Point of Use Water Heater (Under the Sink Heater)

I have a Bosch point of use water heater 2.5 gal...works great...I had the same problem waiting for the water to heat up...It does require some space, but very easy to hook up...

https://cr4.globalspec.com/thread/122541/Mini-Water-Heater-Install-Complete

Agree, these are a pretty common item. The big box hardware outlets show these at about $160 bucks.

Point of Use heater is exactly the common name for them.

Some points to ponder.

If your main concern is convenience and not cost over time, then POU is definitely for you.

But, as soon as the hot water faucet at the sink is turned on, two sets of heaters are energized. One at the sink to heat the cool/cold water in transit from the main tank to the POU tank and the other at the main tank to heat the new, cold, incoming water to the main heater tank.

Then there's the cost of the tank and installation, any added use of energy owing to two sets of resistance heaters running simultaneously for some period, not to mention the loss of under sink storage space. Your specific kW consumption depends on your equipment.

Like I said, if your main concern is convenience and not cost over time, then POU is definitely for you.

But, some things to consider.

I think I agree with Lyn's comment? You don't want to be drawing water from the existing heater for this as it will only add to running costs. Feed the new heater from the cold supply that surely already exists at the sink.

That's not a good idea, you run out of hot water if you do that....you have 30 seconds of hot water and then both feeds are cold....This setup saves energy as the alternative is letting the hot water run until it gets hot, like it is now, this wastes water and uses more hot water from the existing tank, which in turn has to run longer to reheat the water....and the larger tank draws much more electricity than the small 2.5 gallon 120v tank, that only has to run for a short time...

I'm confused!!! Why would you only have 30 seconds of hot water from an instantaneous water heater which is what the OP is asking about?

In my experience all instantaneous water heaters get their supply from the cold inlet and will supply piping hot water for as long as you require.

Even a small under sink tank unit would still be better getting its feed from the cold side rather than wasting heated water from the main tank.

Perhaps I am misinterpreting the intent of your reply.

The Bosch point of use water heater is not an instantaneous heater, it's an instantaneous supply...The 120v 2.5 gallon water heater plugs in to a regular 15 or 20 amp receptacle...1440 watts...it does heat quickly, but not instantaneous...2.5 gallons might be enough for like a small bar sink or guest bathroom sink, but for a kitchen sink I think not...that's why it's best installed on the incoming hot water line...Now they do have larger units for different applications, but to me running out of hot water is just as bad as having to wait for a minute for it to heat up...maybe even worse...

Obviously I missed the bit where the OP was talking about a Bosch tank unit, I just saw the bit about heating the water instantaneously which I would have thought would rule out a tank style setup which, whilst I accept that they heat relatively rapidly compared to a 300 litre monster, are not in the same realm as an instantaneous unit which can supply hot water practically from the moment you turn on the tap until you turn it off again - maybe some 100s of litres later.

If using a small tank type and requiring more hot water than it stores, then your idea is probably better as the roughly 1.5 litres of cold water coming into the tank from the existing hot water line before being replaced with progressively hotter water from the main tank would produce a better result.

Another option is fitting the hot water pipe with heat trace cable and insulation. This helps keep the hot water in the pipe from cooling and may be a better option than a separate heater.

Link

I should have mentioned. The hot pipe, wrappen in insulating foam, runs in a conduit through the slab.

One method is to use a smal pump to recirculate permanently or at certain set times, the hot water to have it ready, so no need of pus heater. But there is a pump, there are pipes...All I want is to provide, to a small pou heater, water comming from the house heater. At the beggining, water is cold and it will be so for more than one minute. Well, if the pou heater starts to heat this water, in few seconds I will have , at the kitchen sink, hot water. The pou heater will have less and less power applied to the heating elements untill the water (coming from the house heater) reaches the set temperature for pou heater. Bosh heater as others, too, have the cold water at the input of the heater. Does anybody know of a reason to not to use the hot water pipe from house heater instead of the regular cold water pipe?

The point of use water heater can be hooked up either way, but if you hook it up to the cold water, you run out of hot water rather quickly with just 2.5 gal tank...and if this is a kitchen sink like mine, not a good idea...I use the hot water for rinsing dishes and hand washing, it starts off hot for about 30 seconds then just warm for a couple of minutes before it begins to get hot again...They do have larger tanks available but the space might be a problem...I am quite happy with my hookup and tank size....

