Probably intends to install it himself too.
If you want mains pressurised water then thermal store.
If you are happy with a gravity system then vented cylinder, which is the most common method when a wood burner or other domestic solid fuel appliance is fitted that has a boiler facility.
I have a gravity system. Two of them in fact in my home. It was an experienced plumber who seconded fitting the second one.
At the moment I don't need mains pressure. If I did I'd just fit a plate heat exchanger.
The disadvantage being that it will likely upset the cylinder stratification that works so well currently with the side arm immersion delivering the hot water direct to the top of the cylinder ready for draw off.
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