Are corroded vents a common problem with sidewall-vented mid-efficiency oil furnaces?

Corroded vents are indeed a common problem with sidewall-vented mid-efficiency oil furnaces. This is primarily due to the fact that these furnaces produce flue gases that contain moisture and corrosive elements, which can accumulate in the vents over time. The moisture can condense inside the venting system, leading to corrosion of the materials used in the vents.

Mid-efficiency oil furnaces are often designed for direct venting, which means that they rely on outdoor air for combustion and vent the exhaust directly outside through the wall. This design can expose the vent to outdoor elements, particularly if the venting materials are not corrosion-resistant. As a result, over time, especially if maintenance has not been routinely conducted, the integrity of the vent system can deteriorate, leading to the risk of leaks and potentially hazardous situations.

In summary, the nature of how these furnaces operate and the materials used in venting contribute to the prevalence of corrosion in the system, making the statement true.