HVAC return with fresh air?

Did an inspection today on a brand new townhome, and ran across a new installation of a heat pump with a return duct running from the coffin box enclosure, up through the attic and pulling air from the rear exterior patio. I’m not familiar with an installation like this. Has anyone heard of new installations here in Florida that are pulling return air from the exterior?

Doesn’t matter if you are in Florida or Alaska the return is normally a closed loop unless there is a damper installed to allow the outside air to be closed when necessary or perhaps if the unit is over sized to accommodate the extra load. What was the SQ footage of the town home and what was the tonnage of the unit.

Heat pump is 3.5 tons and it has 1536 sq ft. I’ve never seen or heard of anything like this so I thought it might be some new design.

Your tonnage and Sq footage are a close match for the humidity down there.
If it was me I would red flag the outside air and require the contractor to explain his supposed theory provided there is no damper installed.

BTW lets call a plenum a plenum not a coffin;-):smiley: but I knew what you were talking about I am just ribbing you.

Thanks for the info Charlie. I already wrote up the report and suggested the contractor explain the why-for’s. There is no damper as far as I can see either. I’m interested in hearing what the contractor says.

It sounds like a Fresh Air exchanger to me Are you sure it isn’t one

It is a fresh air return. However, in 12 years of home inspecting, I’ve never seen one installed in a heat pump system. Was wondering if this is something new or what.

No not something new but it should have a weighted barometric so that it is only pulling so much fresh air. Other wise it will be way overpressurizing the building.


A 3.5 ton Heat Pump system on 1536 sq.ft. seems a little heavy for a Brand New Townhome. I’m sure it is built to “Green/Energy Star” standards based on today’s standards and codes environment. Also, it is in Florida…right ?

That being said… I still see fresh-air installed through the R/A system on occassion in my area, although usually on gas heat w/A/C or dual-fuel/piggyback systems. I can’t remember when I last saw this design on a staright up Heat Pump systen. The ones I have seen lately have had manual dampers or small motorized dampers controlled with inline humidistats, similar to commercial Economizers w/ enthapy controlled operation.
I check the functionallity, and note this unusual design to my clients as possibly/probabley needing increased monitoring/maintenance/service.
I like the design idea on residential systems, and if installed and setup properly, I think can be a great energy saver as well a improving the IAQ of most settings.

The key…installation, setup, maintenance, and monitoring.


I would rather have a controlled amount of fresh air that I could condition and pressurize the building than having air leaks all over the home.:smiley: