without knowing the efficiency of the boiler and the plumbing layout, including the length of the pipe run from the boiler to the cylinder, its not possible to answer this question
In winter, it is oil. Most of the inefficiencies of the system, pipework etc., are taken up by the home heating, so your boilder is heating the cylinder on its way to the radiators. That is why solar works well
(snip).
In winter, it is oil. Most of the inefficiencies of the system, pipework etc., are taken up by the home heating, so your boilder is heating the cylinder on its way to the radiators. That is why solar works well
In summer, that is often not the case. Heating a boiler, flue, and 20M of pipework just to bring 120L in the hotpress from 30 to 60 may be more expensive than using the immersion - particularly if you have a dual immersion, and you are only heating the "sink" part.
However, cheapest of all if off-peak electricity at night. If you have a very well insulated cylinder so that heat loss in the daytime isn't too severe, and/or you shower and use hot water in the early part of the day, that might be best of all.
It is cheaper to boil a kettle to wash the dishes than it is to use either oil or the immersion...
Does the off peak power not have an addition standing/meter charge that has to be factored into the price per watt?
There is also this [broken link removed]from SEAI...There is a really interesting thread here somewhere on this very subject. It had some fine mathamatiinscs working out the cost per unit of electricity, gas and oil. It then worked out how much of each it took to heat a stated amount of water from 10C to 60C.
I'll have a search for it.
There is also this [broken link removed]from SEAI...
ONQ - My point is that there is a good synergy between solar and normaly central heating systems, because in winter, when the solar isn't working, the heating is providing hot water at a lower cost.