I assume that you had to add the ductwork when you had the ac installed, as you mentioned radiators.

I also have a radiator heat/ac cooling home. Our ac air handler is also in the attic like yours. Our basement has no ac also like yours.

Couple of things to ask about. Often these ac retrofits are not ideal design, but practical design to work within the existing home as it relates to ducting and registers. Often there is not a supply and return air register in the rooms, but a ceiling supply register and undercut doorways for return air flow. Our system has a large return air vent in our hallway ceiling going to the attic.

Ask your service tech if the duct registers can be adjusted to force more air downstairs.

Ask if there is good airflow overall and good return air to your system. If not can they suggest any changes? Were your doors upstairs undercut about an inch for return airflow? Can they add some changes to the ducting to get more airflow downstairs?

Ask if the unconditioned basement is contributing to your cooling load on the first floor. Are you running a dehumidifier in the basement? That may help this a bit. If you have a stone foundation, then you likely always will have infiltration here. Do you keep the door at the top of the basement stairs closed?

And you are on the right track as to keeping your drapes closed to reduce solar gain.

Also be sure to run the exhaust fan while cooking and bathing (and then turn off when finished)

As to your drafty doors, that is good to review and will help with your winter bills too.

Great amount of info!

First, I'll call the company that did the install, because you brought up some points which only they can answer.

As for other things; no the doors were not cut for airflow. Not sure if this is necessary as the only one kept closed any length of time is the master bedroom - to keep the cat out. There are only 2 other room up there, other than the bathroom.

The return air upstairs, is in the hallway.

We do have a stone foundation. I had no idea this would play into the problem. Also, we don't use a humidifier down there; mostly because I am sure neither of us would remember to go and empty the thing! We hardly go down there other than to do the laundry (unfinished).

The door to the basement is always kept closed because of the cat. Too many dangerous things for him to get into down there.

I nearly always run the fan over the stove. The stove does generate a huge amount of heat. It's a Viking. Considering how small the downstairs is, this must not help matters when it's running.

Showering, is quick and so early in the day, I can't see how it possibly could contribute.

As for the drafty doors - my heating bills were astronomical. It was my first winter in the house this past season. If that didn't convince me to get them replaced nothing will!

Was this a retrofit? I'm just guessing there is not enough vents downstairs and maybe no return. In fact, the easy thing to do would be to install the system in an attic and only put registers and returns on the upper floor. Getting ductwork to the first floor isn't easy in a retrofit.

Of course your drafty doors don't help and maybe drafty windows. You might look into solar screens on west windows if that is possible. But I am also guessing that your windows are old and that is another area to improve the envelope.

David, did you read my original post? I said that it was an old house, a/c installed when I purchased it and that the unit is in the attic.

Each room downstairs has a vent. Each room upstairs does too, and that is where the return air is. 7 vents in all, for as many rooms. We were lucky to be able to get vents easily to the 1st floor because the closets lined up nicely for us to run everything.

I don't know if this might have anything to do with it but it suddenly occurred to me it might; the house is constructed of terra cotta block - not wood frame. We had heard that unless you keep the house cooled all the time; once it warms up it retains heat in the terra cotta. Not sure if this is true or not.

BTW - the rest of the house, other than the front windows, doesn't get much direct sun other than in the morning. In fact, I lament this daily but I guess I should be grateful on this one account!

I gathered you ran all new ducts but that wasn't crystal clear from your post. The whole concept to me is unusual since I live in the South.

Certainly a masonry constructed house will retain heat more than wood. Not a huge factor in the summer but still an issue.

The issue is most likely that the ductwork for the system was designed poorly. In fact, the end result is almost the definition of a poorly designed (or improperly balanced) duct system. Since the system is all new, you need to call the people that installed it. Obviously, drafty doors not withstanding, this is an installation mistake. A proper install would have accounted for drafty doors and some west facing windows.

Was a permit pulled? Were Manual J and D done? In my state, all of that is required. These studies help to eliminate the problem that you are having.

Yes permit pulled.
What is a manual J&D?

Manual J is a calculation that determines the size of a/c (or heat) needed and Manual D determines the duct size needed.