We have recently purchased a newly built home and have a dual zone central air system. The upstairs themostat has been placed in a bedroom on a wall opposite of a large window that receives afternoon sun. The return air grill is located in the hallway, just outside the same bedroom door. We asked to have the thermostat moved to the hallway, but were told it did not belong there as it would register air from downstairs. Of course, when the bedroom door is closed, it makes the rest of the upstairs too warm (in summer) and cold (in winter). Is this placement a better choice for the thermostat than the hallway? Or how would I find out where it should be placed for the best efficiency? We have had one A/C company come out and they stated the themostat should be placed in the hall, but the builder is still disagreeing, but can not produce the HVAC blueprints.

Hall. Thermostat should not see direct sun, nor should located in a closed room.

Rule is: inside wall, away from drafts or direct sun.

Done deal. Move it.

With a single return, you may wish to consider grills on the bottom of the bedroom doors for better comfort.