Thermal underlay-your views please

[greyvix]

Not exactly exciting, I know. We have taken up the carpet in our lounge and sanded the floor. It looks lovely and is perfect in summer. When it is very cold though, the room is unusable due to draughts through massive gaps in the boards.
DH wants to put another radiator in (we have 1 large rad in the room, plus a fireplace). I want to avoid doing that if I can, because I like to use the fireplace, but have agreed to a new carpet. I would prefer a rug, but fear it would still be cold.
Does anyone have experience of thermal underlay- the felty looking type? Could we get away with thick underlay instead of an extra radiator?

experience is from family business - parents and grandparents though, not me IMHO It does make some difference - although so will any underlay. The felty stuff is obv more expensive and won't do any damage to your newly sanded / polished floor. My parents have it all through their living rooms, but not hallway, stairs etc as my dad (aka king of the carpets) is a tightarse said it wasn't necessary. Their house is always warmer than mine and they use their heating less!!

even better is to put fibreglass quilt between the joists. This either means taking up the floorboards (best done before replacing or polishing them) or else by crawling about under the floor. Some houses have a reasonable crawl space making iot more praxcrical.

whatever you do, don't block the air bricks, which are needed to evaporate away underfloor damp, and prevent rot.