For every one sq ft, you will need a 30 BTU unit. You will need an HVAC expert to determine the right size you need. All experts calculate the needed size and refer the BTU units to the HVAC sizing book.
Still, there are other determinants in play, such as the heating appliances in your home, the local climate, and how the home is insulated. A poorly insulated home will need more heat, and hence a larger heating unit. Also, colder regions will need larger units to suit the need for higher heating.
However, you can do the calculations yourself. Assuming you have a 2,500 sq ft home in need of a heat pump.
For instance, to tell the BTU you need, you can use the 30BTU per sq ft to estimate what will be needed by 2500sq ft. let's say, if 1sq ft calls for 30BTU, then what will 2,500 sq ft need. The multiplication should give you 75,000 BTUs. When converted to tons based on the g heat pump sizing chart, it gives you 6.25 tons of heat. In short, a 75,000BTUs will be needed for a 25000sq ft property. And the larger the home, the larger the unit needed.

Heaters running on electricity and toasters are one hundred percent efficient, meaning they produce as much heat as they absorb. Heat pumps, however, have efficiencies of up to 300 %. They do not generate heat. Instead, they absorb them from the outdoor air or ground and distribute them to colder regions indoors.

Heat pumps, therefore, use less electricity, yet they produce heat effectively. For instance, a ground source heat pump can consume 1kw electricity and deliver about 4kw of heat. Since heat energy is freely available, they are more efficient than other heating units. Using them means you get to reduce heating bills by almost two-thirds.

Further heat pump efficiencies are dependent on the price of fossil fuels vs. that of electricity. The cost of fossil fuel is high and comes with the hazards of hydrocarbons. Again, if you are using pool heat pumps, you have an additional advantage. When your house is cooling, your pool gets heat in return.

It saves energy that is used for heating the pool independently, hence reducing energy bills. Again, you won't install a heat pump in a house that's not well insulated. Insulation means less heat exchange between the exterior and interior air, which minimizes any chances of heat wastage.

Installation of heat pumps will vary depending on whether they are installed outdoors or indoors. Also, if you are installing a ductless system, the location should be unobstructed. For indoor installation, you will need a mounting plate, a driller, and screws. If your system is ducted, make sure you have access to the interior ductwork. If it is inaccessible, you will have to install new ones.

The second step is to create an access point on the wall of the basement or attic to link the indoor unit and the outdoor condenser.

Drilling through the piping lines should get the job done. This should allow passage for refrigerant, electrical, and condensate drain lines. The refrigerant and condensate lines are then connected to the indoor unit. The lines installed will allow the latter to circulate in the outdoor and the indoor condenser.

The next step should involve you connecting the wiring to an electricity supply. All the lines installed should be insulated and a drain installed on the outside for condensation.

Lastly, you have to install temperature sensors, which help in adjusting heat requirements. To make monitoring easy, your heat pump might also feature remote heat sensors that can be accessed through phones or tablets.