Using the information from Step 1, the required heating capacity can be calculated following CSA standard CAN/CSA F280-12 combined with HRAI's "Residential Heat Loss and Heat Gain Manual" or TECA's Quality First^® Heat Loss & Heat Gain software or equivalent. To ensure accurate sizing of heat pumps, the following items must be taken into consideration regardless of the method used:

• The load calculation method must account for:
  • Surface areas and thermal properties of the building enclosure (walls, roof, doors, windows, floors, foundations, etc.).
  • Heat losses of all types, including air leakage in the building, duct losses (where appropriate), and latent loads (i.e. humidity) for cooling.
  • Heat gains from all sources, including solar gains from windows and roof, and internal sensible and latent gains for cooling.

• Load calculation steps and procedures should be followed closely. Regardless of whether or not safety factors are already built-in to the load calculation software or other methods being employed, the use of additional safety factors is not recommended since this may lead to gross oversizing.
• Appropriate indoor and outdoor design conditions and other climate factors for the location should be used.
• The actual building conditions should be taken into consideration. For example, don't use duct loss factors for ductless systems.
• Caution should be taken when applying infiltration estimates, which are often overstated. Blower door testing is recommended for estimating infiltration.
• Special attention must be given in the following situations, where realistic equipment loads may be surprisingly small:
  • Calculating individual, small block loads (e.g. for a single zone ductless ASHP serving an individual room, or loads for individual heads of a multi-spilt system)
  • Calculating loads for one or several rooms served by a mini-ducted system

• In cases where single zone systems are being installed in an "open floor plan" home, it is acceptable to include connected open spaces (including other floors connected via an open stairway) in the load estimates for that zone.