Does an air return duct do anything when the air conditioning or furnace is not running?

Question

I recently had a contractor create a new wall which cut me off from the rest of the house. There is one AC/Heating vent in the room and when the door is closed it gets very, very hot. As soon as the AC kicks on the room gets very, very cold.

The same contractor later told me that I needed a return air intake to cool the room down.

My contractor is a good carpenter, but his HVAC knowledge seems a bit iffy. The air intake return would doubtlessly help the AC run more efficiently, but - would an air intake vent do anything when the air conditioning is not running?

Answer 1

It depends on a few factors but just based off of what you've mentioned I'd say that it probably would be fairly good at keeping the room a more moderate temperature.

This is mostly because the air handling unit will be drawing the hot air out of your room and in the process the cooler air from the rest of the house will displace the hot air. Since you mentioned that the room cools very quickly I'd venture a guess and say that the room has good air flow in and out (air will flow down the path of least resistance) or is very close to the air handler (making the installation of a return simple).

It depends a lot on how easy and/or costly it is to install an air return in the room but it seems like a fairly good idea. The new California residential building codes are actually mandating a whole house vent fan to effectively accomplish the same thing (cooling without needing to run the AC) because it's really effective at reducing the temperature more efficiently.

If you do move forward with installing air return remember that the higher the intake is the hotter the air it draws in will be.