What size boiler please?

[Dan Robinson]

he stated that on reflection, 60 kW would be more appropriate and he wants to go this large to ensure hot water supply is consistent.

Sack him off immediately.

 

[D_Hailsham]

30kW for heating the cylinder is unnecessary.

A 300 litre cylinder fed from a 30kW boiler (assuming the cylinder coil is up to the job) will heat up from 15C to 60C in 32 minutes. However cylinder thermostats have a hysteresis of about 10C so reheating from 50C to 60C would only take 7 minutes. A 25kW boiler would take 38(9) minutes; a 20KW boiler - 48(11) minutes. It's up to you how quickly you want the cylinder to reheat.

Remember that the recommended temperature of a bath/shower is about 40C, so it's not essential that the cylinder is back up to 60C before another person can use the bath/shower. They will just need less cold water to obtain a safe temperature.

 

[pghstochaj]

Thanks for the additional replies. I have got a third opinion and they have also suggested a 37 kW system boiler (the same as the first person who I mistakenly said wanted to fit a 35 kW boiler) which he said will be more than sufficient for heating and to heat the tank. Does anybody disagree with this? I guess the difference between 37 kW and anything bigger is only about reheat time of the tank on the coldest of days, but a small investment now might be better than asking people to wait as there is no hot water left. Or I might find that the house is freezing in the winter and needs lots of new radiators (but at 15 years old I find this quite a low probability).