Which instant water heater

cronley

I am thinking of installing one or more instant tankless water heaters, that only heats water on demand, when the hot tap is turned on, in the kitchen, or in two washand basins in the bathroom & ensuite. I have limescale problem, so a mains fed heater is not suitable. My attic storage tank, and the copper cylinder in my hotpress, contain the mains water, which has been passed through a phosphate dosing vessel. This has overcome the limescale problem. Only two adults in the house - so hot water usage is only for washing pots, and handwashing. Showers are provided by electric tank fed shower, Triton T90Z, with no limescale problem. Bath water is heated by immersion heater, or oil boiler central heating system. I dont want to be heating the copper cylinder for washing pots & handwashing.
There seems to be many mains fed instant heaters, but does anyone know which instant tankless heaters can be fed from the treated water in my attic storage tank, or from the copper cylinder. I came across this one - any views
http://www.watersave.ie/product/insta-80-instant-electric-water-heater/

TPM

Before taking anything else into consideration you need to look at the electrical power usage.
standard main fuse is 63 amps
the t90z is approx 40amps
the water heater you linked is 25 amps
so technically you can not use the shower and the water heater at the same time never mind multiple ones. or allowing for the immersion, kettle etc.

Why do you not want to stick with just the hot water cylinder if it is properly insulated it will stay hot for a long period, and with a time clock you can have the water hot when you are washing the pots.

cronley

Thanks TPM
We can live with not using shower and water heater at the same time. If someone is in the shower, we can wash the pots when the shower is finished.
The way I was looking at it - washing pots needs about 2 gallons of hot water, and random handwashing only heeds half a gallon of hot water. For random handwashing, the sink element of the immersion ,has to keep about 10 gallons constantly hot.
I dont see the sense in keeping 10 gallons constantly hot, when you only need half a gallon for random handwashing, and 2 gallons for washing pots.
So, has anyone else done what I am proposing, & what non mains instant water heaters are available for this.

Idbatterim

would you even wait for the hot water to reach taps before washing hands? i dont. For washing dishes, throw on full kettle and thats it... I take it you are not on a natural gas line or would go for lpg a combi boiler would be perfect for your requirements...

TPM

cronley wrote: »

We can live with not using shower and water heater at the same time. If someone is in the shower, we can wash the pots when the shower is finished.

its not really a case of living with it, if someone hops in the shower and the hot tap is accidentally turned on you could pop the main fuse.

cronley wrote: »

I dont see the sense in keeping 10 gallons constantly hot, when you only need half a gallon for random handwashing, and 2 gallons for washing pots.

if you take a factory insulated cylinder will potentially have a heat loss of less than 2kwh per 24hrs (ref to gledhill cylinders info) , so basically to keep the water hot the immersion would have to run for less than 1hr per day or use less than 2 units of electricity. its not a huge expense to have hot water available, not to mention the fact at the price of the heater you linked it would take a very very long time to save your money back even before you start saving.

cronley

Idbatterim wrote: »

a combi boiler would be perfect for your requirements...

I read somwhere that a combi boiler is too slow for bath hot water. If I was to go for a combi, how would I get bath hot water. Is the combi just piped to the kitchen and washand basins hot taps, and retain the copper cylinder hot pipe to the bath. How would the combi deal with my limescale - must the combi be fed from the mains, or can it be fed with the treated water in my attic storage tank.
If these questions can be answered - would it make sense to change my old oil boiler for a combi oil boiler. The natural gas main is on the road past my house - but above questions apply to the combi option.
Views appreciated.

Idbatterim

ok, I have the traditional crap set up here in the house that I rent. Bloody electric shower that is useless and boiler can heat the hot water tank or it can be done by electricity.

I usually shower and bath down the road in the family home. There is a combi boiler there, it throws out unlimited, scalding water if needs be and with a very fast flow rate.

Ok in my family home, the combi is simply mains fed, there are no tanks, no pumps, nothing, an extremely simple, cost effective set up. Mains pressure is more than adequate, even at first floor level.

How would the combi deal with my limescale - must the combi be fed from the mains, or can it be fed with the treated water in my attic storage tank.

not sure, maybe someone else can advise you on this or ask a plumber...

I would price up various options. What is price of gas kwh v oil. Is your current oil boiler near end of life?

Sleeper12

cronley wrote:

Thanks TPM We can live with not using shower and water heater at the same time. If someone is in the shower, we can wash the pots when the shower is finished. The way I was looking at it - washing pots needs about 2 gallons of hot water, and random handwashing only heeds half a gallon of hot water. For random handwashing, the sink element of the immersion ,has to keep about 10 gallons constantly hot. I dont see the sense in keeping 10 gallons constantly hot, when you only need half a gallon for random handwashing, and 2 gallons for washing pots. So, has anyone else done what I am proposing, & what non mains instant water heaters are available for this.

Not only the 10 gallons of hot water you mentioned above. Go to the kitchen sink and run hot water measuring it in a litre bottle. You'll fill 5 litres of cold water before the water gets warm in a standard house. Another litre of warm water before it's hot, hot. So every time you use hot water at the kitchen sink you leave a gallon of hot water in the pipes between the hot press and the kitchen sink.