Home DIY

couldn't you have an 'exposed' flue that would act like a giant radiator?
Yes you could have a single skin which would radiate heat into the room. This could be an issue if you don't want people burning themselves on it but you could create/buy some sort of guard that would stop anyone from getting too close.

One potential problem would be that the gases inside the flue cool too much, resulting in nasty tar-like condensation inside the flue. I suppose you could have a double skinned lower part and a single skin higher up so you get some heat radiation whilst keeping the gases hotter. This could also make it safer for kids/babies as the hot part would be out of reach.