Review on Studor 20297 Maxi Filtra Admittance Valve by Robert Howell

Purchased December 2015. I installed it just over 2 years ago. We've had a terrible time smelling like sewer gas on a cold morning since our sewer pipe was replaced. This brought a huge improvement. The filter has not been changed for 2 years, it still works. The filter cartridge is tiny and the activated carbon inside must have stopped working long ago. I think the device is really just restricting airflow IMHO. However, it does a great job.