Many of us want our window coverings to look good and provide privacy. But curtains and blinds have other important roles such as blocking out light to help you sleep better and keeping your house cool when the sun shines. David Rogers, a senior engineer at BC Hydro, offers some advice on the best window treatments to provide you comfort at home, while also helping to reduce your energy bills.

How can I make my windows as energy-efficient as possible?

Rogers: When the hot spring sun penetrates windows, the temperature in your home rises — along with your cooling bill. To make sure that your windows with higher sun exposure are as energy-efficient as possible, I suggest using low solar gain low-e film. These thin polyester films use a micro-thin transparent metal coating that reflects heat. They are stuck directly to your existing glass to reflect radiant heat, either from outside or inside, which reduces the amount of energy you need to heat or cool your home. You can do it yourself or have your low-e films installed professionally for between $1 and $8 per square foot. Some manufacturers recently introduced high-visible light transmission films, which are more expensive with installed costs of up to $14 per square foot. In addition to reducing the heat in your home by reflecting heat back outdoors (some films do the reverse as well), the higher-priced version provides about 70% visible light transmission, compared to 20-30% for lower-priced e-films.

Is there a best way to hang curtains to keep heat out?

Rogers: To further reduce heat exchange or convection, draperies should be hung as close to windows as possible. Also, let them fall onto a windowsill or floor. For maximum effectiveness, you should install a cornice, which is an ornamental moulding, at the top of  a drapery or place the drapery against the ceiling. Then, seal the drapery at both sides and overlap it in the centre.

When choosing curtain  backing, which colours can best keep your room cool  on hot spring days?

Rogers: Medium-coloured draperies with white backings can reduce seasonal heat gains by as much as a third. Draperies also stay cooler in the summer, compared to some other window treatments, since their pleats and folds lose heat through convection.