120v Undersink tankless water heaters

[Time2]

I'm about to replace a single handle Delta Faucet that I'm fed up with, as it is very difficult adjust for 'just right' temp water. (I've worked with the company, they won't admit they built a bad model.)

When I do that I also want to add a tankless undersink water heater.
If you have an undersink water heater, what do you think of it?
Because the faucet I'm installing has the hose sprayer built into the faucet, I thought I would use the sprayer hole for a hot water dispenser, but it seems almost all undersink heaters have plenty of capacity to use with the regular faucet. So, maybe I will use the hole for a soap dispenser. My faucet now flows 1.7 GPM. I'm looking at 2 GPM to 2.5 GPM water heater.

I have a 20 amp circuit available for power, so 1500W (2400W?) is the maximum power.
Rant on,

I'm disappointed with Amazon's search function, it keeps showing propane, LPG, 240v units, storage units, toilet seats and pumps, even though I think I'm using proper advanced search terms correctly. Rant off.
Tell me your experience with undersink water heaters.

 

[njhowie]

My Amazon search brings back a good amount matching:
https://www.amazon.com/s?k=kitchen+water+heater+on+demand+electric&ref=nb_sb_noss

And here's an interesting spin, but reviews are pretty bad:
https://www.amazon.com/dp/B01ARQ39CW

 

[OldShooter]

... If you have an undersink water heater, what do you think of it? ...

We have this one:https://www.amazon.com/InSinkErator-H770-SS-Invite-Instant-Dispenser/dp/B000FAVXW4 We moved into this house about 25 years ago, and I think the first one lasted about 20 years before it started to leak.

The faucet has only one purpose: Hot water for my morning Chemex coffee. The temp is set as high as it can go without boiling the water in the tank. There is a timer underneath the sink that turns it on around 6AM and turns it off around 10AM. Sometime during that time a pot of coffee gets made. I doubt that this is the most energy-efficient device in the house, so I'd suggest at least turning it off overnight if you want the hot water all day.

I don't know if they are all the same, but the design of this particular model is clever. Turning the handle opens the cold water line, which enters the tank at the bottom and forces hot water from the top out through the spout. The result is that the tank is never pressurized, there is no need for an overpressure pop-off valve and construction is probably a little less expensive. I like that there is no overpressure valve as the ones on our regular water heater have a slight tendency to leak in old age, something I might not notice under the sink. So I would look for that type of design again. Maybe they are all that way; I don't know.

 

[MissMolly]

We have an InSinkErator also. Love it. Use it every single day. We have had one of these dispensers (not the one we currently have) for over 25 years. And it's been used every single day for those 25+ years.

 

[Time2]

My Amazon search brings back a good amount matching:
https://www.amazon.com/s?k=kitchen+water+heater+on+demand+electric&ref=nb_sb_noss

I appreciate the effort, but I had to go 9 deep to find a 120v tankless water heater that will run on a 20 amp circuit breaker.

And here's an interesting spin, but reviews are pretty bad:
https://www.amazon.com/dp/B01ARQ39CW

OK, but I already have my faucet and the flow rate is 0.63 gallons per minute, I'm expecting 1.7GPM to equal what I have now. Thus, I'm looking for a 2.5GPM water heater. Also, I suspect the 0.63GPM is at a reduced temperature, compared to 0.3GPM.
I'll keep trying.

 

[Time2]

We have this one:https://www.amazon.com/InSinkErator-H770-SS-Invite-Instant-Dispenser/dp/B000FAVXW4 We moved into this house about 25 years ago, and I think the first one lasted about 20 years before it started to leak.

The faucet has only one purpose: Hot water for my morning Chemex coffee. The temp is set as high as it can go without boiling the water in the tank. There is a timer underneath the sink that turns it on around 6AM and turns it off around 10AM. Sometime during that time a pot of coffee gets made. I doubt that this is the most energy-efficient device in the house, so I'd suggest at least turning it off overnight if you want the hot water all day.

I don't know if they are all the same, but the design of this particular model is clever. Turning the handle opens the cold water line, which enters the tank at the bottom and forces hot water from the top out through the spout. The result is that the tank is never pressurized, there is no need for an overpressure pop-off valve and construction is probably a little less expensive. I like that there is no overpressure valve as the ones on our regular water heater have a slight tendency to leak in old age, something I might not notice under the sink. So I would look for that type of design again. Maybe they are all that way; I don't know.

