Sensible & Latent Heat Calculator — Free Online Calculator
Total coil capacity is not just temperature drop — in humid conditions much of the work goes to pulling moisture from the air. Enter airflow, return and supply temperatures, and humidity ratio in grains per pound to split sensible and latent BTU/h, get total load, and see sensible heat ratio (SHR) so you know whether the coil is fighting temperature or moisture.
Enter airflow and psychrometric readings
Total supply airflow through the coil — from anemometer traverse, flow hood, or manufacturer table at current static pressure.
Entering air temperature at the return grille or mixed-air point.
Leaving air temperature after the coil (cooling mode).
Humidity ratio × 7,000 — from psychrometric chart or Dew Point Calculator.
Leaving air humidity ratio after moisture removal on the coil.
Total coil load (Qt)
Sensible (Qs)
25,920 BTU/h
Latent (Ql)
28,560 BTU/h
SHR
0.48
Load profile
Very latent
What it means
Latent load dominates — very humid conditions, high indoor moisture, or limited sensible split. Check return humidity, ventilation loads, and that CFM is not excessive for the moisture removal needed.
See the breakdown
Cooling mode: return should be warmer and more humid than supply. Pair with actual CFM and Delta T when diagnosing comfort, charge, or equipment sizing.
Sensible load reference (Qs = 1.08 × CFM × ΔT)
Sensible BTU/h only — latent load depends on grain depression and is not included. Sea-level psychrometric shortcut.
| CFM | ΔT 15°F | ΔT 20°F | ΔT 25°F |
|---|---|---|---|
| 400 CFM | 6,480 BTU/h | 8,640 BTU/h | 10,800 BTU/h |
| 800 CFM | 12,960 BTU/h | 17,280 BTU/h | 21,600 BTU/h |
| 1,200 CFM | 19,440 BTU/h | 25,920 BTU/h | 32,400 BTU/h |
Sources & standards: ASHRAE Handbook — Fundamentals (psychrometrics, sensible and latent heat of moist air) · ASHRAE Standard 62.1 (ventilation and moisture loads).
The formula, explained in plain English
A cooling coil removes heat two ways: lowering dry-bulb temperature (sensible) and condensing water vapor (latent). Field technicians combine airflow with measured temperature and humidity changes to estimate how hard the coil is working.
Cooling mode sign convention
Return air is warmer and carries more moisture than supply. ΔT and Δgrains are return minus supply — both should be positive when the coil is cooling and dehumidifying properly.
Grains per pound
Humidity ratio in grains per pound of dry air (gr/lb) = W × 7,000. Use matched return and supply readings at the same barometric pressure for accurate latent load.
Reading SHR
SHR near 0.75 is mostly sensible; below 0.60 means latent work dominates. A low SHR with a modest Delta T often explains why the space still feels humid despite “normal” temperature split.
Pair with airflow
These formulas scale directly with CFM — an error in airflow measurement doubles the error in both sensible and latent BTU/h. Verify CFM before using load numbers for equipment selection.
Worked examples
Three scenarios: balanced residential cooling, humid latent-heavy load, and dry mostly-sensible load.
Default — 1,200 CFM, 75→55°F, 110→75 gr/lb
Result: latent load exceeds sensible — typical when return air is very humid. The 20°F split alone would suggest ~26k sensible, but total coil work is nearly 55k BTU/h once moisture removal is included.
Balanced — 1,000 CFM, 78→58°F, 95→70 gr/lb
Result: moderate humidity with a healthy 20°F split — still more than half latent. Equipment sized on sensible load alone would be undersized for peak moisture conditions.
Mostly sensible — 1,400 CFM, 80→60°F, 72→68 gr/lb
Result: dry return air and small grain depression — coil capacity goes almost entirely to temperature. Watch for short cycling or inadequate dehumidification if indoor RH creeps up.
Frequently asked questions
Common questions about sensible vs latent load, SHR, and psychrometric shortcuts.
What is the difference between sensible and latent heat?
Sensible heat changes dry-bulb temperature — you feel it as cooler or warmer air. Latent heat removes moisture from the air without much temperature drop until condensation occurs on the coil. A cooling coil must handle both loads; total capacity is the sum.
What is sensible heat ratio (SHR)?
SHR = sensible load ÷ total load (Qs ÷ Qt). An SHR of 0.75 means 75% of coil capacity goes to cooling temperature and 25% to dehumidification. Lower SHR means more latent work — common in humid climates or when return air is moisture-heavy.
Where do the 1.08 and 0.68 factors come from?
They are standard psychrometric shortcuts at sea-level conditions: Qs = 1.08 × CFM × ΔT (BTU/h) and Ql = 0.68 × CFM × Δgrains. The 1.08 factor combines air density and specific heat; 0.68 converts grain depression across the coil to latent BTU/h. ASHRAE psychrometric charts use the same underlying properties.
How do I get humidity ratio in grains per pound?
Measure return and supply dry-bulb temperature and relative humidity (or wet-bulb), then look up humidity ratio on a psychrometric chart or use a dew point / RH calculator. Grains per pound (gr/lb) is humidity ratio × 7,000. Enter return minus supply grains here for latent load.
What is a typical SHR for residential cooling?
At design conditions, residential coils often run SHR 0.70–0.75. In humid weather or with high indoor moisture, SHR can drop to 0.55–0.65 as more capacity goes to latent removal — and the temperature split may look lower even when total BTU/h is high.
Why does my Delta T look low but the coil is working hard?
A latent-heavy load (low SHR) steals capacity from sensible cooling. The coil may be removing lots of moisture while the dry-bulb split stays modest. Split sensible and latent with this tool before blaming low charge or airflow alone.
Split the load? Quote the equipment in seconds.
Sensible and latent BTU/h tell you what the coil is really doing — TradesQuote turns the sizing or replacement into a detailed, line-item estimate in seconds. Describe the equipment or upload photos, and our AI builds quantities, unit prices, and totals, validated by a built-in quality control agent.
AI line-item estimates
Quantities, unit prices, and totals generated instantly.
Knowledge base
Upload past jobs so estimates reflect your real pricing.
Shareable & signable
Clients review, accept, and sign from a public link.
No credit card required · 14-day free trial · Cancel anytime