The Envirovent system has been installed in for a little under a year now and it has made a marked difference to the humidity levels in our old damp house. I bought a humidity measuring device (might be called a hygrometer can't remember) and since installation our humidity has fallen from about 65% to about 45%. The one negative that I've noticed is that the extractors are becoming a little noisy which I think might be due to failing bearings in the fan motors.