I am not an electrical expert but I would like to pen down here whatever I learnt from internet and by practical experience about Water Heaters(WH)/Geysers. Electrical Water heaters are of two types: a) Instant Water heaters and b) Storage type water heaters.
Instant WH:
It consists of a small stainless steel tank in which heating coils are dipped in water similar to a water heating iron dipped in a bucket of water.Its only that the bucket has a outlet which is attached to your TAP. The only difference between a Water heating iron and Instant WH is the inbuilt safety features provided in an Instant WH.
The basic principle behind a Instant Water heater is that water flows over a heating element and gets heated instantly. So the greater the flow of water the lesser the time for water to get heated and so lesser the water temperature rise.To increase water temperature either we have to reduce the flow of water(which we can’t do if we need to take a direct shower) or increase the capacity of the heating coil ie. KW/hr rating.
By my personal experience a 3KW Instant WH is not able to give you required hot water temperature rise for a medium flow of water through shower.You at least need a 4.5KW/hr capacity. Instant WH are also similar to Storage WH only difference is that they have a small tank capacity say 1Litre to 3 Litre. Having a 3 Litre capacity tank ensures initial hot water supply for a little bit longer period of time.
Procedure for operating a Instant WH:
First ensure flow of water to the Instant WH. Do not open the outlet.Let the water get heated for sometime( 60 seconds for a 3KW Instant WH). In some Instant WH there is a neon sign to display that the water is hot and now can be used for bathing.If you do not have this neon sign better open the outlet and adjust the flow so that hot water with required temperature flows out.
Safety devices:
Good Instant WH use a thermostat to cut off the supply of electricity to the heating element once the required temperature is reached.There is also a fusible plug in case the thermostat fails which will allow hot water to drain out of the WH and not raise pressure inside the Water heater tank due to creation of steam and thus avoid a explosion.Use of Plastic body panel for the WH has two advantages-Does not transmit electrical energy so no shock and also no rusting of the WH body.All these safety devices are available only in Good quality ISI branded WH so always make sure to go for Branded WH from a good company. Good Brands include: Racold, Bajaj, V Guard etc. Do not go for cheap non-branded local makes as they have inferior quality water tanks which can burst, rust and can also lead to electric shocks.
Do not go for any Instant WH below 4.5 KW/hr if you want to directly bath in the shower.
Fitment of a Instant WH:
Fitment is quite easy. The WH electric wire needs to be connected to a good quality plug(Rs 60) which would fit in a minimum 16Amp. Socket(Rs 120).Never remove and refit the plug and socket often because if there is a loose contact the entire socket-plug assembly will burn and might be blow out your house’s fuse.Ensure there are no loose connections and no sparking at the plug.If the socket is far away from the Instant WH location then we need to use good quality heavy duty(higher thickness/gauge) wires to extend the same. Use of thin wires will lead to short circuits and burnout. Make sure you use wires which are protected by a thick rubber sheath.Also use good quality insulation tape at the joint of two wires.
Inlet of the WH is connected to the Inlet Water pipe by use of flexible pipes.Always ensure you make use of a valve at the inlet so that you can close it at your will for further maintenance work on your WH and need not cut off the water supply of the entire building just to service your geyser. Pipes available in market are heat resistant flexible pipes. Use good quality pipes or either they will leak after some time or rust. Kohinoor Brand pipes available in market come with Brass connections at end so rustproof. One pipe costs Rs 150 so for quantiy 2 its Rs 300.Total hardware cost Rs 410 and labour cost Rs 150-200(In Pune).
Advantages of Instant WH:
a)Good for small families and reduces Electricity usage as it need not heat a large quantity of water as in Storage WH.
b)Cheaper than storage WH for eg. I purchased a Instant WH make Bajaj, 3 KW, 3 Litre tank capacity for 2600.Whereas a storage water heater price starts at Rs 6000.
c)Can be installed in tight places or small bathrooms easily
d)Does not spoil the aesthetics of the bathroom because size is less.
e)No energy wastage in heating storage water which is not used.
Disadvantages of Instant WH:
a)Can provide Hot water only for a very limited amount of time for a given flow. Say for a flow of 0.5 litres of water per minute a 3KW/hr Instant WH might be able to provide hot water for hardly 1 minute only.
b)Taking a bath directly under a shower is not possible. My experience with a 3KW Bajaj Instant WH tells that it is able to give hot water only for 30 seconds under medium flow of water to the shower.
Storage WH are good for supply of sufficient quantity of hot water at required temperature, if we choose the right capacity. But they consume more electricity to heat a bigger volume of water.Also storage WH with less storage capacity will lead to insufficient flow rate of required temperature hot water for a shower. Storage WH have to be turned on a few minutes before you want to take a shower so they are not instant. They have heating coils starting from 1500 KW/hr so might take a time to heat up.
Also energy consumed to heat unused hot water goes waste.But these are good for Bigger families and where larger volume of water is to be heated.If you are person who uses a bucket filled with hot water even a 1litre capacity Instant Water heater will suffice your need. They start at as low as Rs 2100.