Steve: If your spray foam installer leaves the vents open, he will be committing the 2nd of the 4 problems I described above. You will most likely have comfort and efficiency problems. You may well have condensation problems. You will be spending a lot of money on a product that likely won't perform as it should. Don't let him leave the vents open. If the installer you've chosen doesn't understand this, you may want to choose someone else.  Spray Coating
There have been a few mentions of intumescent coatingsabove, and it would be helpful to elaborate on them. Intumescent coating is a type of paint that will bubble when it is exposed to heat or flames. The bubbles act as a barrier that is relatively flame resistant. The bubbled coating delays the ignition of the spray foaminsulation. Because of this, intumescent coatings have become more common in building and construction.
A rule of thumb puts two thirds of the coating on the substrate and one third in the air. True HVLP guns use 8–20 cfm (13.6–34 m3/h), and an industrial compressor with a minimum of 5 horsepower (3.7 kW) output is required. HVLP spray systems are used in the automotive, decorative, marine, architectural coating, furniture finishing, scenic painting, and cosmetic industries. Spray Coating