homeguy01
Jun 28, 2007, 03:08 PM
I have a central air system that sends air to both floors of my house. During the summer on days over 80 degrees the system runs constantly, from sun up to well after sun down.
The 2nd floor is always near or at 80 degrees no matter what the main thermostat is set to. We have to freeze the 1st floor to keep the 2nd floor tolerable.
I have a few reasons as to why the 2nd floor is so hot.
1. The ducts serving the 2nd floor are undersized, and too few. I estimate that the airflow to the 2nd floor is half that of the first floor.
2. The ductwork was poorly designed, too many bends. The ducting is not conducive to good airflow. Also, there is no way to balance the system, as they seemed to have forgotten duct dampers entirely.
3. The A/C system is undersized by 1/2-ton. I downloaded and ran an A/C tonnage calculator, putting in insulation values, wall types, door/window numbers, square footage, etc... It spat out that a 3.5-ton system would be recommended. The system in place is 3-ton.
4. The Attic is too hot. Normal convection is not removing enough hot air.
5. Attic insulation has settled over the last 17 years. The R-value may not be what it started as.
My proposed solution is as follows:
1. Make the 2nd floor a separate zone by installing a 2-ton central system in the attic, using insulated plenums and ducting.
2. Downsize the main system to 2-ton and abandon duct runs to 2nd floor.
3. Add a powered attic exhaust on a thermostat.
4. Increase insulation level in attic.
Thoughts?
The 2nd floor is always near or at 80 degrees no matter what the main thermostat is set to. We have to freeze the 1st floor to keep the 2nd floor tolerable.
I have a few reasons as to why the 2nd floor is so hot.
1. The ducts serving the 2nd floor are undersized, and too few. I estimate that the airflow to the 2nd floor is half that of the first floor.
2. The ductwork was poorly designed, too many bends. The ducting is not conducive to good airflow. Also, there is no way to balance the system, as they seemed to have forgotten duct dampers entirely.
3. The A/C system is undersized by 1/2-ton. I downloaded and ran an A/C tonnage calculator, putting in insulation values, wall types, door/window numbers, square footage, etc... It spat out that a 3.5-ton system would be recommended. The system in place is 3-ton.
4. The Attic is too hot. Normal convection is not removing enough hot air.
5. Attic insulation has settled over the last 17 years. The R-value may not be what it started as.
My proposed solution is as follows:
1. Make the 2nd floor a separate zone by installing a 2-ton central system in the attic, using insulated plenums and ducting.
2. Downsize the main system to 2-ton and abandon duct runs to 2nd floor.
3. Add a powered attic exhaust on a thermostat.
4. Increase insulation level in attic.
Thoughts?