Need Recommendation for Tankless Point of Use Water Heater for Kitchen Sink/Dishwasher

[Wren]

Our water heater is about 55 feet from the kitchen sink and it takes quite a long time to get hot water to the sink and dishwater. I'm considering installing a tankless under-counter water heater. In looking for one, I see all sorts of reviews about how little flow they have and there doesn't seem to be a clear consensus on the best brand/model to get. The only fixtures that will be serviced by the water heater is the sink and dishwasher. I don't mind paying for quality and want something that's going to last. My concern is that I've read that they have very low output.

I'll have to run new wiring, but the panel has plenty of capacity for a new circuit and my FIL is an electrician, so that's not a concern.

I'm currently replacing all of the supply plumbing in the house and am using Uponor PEX-A tubing and fittings. The house was built in 1960 and has galvanized pipes.

I would assume that I would run the water supply to the remote water heater from the main water heater and it would only serve to provide hot water until the hot water arrives from the main water heater. Is that the best approach, or should I simply use the cold water supply to run it? If it is supplied from the main water heater, should the supply (PEX A) be 1/2" or 3/4"? I'm not sure if 1/2" tubing would be adequate over that distance to supply both the sink and dishwasher at the same time.

Finally, I have installed closed-loop recirculation systems in the past, but it seems like a lot of trouble to go through just for a remote sink and dishwasher for this house. It would be easier to run the wiring to an electric remote heater, especially since I'm already replacing the supply lines. I'm not interested in any of the recirculation pumps that dump hot water back into the cold potable water as I don't want to drink or cook with water that has been in a water heater.

I've really gotten some great advice here and am really happy to have this resource.
Thanks!

 

[Reach4]

See https://www.hotwater.com/commercial/water-heaters/commercial-electric-tankless/

https://www.supplyhouse.com/AO-Smith-UPVA-110E-UPVA-110E-Point-of-Use-Commercial-Electric-Tankless-Water-Heater-1PH-11kW-240V

Looks very potent. I interpret

• Thermostatic design regulates hot water output

to mean that it can be set up to slow the flow if needed. Once the hot from the first WH arrives, I expect the output flow could then increase.

 

[Sponsor]

 

[Fitter30]

Turn your sink on full hot till it gets there. High end washers will heat up the water.

 

[bigb56]

One thing you'll want to know is your groundwater temperature for your area, then add to that your desired temperature rise at your desired flow rate. That way you can select the minimum KW for your needs. A lot of people don't understand how much electricity it really takes to heat water instantly, if you only have 3,000 watts sure you can get 125F degree water out of it if you throttle the flow rate down to a dribble, but any decent flow rate will take more KW. So general statements like "they have a low output" are meaningless without knowing all of the above. Watts are watts and no matter the brand, the watts are going to determine the output. It's all about temperature rise and flow rate, increasing the flow rate decreases the temperature rise and vice versa.

In our area a decent size for point of use for laundry, bath, kitchen seems to be in the neighborhood of 14KW which is going to need at least a 60 amp 240 volt circuit. Our groundwater temps on average are fairly close to yours in Athens, GA.

 

[Reach4]

One thing you'll want to know is your groundwater temperature for your area, then add to that your desired temperature rise at your desired flow rate.

I had presumed that the plan is to supply the tankless with the output of the main WH 50 ft away. So in that case the ground water temperature would not matter.

Looking back, I should not have presumed.

 

[bigb56]

I had presumed that the plan is to supply the tankless with the output of the main WH 50 ft away. So in that case the ground water temperature would not matter.

Looking back, I should not have presumed.

No you are right and I thought of that when I was just now taking a shower, he did mention coming off the hot side of the existing water heater. In that case he would just use the temperature of the pipe as the incoming number.

 

[bigb56]

Here's a flow rate chart from Rheem, let's say the water in the pipe never gets colder than 62F, a RTEX-11 (50 amps) would provide 105F water at 1.7 GPM and a RTEX-13 (60 amps) would provide 105F at 2.1 GPM. If the larger unit were installed and the flow rate was dropped to 1.5 GPM the water would be hotter than 105F but Rheem is not giving the actual temperature rise numbers so you have to calculate it out.

 

[letusmaster]

I had the same problem in my old house, long wait times for hot water in the kitchen, especially annoying when running the dishwasher or just wanting to wash up quickly. I ended up putting in a 2.5-gallon Bosch under-sink water heater, and it’s honestly one of the best little upgrades I’ve done. I just ran it off the cold line, which was simpler and didn’t require tying into the main heater. It kicks in fast, and the flow has been totally fine for both the sink and the dishwasher. I also considered a recirculation system but didn’t want the hassle or the idea of hot water looping back into the cold line, especially for cooking and drinking. If you're already running new PEX and have help with the wiring, a small electric unit should be pretty straightforward and give you hot water right where you need it without overcomplicating things.

 

[John Gayewski]

So if your going with a tankless that doesn't take much power then it's OK to supply it with hot water as it can only raise the temp 80 degrees or so (going from memory). When we want to really supply point of use heat with a tankless and we have plenty of electricity available we use emax, I don't emember the model, but select your model carefully as you need alot of power and they come in different capacities, but look the same. The problem with these is they are very loud. The contractors click on and off very loudly in my opinion.

Best would be to get a small one or two gallon heater and supply it with your hot water line and 120 power.

