Sensible Heat Ratio Calculator – HVAC SHR & Dehumidification (Free Tool)

Sensible Heat Ratio Calculator: Optimize HVAC & Cooling Systems (Free Tool)

You have an air conditioner. It removes heat from your home. But how much of that is sensible heat (temperature change) vs. latent heat (humidity removal)?

The Sensible Heat Ratio (SHR) tells you. It is the ratio of sensible cooling to total cooling.

A high SHR means the AC mostly cools the air (temperature). A low SHR means it also removes a lot of humidity.

Today, I give you a free Sensible Heat Ratio Calculator.

You enter sensible heat and total heat (or dry bulb and wet bulb temperatures). The calculator shows:

• Sensible Heat Ratio (SHR)
• Sensible cooling percentage
• Latent cooling percentage

Let me explain what SHR is and why it matters for HVAC design.

What is Sensible Heat Ratio? (Simple Explanation)

Sensible Heat Ratio (SHR) is the fraction of total cooling that goes toward lowering the air temperature (sensible cooling) vs. removing moisture (latent cooling).

SHR = Sensible Cooling ÷ Total Cooling

Total cooling = Sensible Cooling + Latent Cooling

Example: An AC removes 40,000 BTU/hr total. 30,000 BTU/hr is sensible (temperature drop). 10,000 BTU/hr is latent (humidity removal).

SHR = 30,000 ÷ 40,000 = 0.75 (75% sensible, 25% latent)

SHR ranges:

• High SHR (0.80-0.95) – Dry climates, mostly temperature control
• Medium SHR (0.70-0.80) – Humid climates, balanced cooling
• Low SHR (0.60-0.70) – Very humid, dehumidification priority

Why This Sensible Heat Ratio Calculator Matters

Here is why you need to calculate SHR.

Reason 1: AC sizing

A standard AC has a fixed SHR (typically 0.75-0.80). If your home needs more dehumidification, you need a lower SHR unit or add a dehumidifier.

Reason 2: Humidity control

In humid climates, a high SHR AC will cool the air quickly but not remove enough moisture. The room feels cold and clammy.

Reason 3: Energy efficiency

Oversized ACs short-cycle. They cool fast but do not run long enough to dehumidify. SHR is important for selecting the right equipment.

Reason 4: Load calculation

Manual J load calculations include SHR. It helps match equipment to the building.

Reason 5: Troubleshooting

Low SHR can indicate high infiltration or moisture sources.

The Sensible Heat Ratio Formula

From heat values:

SHR = Sensible Heat ÷ Total Heat

Sensible Heat (BTU/hr) = 1.08 × CFM × (Entering DB – Leaving DB)

Latent Heat (BTU/hr) = 0.68 × CFM × (Entering WB – Leaving WB)

Total Heat = Sensible + Latent

From temperatures (psychrometric chart):

SHR = (h1 – h2) ÷ (h1 – h3)

But the calculator uses the sensible heat formula.

LIVE Sensible Heat Ratio Calculator

Enter your cooling data. The calculator shows SHR instantly.

💧 Sensible Heat Ratio Calculator

Calculate SHR for HVAC system sizing📊 By Heat Values🌡️ By Temperatures & CFM

🌡️ Sensible Cooling (BTU/hr)

💧 Total Cooling (BTU/hr)

💨 Airflow (CFM)

🌡️ Entering DB (°F)

🌡️ Leaving DB (°F)

💧 Entering WB (°F)

💧 Leaving WB (°F)

📊 SENSIBLE HEAT RATIO (SHR)

0.00

0%

💡 SHR = Sensible Cooling ÷ Total Cooling. For humid climates, look for SHR below 0.75.

📐 SHR > 0.80 = dry climate. SHR 0.70-0.80 = moderate. SHR < 0.70 = humid (needs dehumidification).

