Is there such a thing? I noticed since I've purchased and use my door seal there's a massive pressure difference in the home while I have our air duct machine running....could it be coincidence that yesterday one of our clients called saying after we cleaned the ducts her water heater wasn't working...I'm wondering if it sucked out the pilot light? Then again you'd think the furnace pilot would have also gone out. Anyways I thought it was interesting that I have noticeable air rushing into the house once we start up our machine.