What does ΔT mean?

What the colours mean

• 16–22°FIn range. Your system is moving heat normally.
• 13–16°F or 22–25°FA bit off. Worth keeping an eye on.
• Under 13°F or over 25°FClearly outside normal. Worth a look.

High ΔT: usually low airflow

When less air moves across the coil, each bit of air sits there longer and comes out colder. But less of it is coming out.

Cooling ≈ 1.08 × airflow (CFM) × ΔT, so a higher ΔT and lower airflow partly cancel out.

The real costs:

• Less efficient: a colder coil makes the compressor work harder for less (a few % up to ~10%).
• Slower to cool: more effort goes into drying the air than lowering the temperature (the upside: less clammy).
• Coil can freeze if the big suction line drops below about 40°F.
• Uneven rooms: far rooms get less air.

Low ΔT

The air isn’t being cooled much. Common causes:

• Low refrigerant (often a leak)
• Dirty outdoor coil
• Too much airflow, or the unit is struggling to keep up

Where the targets come from

• 18–20°F is the industry rule of thumb, assuming about 400 CFM of air per ton and normal indoor humidity.
• The exact target depends on your indoor temperature and humidity (manufacturers publish charts). Drier air means a higher target.
• The 25°F red line is DeltaTru’s own “clearly outside normal” threshold, not an industry standard.

Common fixes for high ΔT

• Replace a dirty filter
• Open closed vents and clear blocked return grilles
• An undersized return grille (needs a bigger one)
• Blower speed set too low (a technician can change the speed tap)

Told you need a new unit? Ask a technician to check airflow and charge first. These fixes are often much cheaper.