We put jumpers on as well but even so the heating is now starting to kick in fairly regulary and the oil consumption is now at double the summer use per week but still only about half that of the winter use level.
I don't think it's relevant. The amount of heat given off by a tungsten lamp will be lost if you open the door. It's a tiny amount compared to that required for space heating.
(22,000 * 20)/1000 =3D 440kWhrs @ 10p/unit =3D =A344.00
- =A35 bulb =3D =A349.00
(22,000 * 60)/1000 =3D 1320kWhrs @ 10p/unit =3D =A3132.00
- 11 bulbs @ 20p =3D =A3134.20
=A385.20 saving.