Help understand my hot water system, and is efficient for my needs?

[JonnyH]

We have moved into a large, old house and the bills are very high. I'm trying to figure out the most efficient way to manage the hot water.

In the cellar is an Indirect Hot Water cylinder, controlled by a Honeywell Smart thermostat, and powered by a relatively new 48kw Worcester boiler.

The current schedule has the hot water on for four hours in the morning, and four in the evening.

In my previous home I had a combi boiler, so hot water was produced only when It was needed. In the current system, hot water is being heated and stored whether it is used or not, and I'm trying to figure out if this is more efficient, or even why this was chosen over a normal combi boiler.

We are not a high useage household - but the home is big so maybe it's a way to get hot water around the property.

If I set the hot water schedule to be off entirely - am I right in saying that the immersion heater in the hot water cylinder will heat the water? Is there any way that would be more cost effective for us than heating an entire tank of hot water?

Would I be better moving to a combi boiler system?

 

[Ric2013]

If you have more than one bathroom, a combi boiler probably won't keep up with demand. if you want to run a bath with a decent fill rate, a combi boiler won't usually give it. You can't use secondary circulation to provide hot water quickly to distant outlets if you have a combi boiler. This is probably why you have a cylinder.

Cost of an immersion (if you switch it on) may be less if it is only maintaining a part of the cylinder at a high temperature as standing losses will be lower, but you won't really know until you try a meter reading comparison experiment and it will depend what you are paying for your gas and electric.

In theory there is little advantage in trying to heat the cylinder just before the water is actually expected to be used as modern hot water cylinders are well insulated, but sometimes poor plumbing practices will result in a lot of heat being lost from the cylinder due to poor pipe layout, and, in any case, there will always be some heat lost from a hot cylinder. Also, I suspect that the most inefficient part of the cylinder heating process is heating the last few degrees, so I have an untested theory that maintaining a hot cylinder for the sake of it is actually a waste (the theory holds for my own house, but difficult to conduct the experiment elsewhere).