16°C in itself doesn't have health consequences whatsoever.
> Only when the black mold started appearing did we manage to persuade her that 19 would be more appropriate.
And you made the wrong diagnostic: mold is a moisture problem, not a heating problem per se. Sure heating improve air moisture but it's a very inefficient way to do so. You're complaining about the cost of a problem when you're using the most inefficient possible method to address it.
And again, if world market gas price rise, the consumer cost of gas rise as well, no matter if you have gas production in the country or not.