SOT: 3 phase supply

I suspect ‘they’ decided most people probably charged at night when they wouldn’t be using other high current devices and therefore 80A is probably enough.

We have a gizmo paired with our Smart Meter so we can see our usage profile throughout the day etc. Even allowing for the fact we run the dishwasher and washing machine on time delay to take advantage of Economy 7, even when charging the car, the peak current doesn’t get near 80A. I’ve not checked it with all of the above and running and oven ‘self cleaning ‘ cycle - which we do over night - but even with that, I doubt it would hit 80A.

Yep. Our COP for October, November & December was 5.2, 4.4 & 4.1 respectively so I’m expecting it to pick up again soon.

Tim

I normally run my boiler at its lowest heat setting (increasing it to half power for icy strong winds), from 6:30am to 10:00pm and the rest of the time my solid walls* act like a storage heater. My temperature when the heating turned off last night was 21C and the temperature this morning when the boiler fired up again was 18.5C. I would have to leave the house unheated for over a week in winter to get anywhere near 10C (and it would take at least 2 days at a higher heat setting to restore the full night storage effect of the walls to what it normally is). A thermostat in the living room turns off the central heating when that room is up to temperature, and then the solid wall heat for the rest of the house keeps the rest of the rooms at a comfortable temperature.

I am approaching 80 and my current heating system does everything I want and will probably last longer than I will, so why would I consider the cost of a heat pump and any installation works to be a sensible investment?

• I have an old house in a Conservation Area so I would not get planning permission for adding insulation externally. Internally, I appreciate the heat storage effect of the internal walls so I have no intention of cladding them. I fitted an outside tap to the bottom floor wall and measured the length of drill needed to get from the inside to the outside. That wall was 17 inches thick. I drilled a hole through the wall on the middle floor for the boiler flue, and that was 14 inches thick. I installed an ensuite in the top floor and drilled a hole through the wall for the waste water pipe, and that wall is 11 inches thick. The structure of the wall is red brick covered with plaster on the inside, Natural stone is the outside (hence the Conservation Area inclusion) and between the two is an infill of rubble stone in cement. The house is 120 years old, the shrapnel scars on one of the outside walls indicate it survived a nearby bomb blast during WW2, and I have lived here for 49 years. Obviously it needs some maintenance and updating from time to time (most recently I had the crumbling terracotta roof replaced by new felt, battens, and modern tiles that looked very similar to the original terracotta to preserve the Conservation Area appearance, in 2024). The last thing I need is a heat pump outside and its pipes and electricity supply drilled through the thickest of the historic walls.

It sounds like your house is well-constructed, in the old way of doing things. Into the ubakus.de U-value calculator I put in:

and it gave U=0.611. If I replace the 'slag' with 'sand (dry)' it's U=1.316 and 'gravel' it's U=2.078. (the calculator doesn't have rubble fill so these are the nearest it has)

That's nowhere near current regs (U=0.18 for new builds) but 0.611 is better than what you get from a triple-glazed window (0.7). The large thermal mass of the building keeps things comfortable (especially in summer) so it's really only fighting against your losses that you have to worry about. You might be able to do some measures (eg preventing draughts, improving loft or floor insulation) but perhaps those are infeasible and it is what it is, and it just needs the current level of heating. Which is likely something a heat pump can cope with just fine, by the way.

Perhaps at your stage it's not worth the disruption of replacing your heating system. But there are things the next person who takes the house on could do - eg installing one at the bottom of the garden tucked away somewhere, or possibly ground source or district heating (if that becomes more widespread; village-scale ground source is mostly at the pilot stage currently).

Theo

Whilst there could be efficiency gains from district heating schemes I’d be very wary of being connected to a heating system where I had no control over costs. There is a housing scheme in Edinburgh blighted by ridiculously high heating costs that the residents can’t escape making there houses virtually unsellable.

Its quite hard to measure how much energy you are taking out of hot water.

I can recall the battersea power station scheme taking waste heat from the coal burners. I believe that was charged for.

In Denmark they burnt waste to supply free energy to council flats.

Iceland's geothermal energy is cheaper than the alternatives.

Its all about whether yiur [socialist] government cares about what you have to pay, or your [Labour] government taxes you into poverty

Yes, although Ofgem has recently taken over the regulation of heat networks which should mean it's less of the wild west than previously, and also not left out of schemes like the energy price cap.

Ultimately, the problems boiled down to the wholesale price of gas. A heat network that doesn't use gas would avoid them. For example, some blocks of flats have a communal ground source borehole and a loop that circulates tepid water around the flats, with flats each having their own internal heat pump (roughly the size of a gas boiler) to concentrate the heat into meaningful heating and hot water. The shared network still needs to be paid for, but it's only for electricity to run the pump and for maintenance - much like running the gas grid. Because there's no 'fuel' being burnt it's more decoupled from global commodity shocks (not entirely as it's still exposed to electricity prices).

Theo

Thanks for your assessment. You have seriously underestimated the limestone thickness. They are the local standard "structural" blocks,

The roof space is insulated, though I can't remember whether I used fibreglass or rock wool. Anyway I filled the gaps between the rafters with it so that it stood about half an inch higher than the rafters, then squashed it down that half inch by putting floorboards on top. Other than carpeting it, I don't think I could do much more to stop heat escaping through the roof.

As a bit of background, I went to a specialist plumber's merchants to choose my boiler. The man I spoke to knew everything about all the boilers he could supply and we spent about a quarter of an hour while went through the pros and cons of each one. I went for an old style one which has about 3 moving parts apart from the clock in the programmer. I chose it on the advice "provided you never let the pilot light go out it will last forever". It is doing exactly that. There is a little glass window behind the removable front panel through which I can see the pilot light, and in the light of the pilot light I can see the rest of the internals. It is not getting sooty or dusty, so my decision to not have it serviced because the first thing a service engineer will do is turn the gas off and the pilot light will go out, looks like a good one. That is why I am confident it will last longer than I will.

I recognise that I am not complying with the modern advice, but I am part of the "if it isn't broken don't fix it" generation. On that basis I am still using a 60-year-old car as a daily driver (and it still starts first time every time), and the living room clock keeps perfect time because it is powered from the mains.

This is known as "weather compensation" - something "boxes of fire" are quite capable of doing - although seldom used by many heating installers. Many modern boilers can modulate their output down to ~6kW or less.