Hello All,

I’m sure everyone worries about answering “homeowner DIY” questions for fear of a little knowledge being a dangerous thing…

So let me preface this question with I’m a Veteran Historic Restoration Contractor (25 years in the field) in the process of central A/C return duct layout in my own 2 storey home with full attic and basement.  The air handler and supply ductwork to each room is located in the attic which is part of the envelope; superinsulated with 4″ Icynene in walls and 8″ in the roof, 8″ in the atic floor / 2nd floor ceiling, the rest of the house’s exterior walls sprayed with 4″ of Icynene and the basement / 1st floor joists sprayed with 8″ thick Icenene coming in 12″ from the rim joist.  All A/C duct joints sealed with mastic & taped then either wrapped in insulation blanket where exposed or sprayed with Icynene if in the wall or ceiling.  Triple glazed windows with Low E glass, heat reflective roof sheathing under synthetic slate roof.  Heat Loss Calcs done according to Manual J and heating system is running at 98% AFUE.  Buderus sealed combustion wall hung condensing boiler with outside air intake and direct exhaust.  Because this is a 100 year old home which now meets or exceeds Energy Codes in my area, an ERV system was properly installed and working independently from A/C and heat system so there is NO concern with IAQ or pressure issues.  A/C has dehumidifier and air cleaner (to be connected on the return after you help me figure the duct location) and both will work in heating and cooling seasons with A/C on fan only.  Before updating, air sealing and insulating the rest of the house, basement heat was supplied by heat loss from boiler / exposed piping from steam system.  House how has panel rads in bedrooms, radiant in bath & kitchen and radiant in the basement floor.  Every room is on separate zone.  Although I’m not going for certification, this project follows LEED guidelines.  Everything was thought out and done right with no expense to materials or workmanship.  ALL work meets or exceeds codes and best practices.

That said, I’m here because although I have a HVAC installer to do the system charging and initial start-up, I’m doing all the mechanical install in phases as do the rest of the work on the house.  Usually he just installs the return duct in the 2nd floor hall ceiling in a central location as close to the air handler as possible to keep the run short.  In my house, the only place for the return in the 2nd floor hall ceiling puts the 2′ X2′ duct opening smack in the middle of the floor, uses three 90 bends plus 14′ of duct across the floor to connect to the handler.  I was thinking about installing the A/C return duct in the basement ceiling using the 3′ X3′ chase now gained from where the old boiler’s chimney once was.  Because it was on an outside wall, this path is a straight shot with just one 90 into the air handler 2 floors directly above, not claiming all the valuable floor space in the attic.  That’s not the reason for my visit here though.  I’m in an area with very high water table and the house was purposely built over natural springs so they could tap into the “cooling effect” and also use it for food storage back in the day. In the hole in the floor where they once placed milk bottles to sit in the water,  I now have a sump pump which runs during rain and several days (or weeks) after.  The unfinished basement is typically 65 deg year round without heat or A/C but humidity levels are so high it keeps a 40 pint dehumidifier runniung 24/7 from May to Sept.  No water infiltration or mold problems, but in the hottest of summer days it is noticeably damp.  My installer says he prefers the return intake in the 2nd floor ceiling is because it’s grabbing the hottest air in the house and pulling UP all the cooler air from lower floors.  My thought is since the basement isn’t ducted with A/C supply ducts (additonal cooling isn’t needed there) by placing the return in the basement ceiling it will draw the drier, conditioned air from higher floors, take up the cool but damp air from the basement, running it through the dehumidifier & air cleaner along the way back through the A/C system (possibly helping with efficiency) but my MAIN reason for putting it in the basement is sucking up the damp air and replacing it with drier air.

Does anyone see any issues/ problems / concerns with installing the return air intake in this location?

Is there any code or technical / mechanical issue I’m overlooking?

Any thoughts are GREATLY appreciated.

Thanks!