Immersion worth it?

Dubsey

Hi,

Our immersion had previously been disconnected (power cable cut to it) but I reconnected it (fitted a small joining box). But it takes about half an hour to heat a bowl of water.

I spoke to my plumber about it and he said it's the most uneconomic way to hear water. He checked our pipes and said that we could fit a switch as the feed to the cylinder and the rads are separate.

So the question is should I get this done or just get the immersion fixed or replaced?

Sir Arthur Daley

I dont know why you would get it fixed or replaced since its working. How big is your bowl and was it on sink or bath for that half hour and was there demand on the hot taps on this time?
I imagine your plumber is on about fitting a motorised valve for hw only which would be cheaper to heat water than oil or gas.

Dubsey

Sir Arthur Daley wrote: »

I dont know why you would get it fixed or replaced since its working. How big is your bowl and was it on sink or bath for that half hour and was there demand on the hot taps on this time?
I imagine your plumber is on about fitting a motorised valve for hw only which would be cheaper to heat water than oil or gas.

Hi there. I've had it on both settings and it's performing so bad that the only conclusion that I can come to is that it's either **** or not working properly. There were no other demands. Regarding the options yes he was on about a different digital control that would operate a motorised valve or a simple manual leaver that could do the job.

So my question is: is an immersion that is working properly a better option than using the gas boiler?

jodaw

This gives an explanation. The kilowatt hours will be the same regardless of type of energy used. The figures are in pence but just use current kwh figures for each fuel.

It think natural gas is about 6c, oil about 8c and electricity 20c per kwh.

It takes 1 kCal to raise 1kg (~1 litre) of water by 1 degree C.


1000 kCal = 1.163 KWh

For a 115 litre tank
115 x (60-15) = 115 x 45 = 5,175 kCal = 6.019kWh

With a gas boiler, it is able to condense initially (efficiency 90%), but as the cylinder water reaches 50+ degrees, the efficiency will drop to non-condensing levels, like 70%. Therefore, the worst case scenario is 6.019 / 0.7 = 8.599kWh.

Note that some top-up electric immersion elements are only able to heat the top half of the cylinder, unless you have a direct cylinder, twin element or bottom placed element.

At 16p per kWh, 16 x 6.019 = 96.3p by electricity
At 6.7p per kWh, 6.7 x 7.08 = 72.4p by oil (85% efficiency)
At 3.6p per kWh, 3.6 x 8.599 = 31.0p by gas (70% efficiency)

How old is the current immersion and do you live in a hardwater area? If so the element could be scaled up and the whole heating system not functioning very good at all.

touchdown77

http://thehelpfulengineer.com/index.php/2013/02/immersion-heater-verses-boiler-to-heat-water-at-home/