That is the way I was originally going to connect what I bought, then I saw that many tankless heaters will flow more than what my faucet already delivers, so I changed to just running it through the regular faucet. The seller does'nt mention Voltage or Current, I found in the Q&A it is 120V, still no mention of whether it will run on a 20 amp breaker. I hate be so negative, but I have some specs that need to be met. I don't necessarily need a tankless, I just thought not heating unneeded water was one of the great advantages of tankless heaters. The timer idea is good, but doesn't fit for us. I use cold water for my coffee maker and rinse dishes, morning and evening.
I haven't given up.

 

[OldShooter]

... I found in the Q&A it is 120V, still no mention of whether it will run on a 20 amp breaker. ...

I can't guarantee but I have done a lot of house wiring and have an MSEE: I think it will be exceedingly rare to find a 110v household circuit that is over 20 amps. The result is that no marketer would offer a product that requires this.

When more power than 110/20 is needed, the default is to go to 220 volts. This is typically for electric clothes driers, but my welder, air compressor, and metal lathe are all on 220v circuits. The advantage is lower current = smaller wire diameter, for a given level of power. IMO you won't find a 220 volt circuit under a sink, either.

From a quick search, 120/30 seems to be used when plugging in small Rvs. Not a hookup that a product marketer would expect to be common under people's kitchen sinks.

 

[Time2]

I can't guarantee but I have done a lot of house wiring and have an MSEE: I think it will be exceedingly rare to find a 110v household circuit that is over 20 amps. The result is that no marketer would offer a product that requires this.

I agree, but it's wrong. Five of the first 8 hits are 120 volt units that require a 30 amp breaker. (Amazon) https://tinyurl.com/y4vhcj7u
or use;

https://www.amazon.com/s?k=120v+undersink+electric+tankless+water+heater&crid=2BNSXXXOYDDU7&sprefix=120v+undersink+water+heaters%2Caps%2C291&ref=nb_sb_ss_i_1_28

When more power than 110/20 is needed, the default is to go to 220 volts. This is typically for electric clothes driers, but my welder, air compressor, and metal lathe are all on 220v circuits. The advantage is lower current = smaller wire diameter, for a given level of power. IMO you won't find a 220 volt circuit under a sink, either.

Yep, I agree.

From a quick search, 120/30 seems to be used when plugging in small Rvs. Not a hookup that a product marketer would expect to be common under people's kitchen sinks.

I'm not seeing the RV thing on many 30 amp labeled units. I'm starting to rethink this, one of the 3kW units, 120V at 29 amps, only delivers 0.6 gallons with a 35*F temp rise. That would give me 105*F water at 1/3 the flow I want. Although, I would compromise at 1 Gallon flow at 125*F.

 

[Time2]

Those listed as 110v will work fine for you.

That's just not true. The very first Bosch unit is rated at 120V.
https://tinyurl.com/yymsxtau
The specs say to use 10 gauge and maximum amperage is 30 amps. This is a 3.6kW heater.
https://tinyurl.com/y4vhcj7u

The second hit is rated
Voltage: 120V
Wattage: 3.0kW
Amperage draw: 25A


The fifth hit ratings are,
Watts - Water Heaters: 3500
Amps - Water Heaters: 29
Voltage - Water Heaters: 120


Several of the others are similar in that they require more than 20 amps.


I'm starting to think I either need a storage type undersink unit or add a 240 volt line under my sink.

 

[Music Lover]

I'm not seeing the RV thing on many 30 amp labeled units. I'm starting to rethink this, one of the 3kW units, 120V at 29 amps, only delivers 0.6 gallons with a 35*F temp rise. That would give me 105*F water at 1/3 the flow I want. Although, I would compromise at 1 Gallon flow at 125*F.

A second unit that goes to 125F seems almost pointless considering the recommended temperature of a regular water heater is around 120F.

 

[Exchme]

The problem is in the math, you are asking for an order of magnitude more power than you have.
A flow of 2.5 gpm=1,250 lb/hr. If you are heating by say 80 F, then the heat input is:
1250 lb/hr x 1 BTU/lb/F x 80 F= 100,000 BTU/hr.
Converting to watts is 29,300 watts.
Since watts = volts x amps, at 120 V, that's 244 amps! You have to reduce water flow or have a tank and heat more slowly (or upgrade the electrical).

 

[Time2]

A second unit that goes to 125F seems almost pointless considering the recommended temperature of a regular water heater is around 120F.

