A heat pump works in regions where the temperature remains moderately hot and cold in summers and winters. But in places where the temperature dips below the freezing point a heat pump may not be effective. In exceptionally cold climates there is not sufficient heat available in the air which the pump can extract and send in for warming. You may need to keep a supplementary furnace or room heater to supplement the heat pump.
There is a type of heat pump called geothermal heat pump which sources heat present beneath the earth’s surface to heat the houses. These are effective in extreme climates as well. This is because the earth’s temperature remains constant at 50 to 55 degrees throughout the year. But installing them is quite costly. However you get tax credits to install them.
Heat pumps are eco-friendly than conventional air-conditions or furnaces. They use the heat in the atmosphere or underneath the surface of the earth to warm houses. They do not need to burn fossil fuels. However, air conditioners and furnaces have lesser upfront costs. They are also more compact units then heat pumps.