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So I am considering instant water heater systems, in Indonesia.

Here electricity is typically low amperage (household supplies start at 450W, then 1100W, then 2200W), and there's a strong incentive to avoid high power consumption appliances (because you may also need a generator to back it up, as the power is unreliable)

I was recently in Malaysia and tried a power shower (http://www.midea.com/my/consumer/kitchen_bathroom/instant_water_heater/201505/t20150525_180326.shtml) in a hotel, which was 3800W. This, as mentioned is more than the entire electricity capacity of most houses in Indonesia. It gave a pretty good shower.

Now here in Indonesia they sell electric and gas heaters.

One common model is a Paloma 5 litre (I think this means 5 litre/minute flow rate) gas heater.

According to Paloma's website:

https://palomaglobal.com/product/waterheater/index.html

the flow rate is based on 25C heating above input (so here, with 20C input, you'd get 5 l/minute of 45C water)

They say a kitchen tap is 4l/minute, and a shower 8-10l/minute. So the 5l is only sufficient for a kitchen tap, not for a shower.

According to these data:

https://palomaglobal.com/product/waterheater/lineup.html

the 5l water heater has a gas consumption of 10.5 kW. That's more than double the 3800 W of electricity that I used to shower with in Malaysia.

So what is the explanation:

  • some difference between x,000W of water heating capacity between gas and electricity
  • my 3800W shower actually wasn't very powerful, I just got used to terrible low water pressure in Indonesia and it seemed good in comparison
  • some difference between the way the shower pumps water and a simple water heater which then obviously requires a separate shower?
  • something else?
  • Can we say for example: 10,500W = 5 litres/minute @ 25CΔ (based on manufacturer's spec) So 1 litre/minute @ 1CΔ = 10500/5/25 = 84W/minute/CΔ Therefore, if the water was heated by, say 10C, then 3800W/10/84 = 4.5 litres/minute. So I may have had a 4.5 litre/minute shower at 10C above input temperature? Or some permutation along these lines? It only seemed ok because (a) the input water is not that cold, and (b) the flow rate was good enough. And would the 5 litre/min gas water heater deliver, say, 10 litres/minute at 12.5CΔ ? – thelawnet Oct 1 '16 at 15:31
  • I have not seen a Gas water heater that uses electricity. Other than for lighting the pilot and possibly a digital control. – Ed Beal Oct 1 '16 at 15:50
  • sorry maybe I wasn't clear. 'They sell electric as well as gas heaters'. Not combined dual fuel. The gas heaters use D batteries for ignition from what I could see – thelawnet Oct 1 '16 at 15:53
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    Electric On demand water heaters have to heat the water quickly and draw high amounts of current while in use where a tank water heater slowly heats the water and keeps it in the tank so they have lower kW draw but keep the water hot all the time over all efficiency is lower and they take time to recover where the tankless or on demand have no recovery time. – Ed Beal Oct 1 '16 at 16:02
  • You're working at this backwards. I didn't see anything that provided the heat rise of the electric unit. The efficiency of the gas unit is listed at 83%. A typical tankless electric water heater might have a 90% efficiency. That means at 5L/m, the temperature rise of the electric unit would probably be around 10C. – Comintern Oct 1 '16 at 17:06

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