What a selling point! No full heating system, warm in winter, cool
in summer and fully sound suppressed throughout. See if any estate
agent would see those benefits and sell accordingly.

Nah, they'd just knock off several thousand because it doesn't have GCH.
Besides, how can it get away with no heating at all? Even with perfect
insulation, with no heat source, it will settle to average outside
temperature. You can't rely entirely on human heating, as it would take time
to heat the thermal mass when you get in. However, it could be a case for
electric heating, as the losses are so tiny, that the reduced installation
and maintenance cost of a simple electric installation to quickly preheat
could outweigh the running cost (and environmental) benefit of gas.

Christian.