The prices for rate DT are set in such a way that customers will use electricity to heat their home when the temperature is above or equal to -12°C or -15°C (depending on the region), when the lower price applies to electricity used. When the temperature drops below the cutoff, the higher price goes into effect, and it’s less expensive to heat with fuel. This higher price has the effect of lowering demand for power during peak periods, which are generally winter cold spells.
Customers who pay rate DT can save in summer by using electricity for air conditioning or to heat a pool. However, dual energy is cost effective for all Hydro-Québec customers, because reducing consumption when it is very cold avoids costs that are higher than summertime power costs.