Hot water tank - heat loss

[TomC]

Hi - I'm considering updating HW system, and space is an issue. Was initially going for Combi (gas) but concerned re hot flow rates, so looking instead at unvented tank in the loft.
I thought this seemed rather inefficient - lots of hot water in cold place. So checked heat loss figures given by manufacturers. Ariston for eg say 2.4kWh per 24 hrs - this seems a lot to me. If you use a 20kw boiler to heat a tank of water in 1 hour, that's 20kWh. If you lose 2kWh in 24hrs, that means 10% loss.
Or possibly not! Any ideas / thoughts appreciated. Thanks,

[Dan Robinson]

A modern unvented cylinder should reheat in 22 minutes.

There are better performing tanks out there than the Ariston. OSO, Tribune etc., I would avoid Megaflo now. They are ownded by Baxi and are already showingsigns of decline.

Also remember that an unvented cylinder is heavy. You will almost certainly need to reinforce your celing joists.
_________________
Dan Robinson
Jennings Heating Ltd
forums@jenningsheating.co.uk

[SimonD]

Ariston claim to have one of the best insulation packages of all unvented cylinders. Their price performance ratio makes them very competitive. We wouldn't fit any other Ariston products but there is nothing amiss with their Primo cylinders.

2.4kW in 24hrs is very very low. That is the same as giving off 100w per hour of heat energy. A 20kW boiler would waste 5 mins firing per day replacing this heat, by my calculation.

If you want to save money, ask yourself what happens to the heat in most modern condensers when the pump runs on for 5 mins after every firing cycle to discharge heat from the heat exchanger? It is intentionally wasted. Bet you didn't read that on a web site.

To my knowledge only Buderus and Kidd boilers do not do this.