Should I close my basement vents to force more air upstairs?

No, never fully close them. In Sandy's high-altitude environment, the AC system is already working against thin air at 4,450 feet, and the blower motor fights static pressure that sea-level ductwork specifications underestimate. Closing supply vents increases backpressure on the blower motor, which can freeze the evaporator coil, burn out the motor windings, or trigger a compressor lockout that turns a comfort issue into a $1,200 to $2,000 emergency repair. The correct approach is balancing, which means partially closing basement vents while keeping at least 75 percent of the duct system open and having a technician verify static pressure stays within the equipment manufacturer's specification after the adjustment.

Why is the upstairs still hot even though the AC runs constantly?

This is usually caused by thermal stratification combined with inadequate return air flow. In many Sandy bi-level ramblers built through the 1970s and 1980s, the upper floor does not have enough return vents to pull the accumulated hot air back to the blower for cooling. The AC delivers cold supply air to the upper floor, but the hot air has nowhere to exit, so the room temperature never drops meaningfully. Solutions include adding return air ducts to the upper floor, upgrading to a high-static ECM variable-speed blower that can overcome the pressure imbalance, or installing a ductless mini-split to serve the hottest upstairs space directly. A proper diagnostic measures static pressure and return adequacy before recommending a specific fix.

Is the AC too small for the bi-level, or is it the ductwork?

In roughly 90 percent of Sandy bi-level cases, the AC tonnage is correct for the home's square footage, but the duct velocity and static pressure are wrong for the altitude. Air at 4,450 feet is roughly 12 percent less dense than at sea level, which means the ducts need to move more CFM to deliver the same cooling result. If the original installation never applied altitude adjustment to Manual D duct design, the system feels undersized even though the equipment matches the Manual J load calculation. The fix is usually not a larger AC. It is duct modification, return air adequacy correction, or ECM blower upgrade that restores the airflow the altitude demands.

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