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Campaign, Stalwarts, Surplus Injectors (generator T2).
Have a healthy oil income (oil still growing).
When the temperature is warmer (-30c), power down all your heat consuming districts, engage overdrive and Surplus injectors. You can also just disable buildings and staff the districts to 10%.
If you have Heat Surplus (top center UI) two times bigger than Heat Demand the achievement will unlock.

There might be other ways to unlock it.