Tankless or Stainless to upgrade from 50G NG?

[adjacent]

Thanks @jadnashua and @Dana

Another question - in installing a tempering valve on to a water heater, are there any additional things a plumber would need to add? I believe also an expansion tank (due to WH heating to higher temp, for thermal expansion), but not sure if there are also check valves or the like that are necessary. I ask because the plumbers I've talked to don't seem to be experienced in installing these. Thanks!

 

[Jadnashua]

If you don't have a closed system, that extra volume literally just gets pushed back into the supply system. It becomes a problem if they have a check valve there (many utilities are adding them as they do maintenance), or you add a PRV, both of which create a closed system. Where I live, they require an ET to pass code as they're adding check valves to satisfy federal guidelines, and they don't want customers to have issues of the T&P valve opening each time the WH reheats water.

 

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[adjacent]

If you don't have a closed system, that extra volume literally just gets pushed back into the supply system. It becomes a problem if they have a check valve there (many utilities are adding them as they do maintenance), or you add a PRV, both of which create a closed system. Where I live, they require an ET to pass code as they're adding check valves to satisfy federal guidelines, and they don't want customers to have issues of the T&P valve opening each time the WH reheats water.

I don't believe I have a closed system. How could I confirm that?

So it sounds like as long as there is not a check valve or PRV, an expansion tank is not necessary, even if I'm planning to have my WH going at a high temperature setting - is that right?

This may be a good thing because even though an expansion tank is not that expensive, the space above the water heater with the piping is limited. Or is it better to just add one, must in case?

 

[Lifespeed]

I'm surprised you're (or your internet advisors) are coming to the conclusion this is not a good tankless application. It seems ideal to me; occasional very large volumes of hot water with more routine smaller draws. Why heat a giant tank to high temperatures (with the associated losses) to barely fill a tub? There are tankless that can supply 11GPM, the Noritz NRC1111 is one but there are others. You can use a recirculation pump so long as you use a proper control setup and don't cycle it every 5 minutes. The tankless can control the pump, or you can use an external control like the Readytemp I use, which is very configurable and easily automated with a plug-in timer or home automation control.

The two caveats with tankless are the upgraded gas line, and you either have to soften the water, which is my solution in the SF bay area as it saves the rest of the plumbing and appliances, or descale every year.

Edit: as to the expansion tank, I think like many things it is required by code, but is only strictly necessary under certain conditions. I did not install an expansion tank in my system. Really, I think an expansion tank is mostly appropriate for a tank hot water heater. With a tankless, the only volume is in the pipes, there is not a large volume of hot water to expand into the plumbing system. But I think building code is one-size-fits-all.

 

[Jadnashua]

Many places in CA have a relatively mild changes in temperature (obviously, some in the mountains do not!). This makes things much easier on a tankless system. What can really stress things with them is say 60-70 degree input water in the summer, and barely above freezing in the winter (like where I live). IN that case, when drawing a moderate amount of hot water, the thing can not keep up. Note, those specs are all pretty much based on 50-degree inlet water temperatures...their performance changes radically when it changes to nearly freezing. Throw in the significant upfront hardware and potentially infrastructure costs to install one, then the nearly annual maintenance, verses a quality tank (which tends to have much better insulation than in the 'old' days) with unlimited volume until the tank runs out (that's why it's important to size it properly), and a tankless becomes harder to justify.