How are the two levels of the house connected? Does the lower level have air returns and registers?

One return only on second floor, registers in every room/hallway throughout both floors

how many returns on main floor?....I suspect that your issue would be improved by relocating thermostat...

TD

No returns on the main floor, only on the second floor. It’s an attic unit. 7 registers on each floor. There’s a thermostat downstairs but it’s for heat only (heat is 2 zones, a/c is one) BUT since we have the sensors down here I don’t follow how moving thermostat would help? I can get the downstairs comfortable, but then the upstairs is in the low 60s and I’m sick of having $300 electric bills :(

I’d love to have it be 2 zones at some point but the a/c unit wasn’t that old we were told on move in. I forget the exact age but we were told it should give us 7-10 more years by inspector, it’s been 2. But considering we didn’t have this problem previously, while I’m sure zoning would also rectify it there’s gotta be a simpler way!

Sounds like an airflow issue. Have you looked at the dampers in the attic ductwork? Maybe they got bumped? Inspect the ductwork to see if anything has come loose. Then try adjusting the airflow to send more downstairs.

Relocating the thermostat downstairs will make the downstairs temperature reach set point but upstairs will still be 6 degrees cooler.

The sensors already do that though, sorry I guess I could have explained them in more detail. Nest and other smart thermostats have sensors you can get and put in areas that you need to keep comfortable - living areas, baby rooms, etc. Ours are set to keep the sensors downstairs at 72 during the day and upstairs where the thermostat is at 72 at night.

I'll send someone up to check the dampers as soon as I can. I just had knee surgery and my SO has a back injury but we're hoping to get a family member over in the next few days to go up and check for us!!

Moving the thermostat will not help this problem. You can't solve HVAC design problems by moving thermostat or putting in these remote sensor things.

Basically these gadget makers are just interested in selling you more gadgets. If your location isn't so hot it might help, but typically in short order you see the limitations of such.

I live in and fix air conditioning problems in a otherwise hot climate. (Katy, Texas area) You have quite a few challenges in what you have explained as your situation. There could very well be other problems than what I say in this post... *read carefully*.

Design is a critical attribute as to how well or poorly an AC system will work. Location is another factor --- due to climate concerns.

In a 2 story structure you have two separate living areas divided by floors. With only 1 AC system to cool both floors of a 2 story structure that is going to present problems. Because the thermostat that decides if the system is on or off is limited to sensing temperature from an area of about 5 feet around where the thermostat is placed.

So let's put in sensors! Well as you have seen this only keeps the system running and dumping cool air into areas that are already cool making them colder.

Let's move the thermostat? uh no, it will never work. If a sensor won't fix it neither will moving the thermostat will make a difference.

Design: returns are useful in pulling hot air / keeping this air from being trapped. However, having a lower level with no return and HVAC system in the attic you're talking major expense to fix this the right way.

If you were to figure out a way to run a new return from the lower level (where it's warm) then duct this to the system in the attic... this would help. Think boxed in chase on second floor to attic with filtered return grill cut in thru the ceiling to the first floor. (The return grill would ideally be in the ceiling on the first floor in the room that is warmest for AC season.) Yes, you will give up floor space on 2nd floor to accomplish this.

Next step would be to zone this system for better control. First floor would be zone 1, Second floor would be zone 2. Ideally for a HVAC zone system to be all it can be would be to have at a minimum a 2 stage AC and 2 stage heat.

Zoning is a complex thing. If it's not done right more problems will ensue. The system needs to be able to work well in every season... when it's not so hot outside as well as when the heat wave comes.

Just as with the gadget makers there is an awful lot of garbage that has come out over the past few years in zoning controls. If you do it on the cheap, with the inexperienced it probably won't last long and problems could be quite severe.

I have a 4 zone system in my single story home. I wouldn't put something in my own home if it didn't actually work. BUT, equipment selection as well as design are just as important.

Design are the invisible things that very few people talk about when dealing with problems. They would rather sell you a gimmick.

As I said earlier up in the post --- I service the Katy, Texas area.

If the system was working properly the previous year, I would have someone check the duct work for non functioning dampers. My sister had this exact same problem. The upstairs was quite comfortable unless they tried to heat/cool enough for downstairs, then upstairs became either to hot or to cold depending on the setting. As soon as I went into the attic I found two dampers that were not working. Once they were replaced it was almost like a new house.

Still want to know how the two levels connect...an open wide stairway is much different than a narrow stair with doors on each end.

@ North Texan - sorry I missed that! It’s an open staircase - foyer is wide open to the second floor and with a big window at the top so I really would have expected the upstairs to be much warmer

I really would have expected the upstairs to be much warmer.

Rebecca, usually the upstairs is warmer. However, in some cases due to design of the system it doesn't quite work out that way. (it's quite rare, but I've seen it before.)

Think of this in terms of how far the air must travel to make the difference in the change of temperature within a room.

Your HVAC system is in the attic. The top floor is where the return is. This gives the upper floor the advantage because the warmer air is pulled from the space AND the distance the cool air must go is much shorter than the lower level.

It's possible as well that the upper floor ducting may be larger than the supply going to the first floor. This would aid in cooling the upper floor as well.

I have this same situation as OP but we have a new central air system (in the attic); the upstairs are brand new flexible ducts while the downstairs has original rigid ducts running up and inside second floor closets (were not replaced). I'm thinking this is part of the problem why the first floor is warmer and the second floor is chilly. To the OP, has there been any improvements? I'm in CT too.

It's an airflow issue. You have too much (cold) air going to the upstairs. You need to send more of it to the downstairs. This will be an even bigger issue in the heating season if you don't get the ductwork adjusted better.

Thank you for your reply. Heating is through old style radiators, oil heat. Ducts are only for the central air. I will have company check the dampers as someone here previously suggested. We had cellulose insulation blown in after the central air install, perhaps they accidentally disturbed the duct work going into the downstairs registers?