Everyone needs to bear in mind that "point-of-use" and "instant" are not the same. SE has a point-of-use heater with a small tank and a fairly low-kW 120V element, which suits his usage profile. The OP is looking for an instant (tankless) heater with a fairly high-kW element and no tank.

Tankyou for the clarification....the small pou tank accomplishes the same goal with a much lower electric demand...the only caveat being need for tank space under cabinet...

Point of use for kitchen, main for bathroom.

P.S. Wots hot water?

What we have is, failure to communicate.

Thanks, Warden.

--Cool Hand Luke

My mother used to use these local water heaters for washing customer's hair when she owned a ladies hairdressing salon. One unit to each hair wash station which was flexible, easy to plumb and economic as there was no requirement for a central tank or standing hot water. There would be no problem plumbing it into a hot water supply but they are on/off operation and the input power (Kw) cannot be varied. The heat of the water depends on the flow rate, so hot water would be created in 3-5 seconds at a low flow rate and the temperature would, or the flow rate could, increase as the preheated water arrives at the unit. So after the lag you could draw water at your required temperature at a higher rate, for a set volume your heaters would run for a shorter time and the energy cost is not much different to your present set up. The power requirement is higher for a shorter time but you don't waste unusable water (too low a temperature) while the hotter water is traveling along the pipe. The lowest energy use would be a cold water feed to the instantaneous unit thus avoiding wasting heat and water while you wait for it to become hot enough to use and the energy lost as residual hot water standing in 40ft of pipe goes cold.

You can get instant hot water by running a small bore pipe (10mm) from the tap to the cylinder & stab it into the tank, it will circulate the water so you will always have instant hot water, this works if the cylinder is higher than the taps if not you will need a bronze pump to push the water round, this is better done during the build then you can do all the taps in the house.

Bazzer

almost right. many POU heaters have an INFEED Temp switch such that when the HOT water gets to the unit it will shut off. also, many do not have a tank just a heat-exchanger. additionally, you can run a line from the farthest hot faucet back to the BOTTOM of the water heater. it will generate a passive loop to heat the entire line. both systems are very good. to the second option, there are small 120 VAC pumps that you put inline and have a 3-5 minute timer. you get up, push button, water circulates, no loss and you have hot water. all very simple options.

Don & Bazzer, circulation is going to considerably increase energy consumption = ^power bills^.

Just P.O.U. should be enough

Friends,

Many comments and some confusion. The OP is asking for help to get hot water at a kitchen sink without the time lag for 40-feet (12-meters) of pipe containing water that has cooled down, to deliver hot water from the tank after also heating up the pipe and its surrounding environment. This question can be answered from a number of viewpoints, and the OP will have to choose the way forward.

New small tank "Point of Use" type water heater: Requires a 120v, 1.4kW power connection. Will have water heated to its set temperature ready for nearly instantaneous use until its supply is exhausted. If connected to the hot water line for its incoming water, the water at the sink will initially be hot, then cool down if more than a gallon (4 liters) is used, but then come back in temperature as the incoming water changes from cold to hot (from the home's main heater). For a quick rinse of a couple dishes the water will be hot. No need to run water for an extended time to get hot water. Fairly simple and reasonably low cost. If very well insulated, is low on energy requirements.

New small instantaneous (tankless) water heater at the sink: I have seen some of these installed in a developing country's bathroom shower heads. This version is quite small and works well if the water flow is low. Draw's energy only when in use. I doubt that they are available in the USA, and do not recommend them.

New large instantaneous (tankless) water heater at the sink: Requires separate new 240v electrical supply. Can supply unlimited amount of water. Newer versions have controls that vary the voltage to the heating elements as needed to maintain a nearly constant output temperature. Can be connected to either the hot or the cold line for its supply source. Probably requires more space than a small point of use heater. Draws energy only when in use. Highest installed cost.

Recirculation of water in the hot water pipe: If not by gravity flow (source tank higher than piping), will require a pump. Also requires supply and return lines (but this can be done with concentric piping of a smaller supply line within the larger diameter return line). Probably requires running new pipe(s) and costs associated therewith. Energy cost higher than the point of use tank, and higher maintenance costs if a pump is used.

What will you use? Choose the best balance between installed cost, space requirements, ease of installation, and energy use. None of us can do this balancing for you.

