changing oval duct to round?

Here's the jist of my issue. We have forced air system - 2 story house, Vinyl siding in the greater Philadelphia region. Heater is brand new (2018) AC is older (2012). our upstairs is cold in the winter and hot in the summer. We use Gas heat. Single Zone, using Nest thermostat. The trunk from the air handler is located in the basement and distributes air through ductwork to rest of house.

We have insulated the attic (sealed), replaced windows but temps are still not comfortable in the upstairs without using space heaters in all 4 bedrooms. The vents air pressure is faint, it feels like air is blowing through a straw. If our downstairs is 70, the upstairs is 62. There are no air returns, except one in the master bedroom which may be part of the problem. The master is usually about 66, (when downstairs is 70) but has 2 vents as its much larger and has a bathroom with another vent

The ductwork leading to the upstairs from the basement are oval in the wall bay then transition to round in the ceiling joist, and run to the wall, where the vent is located underneath the window.

We are thinking of renovating the room where the oval ducts exist and will be creating a pass through a doorway. Would it make a difference, if the wall ducts were six inch round and we furred out the wall to accommodate the ducts, or would that likely not have any effect on the issue?

 

You need to have a heat load done on the upstairs first. This will tell you the size the duct needs to be. 6in duct is only good for 100 cfm. That isn't much air in even the smallest of bedrooms. A 2nd unit just for the second floor is the best way to fix this.

 

So for air to go up, there needs to be same amount going down. It can help to close off duct on first floor and keep doors open thus creating a flow back down to the first floor where return ducts exist!

 

Do I want a manual J performed? How do I go about requesting this? I think I attempted to do this last year and most HVAC contractors looked at me funny and started giving me quotes for new systems, zones or other systems.

 

Did you check to see if you have adjustable dampers on your supply's to the rooms. They would most likely be at the beginning of the pipe coming off the main truck line.

If you have them, damper down the ones on the first floor to allow more heat upstairs. This is how you balance, as best you can, warm air systems. Unfortunately with 2 floors on 1 unit it can be pretty difficult sometime, especially if they undersized the pipes to begin with.

As far as oval or round pipe, if compatibly sized they carry the same amount of air.

Hope this helps a little.