Page 8, lines 24-29: In addition to the filtration efficiency, the equivalent volume of cleaned air is an important metric describing the efficiency of an air cleaner. Has the manufacturer tested this air cleaner for its Clean Air Delivery Rate (CADR)?

Page 8, line 50: It would be helpful to briefly describe the method for PM2.5 sampling in addition to giving the reference to the previous paper.

Page 10, line 8: Please give the pore size of the Teflon filter.

An interesting result that deserves more discussion was that no significant difference was found in endotoxin loadings between baseline and follow-up. There is quite an extensive discussion about the possibility of the collected endotoxin being released into the air from the HEPA filter. In this study, however, the loadings in both HEPA and control homes decreased slightly (although not significantly). Could there be other confounding variables that were not assessed, for example, seasonal variation in endotoxin levels?

The revised manuscript is acceptable.