Question about expansion tank number, size, location

random12345

Got a two-family property where two hot water heaters have leaked while still under warranty. Both were A.O. Smith GCRL-40, 40 gallon, 40k btu, 6 year warranty, short, atmospheric vented into chimney purchased at the same time in July 2018. The first leaked after a little over 4 years and was replaced under warranty, and now the second has leaked after nearly 5 years. I know this could be just coincidence, but I'm thinking there might be something else going on. One possibility is the expansion tanks are too small. Both are Watts ETX-30. Both apartments have cast iron radiators. It's a gas hydronic heating system, one boiler is 164k btu, the other is 140k btu. There's only one metered water main that supplies both apartments. Should the hot water heaters each have their own expansion tanks as well? Both tanks sounded hollow when tapped so I think the bladders aren't ruptured. Haven't checked the anode rods, but that's next on my list. I'm going to need to call a plumber regardless, but I thought I'd ask here as well. Pics below. I couldn't find an answer online about how many expansion tanks are needed and the best installation location for them when you have multiple boilers and hot water heaters. The tank size I can attempt to calculate once I know the volume of the system, but that requires going into the apartment and measuring the radiators. Can't do that until July.

Big Ed_4

In a closed system you need a tank to take up the thermal expansion tank . Your heating system is a closed system .

The water company has been installing check valves to protect the water supply . Which would close your domestic system and you would need a thermal expansion tank on the cold water line . The tank used is different then the one used on a heating system .They are ST tanks . Running the hot water heaters with out a thermal expansion tank can put a lot of stress on the heaters internal. tank ...

EdTheHeaterMan

A.O. Smith GCRL-40 is a water heater and that is supposed to operate as an open system to make Domestic Hot water (DHW). The EXT-30 tank has nothing to do with the DHW system. The EXT-30 should be connected to the closed system of the heating boiler(s).

A DHW heating tank is an appliance to itself and has no connection to the heating boiler. The Heating boiler(s) are appliances to themself and have nothing to do with the DHW tanks.

They are separated by a fill valve that will take the city water pressure of over 50 PSI (in most cases) and shut off by way of a hand operated valve as a minimum separation between the lower operating pressure (from between 12 to 18 PSI) and a back flow preventer by code. usually there is an automatic feed valve that will automatically reduce the feed water pressure down to the cold static pressure of the closed system (12 - 18 PSI).

The fact that the DHW tanks failed within the warranty period has nothing to do with the expansion tanks on the closed system. I'm not sure that adding an expansion tank the the DHW open system would make a difference. If the A O Smith DHW tanks were over pressuring, the relief valve(s) would be discharging from time to time.

I believe that you may have a water chemistry problem or some other issue that may be causing premature failure of the DHW tanks. If you want the tanks to last longer, have the water in those tanks analyzed to see if there is a problem that can be corrected by someone like the Culligan man! ...or other water treatment options.

At least you got some warranty water heaters. I find that water tanks with 6 year warranties usually last at least 7 years but not much longer. If you get the 10 year warranty models, they last 11 years. You should feel blessed!

random12345

@Big Ed_4 Are you saying I should get an additional tank on the cold water supply for the house?
@EdTheHeaterMan Thank you, as always for your help. The water heater manual says that an expansion tank is necessary, but I thought that the tank on the boiler circuit served that function since the boiler and DHW heater are supplied by the same cold water line. I think I need to get a plumber to review everything. I'm not sure the boiler is piped correctly after everything you said. I am going to check the anode rods on both heaters. After calling A.O. Smith tech support I learned that you can get the 6 year warranty extended by 4 years simply by installing an additional anode rod. You buy the rod from the distributor, and they give you a sticker that you slap onto the tank. Cheap insurance I never knew about. Next time I buy a water heater, that's what I'm going to do. This doesn't apply to warranty replacement heaters, you can only do it for new ones.

EdTheHeaterMan

To better understand your boiler and potable water systems I have the following illustration.
I have combined a plumbing diagram for potable water with a closed system diagram.

The potable water system may have pressure from 35 PSI to 80 PSI depending on your source of city or well water. If your water utility provides pressure any higher than 80 PSI then you MUST have a pressure reducing valve on the water inlet to your home (Most homes do not have this). Appliance and fixture failure are more common the higher your water pressure is... But that hot shower feels sooo good!

Assuming you do not have the pressure reducing valve at your meter or water inlet to the home, there may be a check valve on your system in case there is a need for service on your street water lines, this way the higher pressure in your home will not send water backwards into the common system pipes in the street. These check valves are called back-flow preventers.

Now consider this: Without a back flow preventer at the meter, cold water can enter your home and fill up the water heater. As the cold water in the water heater gets hotter, it will expand. The expanded water needs a place to go. Since all your faucets and taps are closed most of the time, that extra water will just back up into the street thru the water meter. That can not happen if the water company installs a back flow preventer. so now the water can not expand back into the street. in that case, you will need a DHW expansion tank. i have illustrated both tanks using different colors. The white tank is for higher pressure open systems (as @Big Ed_4 indicated for DHW)). The blue tank is for lower pressure closed systems.

If you look closely at the connecting pipe from the house lines to the boiler feed pipe, there are several items on that line. A back flow preventer and a pressure reducing valve (or auto feed) that will maintain the closed system pressure at 12 PSI (or what ever you set the pressure to based on your system needs) and at least one manual valve for servicing the system

Hope this diagram helps. I believe that you may already have some of these parts on your system, however the closed system expansion than can not help you on the house pressure side as you already understand.

