This article was inspired by a letter to GreenBuildingAdvisor.com in which a person complained that their contractor had purposefully left holes open to the outside amidst a spray foam installation in the attic. Some investigation revealed that the holes were left in order to provide air to the atmospheric combustion furnaces that warmed the house, but the problem still remained that the purpose of spray foam insulation (chosen primarily for its benefits in airtightness) was undercut by the need to leave open airways to the outside. In this way, spray foam is incompatible with this type of HVAC installation on a system level.
Read the full article here: Spray Foam Insulation Does Not Work with All HVAC Systems