Oh I believe I missed up my HVAC load from my theater. The room gets pretty cold if my wife sets the AC to 68 seems colder than that. Is there a simple formula to calculate the needed return size for a room that's 28x13x7.5? I have two feeds in front and one 12" return in back I suspect I need to double the return size or number. Or add some kind of thermostat controlled dampener.

Any ideas suggestions would be very welcome, it's not terrible but it does seem to stay a little cooler than it should.

Could it be your HT HVAC is more efficient than the rest of house. i.e. takes longer for room where thermostat is to get to 68deg and HT is still being cooled?

Maybe try reducing the flow thru the feeds or as you say use thermostat controlled dampers.

Cheers,
Mark

Calculating return size is done with knowing what the supply CFM is, what goes in must come out. Size the return grille for 250 fpm and the duct for 400-500 fpm. From what you have written though it sounds like you just need to turn your thermostat up, 68F is way too cold A/C systems are generally designed/sized to deliver 75F on the hottest day. Heating systems are designed to maintain 72F on the coldest day.

You need to consider a few things.

-air balancing (measuring the correct CFM to each room diffuser)
-zoning system (shuting off the excess conditioned air to rooms or zones that don't need it)
-thermostat location or a multiple sensor thermostat

Bill

EDIT: Is this a two story or a bungalow?

It is true my theater is extremely insulated. My wife is getting better now that our kid has been born, for a while there it was pretty bad. So I think I will shut one of the vents to see how that works.

This is a single story with a theater in the basement. The furnace is a really high efficiency off the top my head its in the 90% range.