Hmm, mine is at 132*F*, but my interest in getting an undersink heater is so I don't have to wait 31 seconds and draw 7/8ths of a gallon of water before I have hot water. That's the kitchen sink, it's only 7ft from the water heater, the bathroom sink is 38ft from the water heater, and take much more time to get hot water.


* I like hot showers and hot baths.

 

[Time2]

The problem is in the math, you are asking for an order of magnitude more power than you have.
A flow of 2.5 gpm=1,250 lb/hr. If you are heating by say 80 F, then the heat input is:
1250 lb/hr x 1 BTU/lb/F x 80 F= 100,000 BTU/hr.
Converting to watts is 29,300 watts.
Since watts = volts x amps, at 120 V, that's 244 amps! You have to reduce water flow or have a tank and heat more slowly (or upgrade the electrical).

Physics! I understand the temp rise vs flow. I just didn't run any numbers, I assumed that since they were on the market, I thought were doing the job. After reading the specs, and customer experiences, I need to change my expectations. And maybe have a strorage type undersink unit. But that just goes against the tankless idea

 

[OldShooter]

FWIW before we replaced our (leaking) conventional gas water heater last year I looked hard at tankless, as the idea made sense to me. The location would have been in the basement with both natural gas and heavy electricity easily available. What I found was that tankless seemed to pretty much guarantee a delay for first hot water and guarantee low flow rates. So I just replaced conventional with conventional.

 

[Time2]

FWIW before we replaced our (leaking) conventional gas water heater last year I looked hard at tankless, as the idea made sense to me. The location would have been in the basement with both natural gas and heavy electricity easily available. What I found was that tankless seemed to pretty much guarantee a delay for first hot water and guarantee low flow rates. So I just replaced conventional with conventional.

There is one other not energy wasting solution to the wait at the faucet for hot water. That is to install a small pump at the farthest faucet from the water heater. It pumps water from the hot water pipe into the cold water pipe, this causes the hot water to always be flowing a little, so it is always hot at the sink.

 

[calmloki]

There is one other not energy wasting solution to the wait at the faucet for hot water. That is to install a small pump at the farthest faucet from the water heater. It pumps water from the hot water pipe into the cold water pipe, this causes the hot water to always be flowing a little, so it is always hot at the sink.

When doing our house the mason who did many custom showers suggested a Grundfos circulating pump, like this:

https://www.bigfrogsupply.com/produ...-NDjeP4zI1SU4Ufspm_L4yhXqVFXAcARoCNKgQAvD_BwE

I just brush my teeth before shaving or showering.

In the garage we stuck a 5 gallon tank type 120V water heater under the sink. Instant hot water, acts just like a normal water heater, and fairly inexpensive by comparison. I'm a simple man.

 

[Out-to-Lunch]

There is one other not energy wasting solution to the wait at the faucet for hot water. That is to install a small pump at the farthest faucet from the water heater. It pumps water from the hot water pipe into the cold water pipe, this causes the hot water to always be flowing a little, so it is always hot at the sink.

I know such devices exist, but I really think this is a misconception to think that this saves energy. In the normal situation, i.e., without such a pump, you lose the energy of the water in the pipes to the surroundings. The energy loss ceases when the water in the pipes comes to room temperature. If, instead, you constantly recirculate the water in those pipes with fresh hot water, you will continuously lose energy. This is an energy-losing proposition.

What such an arrangement saves you is a small amount of water, i.e., you will not waste as much water waiting for hot water to reach the faucet. Where I live, water is CHEAP and energy is expensive. As @Koolau may say, YMMV.

 

[meierlde]

Note the real question is how fast does the cup need to be filled. If you recall it takes the same amount of energy kwh to heat water to a desired temp in 1 min or 1 second, but uses energy KW at 1/60th the rate of 1 second. Take the above example and go from 2.5 gpm to .25 and the amperage goes from 29k to 2900 So for example if you were to be willing to wait 1 minute to fill cup of one cup capacity size that would be .025 gpm meaning you would need 290 watts so 30 seconds is definitely doable.So the trick is to limit the flow to that that which the power available is able to meet the desired temperture range.

In my house when we first moved in we had an electric tankless heater in the kitchen, and it heated water ok for coffee, but failed miserably if the dishwaster was on. So an alternative also is to bring the hot water pipe to the sink and branch the on demand heater after the dishwaster from the supply. Of course in this case you might well get super hot water out if the hot water is there and flow is low.

