Hi, While installing an HRV I recently had a cold air return added to my unfinished basement - in hopes to add some air movement to an old and sometimes damp area. The contractor added a 6" circular return from the inlet plenum across 6'-8' and down to 18" above floor level. One 3" supply was already in place but had been taped off (obviously I removed the tape). My question is does this setup result in a negative pressure in the basement which could pull moisture or gases through the concrete foundation? We have recently noticed a significant increase in pink/white staining of the concrete (efflorescence or calcium deposit?) - I'd like to understand the cause before I try cleaning with vinegar, etc; When I had my HRV/Furnace contractor to come back and discuss with me, his comments were: (a) the return/supply situation is not an issue - the return cannot pull more than is available to it (or at least that's what I think he was trying to say) (b) the white/pink stains are calcium buildup that can be cleaned off Perhaps it is related to the basement drying out with the installation of the HRV?