Hi,

I moved into a three storey Victorian semi six months ago. In the last
few weeks of Summer sun the house was toasty. It got a bit cooler in
Autumn but has been absolutely freezing since winter set in.

We have twenty, single-glazed sash windows. I have temporarily put
secondary glazing film on the windows as they are very draughty. That
has made an improvement, but not enough!
The ground floor has a suspended timber floor with approximately 2' of
space underneath except for a small area in the middle of the house
where there is a cellar. It may be my imagination but the cellar seems
to be one of the warmest parts of the house.....
None of the reception or bedrooms have carpets - sanded floorboards
throughout. It looks like previous attempts have been made with
silicone to seal the gaps between the floorboards but this appears to
have disintegrated, presumably due to the movement of the timber
throughout the year. From peering between the gaps between the
floorboards there appears to be no insulation between floorboards and
the ceiling of the room below (or bare earth in the case of the ground
floor).
Both reception and bedrooms have fireplaces; most have a 'flap' on the
fireplace to close the flue, those that don't I have temporarily
blocked with a pillow in a bin bag with a bit of kitchen waste pipe at
the side to provide ventilation.

I realise this house will never be as energy efficient as a modern
house but I desperately need to improve its heat retention. Where am I
likely to be losing the most heat and what can I do about it? I can't
afford to replace the windows. Does anyone have experience of the
relative merits of secondary glazing units versus the brush pile
draughtproofing that you get from the likes of Reddiseals?
What about the floors? What's the best thing to seal the gaps between
the floorboards? Would insulation under the floorboards provide a
significant difference compared to merely sealing between them?
Anything else I should look at?

Many thanks!

Paul