Big fan of the bags here - our rooms are not heated at night in winter normally either but here found they rarely drop below 14 - so depends on the house and location in Mel (ours is small and we have double glazing so that helps as is a flat get some heat from downstairs no doubt) - if was going to be really cold I did use an oil heater - but not normally over night just in the evening - and that seemed to keep it warm enough for me (the kids seem fine when is cool but I found breastfeeding hard when was freezing). I would also put on more than one layer underneath a 2.5 bag when very cold - e.g. a short sleeved and no leg onesie under a full cover one. No matter how cold they never have wanted their hands covered (I have tried because the cold hands on your boobs in the night is horrible :-)). Also depends on how many people in the room as to what temp will be - so last winter DS was in with us in the main, and this winter is in with his sister and keeps the room temp up.

Coming from the UK though it is perfectly normal to keep bedrooms at that temp overnight - and has been for several generations - Grobags at least are a global brand and I honestly think that they don't realize how cold houses (relatively) are kept over here - I am used to it now but all relatives constantly complain - my parents house I am sure never drops beneath 22 degrees. I am sure is healthier the way it is here.