Hi All! I have a new constuction home with dual zone HVAC system, 1 zone per floor as standard setup. My question is for the return air system, should the return vents be active in both zones when only one of the zones is actually heating or cooling? I found it strange that when the heat was off downstairs but was on upstairs, that all the returns in the house were active, on both floors. Felt like it was sucking all the hot air from downstairs while it wasn't replenishing it. Any help or insight on this would be appreciated to see if I have a problem or if this is the way it should be! Thanks!
Don't think I seen anyone zone the returns.
If you try to fail, and succeed.
Which have you done ?
This sort of setup isn't intended to allow for big temperature differences between the two floors. The zoning is there so that you can maintain one temperature on both floors, or slight differences between. I'm just mentioning that so you can look at the system with reasonable expectations. Without the zone control, the second floor would always be warmer than the first floor, both in heating and in cooling season.
It's standard practice for the returns to be unzoned, and it works fine that way. If things aren't working well, look for some other problem.
have never seen zoned returns.
The posts and comments made by me are in no way affiliated with any company or organization. They are simply my personal opinions.
Return has several jobs
Most common is bringing back return room temperature air, this room temperature return air helps maintain a set point with out using so much energy. Another reason is to bring back a specific amount of air to let the unit fan run at a given load, to provide cfm using as little energy. You should not be pulling so much return air that it affects other areas of a home. Commercial and residential are different animals but work on the same principals. Commercial controls return air residential does not.
You have a good point and you could add a damper control to the main return duct but that would cost money. You could even have the set up with digital controls that read cfm supply and cfm return but it all cost money. If you would like ask them to add a control damper that opens and closes as the zone is in use. A well controlled and well balance system is the best thing you could have it will provide comfort and energy savings.
Update please and good luck
Some migration of supply air from one zone to the return of the other is likely,your sounds like too much.
Most systems can "slave" a return damper to oprate with the suppy damper,but it's not often done.
I'd be concerned that the return duct for the second floor is too small.When it's the only zone calling it gets increased air flow and the return may not be sized for it.
The return duct system ,without dampers is open to both returns,the air will take the path of least resistance.Slave dampers could solve it,but if the second floor return is too small,it wil create another problem.
If the downstairs return is oversized a damper it that return duct may solve it,by keeping it from being the path of least resistance.
Call your contractor and discuss the options.