As I mentioned earlier, this is a huge problem in this country. First off, I'd advise anybody to print off Shedman's post for future reference. It's everything you need to know on the decorating side :o))
Plenty of other countries have similar climates to ours, but they often have a rather different attitude to heating. Maybe they're lucky, and energy costs are lower, but it's more than that. This mild autumn/winter, I've seen so many posts on how folks have managed to delay the annual heating turn-on.
I can understand their joy, but we do have a rather "puritan hairshirt" attitude towards creature comforts here. Heating is not there just to keep US warm. What's forgotten is that heating & ventilation are also essential to keep the fabric of the building in good condition.
In the cases of Chess, Droopy, and Birdie, one would need to know the construction details of their buildings to be sure, but I'll hazard a guess that the insulation levels are nowhere near those that we build into houses today.
Of course I can understand completely the notion of de-humidifiers saving on heating, but ............ I honestly think it's the wrong way of looking at it. De-humids simply deal with the symptoms......... not the causes. In an ideal world, buildings would be kept at a constant temp. 24/7. We can't afford that with older properties. Gentle background heating as late into the night as possible......... as as early in the morning as you can, helps a lot.
My own personal little rant is that I wish people could spend as much care on their insulation/heating/vapour extraction as they do on their cars and their clothes.............. but then, I'm not into cars, and I dress like a builder ;o)