The study recorded the in-store temperature of 73 shops along Oxford Street in London. It found that that every shop was hotter than the 18°C recommended by the Chartered Institute for Building Services Engineers.
The survey also reported that 92 per cent of the stores visited had left their exit doors open.
Energyhelpline.com business services director Jonathan Elliott said: 'Staff are in T-shirts and the doors are wide open, so it's no wonder the heating is being cranked up. It may be reasonably mild now but we're in for a bitter winter.'
The average shop temperature was 23.6°C. The hottest shop was the 90,000 sq ft (8,360 sq m) Topshop flagship, at 27.2°C.
Ken Parsons, a professor at Loughborough University's Human Thermal Environments Laboratory, commented: 'It may be because the workers wish to wear light fashionable clothing. It may also be that in the winter, the first impression for the shopper who may be cold will be the pleasure of moving to a warm and welcoming environment. After 20 minutes or so, this will wear off and unless clothing is reduced the customer may become unpleasantly hot.'
The 10 hottest shops were:
Outlet Store 25.4°C
Clinton Cards 25°C