 

[Wren]

Thanks for the responses.

Firstly, If I put in a remote water heater, it will be tankless. I don't have room under the sink for a tanked water heater and the boss has already nixed that idea. It's either live with the wait for hot water or go tankless.

​

I had presumed that the plan is to supply the tankless with the output of the main WH 50 ft away. So in that case the ground water temperature would not matter.

Looking back, I should not have presumed.

That was initially the plan and would provide for backup hot water from the main water heater if the remote one craps out. It appears that some units have an adjustable set point and I would assume that as soon as the hot water arrives, the remote heater would turn off.

I've been looking at this unit:

https://www.supplyhouse.com/Stiebel-Eltron-200056-DHC-E-12-15-2-Plus-Tankless-Electric-Water-Heater

With that being said, it would simplify plumbing if I could connect off of the 3/4" cold water trunk line that is also supplies the kitchen cold and the garden spigot under the kitchen. The service entrance is about 20' from the kitchen sink and the kitchen is on a crawlspace, so the supply pipe would be subject to approximately ambient air temps until the water from underground arrived. While the crawlspace has closed vents during the Winter, it's not insulated. I'm not certain if that's a good idea or not, but my gut tells me that it would be better to run a line from the main water heater to supply the kitchen.

The water heater is located in the garage/utility area and I was planning on running a 1/2" PEX A line from the water heater to the kitchen. As mentioned, the only hot water fixtures in the kitchen are the sink and dishwasher. The other fixtures are next to or above the water heater and we get almost instant hot water since the upstairs bathrooms are directly over the water heater. The house is a split-level. Will a 1/2" PEX A line be sufficient for the sink and dishwasher? I would think so.

 

[bigb56]

That looks like a decent unit. They show a 90 degree temperature rise when wired to the 14.4K circuit but I don't see anywhere where they say at what flow rate you will get a 90 degree rise, is it buried in the text somewhere? I don't like it when manufacturers are not forthcoming with all the numbers you need. You might want to give them a call.

Looking at the chart I will link, with 14.4KW you will probably get just over 1GPM for a 90F rise, at 2 GPM you'll get a 50F rise. Of course depending on your average incoming temp you may not need a 90F rise, and maybe it's not a concern since you'll eventually be getting hot water from your main tank anyway.

The numbers on this chart should be very close if not exact across different brands since as I stated earlier watts are watts regardless of the manufacturer.

Flow vs. Power Required - Chronomite

www.chronomite.com

 

[Wren]

It appears that the Stiebel Eltron heater in the link above, the DHC-E 12/15-2 Plus, would provide 105-degree water at a rate of 1.9 GPM at an input temp of 52-degrees. It's the bottom unit listed in the chart below. I would imagine that would be sufficient as my kitchen sink flows about 1 GPM, although I'm not certain the filling rate of the dishwasher. The slightly less-powerful 9.6 Kw model would probably be sufficient, but there's not much difference in price so I would probably go with the larger unit.

The chart you linked to shows to get a 50-degree rise it would take 14.6 Kw at 2 GPM, so the two charts seem to be in agreement.

 

[Fitter30]

It appears that the Stiebel Eltron heater in the link above, the DHC-E 12/15-2 Plus, would provide 105-degree water at a rate of 1.9 GPM at an input temp of 52-degrees. It's the bottom unit listed in the chart below. I would imagine that would be sufficient as my kitchen sink flows about 1 GPM, although I'm not certain the filling rate of the dishwasher. The slightly less-powerful 9.6 Kw model would probably be sufficient, but there's not much difference in price so I would probably go with the larger unit.

View attachment 105404

The chart you linked to shows to get a 50-degree rise it would take 14.6 Kw at 2 GPM, so the two charts seem to be in agreement.

12kw @ 240vac 50 amps
14.6 kw @240vac 61 amps
Code for wire size is 80% # 6 wire thwn is 65 amps #4 thwn 85 amps
Might want to rethink a aux heater. A recirculation for the hot water line would be a cheaper investment. One that fits under the sink. Could wire it with a timed switch or a Alexa relay before starting the dish washer. Have you investigated if the dishwasher heating element comes on to heat the water if temp is low? Call the manufacturer tech line with complete model and serial. Sanitize mode will bring it up.

 

[Wren]

12kw @ 240vac 50 amps
14.6 kw @240vac 61 amps
Code for wire size is 80% # 6 wire thwn is 65 amps #4 thwn 85 amps
Might want to rethink a aux heater. A recirculation for the hot water line would be a cheaper investment. One that fits under the sink. Could wire it with a timed switch or a Alexa relay before starting the dish washer. Have you investigated if the dishwasher heating element comes on to heat the water if temp is low? Call the manufacturer tech line with complete model and serial. Sanitize mode will bring it up.

I appreciate your input, but I'm not going to be using a recirculation loop for this project. It's not a cheaper option to me when one considers the cost of the pump and extra piping, not to mention the extra work of hooking it up. It's either a tankless or wait for the hot water. It's just not worth the trouble to install a circulation pump, etc. just to service a sink and a dishwasher.
Also, I'm not concerned about the dishwasher's ability to heat water as the water that currently comes from the water heater is plenty hot, but I do want to decrease the wait time for hot water at the sink.

 

[John Gayewski]

Be prepared for the boss to hate the large thump/click every single time the hot goes on.

The one gallon heater is pretty tiny.