The AAV topic comes up frequently on this forum. The majority of the professional plumbers are very outspoken and do not have any use for them at all. Their reasoning, although sound, makes using and AAV a mortal sin. I think we are often guilty of overstating facts on issues we have strong feelings about, and the AAV is one of these issues. As near as I can tell, the only problem with them is that because they are a mechanical device, they can fail. This is true. However, the failure rate is really quite small and, as long as the device is left accessible, they are quite easy to replace. Given the option of a through the roof conventional vent and an AAV, of course the through the roof is preferred. However, when it is nearly impossible, when it would be very expensive, or it would be otherwise impractical to use the convention vent, the use of an AAV does have a place.
