We've just replaced an old fireplace back-boiler with a log boiler and have turned our old, draughty Victorian House [approx 250 sqM] into a hot house...way too hot for us, plus we have more than enough DHW. Plus it looks nice.
The only disadvantage is that the log boiler doesn't load itself so we are pretty much much tied to firing it up in the morning, but the residual heat in the house keeps the place reasonably warm after the last log has burned out.
The boiler we got [28000btu] has only 2 tappings, or ONE feed, but we craftily plumbed in the radiators and the DHW tank with a 28mm Tee. What happens is that the boiler feeds the Hot water cylinder [An old Primatic, or self-venting unit, 90litres or so] if the radiator pump is not switched on. As soon as the pump is turned on the boiler biases towards the heating, but by then the DHW cylinder is hot. This takes 35 minutes to charge the DHW cylinder.
A few problems...make sure the Gravity feed pipe to the DHW cylinder rises gradually with no down turns whatsoever....this can create disturbing rumblings as air and water collide [er...bubbling..]