The solid-fuel stove.

Saros is just as much fun in the depths of winter (should it ever happen again with all this global warming!) as it is in the summer. Once the fire is lit, it keeps the whole back end of the boat really cosy, and you'll sometimes find you might even want to open the doors and windows to cool down a bit.

The fire is controllable enough (with a suitable slow-burning fuel) to even keep going overnight, so just clearing the ash in the morning and adding more fuel is enough to keep it going 24 hours a day.

Saros is amazingly well insulated with Rockwool in between the attractive pine lining and the steel shell, and even when there's snow on the roof, it doesn't melt despite the living space being really warm.