The problem could lie elsewhere in your home.Do you know if you have a fresh air intake on your heating and cooling system.
- If your home was completely insulated with spray foam it may be too tightly sealed and require fresh air.
- Fresh air is usually introduced to the interior of the home by means of an air intake which draws fresh air in while the heating cooling system is running.
With out this you could be building up toxic levels of formaldehyde, VOC's from paint, carpet and spray foam in the attic.
For more information:
Read "We've got moisture/mold issues after spraying closed cell foam in the rafters of our 1925 home's unfinished attic." a Q&A answered by Lucas Johnson.
Also, check Randy Potter's Q&A "What is the most energy efficient way to mechanically ventilate a home to bring in cool night air, after a hot day?"