What is the outside temperature when it takes an hour per degree?

Is there an air return in your son's room or is the door left open. You can't pump in air if the air that's in there can't escape.

Thanks. Outside temps at night have been in the mid 50's to mid 60's.

There is a return in each room.

If outside is 50-60, why do you have to turn the AC on ?

I would be concerned if it takes 3 hours to go from 74 to 71 degrees when the outdoor temperature is only 62 degrees. That is basically a no heat load condition. I assume only one of the 6 zones was calling for cooling when this happened.

The temperature difference between supply and return on a new system should be in the 15-20 degree range. So if the contractor says the AC is designed to cool the house to 70 degrees under heat load conditions, then the supply should be in the 50-55 degree range. In this scenario the heat loss is very small so I would expect to be able to reach a temperature of 66 degrees,

Have you measured the supply temperatures for the 6 zones?

Buy your son a room fan. Cooling a house lower than 70 degrees shouldn't be necessary.

I'm surprised to hear a newly constructed home has 8 tons of cooling. Presuming modern and enlightened building techniques were designed in and used, that's likely to be needed only for a house of 9-10000 sq feet.

If interior humidity is a problem, maybe you've got too much tonnage and it isn't running long enough. Have a built-in dehumidifier or two installed.

Thanks All.

@mike_home, It's likely that one or two of the other zones were calling at the same time.

@Elmer J Fudd, house is unfortunately 8800 sq ft conditioned space. It should not be necessary to have to use a fan in a new house in 2020. For best sleep it's recommended that rooms be 65°f, <550ppm CO2 and humidity between 35 and 50%.

That said... We all travel quite a bit (outside of Covid) and have frequently stayed in places with no or poor AC where fans were necessary. Not a big deal. But just like we like having indoor plumbing and nice toilets when we return home, we also like AC when it is hot or humid outside. There's nothing wrong with that. The technology exists for it. It's actually quite standard in most buildings now.

"It should not be necessary to have to use a fan in a new house in 2020."

It should also really not be necessary to cool a room to 65 degrees for sleeping. Put in an overhead fan and call it a day.

Getting even air flow and temperatures from room to room is rarely achieved, not even in commercial buildings. To experience temperature differences, especially for rooms with different compass point exposures, is not unusual.

Ducts were aero-sealed of which pressure testing is a necessary part.

All ducts are in conditioned space except for a 5' portion of the supplies to the north bedroom. These are insulated duct plus have 7" of closed cell foam so s/b good.

Air leaving supplies is 59°f (using Thermopen Mk4). HVAC folks measured about 95 CFM at each supply.

Supplies and returns are all hard duct w/ rectangular trunks and usually round branches. The only flex is for bath exhausts.

(It does amaze me that in 2020 these zone panels cannot provide current and historical information such as air temp entering & leaving the air handler, when thermostats have called for what, and what the zone panel is telling what to do.)

@Elmer J Fudd, This is 2020 and it is totally OK to utilize the technology we have to create a healthier and more comfortable environment for better sleep.

By your reasoning perhaps we shouldn't have indoor ovens, ranges, refrigerators, toilets and a host of other things including the very internet you used to post on this forum. Perhaps we shouldn't use ventilators to bring in fresh air when it's not practical to open windows?

If it was purely a comfort/preference thing I might agree w/ you but studies consistently show that people get better sleep when temps are cooler and with 65° being the ideal. We also know that good daily sleep is critical to overall health and wellbeing. Maybe you should try cooling your room down to 65° to get a better nights sleep.

Try finding an HVAC contractor who will do something other than roll his or her eyes, either in your presence or later, when you complain that you can't cool a room to 65 degrees. Why might that be? They'll probably suggest a mini split and be happy to sell you the project, whether needed or not.

"studies consistently show ....."

My life experiences consistently show that people who think they know more than the experts they hire and have an attitude of entitlement for what they think they should have, sleep less well and are much less happy in their lives than people whose expectations are more reasonable, less self-possessed and more easily achieved.

If your son likes sleeping in a cold room, there are plenty of places with a cold climate he can move to. Or, set a good example for him as a father who teaches life skills, suggest he get his own home and work it out himself.

You don't happen to have electric duct heaters that are trying to keep the temps in the 70s, do you?

Nope, no duct heaters, electric or other.