To properly answer your question, we need to first explain how heat pumps work.
A heat pump doesn’t actually produce heat. It transfers heat extracted from the outdoor air to the house. That’s what makes it more energy efficient. Since the available heat reduces as the outdoor temperature drops, each installation has a balance point, which is when the temperature required by the heat pump to heat the home at a level equivalent to the home’s heat loss.
Let’s assume the current balance point of your installation is −12oC. At a higher temperature than this, the heat pump can, for example, supply 3 kWh of heat per kWh consumed, which represents a coefficient of performance of 3.0 (the exact performance depends on many factors). In comparison, an electric heating system without a heat pump is generally made up of electric elements that consume 1 kWh per kWh of heat supplied, for a performance coefficient of 1.0. The savings generated by a heat pump are a result of the difference between these performance coefficients.
A heat pump with a balance point of −20oC is necessarily more powerful than your current one. It might also be too productive for your cooling needs, unless you choose a model with a two-stage compressor or with variable speed. Up to −12oC, this new heat pump will not generate additional savings. However, between −12oC and −20oC, since its performance coefficient is between 2.0 and 1.5, you will see savings of 40 %. In Montréal, this temperature range represents between 15 % and 20 % of your annual heating cost, which would translate into additional savings of up to 5 %.
You should know that changing your heat pump may require significant adjustments to your ventilation system.
For more information, we encourage you to consult a specialist.