New immersion heater or inline instant hot water system

easyryder1978

I currently rent a house with 3 tenants. House is all electric.
Shower is electric so all they really use hot water for is washing up. (And not very often believe me lol).
Immersion heater is donkeys years old and is wrapped up in a jacket but seems to cost a lot to leave on economy 7 all the time. Would I be better installing an instant water heater under the sink or investing in a newer immersion heater to save money? Thanks in advance.

footyguy

easyryder1978 wrote: »

I currently rent a house with 3 tenants. House is all electric.
Shower is electric so all they really use hot water for is washing up. (And not very often believe me lol).
Immersion heater is donkeys years old and is wrapped up in a jacket but seems to cost a lot to leave on economy 7 all the time. Would I be better installing an instant water heater under the sink or investing in a newer immersion heater to save money? Thanks in advance.

If the immersion heater is not broke, a new one is not going to save money.

Reducing the tank thermostat temperature to about 60-65 degrees would be good start. It's amazing how many people have their thermostat set at 80 degrees or above, which usually means the top of the tank is boiling away, whilst the bottom (where the thermostat probably is) never reaches the desired temperature.

This is particularly so if you leave leave the heater on for all 7 hours of cheap rate electricity every night. Fit a time (cost of timer typically less than £20) and restrict heating to about 2-hours per night, which should be plenty long enough to heat a tank of water, even from room temperature.
If not much hot water is used (since they have an independent electric shower) then chances are the tank water will still be quite warm the next nightr, so perhaps only 30mins-1 hour heating is required.

I'm not sure what type of in-line instant electric heater you are thinking about, but it'll need to be a really beefy one to heat mains pressure water to an adequate tempearture as needed. An electric shower is typically 8-12kW and the water flow from that is quite restricted (and of course only one outlet - the shower)

Combi gas boilers (ok perhaps say 75% effecient) tend to be at least about 90,000btu (so about 27kW) ... so actual heating capacity of about 20kW once efficiency is taken into consideration.

You'll need some very special (meaty) wiring to allow a load of 20kW. I know someone who installed their own wiring for a 12kW shower and they said that was a nightware as the 'cable' was more akin to a solid bar.

20kW is about 90A - about the maximum capacity of any domestic supply (some domestic proerties are fused as low as 75A, others up to about 125A)
You would need a new consumer unit just for the 20kW heater, which may need it's own independent supply. Either way, you would need probably need permission of the electricity company, who probably won't grant it without putting you on a business supply ... and they could even claim you'd need to pay for your own substation.

Tell us more about this instant electric water heater you are considering, as I've obviously got the wong end of the stick here.

macman

Heating the same amount of water on a single rate tariff (which is what you'll need to switch to if you remove the immersion heater) is going to cost 250-300% more.
And what about the heating-does that not also utilise the E7 rates with night storage heaters?
Have you established that the immersion is properly wired to the E7 side? If it's being constantly left on peak rate boost then it will cost more, although the thermostat and insulation should limit that extra cost.

easyryder1978

I was looking at putting something like this under the kitchen sink. Put in the eBay number below.

171483837252

the immersion heater only comes on at night. There is a controller but I don't think I can set how many hours it switches on for. It does allow me to boost the heat during the daytime.

jbuchanangb

I put in a 3kW device to supply just one basin the downstairs loo, with very occasional use. It just about copes as long as the tap isn't turned on full pressure! You will certainly need special wiring for a 7.5kW device, and need to do a bit of research about water pressures and how many outlets in can serve.

Pincher

easyryder1978 wrote: »

Shower is electric so all they really use hot water for is washing up. (And not very often believe me lol).

I use the Dishwasher to de-clutter.
I suspect it is more efficient than washing dishes piece meal.

easyryder1978 wrote: »

Immersion heater is donkeys years old and is wrapped up in a jacket but seems to cost a lot to leave on economy 7 all the time.

Unless the tenants shower during E7 hours, I think you should go on single rate tariff.

footyguy

easyryder1978 wrote: »

I was looking at putting something like this under the kitchen sink. Put in the eBay number below.

171483837252

the immersion heater only comes on at night. There is a controller but I don't think I can set how many hours it switches on for. It does allow me to boost the heat during the daytime.

7.3kW - thats like a cheap. low-powered electric shower.

Don't expect very fast flow rate, and you'll have to hope your tenants don't want two hot water taps on at once. e.g. one washing their hands the bathroom, whilst another is using hot water in the kitchen.

As jbuchanangb says, you'll need special wiring installed for that power (similar to an electric cooker point)

I think you would restrict your letting opportunities by installing such a device in lieu of the current system.

£48 plus electrical & installation work?
You could have a timer supplied & fitted for about £48 (if you know a good spark)

footyguy

Pincher wrote: »

...
Unless the tenants shower during E7 hours, I think you should go on single rate tariff.

:huh:

E7 hot water heating takes advantage of the cheap rate electricity by heating the water at that time. It is stored until required. i.e. The tenants can take a shower any time

DJC1690

have you got Horstmann E7QUARTZ Economy 7 Quartz Electro-Mechanical Immersion Heater Controller With Integral Timer & 60 Minute Boost?

Pincher

footyguy wrote: »

:huh:

E7 hot water heating takes advantage of the cheap rate electricity by heating the water at that time. It is stored until required. i.e. The tenants can take a shower any time

One cylinder for one landlord and three tenants?
The words "all the time" says something else to me.