What type of pressure does supply leaks cause the house to be under with respect to the outside?

Supply leaks in a home indicate that air is being introduced into the living space from the outside due to the inability of the conditioned air system to maintain function. When supply ducts have leaks, outdoor air enters the home, which increases the internal air pressure relative to the outside environment. This condition leads to the home being at a positive pressure with respect to the exterior.

However, considering the question focuses specifically on how leaks affect the overall pressure dynamics, it’s important to understand that leaks in the duct system often create a scenario where, instead of the desired balanced pressure, the house can actually operate under a negative pressure if there are also exhaust paths or if other air-handling systems are in play that remove air from the conditioned space.

Thus, while leaks can sometimes introduce a positive pressure scenario, it is essential to recognize that the dominant effect of supply leaks tends to increase air pressure inside, creating a tendency towards negative pressure in response to the overall air management strategies employed.