I'm struggling to find a reference to the floor temperature and how to
calculate heatloss though the floor.

I have, through a link on the diyfaq:
http://wiki.diyfaq.org.uk/index.php/...heating_design

a link:
http://yaph.co.uk/heating/boiler_sizing.xls

but that assumes a temperature difference for the floor of 27C which
can't be right.

I don't seem to have joy with other links on this page:
http://www.idhee.org.uk/calculator.html
goes to 404 not found,

http://www.est.org.uk/uploads/docume...dings/ce54.pdf
goes to DNS error

http://www.quinn-radiators.co.uk/downloads_heatloss.php
jumps to their home page.

Does anyone have a reference link for u-values and prospective ground
temperature?

Many thanks