 

[Telly]

Not tankless, but I have looked into ideas to get hot water to the kitchen faucet without running it and waiting for a while. It's about 50 feet from water heater, via copper tubing under slab.

Looked at a small electric tank heater, have room to put one under sink. Problems were the tank warranties were only 2 years! A leak there would be a major major mess! Also, I would have a very hard time getting a separate power feed down into that area. At corner with a hipped roof, windows, and doubled 2x12 headers extending both ways for quite a few feet.

Looked at recirculating pump with timer. Nope. Bad idea for us. As Out-to-Lunch points out, it turns both hot and cold water piping into a heating system, radiating heat everywhere and firing up the water heater to do so. Also, in our climate, we want COLD (Cool here) water to come out of a cold water faucet, not warm or hot! And via piping on the way, we don't need heated water for toilets!

So if we need hot water there, we just have to run it. Run it for a while to get it hot before hitting the Start button on dishwasher. Otherwise, the dishwasher heats the too-cool water up to temp, which stretches cycle, and uses more energy electrically ($$) to do so than our gas WH would.

 

[Time2]

I know such devices exist, but I really think this is a misconception to think that this saves energy. In the normal situation, i.e., without such a pump, you lose the energy of the water in the pipes to the surroundings. The energy loss ceases when the water in the pipes comes to room temperature. If, instead, you constantly recirculate the water in those pipes with fresh hot water, you will continuously lose energy. This is an energy-losing proposition.

What such an arrangement saves you is a small amount of water, i.e., you will not waste as much water waiting for hot water to reach the faucet. Where I live, water is CHEAP and energy is expensive. As @Koolau may say, YMMV.

I just got up and read my post about the circulating pump. I meant to say "not energy efficient solution" I wanted to change it but, the edit function is gone.
I agree this solution wastes energy in lost heat to the pipes surrounding. But it does work, I had a house with the water heater in the basement, I had a return pipe installed and it work perfectly with gravity alone. The hot water rose and the cold water sunk. Although in this case it only worked at the kitchen sink.

 

[Music Lover]

So if we need hot water there, we just have to run it. Run it for a while to get it hot before hitting the Start button on dishwasher. Otherwise, the dishwasher heats the too-cool water up to temp, which stretches cycle, and uses more energy electrically ($$) to do so than our gas WH would.

Run the water at first so that hot water is in the pipe close the dishwasher. But rather than wasting it down the sink use it to fill containers for drinking water, a pot for cooking later, or to water the plants.

 

[38Chevy454]

Late to the discussion, but I agree that if you really want a tankless water heater, you will need to upgrade to a lot bigger electric circuit. That means 230v circuit and 30 or more amps. If you want to stay with 120v, just go with a small tank type heater under the sink. It won't require much more room than the tankless setup. Something like that will give near instantaneous hot water. Or do as the other suggestion and put a recirculating system for your main hot water supply.


The main problem you have is insufficient power at 120v 20A circuit to run a tankless. The solution is to run a small tank reserve, and let the lower power run longer time to heat the water.


I have a half bath in my detached garage, with a 7 gal 120v water heater. It has always produced sufficient hot water for what I want to do in the utility sink. I even adapt a hose to the faucet and use warm water to give dogs a bath where the hot water holds out. The 7 gal is going to take up all the space you might have under a sink, but a smaller one would be possible. Yes the issue of a leak someday is something you need to be thinking about, just like any tank type water heater.

 

[Music Lover]

Yes the issue of a leak someday is something you need to be thinking about, just like any tank type water heater.

True, but a leak in a utility area or basement with a floor drain near by isn't as bad as a leak under a kitchen sink that's possibly surrounded by 1500 square feet of nice hardwood flooring.

 

[Out-to-Lunch]

I just got up and read my post about the circulating pump. I meant to say "not energy efficient solution" I wanted to change it but, the edit function is gone.
I agree this solution wastes energy in lost heat to the pipes surrounding. But it does work, I had a house with the water heater in the basement, I had a return pipe installed and it work perfectly with gravity alone. The hot water rose and the cold water sunk. Although in this case it only worked at the kitchen sink.

Ahh, I see. If your message read the way you meant it to, I would have nodded my head and said "I'm glad someone understands the tradeoffs of those!"

(On a side note, I do wish the "edit" function lived a little longer than it does.)