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Old 3rd October 2018
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Naughty Nigel Naughty Nigel is offline
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Re: The Minefield of Energy Providers

Originally Posted by Otto View Post
But your boiler could be heating the water while you're using the shower. I generally prefer a bath to a shower and I know that the boiler doesn't take long to reheat the water after filling the bath, probably no more than 10-15 minutes. I can hear the boiler running (oil boilers are noisy!) and while I've not actually timed it, it feels like about that long before it cuts out again. You might find that your boiler reheats the water used for a shower in the time it takes you to dry yourself off afterwards!
I take your point Richard but there is a subtle difference between condensing gas boilers and oil boilers.

The water in oil boilers needs to work at a high temperature (typically 80 ~ 85 C) to minimise sooting of the heat exchanger. This significantly reduces the time taken to heat water in the cylinder. From memory the effective heating provided by water at 85 C in the primary circuit is 4 KW, assuming a cylinder water temperature of 25 C.

Condensing gas boilers, on the other hand, work most efficiently when the circulating water is at or below condensing temperature, which is usually about 67 C. Efficiency at or below condensing temperature is claimed to be as high as 97 or 98%, but this drops to about 85% when the water temperature rises above condensing temperature. This is why modern radiators have been redesigned with greater surface area to work efficiently at lower temperatures.

Clearly this also has an effect on the transfer of heat within the hot water cylinder, and the maximum water temperature achievable in the cylinder.

That said, I am still keen to do it!

Naughty Nigel

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