I don't have heavy duty curtains, just a couple. The Venetian blinds are pretty and make my rooms appear bigger than their reality, but they don't keep the heat out. Probably these days double glazing would have been built into these dwellings but, despite my enqiries re this, wasn't worth expecting it would work after the townhouses were already built....most days, no one large west facing windows has an external blind....it helps even during cold days in keeping some warmth inside....
