Uncoated single- glazed windows are considered to be the weakest thermal component in the building envelope. Heat conduction through such windows is almost 10 times that of insulated walls, with energy wastage from windows accounting for more than 50 per cent of an air conditioner’s energy consumption. Compared to single glazing, double glazing reduces heat conduction by half.
It’s expensive to retrofit double glazing but you could try cheaper options to reduce the loss of heat from within, with window films and with blinds and curtains. Open blinds and curtains to let in winter sun during the day, and close them in the afternoon/ evening to help prevent the radiant heat inside from escaping through the glazing as it starts to cool outside. This reduces the burden on your heaters.