During a Hamilton home inspection BLT observed a negative slope on an exhaust for a high efficiency furnace. He also noticed that the exhaust had been tagged as a violation for safety reasons. The explanation being, the condensate can run down the exhaust and possibly freeze at the discharge point exiting the basement foundation. The implication being, a negative pressure in the vent connector and a vent motor shut down, all exhausts vents are required to have a positive slope. BLT alerted his client and her agent of the safety hazard.