When is the HEATKITB80 heater kit required for installation?

The HEATKITB80 (Freedom Heater Kit) must be purchased when appliances are installed less than 6 1/4" (160 mm) apart from one another but are not connected side-by-side. This kit is also recommended for any installation in areas subject to extreme humidity. It helps prevent condensation-related issues in close or humid installations. (Page 42)