Series connected electric heat in gas central heating circuit

Does anyone do an electric immersion heater in a thermally insulated chamber (which need not be large) with 3/4" inlet and outlet pipes ? In an existing conventional gas combi boiler central heating circuit, that could be series fitted before the gas burner, and normally take surplus solar electricity when sent it from a solar “diverter” switch as some of the emon devices can do. (or by a £5 mechanical segment timer; ON during all the best hours for local solar, with straightforward user override). The emon might also want to log pipe exterior temperatures (return from radiators, after electrc heat, after gas heat) similar to level 2 logging but with more temperature sensors.

Households with small solar surplus might prefer a 0.6kW heater element, though of course it could work with bigger, all the way up to 28kW+ rated power of the gas boiler as suits available solar photovoltaics and water heating load. Gas heat is still available for when the sun isn’t shining, but gets used less. Grid export of electricity is still available for when the thermostats or emon say don’t preheat the central heating water. The only wet plumbing task is one item professionally installed, possibly cutting under the kitchen surface under the existing gas combi boiler, with the central heating return pipe cut and extended.

It needs a suitable leak proof doodaa containing a conventional thermostatted immersion heater element.

Why not do this ?

Something like this?

Go to a local DIY shop or plumbing factor. Or this, cheaper And insulated

Spot on if the pipe fittings can be made to connect to existing hot water pipework. “Willis Jacket” is the phrase which I needed.
Does anyone know a hot water plumber or someone who’d fit one of these ?

I’ve been looking at these - they take warm water and modulate right down.

It would be great to have enough solar photovoltaics to run the 12/14 kW water heater for free.

Perhaps that is good for the staff washroom at a factory with three phase 415V solar in the 20 to 200 kW range and also for office building supplimentary heat? At that scale, I’d think that they’d be better having quite a large heat pump on the central heating circuit instead, and it is a big enough job that estate agents never do it.

I’ve looked up Willis Jackets and the most prominant seller of “unvented” only does one size; 3kW. To get enough surplus solar for that reasonably often should need a change to the MCS regulations or whatever it is to permit 32 Amp single phase home solar; same wiring regulations as a cooker circuit or a 7kW Tesla vehicle charger. Who’d we ask for that ? My roof here is much too small for that much solar; I’m stuck within <3kW(peak) and my surplus is usually small.

The only good news is that I was mistaken about pipe sizes; 15mm might fit in series with some of the home gas combi boilers and existing central heating pipework including existing radiators.

Does anyone have a rule of thumb similar to “in order to decrease central heating circulation temperature from 60C to 45C without loss of amenity, expect to increase the surface area of radiators, so for minimum-cost retrofit, add second radiators or modern alternatives in series to the existing radiators in the living room and where space allows.
Do not waste effort removing known-good pipework.”

It has 15mm fittings but 15 to 22mm adapters are readily available as solder or compression. Any plumber could fit this including the wiring or you could do it yourself and plug into a 13A socket.

They take a cold water feed and heat it to 43°C, 50°C or 55°C instantaneously but cost £350 and need a juicy supply current! (40 to 55A). Quoted flow rate is 1.3 litres per minute - feeble!
You do better with an electric shower unit.

Flow rate will vary on how warm the incoming water is. They quote based on cold mains water but the system modulates the flow to achieve the target temperature.