Hey everyone - I'm looking for some advice regarding issues with stratification I am experiencing. I only experience it in the cooling season. The heat works very well.
The home is a 1950s ranch with an uninsulated basement in the coastal NY metro area. Ground floor square footage is about 1200 square feet. It has a low pitch roof with cathedral ceilings throughout - therefore no attic space. The furnace/air handler is located in the basement.
When we moved in last May, the air conditioning was not keeping up. The furnace was from the 1980s and the AC unit was from the 1990s. We replaced both. The AC unit is a 2.5 ton Trane. After the install, we still had issues with the system keeping up due to stratification. The supply registers are all low wall registers on exterior walls. The return is a low wall return in the main hallway. The temperature at the floor is typically below 70 degrees, but at the thermostat level it is rarely lower than 74 degrees in the daytime. All of the cool air stays along the floor and is taken in by the low return.
I am confident the AC unit is the proper tonnage. I performed my own Manual J using CoolCalc to confirm the contractors sizing.
My initial thought was to have the return upsized and relocated to high on the wall it is currently on. In theory, this would pull in the warmest air near the peak of the cathedral ceiling and reduce stratification. My HVAC contractor agreed this would help, but also suggested redesigning the entire duct system. From what I am told, the current duct system is from when the house was originally built, or at the newest, from when the furnace was last replaced in the 1980s. The house was not build with central air. Therefore, the ducts are designed only for supplying heat. All of the supply runs are 4 inch galvanized. They are probably also very leaky. The ducts I can see in the unfinished portion of the basement were very leaky until I sealed them with foil tape.
The contractor also suggested making the supply registers in the main living area high-low registers. This doesn't seem like it would make a major difference, as long as Manual T is followed and the registers throw the cool air in an upward direction. Doing this would also remove insulation in a south facing wall. Can anyone confirm this is a bad solution?
I am currently saving for a wedding, and if it is logical to do so, I would prefer to fix this problem in phases. Redesigning and installing a whole new duct system is a bit more than I can spend right now. I can easily afford to upsize and relocate the return. Would this be advisable? Should there also be a dedicated return in the basement even if the basement does not need any cooling? At 1000 cfm, what size return grill and duct is appropriate? I have read up on the subject and it seems like ~1.75 square feet of cross sectional area would be appropriate.
Thanks in advance!
The home is a 1950s ranch with an uninsulated basement in the coastal NY metro area. Ground floor square footage is about 1200 square feet. It has a low pitch roof with cathedral ceilings throughout - therefore no attic space. The furnace/air handler is located in the basement.
When we moved in last May, the air conditioning was not keeping up. The furnace was from the 1980s and the AC unit was from the 1990s. We replaced both. The AC unit is a 2.5 ton Trane. After the install, we still had issues with the system keeping up due to stratification. The supply registers are all low wall registers on exterior walls. The return is a low wall return in the main hallway. The temperature at the floor is typically below 70 degrees, but at the thermostat level it is rarely lower than 74 degrees in the daytime. All of the cool air stays along the floor and is taken in by the low return.
I am confident the AC unit is the proper tonnage. I performed my own Manual J using CoolCalc to confirm the contractors sizing.
My initial thought was to have the return upsized and relocated to high on the wall it is currently on. In theory, this would pull in the warmest air near the peak of the cathedral ceiling and reduce stratification. My HVAC contractor agreed this would help, but also suggested redesigning the entire duct system. From what I am told, the current duct system is from when the house was originally built, or at the newest, from when the furnace was last replaced in the 1980s. The house was not build with central air. Therefore, the ducts are designed only for supplying heat. All of the supply runs are 4 inch galvanized. They are probably also very leaky. The ducts I can see in the unfinished portion of the basement were very leaky until I sealed them with foil tape.
The contractor also suggested making the supply registers in the main living area high-low registers. This doesn't seem like it would make a major difference, as long as Manual T is followed and the registers throw the cool air in an upward direction. Doing this would also remove insulation in a south facing wall. Can anyone confirm this is a bad solution?
I am currently saving for a wedding, and if it is logical to do so, I would prefer to fix this problem in phases. Redesigning and installing a whole new duct system is a bit more than I can spend right now. I can easily afford to upsize and relocate the return. Would this be advisable? Should there also be a dedicated return in the basement even if the basement does not need any cooling? At 1000 cfm, what size return grill and duct is appropriate? I have read up on the subject and it seems like ~1.75 square feet of cross sectional area would be appropriate.
Thanks in advance!
source https://hvac-talk.com/vbb/threads/2240581-Duct-Redesign-Stratification-Issues?goto=newpost
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