Snug-fitting curtains and blinds on windows can prevent heat loss and gain as they trap a layer of still air next to the window. Window furnishings are a good way to deal with problems with existing windows. Heavier fabrics and multiple layers of fabric give the best thermal protection.

If you're installing blinds, look for an insulating fabric and ensure they're well-fitted to restrict air movement around the window to prevent unwanted heat loss or gain. For an energy-efficient option honeycomb or cellular blinds are an excellent choice as they trap air within cells and act like a double-glazed window.

If you're in a hot climate, use external blinds and awnings to provide shade in summer. Blinds which are white or near-white on the outside or have a reflective surface will reflect more heat back outside.

Pelmets

Fitted pelmets will prevent heat loss above the windows. Pelmets can be made of any material as long as it creates an air barrier. If you're renting you may be able to make temporary pelmets from cardboard, timber or other stiff materials. Bubble wrap or a thick piece of fabric are also options. Pelmets need to be flush against the wall and sitting above the track, and reach to or past the curtain. Most pelmets reach over the curtain. However, you can also build a hidden or near-invisible pelmet as a single flat strip that sits behind the top of the curtain and just reaches its back edge.

An alternative to sealing the top of the curtain is to seal the base and sides to prevent cold air being drawn in. Floor-length curtains will stop air entering at the base. The curtains can be held in place by weighting the hems so that they stay in contact with the floor. If your curtains are just short of floor length, two heavy fabric-and-sand 'sausages' such as those used to block gaps under doors can hold the lower curtain edge trapped between them. Temporary tape, magnetic tape or Velcro can hold the curtain sides in place.