If you have older windows, you will be able to reduce heat loss by replacing them with modern double or triple glazed windows. There are lots to choose from in style and frame material (e.g. uPVC, wood, aluminium, aluminium and wood combined) as well as cost.
It’s worth having a thorough read around and ask lots of questions of suppliers when they quote. For energy efficiency, look out for the u value and window efficiency rating. Sometimes the u value refers to the glass, but you need to also look for the whole window including the frames. The way the frames are constructed matters and they should be made to be thermally efficient. You also need a good installer who will make sure you do not have heat loss between your walls and the window frames.
Find out more:
Energy Saving Trust – Reducing home heat loss
Centre for Alternative Technology – Eco-renovation
Low Carbon Oxford North – housewarming
Cosy homes – energy efficiency for home owners