Concerns had been raised, but nothing had been done, the source said.
It was well known the supermarket was an old building and the heating system was shot, but there had been no attempt to install temporary heaters while a more permanent heating solution was found, the source said.
The store had a high turnover of staff, many of whom were school-aged, in part due to the "rotten cold" conditions.
"Who wants to go freeze their arse off for minimum wage?" the source asked.
The source put the issues down to "a real lazy old school Kiwi attitude" among senior management at the store.
It was "disgraceful" staff had to put up with such conditions, especially since Covid-19 pandemic had been very stressful for supermarket workers, the source said.
The store was very cold when an Otago Daily Times reporter visited it one night this week and packing staff were wearing jackets and beanies while they worked.
Countdown director, corporate affairs, sustainability, health and safety, quality and food safety Kiri Hannifin said the store had a heater that was on 24/7.
It was not turned off but was getting old, and could be a little intermittent.