How can we be more energy-efficient in heating our water?

Question

We live in a very large, old house (in the UK) with 8 bedrooms, heated by an Ideal Instinct Heat 60 boiler (about six years old) supplying 32 radiators and a 295-litre (65 gallon) water cylinder. With the latest price rises, we are currently estimating an annual cost of up to £12,000 for gas alone, which we just cannot afford.

We are implementing all the cost-saving measures we can think of as regards the heating (the main one being leave it off until our fingers turn blue!) but the thing that bothers me is the water. There are only 3 of us in the house, so heating 295-litres of water at a time is hugely wasteful. We don't have a smart meter, but by my rough calculations I reckon it's currently costing £6-8 per day for water alone.

We installed the system when gas prices were much cheaper, thinking that even though there weren't many of us in the house, a future owner would probably have a much bigger family, so a cylinder would be more appropriate than a combi. But gas prices have now risen so much that we are having to reconsider.

I have a few questions; if someone has the time to consider them, I would be most grateful:

Question 1 - I am assuming that this is a clear 'no', but can you get boilers that work in either 'combi' or 'conventional' mode, so you can switch between modes?

Question 2 - Are there combi boilers that can cope with the demands of 32 radiators and 6 bathrooms, and how much are we likely to have to pay for one (supplied and fitted)

Question 3 - Is there any other way to reduce the capacity of our cylinder, so we are heating less water every day (e.g. would it be worthwhile replacing the big cylinder with a much smaller one, with the option for a future owner to switch back?)

Many thanks for your time.

Answer 1

A six year old boiler should be quite efficient, so replacing it seems unlikely to be a good choice. A really well-insulated water cylinder takes days to cool off with no use, so it's quite true that the heat used there (if not being wasted by poor insulation or uninsulated/poorly insulated pipes) is almost entirely just the hot water you actually use. So be sure you have no hot water leaks, and put the insulation to it, rather than replacing it.

Concerned about your hot water cylinder wasting energy? Add more insulation to it. Add more insulation to its pipes. How big it is is almost immaterial to how much energy it uses, if it's properly insulated.

Concerned about the sky high cost of heating a very large, old house? Air sealing and insulation are the commonplace, everyday, boring things that make a HUGE difference in fuel consumption, but nobody thinks to start with them, usually, because they are commonplace, everyday, and boring. Caulk or foam air leaks in the house and insulate the house to limit waste of heat for heating. Use heat shrink plastic films over drafty windows to allow light in but block drafts and add a bit of insulation. Use rigid foam insulation and/or blankets/heavy drapes (held right to the window, not spaced out as drapes usually are) to block windows in unused areas, if you are heating those areas at all.

The other standard practice for large old houses in winter with only 3 people occupying them is to close off large parts of the house and only heat what you actually need to live. Either run the rest of the house at 7°C (not lower or you risk some parts freezing) or turn it off entirely, depending on the potential for freezing and whether you can manage to drain all the plumbing (or fill with non-toxic antifreeze) in the closed off sections, or not. If your heating loop is closed, filling that with non-toxic antifreeze mixture rather than straight water will keep the unused radiators from freezing up.

Answer 2

First of all, I'm not sure what you mean by "conventional and combi" modes...would that mean domestic hot water and hot water for heating? If you could provide a layout of your current system that would be helpful. When you do so, please EDIT your answer clarifying your questions and adding the diagram.

That said, from what we know now:

I wouldn't consider reducing the size of the hot water tank. You have a large system that needs lots of hot water. Once the water is hot, it stays hot unless the tank is poorly insulated, which can be fixed by adding an insulation blanket around the tank. With no usage it would only require very occasional firing to maintain temp. You aren't heating 295 L of water at a time, you are maintaining temp of 295 L of water and the gas required to do that is totally dependent upon usage (by your heating system) . Also, since your boiler is only 6 yo it's probably pretty efficient to start with.

So it doesn't matter if you're heating 50 gallons or 500, what drives your gas consumption is USAGE . Since you said it was a large home with only 3 ppl living there, are there zones you can turn down the heat in? Most radiators have valves as well to control the amount of heat delivered to that room that could be throttled back. Dependent upon your personal usage of the house AND how the piping is laid out, your best investment might be to create zones (if they don't already exist) that can be set to not heat unused parts of the home or partially heat those bits to avoid any freezing pipes.

Also if possible adding insulation to the home may reduce the heating expense. Even clear plastic over single pane windows can help.

Lastly, and this is off topic and might get deleted by a moderator, but let me say in compassion, I really feel for my EU brethren and what you are going thru with energy prices due to this stupid war.