The finished portion of my basement was completed after the original construction. I've found a few questionable practices, including the lack of an HVAC vent in the basement bathroom (shown in green below). I don't know the first thing about the air portion of HVAC systems, but I'm assuming a good design would have incorporated one. Do I need to install a vent?

Furthermore, do I need to add more vents/ducts to the main finished area of the basement (shown in red below)? The red dots below are where the current vents are installed in the room.

The current system that serves this portion of the house also serves another ~1,350 sq ft on the main level. There is an air return on both levels. The unit is a 3 Ton / 90,000 BTU split gas.

I am about to remove all the exterior-wall drywall to insulate (they kindly left all exterior walls uninsulated, even those above grade), and ceiling drywall to run various wires and cables. This would be an excellent time to run additional HVAC ducts if needed.

The lack of insulation really throws out the "does it feel comfortable as is?" test.

  • "Den" => ~402 sq ft
  • "Bath" => ~60 sq ft (modified for discrepancies in floor plan below)

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2 Answers 2


I'd say maybe you don't, if it doesn't have any exterior walls, which it does, so that's a yes.

Drywall is the enemy. This is also a good time to upgrade any of the electrical on the interior walls as well. You're two steps from a gut job; go for it.

As to whether you need more registers elsewhere, I don't know; I'm not a math wiz: calculate the heat load and the corresponding ventilation requirement (that's the part i pay for).

  • I'm definitely planning on addressing some electrical issues while it's opened up. I'll check out the heat load calcs, thanks!
    – mjohns
    Jul 23, 2015 at 1:31

To be honest it just depends on how many cfm of duct work u already have installed in your home your unit is designed to cary 1200 cfm of air at 3 tons so if you've already reached 1200 cfm you would not have the capacity to supply another vent unless you had one room that stays cooler than the rest that you could downsize the duct on to provide you with the proper air flow needed to supply a 6" drop for your bathroom this is coming from 10 years exp.in heating and air-condition both residential and commercial

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