Making sure you reduce heat loss by focusing on insulation and good windows is the first place to start. Recommendations are for at least 200mm of insulation in wall cavities. It is also essential that windows are air tight, as any drafts will drastically increase heat loss.
If you are fitting bi-fold doors in your new extension, you should opt for the best performing glass that you can afford to minimise heat loss.
Another way to keep your new kitchen warm this winter is with underfloor heating. Underfloor heating provides a constant low heat over a larger surface area, in comparison to radiators, which only heat the surrounding area.
You can find a whole host of information about underfloor heating at the fantastic Home Building website :