Left tap running overnight

Gothicfairy

bobmedley wrote: »

OK. A 3/4" bath tap typically flows at 0.3l/sec - assume it was left full on for 12.5hrs, so the sum is 0.3 x 60 = 18l per minute x 60 = 1,080l per hour x 12.5hrs = 13,500 litres total

United Utilities (my supplier) would charge £1.374 per 1,000l to deliver and £1.084 to take it away total = £2.458 per 1,000l x 13.5 = £33.18

If not metered, then the cost is zero.

I am not a gas customer so just guessed at 2.9p per kw for that calculation, but the OP can redo the sums with their own figures.

If we assume the boiler was keeping up with the water flow, and the temperature rise needed was from 8 deg c to 60 deg c then the energy needed is *something* like 800kw, that gives 800 x £0.029 = £23.20.

I think that is absolute tops, as I suspect a tap on full would be adding water quicker than the overflow can get rid of it therefore it would have overflowed. Depending on their boiler size I also doubt it could raise the water to 60 deg c quickly enough & on a constant basis especially with winter temp mains water - it would have to be outputting 64kw per hour. An easier assumption is to take the boiler rating (maybe 30kw?) and times that by 12.5 so giving 375kw for example (this just assumes the boiler was running flat out for 12.5 hrs & means the costs are even lower).

The answer for the original question is to put £60 aside and don't do it again.

Besides, as somebody has pointed out leaving the plug in would have been catastrophically more expensive

I do like your thinking Bob and thank you for taking the time to post that.