--JMM

I first got interested in point-of-use water heaters a few years ago when I read an article about a house designed to be as kind to the environment as possible. The house was built in CA, Land of Drought. The family that commissioned the house were equally interested in conserving water and conserving the energy that heated the water. So I consider heating at the source to be of particular worth in arid areas.

Mr. BIS and I have friends who live in Santa Cruz, CA. During drought cycles they catch as much of the waiting-for-hot-water water as they could and saving it for dishwashing and watering plants. I can't imagine what a chore this is; I'm very grateful for our well water even if it is the hardest water I've ever experienced.

JMM, I couldn't say it better, although I tried!

What I want is to have hot water after a reasonable waiting time. The kitchen sink is not a shower, barely needs 1.5 gpm. A pou heater, a 1-2 KW, under the sink, would do the trick. But, I want this pou heater to heat the water coming from the main heater (where there are 50 gallons of 149 F waiting to be used). If I connect the input of the pou heater to the hot water pipe coming from the main heater, I hope that the small guy willheat the water (within seconds), and continue to heat the water coming. But this water, gradually, has a higher and higher temperature. Thus, the pou heater, also gradually, decreases the power to the heating elements until it stps heating water that comes at the set temperature of the pou. Of course, the hot water coming from the main heater shouldn't have a temperature higher than the protection set temperature of the pou.

My question was if there are contraindications to use hot water as input to pou, and why Bosch (and others) didn't use the hot water as input?

It won't save much, if any, energy; and it may require more sophisticated temp control on the POU heater.

Indel,

I have not researched to see if any of the small pou heaters (with tanks) have a proportioning controller instead of an on/off thermostat switch. If they do, I would expect their prices to be significantly higher. The economics of marketing would suggest to me that none of them would have such a controller.

Water heaters are made with the hot outlet coming from the top of the tank and the cold inlet delivering to the bottom of the tank, so nearly all the tank's capacity is available as undiluted hot water (since the incoming colder water has a slightly higher density and would stay towards the bottom). This is why I said you would have an initial delivery of hot water, then a period of cooler and then hot again as the supply from your main heater arrives.

If you were to do the unorthodox plumbing connections with the inlet on the hot side and the outlet on the cold (bottom), you would see more mixing of the initially cold water coming from the main hot water heater, and the temperature delivered to the sink would generally be a little lower than the max and a little higher than the minimum. That is worth thinking about, even if it raises many eyebrows.

I would set the temperature of the local pou heater lower than that of the main heater. On a side note, decades ago (1980's) our engineer instructor pointed out that the calculated break even point between energy conservation benefit and the cost of adding insulation to a hot water heater's tank was around R-60. This was done on a basis of adding one R per calculation.

Let us know what you decide to do. --JMM

To conclude the discution about pou water heater that connects in line with the main water heater, this is what should be said about such a device:

The Eemax “Thermostatic” heater is specifically designed

to take in cold or preheated water and heat it to temperatures suitable

for the normal domestic usage up to a maximum of 140 F

Short statement, concise! I have changed my opinion about Bosch, which I considered an innovative company when, in fact, they are a bunch of technical dynosaurus that keep the same temperature control from before WW2.

The Eemax EX3012T is about $200.

Thank you, guys, for helping me with your oppinions

This unit won't work well for your application....it is a tankless underpowered heater...

"Yes, the EX3012T is 110V. It could work for a bar sink(maybe). This unit will provide a 41°F temperature increase at a flow rate of 0.5 GPM. If your water flow rate is higher at 1.0 GPM, then your temperature increase will be 20°F. You would add number that to your cold water temp. to determine your output temp."

And sells for over $300 ....a waste of time and money...kitchen sink has a standard flow of 2.2 gpm...

At the standard flow rate the heating by this unit would hardly be noticeable, if at all....

https://www.amazon.com/Eemax-EX3012T-Thermostatic-Electric-Tankless/dp/B006FRA0IO/ref=sr_1_2?ie=UTF8&qid=1541518274&sr=8-2&keywords=+Eemax+EX3012T

I might also add that at a 3000 watt rating on a 120 volt circuit, the amp requirement would be ~25 amps. This would require a dedicated circuit and special breaker as the standard 120v max breaker size for residential use is 20 amps. All in all a lot of expense for something that doesn't really work properly. If you're going to have to go to the expense of running a dedicated circuit, why wouldn't you just run a 240v circuit?

