The present invention provides an apparatus for supporting stacking of a top heating, ventilation, and air conditioning (HVAC) unit on top of a bottom HVAC unit. The apparatus includes a base member configured to mount to a top cover of the bottom HVAC unit. The base member comprises an upper base portion with a top surface configured to receive at least a portion of a base rail of the top HVAC unit. The apparatus further comprises a stacking insert extending away from the base member. The stacking insert has one or more sloped surfaces extending above the top surface of the upper base portion. The top surface extends from a base of the one or more sloped surfaces in a plane substantially parallel to the top cover, when the base member is mounted to the top cover of the bottom HVAC unit.