Any way to improve HVAC flow?

 

A two story home with one HVAC zone is always going to be a problem. With an opening between up and downstairs like a stairway or balcony means the warm air always wants to end up upstairs and the cool air downstairs and is free to move as it wants.

How many cold air returns do you have? Where are they located?

If you have only one cold air return on one floor it might help adding another on the other floor. You can adjust the dampers on your registers. In winter partially close the registers upstairs and leave the ones on the 1st floor open. In summer reverse it and partially close the registers on the main floor and fully open the 2nd floor ones.

You can try leaving the fan switch in the "on" position so the circulation fan runs continuously. This will constantly stir the air and help fight the natural tendency for hot to go up and cold down.

Closing doors to rooms can cause problems. If the HVAC air doesn't have a free path to get back to the return then it diminishes what that room gets. So, a room with a closed door will receive less heating and cooling.

 

Not an HVAC suggestion, but you may also want to check if there are any drafts around the windows in their rooms. We have an issue in one of our kids' rooms that has 6 windows. We had some poorly installed windows and addressing the insulation around the windows made a significant difference in the room.

 

"but the electrcial system can't handle any more" Suggest an older home.
There's no location in your profile so we have to guess how much insulation should be in that attic.
https://www.energystar.gov/index.cfm...sulation_table
Old single pane wooden or aluminum framed windows?
Attic ever been air sealed?
I've worked on many an old house with balloon framing that had no insulation in the walls and no fire blocking so the walls where always cold.

 

You've got major issues with your duct system and possibly insulation too.

Lack of return alone will not cause this.

In the winter both floors should be roughly the same temperature, in summer it may be slightly warmer upstairs especially if the furnace is in the basement.

If the duct system is designed correctly, two stories can heat and cool just fine on one zone. Zoning and multiple systems are used to cover up for poor duct design.

Without looking at the entire layout and doing testing as well as checking insulation and air sealing, impossible to tell what's going on.

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Posting the following information may be helpful:

1. Location, size and construction type of the house. Detached vs semi vs town-house. Any part of second floor surrounded by attic?

2. Make and full model numbers of furnace/airhandler/heatpump or a/c

3. Location of air ducts and equipment. Basement, attic, crawlspace?

4. Number of returns, sizes, location

5. Number of supply branches upstairs vs downstairs and branch size going to each room (usually 4, 5 and 6")

6. Whether the ducts are metal, flex, or duct board

7. Sizes of main trunk lines and setup. For setup, like is there a trunk in a basement that all the branch ducts come off of? Or do all the branches come off at one point? Is there a second trunk for the second floor?

8. Insulation in attic - how thick is it? What materials? Insulation in basement and exterior walls? (you can remove electrical switch plates on exterior walls and stick a tooth pick between the wall and box to see if there's insulation)

 

Two floors two systems! Best for comfort plus you have redundancy.