Thermostatic Mix Valve to Extend tank capacity

[Hogan]

Hi all

I went round and round about potentially getting a tankless to replace my 2x 50gal heaters that are piped in series and are 20yrs old. Ultimately decided to go with a 75gal but it was suggested to add a TMV so I have the optionality to turn up the heat on the tank and make my hot water go longer if I need to.
I like the solution because while I am probably on the edge of needing one or not (we have a jetted tub that gets very occasional use, and I measured at 65 gals total water to the level one would typically fill to (tub claims 90 gal capacity I think) if I don't really need it I can still just run the heater at 125 or something, or if I decide we do need more then can run it up to 135 or so.

But my question is are there any downsides to these valves? Is there any pressure loss from having it? It would be a 3/4 valve and pictures make it look robust. Do the valves last a long time? Seems a great optionality to add and it isn't going to add much cost to the install (vs going back and trying to add one later) because the guy already needs to redo all the piping from the 2x 50s. But if there is some downside I am missing then I wanted to understand before I pull the trigger on it

Thanks

 

[John Gayewski]

There's not really a downside other than it's another component.

They will have some pressure loss but it's nothing extreme and likley won't effect most things.

I would get it.

 

[Sponsor]

 

[Hogan]

There's not really a downside other than it's another component.

They will have some pressure loss but it's nothing extreme and likley won't effect most things.

I would get it.

Thanks, good to know

I guess unless it ever failed in such a way that it just let in too much cold water all the time. I guess in that case I could just get a new one and install it. If he put a ball valve on the hot water output above the valve then I could just shut that and shut the cold inlet and isolate the mixing valve to change it out.

 

[Jeff H Young]

I think cranking up the hot and then stepping it down down heat with a mixing valve is a fine idea. its safer
However just turning up the heat will accomplish exactly the same results except 2 things youll never get really hot water when you dont want it ( scalded) and youll never get water thats super hot if you need it because youve got the mixing valve preventing really hot water from coming out . Adults that are aware might not care but some that arent all there could hurt themselves or children or really old folks .
cost isnt huge its a very simple installation , on a new install it might not take 10 minutes time

 

[Fitter30]

Here a hot water mix calculator just change settings to gpm

Water Mixing Calculator | Spirax Sarco

This calculator will help to consider the mixed temperature of two water streams, its flowrate, percentage flow and actual flow of each stream.

www.spiraxsarco.com

 

[Hogan]

So I got my new tank installed and it looks great. Only problem is my plumber forgot to install a check valve on the gravity recirc lines that he tied directly to the cold water inlet that also crosses to the tempering valve. So any time the hot faucets are open the cold water side also heads upward into the recirc lines and thus the water is cold. Whoops. For now I just closed the ball valves he (thankfully) added on those two recirc lines coming down, so I can get hot water. Assume it will be a simple fix for him to come add a check valve over there.

Unit is nice and quiet though!

 

[Hogan]

Double post pls delete