dead air diffuses out of the front openings this represents a tiny airflow both directions warm air flowing out and colder air flowing in however the rate of diffusion depends on the opening size it should be noted that there is only random diffusion since the pressure on all sides of the unit is approximately ambient u2014 if there is excess pressure on the rear side possibly caused by a furnace blower or air conditioner there will be an increase in diffusion from rear to front due to the pressure gradient this effect is greatly reduced if there is a layer of sheet rock or plywood on the ceiling below the insulation which is the typical case in general then the random diffusion flux is independent of temperature difference to the first order and really only depends on the opening size and the total number of openings where j is the random diffusion flux u is a mobility constant for air d is the opening diameter and n is the number of openings alpha is a opening offsetting parameter that is maximum when the openings are aligned in the above equation the spacing between the panels has been ignored since for the most part it does not play an important role after thermodynamic equilibrium is reached a typical spacing or separation can be between u215b inch or smaller to several inches such as two or three inches or greater the opening offsetting serves to reduce the diffusion flux opening offsetting is more important for panels that are closer together than it is for panels that are widely spaced thus the exact value of alpha as a function.