Big Ed_4

Yes, one for each meter , ST12 size tank, either way you are good....

random12345

@EdTheHeaterMan Thank you for that diagram and explanation. I don't think I have a back flow preventer on the cold water main from the street, but I definitely have one on each boiler. The plumber will coming tomorrow to take a look at things. I'll let you know what he says.
@Big Ed_4 I will ask the plumber about installing an ST12.

mattmia2

If you don't have any sort of check valve that keeps the water from flowing back in to the main then you don't need an expansion tank for your domestic water heaters(some water meters also only allow flow in one direction but most meters allow flow in both directions).

If there is a place to install a second anode I would do it in both water heaters. You don't have to buy it from AO smith as the kit which is probably marked up to help cover the extended warranty. I would then check them about every 2 years and replace them when they are depleted if the tanks are going that quickly. Another option is to replace the anode with a powered anode although the up front cost on those is higher and you need to make sure your tenants don't unplug them.

random12345

@mattmia2 Thanks. I'll check the meter. I tried getting the anode rods out today from both of the old heaters. Bought a socket wrench and 1 1/16" extended socket. Even got a long piece of pipe as a breaker bar. Couldn't get it out. Not strong enough. There's no way I would be able to replace those on my own. I don't even know what they look like. I might try one of those iPhone endoscope cameras dropped through either the hot or cold nipples to take a look.

mattmia2

They are a lot easier to remove on a new water heater. An impact wrench is a good way to get them out for an autopsy.

Big Ed_4

If the water meter has been changed in the last thirty years , it would have a check valve built in ...

hot_rod

I would use an expansion tank on any water heater theses days. Water providers are adding backflow preventers either in the meter pit or the lateral somewhere. If you don't have one already, you will someday. A thermal expansion tank is not an expensive add on.
I believe a thermal expansion "device" has been a code requirement for some time now.
A "device" can be an expansion relief valve also. Watts makes a few versions built into toliet ballcocks and ball valves.

Different states use different codes. Backflow devices may be required by code, or the water provider.

If you have a private well, it's your call.

mattmia2

Big Ed_4 said:

If the water meter has been changed in the last thirty years , it would have a check valve built in ...

Mine was changed about 2 years ago and about 20 years before that and nether had a check valve.

random12345

Plumber who works in our town came by today and reviewed everything. He thought the two water heaters had simply reached end-of-life because they're designed to fail just beyond the warranty, which in our case was 6 years. No backflow preventer anywhere on our water main, and he didn't think a water chemistry issue was likely either. He didn't think an expansion tank was worth getting, but identified several small leaks on our brass water main that is likely original to the house (1910). He did not think it needed to be replaced right this minute, but thought it was likely to fail at some point. Apparently, failures are discovered when the pipe starts spraying a fine, audible mist and/or the water bill goes up. He recommended that when we did the replacement, we should install a separate meter for each unit in the house so tenants can be billed for their water usage instead of us.

Big Ed_4

It looks like a galvanized pipe to me...

random12345

I think you're right about that section. It may have been replaced/added more recently, but there are other leaky parts where the corrosion is green. That's gotta be brass.

EdTheHeaterMan

There is also an obsolete wire in that picture. Does anyone still use a landline for communication with the outside world?

Ok,Ok, I expect to get someone to click on the "Off Topic" icon below. LOL

But that is why I did it!

random12345

I do. I don't think anyone in that house has for a very long time though. I can't see why a tenant would pay for that in addition to cell service.

Larry Weingarten

Hi @random12345 , About anodes, there is another approach when the hex head type won't come out. There is a combination style that incorporates the hot outlet pipe with an anode suspended underneath. I'd just get those, made with magnesium, and install them as you can't remove and "read" the old anodes.

Yours, Larry

random12345

Interesting. The plumber I talked to didn't think water chemistry was a problem in our area. The distributor apparently sells an extended warranty that comes with an additional anode rod as you mentioned. When I have to get a new water heater, I think that's what I'll do. I also considered getting a cheap industrial waterproof endoscope for $50 or so on Amazon and trying to get a look that way...but I'm dragging my feet on that. My sense is that WHs are designed to fail. I will keep your suggestion in mind.

Larry Weingarten

Hi, Water heaters are designed to last the warranty period and a day. Thing is, they can be maintained, which almost nobody does. I do, and have gotten over fifty years from tanks. I've worked on thousands of heaters and the failure rate stayed below half of one percent yearly.

Yours, Larry

mattmia2

I wrote this a couple days ago, it seems to be answered but doesn't seem to be in the thread:

Is just the section that is leaking galvanized or is it all a mixture? If the underground part is brass, someone skilled could replace the galvanized part.

I disagree that it is just the way it is with the water heaters, if you keep the anode maintained it should far outlast the 6 years. Lots of plumbers don't understand the function of the anode.

mattmia2

If the brass is leaking it is likely a bad joint rather than the pipe. if the underground is brass you probably can build new piping off if it without digging it up.

random12345

It's not underground. Except for that one galvanized part, it's all brass and in the basement rafters. Multiple sections on both the fittings and straight parts are green and have many small leaks that have sealed themselves. When it eventually fails, I'll replace the whole thing and probably put separate meters.

mattmia2

I mean the service, is it brass or galvanized or copper or lead? The part in the basement is easy enough to replace.