The house has a dual fuel heat pump and gas furnace system. The furnace is a 90% efficient Amana unit that can be operated as a non-direct (one pipe) or direct (dual pipe) installation. The installer chose non-direct for the vent and chose to let the combustion air enter from the vented crawl space. The vent pipe was not installed per manufacturers instructions. It had three significant errors. The 2" PVC fittings were not glued, the PVC fittings were of the pressure type instead of DWV (drain waste vent) and the vent pipe had a high spot in the middle with most of the slope toward the outside.
The failure to glue the fittings is the most serious issue. There is a high probability that the joints would eventually pull apart from vibration and being bumped or jostled around. This would result in carbon monoxide being dumped into the crawl space directly below the living space. Use of pressure type fittings instead of DWV is bad also. The hard turns of the pressure fittings restricts the flow of the vent gases and can disturb the safe operation of the furnace. Failure to slope the pipe back to the furnace may not ever cause a problem in South Carolina but it is an obvious violation of safe installation. The slope is designed to return condensate to the warm furnace instead of dumping it to the cold outside. If the outside air is cold enough, the condensate could freeze and build up enough ice at the discharge to block the vent opening. This could cause carbon monoxide to back up into the crawl space and impact the furnace operation.
The vent system will be converted to a properly installed direct vent two pipe system as part of the crawl space closing project.
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