noritz tankless

Brain Ross

I know it's not a heating question, however I'm installing a Noritz tankless with Norits isolation/pruge valves on both hot and cold lines. Generally I like to install a thermal expansion tank between the heater and the cold water shutoff valve but using this prebuild iso/pruge valve and its union connection doesn't leave any room for an expansion tap! should I install the expansion then between the cold water inlet after the valve and the prv?

kcopp

You will....

be fine having it in the system after the iso valves. The system will be off if the isolation valves are closed. Keep it simple.

Buergermeister

Expansion?

Since the water in the heater is roughly room temp when it stars, then only heats when there is flow. Then once there is no flow, shuts off. The water should shrink. So any thermal expansion should be negligible, its contraction that should be happening, and that should be taken care of by the city feed.  I would also assume you are using this as a Water heater not a boiler, other wise I would recommend the tank and feed near the suction side of the pump.  We have installed a few of the Noritz branded heaters and never been back to service one yet, but every other brand of tankless heater we have installed we had to go back and repair. Hope you have the same luck.

Mark Eatherton

What burgermeister said....

Great minds think alike :-)



http://www.heatinghelp.com/forum-thread/140045/expansion-tank-location-with-tankless-heater



Unless its being misused as a space heater, no expansion is going to occur, hence no tank is necessary. Unless of course a misguided AHJ is demanding one...



ME

kcopp

Most of my.....

installs I don't use one but I did have one last year where It needed one. It was a Noritz NC 380. No matter how carefully the faucet closed the expansion of the water would get the PRV to weep or down right open. A potable water  extrol fixed that.

Mark Eatherton

High incoming pressure?

What was the incoming water pressure Kevin?



I can see that if it is high enough to begin with that it could pose a problem on that ends. Sounds like possibly a pressure reducing station would be more appropriate than an EX tank tho...



Just wandering.



ME

kcopp

It was about 70 psi.

Not huge... but it was in an old mill. I did try one of the sioux chief water hammer arrestors but that did not work. The input on the unit was 380,000 btu... that much water heating to stop on a dime was an issue.

Mark Eatherton

Residual refractory heat...

Dependingupon the thankless design, I guess it is possible that a ceramic type of refractory could hold enough residual heat to cause problems on burner cessation following a long bunr period.



The thankless heaters I've employed (and owned) have NO ceramic insulation in the combustion chamber, hence not a lot of residual heat from the combustion process.



If I were in your shoes, I'd probably employ the same fix.



ME

Jack

I would not use one...

unless it proved necessary. Every system has a personality and a very small percentage of the units (100k+) I've been involved in required an expansion tank. If you are worried about it, place a plugged tee in the piping to accommodate your expansion tank should it be proven necessary.