalogs....I am pretty sure it will need a et60...also you can remotely install the expansion tank by some copper/pex and a couple of adapters....kpc

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Doug_39

Modulating boiler w/ max btu output of 137,700. You're right about the Amtrol worksheet, it is handy, but venturing a guess regarding total system gallons is a bit beyond me. We do have a good spot for permanent relocation, but your idea about the pex makes me think that we could try out the 60 from the same junction which feeds the 30 before messing with the copper.

Doug_39

Correction: the indirect is 40 gallons, not 72.

Ragu_5

On the bright side...

One can never have too much expansion.

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Brad White

I am with Ragu

Add at least another tank.

The method of sizing an expansion tank by system BTU capacity is based on limited runs of copper pipe and ignores the real variable: The system volume.

Sort of like flipping a coin for "heads"- half the time you are correct yet feel good about it if you ignore that annoying "tails" part

When release from the relief valve happens on temperature, I suspect tank volume. For the cost of a second tank, connected next to the first, that should solve the problem. For some reason when I have done this, the 29-30 PSI readings formerly experienced seem to settle around 24-25... just seems to work out that way as a coincidence.

Glenn Harrison_2

If you use the cheater sheet I use

based on the 137,000 BTU's and cast iron rads, you are on the border line of a number 60 or a number 90 tank. Being a modulating you probably could get away with the 60, IF you don't have a lot of piping holding extra water to put you over the edge on the 60.

Attachments are - Sizing cheat sheet, cross reference from Flexcon tanks to others, Flexcon spec sheet.

Hope they are helpfull.

Doug_39

Many thanks, Glenn, for your post and the attachments. Looks like 60 it will be.

Doug_39

Does the indirect need the extra 30?

The existing Amtrol Extrol 30 is connected under the scoop (?) just before the split between the 14 radiator heat zone and the domestic zone. If we end up adding another AE30 to the system, should it be hung somewhere on the indirect zone? The domestic side is currently somewhat isolated from the heating side by a Flow Check (which is located between the Taco 010 circulating pump for the domestic zone from the boiler and the indirect) and a Backflow Preventer (which is located between the cold water pipe which supplies the indirect itself and also a mixing valve above the indirect (which enables us to set the thermostat on the indirect at 140 which gets mixed down to 120), and an Autofill Valve which regulates cold water intake into the scoop. In other words, does the current AE30 provide any relief for expansion which takes place on the domestic zone?

Doug_39

Before we do anything else, should we turn down...

...the thermostat on the water heater from 140? Could it be that heating the domestic water that high (before mixing) is contributing to our problem?

Doug_39

The boiler's a Trinity T150....

.....and the indirect is a MegaStor 40 gallon unit.

Ragu_5

Doug...

The expansion tank serves the entire system (including the indirect zone). With 14 rads, you have some serious volume in that system. Have a #60 installed, but have the installer check the pressure in the bladder; most expansion tanks come out of the box with very little air in the bladder.

I'm curious: with 14 rads and a Trinity, are you using the reset function on the control? What kind of water temps are you able to run with? Thanks.

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Doug_39

Ragu, not all of the 14 are monsters....

....in fact, I'd say that about half of the 14 are fairly small radiators of the size you'd expect to find in a bathroom or hallway. As of 6am this morning, the Sentry controller says that we have outdoor temps (mostly) of 25F, and that the boiler water temp on the meter topped out at about 165F. The temp on the gauge at the start of the radiator zone topped out at about 150F and the gauge at the return position on that run maxed out at about 125. It was when the system reached this 150F mark that the Sentry cut back the Trinity from max output (205) to lower amounts. This cycle ran about 40 minutes from fireup to shut off.

Ragu_5

Thanks, Doug...

The Sentry Control on the Trinity is a good feature, especially in your application. You are definitely using the reset features.

Yes, please go with more expansion.

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Eric Johnson

Two 60s

I'm going to be merging two systems (wood and natural gas), both of which are pressurized and both of which have Amtrol 60s. The system has 15 cast iron rads and lots of large-diameter iron pipe. Each boiler is around 200K btu.

Would it be correct to assume that 2 60s on this arrangement will give me enough expansion?

Doug_39

Loose ends.....

....to tie up. Still need your thoughts on a couple of questions:

1. Do you folks ever install separate expansion tanks on your indirects? I've been advised that since our indirect is isolated from the current expansion tank by backflow preventers and flow checks, that the indirect may need its own expansion tank.

2. Could installation of an expansion tank for the indirect be avoided by using the mixing valve on the indirect just of safety purposes and dropping the thermostat on the indirect from 140 to 120, rather than continuing our current practice of using the mixing valve to increase the effective output of our indirect by cooling the 140 to 120 at the mixing valve?

3. Does it matter where we locate the additional expansion capacity on the radiator zone? Right now, the expansion tank is located shortly after the start of the supply run from the boiler (just below the scoop) prior to the split into the radiator and indirect zones and the respective Taco circulating pumps for each. Is this the best place for us to increase expansion capacity, or, if there needs to be separate expansion capacity for both zones, can the increase in expansion capacity for the radiator zone go anywhere on that run (including a potential site on the return as it approaches the boiler)?