Hi,

I recently noticed my split system Carrier heat pump seems to be running more than normal this Summer, and after checking the obvious culprits it appears something abnormal may be occurring. I should probably also mention that I had a new roof put on a few months ago which has a different type of ridge ventilation that is not as efficient in letting heat escape from the attic as rapidly as before. The AHU is inside the home and the ducts are in the attic (the round flex type, coil core with insulation wrapped by black plastic).

The Delta-T looks within reason, about 22 degrees. However, when I measured the vents closest and furthest from the AHU, it yielded strange results. The closest vent (about a 5 foot run) measured 5 degrees warmer than at the AHU, while the furthest vent (about 50 feet from the AHU) measured 7 degrees warmer than at the AHU. It seems reasonable that the delta between the two vents is about 2 degrees. HOWEVER, clearly there is a 5 degree increase occurring in both vents that isn't making sense to me, and my best guess is the "duct juncture box" in the attic which the AHU connects directly to must have a leak that is sucking in enough hot attic air to cause a 5 degree increase in the air being blown throughout the home. The "duct juncture box" is made of duct board and mastic.

Does this theory sound likely, or would attic temps of 125-135 degrees simply be to blame?

Thanks,

Sonic