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enter image description hereAs an alternative to traditional tankless heaters, aliexpress sells a variety of cheap taps incorporating a heater, for example:

220V 3000W Instant Electric Faucet Tap Hot Water Heater

This looks too good to be true, looking at the compactness and at the price. Hence I was wondering if anybody has any kind of opnion/feedback about such products, for example with respect to safety, durability, doing what they promise, or any aspect.

Thank you!

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    Believe your gut. Too good to be true, electrical appliances that have potential to burn your house down/scald you/electrocute you, aliexpress "you're the importer" not tested or listed by any reputable organization - what could possibly go wrong...
    – Ecnerwal
    May 14, 2020 at 1:56
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    Yeah, with electrical in general it pays to be careful. With electrical and water together... be EXTRA careful. May 14, 2020 at 2:02
  • Have you looked at point-of-use heaters that come from somewhere other than the Cheese pipeline? Also, where on this planet are you, roughly? May 14, 2020 at 3:26
  • @ThreePhaseEel: I am in UK.
    – anon
    May 14, 2020 at 10:37
  • @ThreePhaseEel: I couldn't find any as compact.
    – anon
    May 14, 2020 at 23:36

2 Answers 2

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First, it's Alibaba, for Pete's sake. Do you even have to ask?

Even if we take this product seriously, I think it's too much heater crammed in too little space. Either they're wildly sacrificing safety standards, or they are constricting flow down to a trickle. Or both.

If such a thing were made by a reputable manufacturer such as Siemens, GE, Chromalox, etc., I would expect a plain faucet as a head-unit, and the guts of the machine to be under the sink.

3000W is certainly not enough energy budget to get a water flow you would consider "reasonable" at a sink faucet. Go look up the flow vs temperature-rise data that is readily avaialable on the Web. You'll see 3kw is not enough.

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  • Agreed. Specific Heat Capacity of water is 4200 J/Kg/°C. So, for (say) 40°C temperature rise, 3kW would heat a little under 18ml of water a second. That's not a lot.
    – SiHa
    May 14, 2020 at 6:09
  • @SiHa In moderate climate zones (e.g. Central Europe), the water tubes in 1m depth have ca. 11 deg Celsius. 51 deg Celsius is too hot for the human skin. More realistic is a throughput of 1.6l/min and a temp of 39 deg Celsius where 3kW is sufficient. With a counterflow heat exchanger the throughput could be increased by 30-40%.
    – xeeka
    May 14, 2020 at 6:47
  • ... and all the pipes/tubes inside the building have a temperature close to the room temperature, i.e. for short time use, the needed temp rise is much smaller.
    – xeeka
    May 14, 2020 at 6:55
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    @anon Sorry to offend you. Don't get me wrong, I use that junkstream all the time on low-voltage stuff. But if it touches AC mains, it must have a UL listing with file number or reputable NRTL equivalent. None of their stuff ever does: it's always the faked CE mark. "Hit or miss" is not allowed with AC mains. May 14, 2020 at 16:09
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    @anon many NRTL s are European... BSI, TUV. Their function is to independently test the device for safety. The EU has a mark that looks identical to China Export, it means the manufacturer self certified. That's only as good as the manufacturer lol... May 15, 2020 at 1:24
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In combination with a proper wiring and a mandatory GFCI, it is certainly worth the ca. 30$. It should be no risk - it is assumed a blank heating wire is used:

  1. Electric current does only flow if enough water current is detected
  2. Normally this device is only used with a person present in the same room
  3. Any dangerous residual current to the metal sink or water would force a power cut by the GFCI
  4. A fire started by that device is very unlikely since the heating element is surrounded by water and in case of a malfunction (water signaled by the sensor, but no water flowing) that heating wire will simply burn through entering a fail safe status
  5. A water flow fuse/guard system should be anyway installed even in private houses/appartments

As for the 3kW: yes, the flow is restricted, but that would encourage to save water. The longtime experience with a standard tankless 3600W heater with blank wires shows that it is sufficient for kitchen or bathroom use, if the water enters with a temperature of 11 deg Celsius or more. Only very fatty plates or pots are more difficult to clean, but we all should avoid eating too much fat, shouldn't we? Anyway that would be the task of a dishwasher.

It is full sufficient for hand/vegetable/fruit washing.

It can be very useful as "afterburner" for heat pump systems since the COP will decrease the more energy must be pumped into the domestic water.

And there is the option to add a counterflow heat exchanger, which can be easily made, e.g. search for "Rob the plumber" on youtube. That way it would be converted to a virtual 4-5kW heater.

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  • I think you're assuming it's capable of anti-scald. If not, the "afterburner" function would be Very Bad. May 14, 2020 at 6:23
  • @Harper-ReinstateMonica If the heat pump works until 32 deg Celsius, this faucet could deliver the missing energy to get 44 deg Celsius. Why is that afterburner very bad, if the maximal temperature could be adjusted resp. the LED shows the temp value?
    – xeeka
    May 14, 2020 at 6:30

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