Plumber recommending not to install expansion tank with new heater

[greenjp]

I am getting ready to have our 19 year old Rheem 75 gallon gas water heater replaced. It's still working I'm just doing it now to avoid having an emergency in the future. FWIW in the 10.5 years I've been living in this home I haven't touched the thing once - never drained it, replaced the anode rod, etc.

One of the plumbers I've spoken with, who seems like an honest guy and if Yelp and similar are to be believed has a good reputation, is quite adamant that an expansion tank while technically required by code is not actually beneficial to the homeowner, but rather will be a headache at some point, and recommends not installing one. We do not have one now. Of course this means the install wouldn't be permitted/inspected which I don't necessarily have a problem with given some of the other stuff in my house.

So - technical thoughts on the pros/cons of an expansion tank? Practical considerations of not having the installation permitted? Thanks!

 

[Reach4]

I am not a plumber. You may not have a check valve with your water meter yet. If you have one, you want the expansion tank.

You can get a garden hose thread pressure gauge pretty cheaply. You can take a hot shower, and then stop using all water. Quickly go check your pressure gauge. If the pressure is rising as the water heater re-heats, then you have a check valve and already need an expansion tank.

If you don't need one yet, you could ask him to install a non-steel tee that you could use to add an expansion tank later if they change your water meter.

 

[Sponsor]

 

[Phog]

I just want to add that pressure measurements are not necessarily a definitive test of whether a check valve is present in that incoming service line. If you have a leaky fixture elsewhere in the system that can relieve pressure too. Thus making a system appear to perform fine, which would otherwise need an expansion tank.

But then imagine down the line you fix your drippy faucet (or toilet, or outdoor hose bib, or whatever), fully sealing up the system. Without the pressure relief of the drip, it can cause your water heater T&P to start venting.

I would directly ask the plumber what his reasoning is. If he says he examined your service line & you don't have a check valve, then he is completely correct that you don't actually need an expansion tank at this time. But, if he's just going off of the old "it's a working system and I won't monkey with it it" theory, and he never actually looked at your service regulator, just be aware that you could have to install one down the road.

Regardless, installing an expansion tank at a later date is a pretty simple process (DIY level for anyone with rudimentary plumbing skills) and there is no reason you have to put a lot of thought into this decision right now. As Reach4 says above, if you're really concerned just have him install a capped-off Tee in the line for a potential future expansion tank.

EDIT -- I should disclose that I'm also not a plumber!

 

[Jadnashua]

Let's look at why there are expansion tanks in the first place!

Water expands as it is heated...copper pipe, for general purposes, doesn't. Rubber hoses tend to, which would include those feeding most faucets, toilets, washing machines, etc. will, even if they are covered in potentially SS mesh.

Many municipalities either already have or will be installing check valves to help protect their system from potential backflow that could pollute the system. If you have high water pressure, you may have a pressure reduction valve that also has a check valve in it.

So, what happens when you use some hot water, then the incoming, denser, water gets heated...if there's a checkvalve, the water pressure immediately starts to rise, ballooning out anything that can balloon, and if there isn't a leak somewhere, will eventually reach the 150psi that will cause the T&P valve to open up on your WH. That frequent raising/lowering of the pressure, ballooning out those flexible hoses, stressing the seals on your faucets and other valves will eventually cause them to prematurely fail. An expansion tank will prevent that if it is installed properly and working.

But, if you do not have a check valve, that expanding water will just push out back into the water supply system. If your local codes require an ET, it is highly likely that they plan to install a check valve if they haven't already. When that happens, every time you draw hot water and the WH turns on, you'll quickly have water leaking from the T&P valve and creating undue stress to everything in the water system in the house.

ETs don't last forever, and when it does fail, your first indication may be the WH's T&P valve leaking. But, they aren't really expensive, and are quick and easy to replace. In the meantime, you may have had water damage from the WH leaking, or a hose blow out, flooding the house (well, that can happen anyways!), or find yourself replacing a dripping faucet way before you would have to if you had a good ET in the system.

 

[FullySprinklered]

You can drive without a driver's license until you get pulled over.

 

[MACPLUMB]

What jadnashua said from a Master Plumber

 

[greenjp]

Thanks for taking the time Jim. I'm familiar with your 'work' on another forum

Now to reconcile that understanding and the solid logic with the fact that my 19 year old house hasn't ever had one and hasn't had any of the potential problems it would cause. We do have a pressure reduction valve just before the main shutoff valve. I've only had to replace one shower valve cartridge and one bathroom sink cartridge. Haven't seen any leaking from the current heaters' relief valve. Dumb luck or maybe our pressure reduction valve doesn't double as a check valve/backflow preventer?

 

[Jadnashua]

Some PRV's have a built-in relief valve, but it won't open until the house pressure exceeds the supply pressure so it can push back. Kind of defeats the purpose of keeping pressure stable. More likely, the PRV isn't really working any more, or, something else in the house is leaking when the pressure rises. A very common place is the toilet fill valve...no visible symptoms as the water just ends up going down the drain, not leaking onto the floor where you'd notice. It doesn't take much of a drip. If you want to check, get a pressure gauge...one with a second, tattle-tale hand that shows peak pressure and leave it attached for a day or two to notice the 'normal' and peak pressures. The T&P valve on the WH doesn't open until 150psi (assuming everything else is working), but code wants the pressure to be NGT 80psi within the house.