The Boy That Cried PV Extension

[Krill]

I've been wondering recently on the benefit, and frankly feasibility, of having the output from a DHW cylinder run through an electric boiler (I think nowty still has his cylinder plumbed to go through a gas boiler). The point being all the benefits of the normal cylinder and ToU tariffs with the potential to turbo boost the output if needed for flexibility.

This would mean a smaller EB but the running costs (as heating from a higher starting point) should be far smaller still, only use the EB when absolutely needed. With thermostatic mixers and running the DHW temp higher during higher use periods ie visitors even a 125l volume could be stretched quite far IMO.

The problems are one of space and wiring though, and additional costs, but it does provide the flexibility most people demand with a gas combi boiler

[Stinsy]

I've been wondering recently on the benefit, and frankly feasibility, of having the output from a DHW cylinder run through an electric boiler (I think nowty still has his cylinder plumbed to go through a gas boiler). The point being all the benefits of the normal cylinder and ToU tariffs with the potential to turbo boost the output if needed for flexibility.

This would mean a smaller EB but the running costs (as heating from a higher starting point) should be far smaller still, only use the EB when absolutely needed. With thermostatic mixers and running the DHW temp higher during higher use periods ie visitors even a 125l volume could be stretched quite far IMO.

The problems are one of space and wiring though, and additional costs, but it does provide the flexibility most people demand with a gas combi boiler

Even a 30kW gas combi is pretty slow to fill a bath. This is precisely why we have DHW tanks. A 3kW immersion can heat 250L of water from 10-60℃ in about 5hrs, this puts very little strain on your max demand and is perfectly reliable with zero maintenance for decades, and is economically viable on ToU. But is no good for “on demand”, you can’t expect the Mrs to wait 5hrs for a bath.

Electric boilers still require a DHW cylinder, but can reheat it much quicker because of their 10-14kW rating. On the other hand they’re very noisy, more complex and therefore likely to be unreliable, they cause big problems with max demand (particularly if you also charge an EV). You could therefore make use of a much smaller cylinder and rely on it being quick to reheat but you lose out on ToU.