SmartAC.com tracks the temperature difference between supply air (coming from vents) and return air (going back to the system) to measure system performance. This measurement, called Delta T, indicates whether the system is heating or cooling effectively.
How SmartAC.com Measures Performance
SmartAC.com sensors measure temperature at the supply and return vents, not directly at the equipment. This means readings may differ from a true Delta T measurement taken at the air handler or evaporator coil.
Focus on the trend, not the specific number. The real value is tracking how performance changes over time for that specific unit in its environment. A system that consistently reads 16°F and then drops to 12°F is showing a meaningful change worth investigating, even if neither number is outside the typical range on its own.
Typical Ranges
Mode | Typical Delta T | Example |
Cooling | 14-20°F | Return air 75°F → Supply air 55-61°F |
Heating | 20-40°F | Return air 65°F → Supply air 85-105°F |
These are general guidelines, not absolutes. Actual readings depend on several factors:
Humidity: High-humidity environments often produce lower cooling Delta T (12-14°F can be normal) because the system is removing moisture, not just cooling air.
Equipment type: Systems with fixed orifice metering devices may show lower Delta T than TXV-equipped systems, even when operating correctly.
Airflow settings: Units configured for enhanced dehumidification (common in humid climates) run at lower CFM and may show different readings than standard ranges suggest.
Operating conditions: Delta T fluctuates during startup and stabilizes as indoor conditions normalize.
What Affects These Numbers?
System Type Matters
Single-speed systems typically show consistent readings within the healthy range. Dual-speed and variable-speed systems may show lower Delta T values when running at reduced capacity for humidity control or to maintain setpoint. This is normal operation, not a problem.
Heat Pumps Are Different
Heat pumps typically run at the lower end of the heating range (20-30°F). The supply air feels warm rather than hot compared to gas furnaces. This is normal for heat pump operation.
When to Investigate
Look for changes from the system's baseline, not just whether a reading falls inside or outside a range.
Cooling concerns:
Delta T trending downward over time
Sudden change from previous readings
System struggling to reach setpoint
Heating concerns:
Delta T trending downward from the system's normal baseline
Sudden spikes above the system's typical range
System cycling frequently
These patterns may indicate airflow restrictions, refrigerant issues, or other service needs.
What Members See in Their App
Members can view their system's cooling and heating performance on the insights area of the home app. The app displays the current Delta T reading showing the weekly trend.
