Tankless hot water return loop

northlakes

I’ve read a number of threads on tankless and recirc but not sure I’m up to speed. I’ve got a kitchen sink on 2nd floor that takes a long time to get hot, I tried a little under sink 2.5 gal unit but after 5 months the anode is already looking bad and I’m definitely not up for replacement twice a year, with it on top floor it feels like too much of a flood hazard with that level of maintenance.

Distance to sink is about 30 feet from the heater and it’s a bit surprising to me that it takes that long to purge, the fixture has a low flow but seems to take a couple of minutes to get hot. Tankless seems plenty big at 199000 btu.

I’ve read about complicated pump and sensor systems but is there any way to speed up the purge with a loop that has an aquastat valve inline or something? It’s not a super long run so it seems to make sense in my novice head that a loop would speed up the purge time by a factor of gpm loop/gpm fixture, lowering pressure until aquastat valve closes and then resuming normal pressure?

About 20’+ of this run is 3/4” and about 10’ remainder to sink is 1/2” copper. I’m assuming this is what makes it slower to purge than similar length runs with less 3/4” in the run. I could try bypassing that run with all 1/2 pex direct to sink but not sure how much faster it would get? 

Strong sense I‘ve got this wrong, but appreciate any help sorting it out. 

rick in Alaska

You really need a return line from the sink to be able to do a good recirc. Various manufacturers make a system where that is not the case, but a dedicated line works the best.
A smaller line from the heater the sink will definitely speed up the response time though.
Rick

Snowmelt

It’s all about flow and head loss get a 1 inch pex going back ….. more gpm faster heat , don’t forget check valves

Larry Weingarten

Hi @northlakes , Do you have a photo of the five month old anode rod? They can look pretty funky at that age, but still have lots of life in them. Do you soften your water?

Yours, Larry

northlakes

Larry Weingarten said:

Hi @northlakes , Do you have a photo of the five month old anode rod? They can look pretty funky at that age, but still have lots of life in them. Do you soften your water? Yours, Larry

Good point, It’s a matter of just knowing I won’t be able to keep up on the maintenance so I took it out. The rod looks like it has another 3-4 months in it but I’d rather not worry about new rods at all. 

MikeAmann

Since the rod is already out, install a powered titanium anode.
The rod never gets consumed. Here is the one that I use:
https://www.ebay.com/itm/142271777319?_trkparms=amclksrc=ITM&aid=1110006&algo=HOMESPLICE.SIM&ao=1&asc=20200818142401&meid=2e4a60c08484403396073f417b3ddb5a&pid=101124&rk=5&rkt=12&sd=175362282626&itm=142271777319&pmt=0&noa=1&pg=2563228&algv=DefaultOrganicWeb&brand=TEC&_trksid=p2563228.c101124.m2109

kcopp

MikeAmann said:

Since the rod is already out, install a powered titanium anode.
The rod never gets consumed. Here is the one that I use:
https://www.ebay.com/itm/142271777319?_trkparms=amclksrc=ITM&aid=1110006&algo=HOMESPLICE.SIM&ao=1&asc=20200818142401&meid=2e4a60c08484403396073f417b3ddb5a&pid=101124&rk=5&rkt=12&sd=175362282626&itm=142271777319&pmt=0&noa=1&pg=2563228&algv=DefaultOrganicWeb&brand=TEC&_trksid=p2563228.c101124.m2109

Thats a great idea but it will not fit in a 2.5 gal mini heater...

If only they made a 2.5- 4 gallon SS point of use mini WH tank.

Larry Weingarten

Hi, Another option if you have adequate water pressure, is to run a dedicated 3/8" line from the outlet of the tankless directly to the sink. This will greatly reduce volume of water in the line giving you faster hot water. Can you snake PEX up to the sink?

Yours, Larry

northlakes

MikeAmann said:

Since the rod is already out, install a powered titanium anode. The rod never gets consumed. Here is the one that I use: https://www.ebay.com/itm/142271777319?_trkparms=amclksrc=ITM&aid=1110006&algo=HOMESPLICE.SIM&ao=1&asc=20200818142401&meid=2e4a60c08484403396073f417b3ddb5a&pid=101124&rk=5&rkt=12&sd=175362282626&itm=142271777319&pmt=0&noa=1&pg=2563228&algv=DefaultOrganicWeb&brand=TEC&_trksid=p2563228.c101124.m2109

I looked for one that would fit this little 2.5g heater but it looked like a serious fab job was in order ha 

northlakes

Larry Weingarten said:

Hi, Another option if you have adequate water pressure, is to run a dedicated 3/8" line from the outlet of the tankless directly to the sink. This will greatly reduce volume of water in the line giving you faster hot water. Can you snake PEX up to the sink? Yours, Larry

That’s exactly what I did but used a 1/2 and cut the arrival time about in half. (Didn’t even think to try 3/8.) I’ll see how that goes and maybe consider another return line later if it seems like it’s needed.

One thing I noticed after was the tankless started acting like the flow sensor was being triggered and doing little growls all day. I then remembered I didn’t purge that old branch I’d orphaned, and it was just like a column of air sitting there. Could that cause enough spring in the system to cause a flow sensor to trigger? Haven’t been able to sit with it long enough to check after I got the air out of that line.