Yes, it is a good idea to run an EX55T or EX65T at 240V. In fact I do have the 240V outlet from the electric stove which I replace with a gas stove. My house has been flooded by Harvey, last year, and I remodel it with new gas pipelines.

As for the temperature rise function of flow, I am not much cocerned, I do not use the high end of flow. And price is still bellow $200, on ebay, for a new device.

Bear in mind that these tankless heaters are not instantaneous, they take a while to heat up...The only way to get instant hot water is with a ready supply...The brand you seem to be stuck on is not highly recommended and is quite a bit cheaper than the industry norm...so I'm curious, why are you going with this brand?

We bought a house that had multiple small tank (4 to 8L) POU devices. Each and every one of them was a heat loss in the system every hour of every day. There were four of these small units and each failed around the tenth year in service. Their power was billed at "day" rate as they are connected to demand power. The main water heater was "off peak" and so only drew power during the cheap period.

That house (as many we have lived in) used rainfall tanks for supply so we were particularly aware of our water usage. Town retic was at least 10km away so not an option.

We chose to remove all the sink units and utilise the hot water with the associated delay.

We chose to use that initial flush of cooled hot water in the line to fill the jug/kettle to be used later for coffee/tea and not to run any cold water for sink until the hot was "too hot".

If you choose to use an "instantaneous" heater in-line with the pre-heated water, then you can personally regulate flow through that device until the pipe volume has been processed and then turn up the flow once the main hot water has arrived.

In short, don't get a tank unit.

SE, a 6.5KW heater will rise the cold hot water (just like that) temperature to convinient level in few seconds, besides can be connected to the hot water pipe. THat was in my mind the efficient way to use a pou heater. The heater with a tank will use more electricity than this one for a, say, one week period of time, and has, at the standard kitchin sink flow, almost permanent hot water. As I said I am remodeling the house. I will instal a walk in tub and I expect it to be used intensively (next Sunday I going on a cruise and plan to spend all the time in the jacuzzy). Such a walk in tub will require a good tankless water heater. A gas one (about 120,000 BTU). The new water heater will be close to the walk in tub but still, far from kitchen, so this EX65T will not be retired. Thank you for the help

That's not true, a lot of these tankless heaters have delay(30 sec or more) due to water flow sensors and other instrumentation....not to mention the nature of resistance heater elements...

read for yourself...

https://www.smarthome.guide/best-electric-tankless-water-heaters/

...check the prices, these are rated the best...

Put a pan of water on the stove and turn it on high......that gives you some idea...

...and a Jacuzzi has a recirculatory heating system...

" The in-line water heater maintains your same warm and cozy water temperature for as long as you want to soak."

http://www.jacuzzi.com/baths/walk-in/

I might add that my 2.5 gal tank is connected to the hot water line, that is the recommended method...and you still haven't told us why you have chosen this off brand unit, is it strictly based on price?

I would advice you just get a hot water heater that can serve both needs. There are lots of point of use water heaters that will still supply hot water at that distance even if the water is being run simulteneously. So do not aim at just supplying for the kitchen zinc. see Top10den for the best rated ones.

https://top10den.com/best-electric-tankless-water-heaters

Based on your query if 135°f is your take then you should probably get an eccotemp. Most electric tankless water heaters will heat water in less than one minute as long as you are not living in antarctica. Lol!

Well, I have purchased the SPEX65T tankless water heater. No luck with the first one but I got an immediate shippment of a new one. In use for about three weeks. It coincided with an unusual cold period fot South-East Texas. Normaly, hot water comes from a 50 gallon main electric water heater at a large distance from the kitchen sink. Warm water comes in over two minutes to the kitchen sink which is, for some people (me, for example) extremely agravating. The model of tankless water heater is among few models that accept as input water, preheated water. The results: in the morning, temperature outside 3 degrees C, in the house 10 degrees C (I am still living in a trailer). All my measuring equipment has been under 39 inch of muddy water, so inoperational. But I got 55 degrees hot water in 7 seconds. How do I know? That's my sensitivity for hot water. The flow is bearly to keep the heater working but after two minutes, if necessary, the flow is three or more gallons a minute, from the main water heater. Also, I have set the limit for SPEX65T to 57 degrees C, hot water from the main heater being 60 degrees C, thus the SPEX doesn't energize its resistences. Therefore I got what I was looking for. I hope that in about 35 years I will break even with the price/cost of electric energy...