Consideration must be given to the following during the installation of duct systems for centrally ducted or compact-ducted ASHPs:

• Duct system design must follow NBC (Section 9.33.6) and the TECA Forced Air Guideline, HRAI Residential Air System Design manual (SAR-R2), or ACCA Manual D.
• Ducts systems should be designed to minimize friction losses.
• Pay close attention to available static pressure, especially with mini-ducted air handlers.
• New supply and return ducts must be sealed with suitable long-life material to minimize air leakage.
• Duct sealing materials should be rated to UL181A or UL181B specifications and used in accordance with the manufacturer's instructions.
• Avoid ducts in unconditioned spaces when possible.
• If ducts and/or air handlers in unconditioned space can't be avoided, all joints and seams in duct should be thoroughly sealed with duct mastic and all components should be insulated to a minimum of above grade wall building code requirements.
• When installing central ASHP systems using existing ducts, always ensure that ductwork is adequately sized for the heat pump air flow requirements and available static pressure. The TECA, HRAI, and ACCA documents noted above are useful references to assess duct capacity.