How to Use This Sensible Heat Ratio Calculator

Method 1: By Heat Values

Step 1: Enter sensible cooling (BTU/hr)
Step 2: Enter total cooling (BTU/hr)
Step 3: Read SHR

Method 2: By Temperatures & CFM

Step 1: Enter airflow in CFM
Step 2: Enter entering and leaving dry bulb temperatures (°F)
Step 3: Enter entering and leaving wet bulb temperatures (°F)
Step 4: Read SHR

Real Examples: Different Scenarios

Example 1: Standard AC unit

• Sensible: 30,000 BTU/hr
• Total: 40,000 BTU/hr
• SHR = 0.75

Result: Standard residential AC

Example 2: High-efficiency AC (dry climate)

• Sensible: 34,000 BTU/hr
• Total: 38,000 BTU/hr
• SHR = 0.89

Result: High SHR, good for dry areas

Example 3: Dehumidifier-focused system

• Sensible: 20,000 BTU/hr
• Total: 32,000 BTU/hr
• SHR = 0.625

Result: Low SHR, high dehumidification

Example 4: Airflow and temperature method

• CFM: 1,200
• Entering DB: 80°F, Leaving DB: 55°F (ΔT = 25°F)
• Entering WB: 67°F, Leaving WB: 55°F (ΔT = 12°F)

Sensible = 1.08 × 1,200 × 25 = 32,400 BTU/hr
Latent = 0.68 × 1,200 × 12 = 9,792 BTU/hr
Total = 42,192 BTU/hr
SHR = 32,400 ÷ 42,192 = 0.768

SHR by Climate

SHR for Different AC Types

Latent Heat and Humidity

Latent heat is the energy used to remove moisture from the air.

Grains of moisture: 1 lb of water = 7,000 grains. 1 grain = 0.000143 lb.

Latent heat formula:

Latent (BTU/hr) = 0.68 × CFM × ΔGrains ÷ 1000

Or simpler: Latent = 0.68 × CFM × (Entering WB – Leaving WB)

Example: 1,200 CFM, WB drop of 12°F
Latent = 0.68 × 1,200 × 12 = 9,792 BTU/hr

SHR and AC Sizing

Problem: Oversized AC = short cycling = poor dehumidification.

Example: House needs 24,000 BTU total with SHR 0.75. A 30,000 BTU AC with SHR 0.80 will run short cycles. It will cool fast but not remove enough humidity.

Solution: Use a properly sized AC. Or use a two-stage or variable-speed AC that runs longer at lower capacity.

Typical SHR by Building Type

How to Measure SHR in the Field

Step 1: Measure airflow (CFM) at the supply or return
Step 2: Measure entering and leaving dry bulb temperatures
Step 3: Measure entering and leaving wet bulb temperatures
Step 4: Calculate sensible heat: 1.08 × CFM × ΔDB
Step 5: Calculate latent heat: 0.68 × CFM × ΔWB
Step 6: Calculate total = sensible + latent
Step 7: SHR = sensible ÷ total

Frequently Asked Questions (FAQs)

1. What is a good SHR for an air conditioner?

0.75-0.80 for most homes. Lower for humid climates (0.70-0.75).

2. What does a high SHR mean?

Most of the cooling is sensible (temperature drop). Little dehumidification.

3. What does a low SHR mean?

Significant dehumidification. Good for humid climates.

4. How do you calculate SHR from psychrometric chart?

SHR = (h1 – h2) ÷ (h1 – h3), where h1 is entering, h2 is leaving, h3 is saturation at leaving DB.

5. What is the formula for sensible heat?

Sensible (BTU/hr) = 1.08 × CFM × (Entering DB – Leaving DB).

6. What is the formula for latent heat?

Latent (BTU/hr) = 0.68 × CFM × (Entering WB – Leaving WB).

7. Why is SHR important for AC sizing?

If you oversize the AC, SHR is too high. The AC cools fast but does not dehumidify. Room feels clammy.

8. Can SHR be greater than 1?

No. SHR cannot exceed 1.0 (all sensible, no latent).

9. What SHR do I need for a basement?

Basements need dehumidification. Look for SHR below 0.70, or add a dehumidifier.

10. How does low airflow affect SHR?

Low airflow reduces both sensible and latent capacity. SHR may increase or decrease depending on conditions.

Common Mistakes

Mistake #1: Using the wrong constants

Use 1.08 for sensible (standard air density). Use 0.68 for latent.

Mistake #2: Mixing up DB and WB

Dry bulb measures temperature. Wet bulb measures humidity. Do not confuse.

Mistake #3: Assuming SHR is constant

SHR changes with airflow, entering conditions, and equipment. Measure at design conditions.

Mistake #4: Ignoring infiltration

Air leaks add both sensible and latent loads. Include in load calculation.

Mistake #5: Sizing AC by square footage only

Square footage does not account for humidity. Use Manual J with SHR.

SHR in Manual J Load Calculations

Manual J is the standard residential load calculation method.

It includes:

• Sensible loads (windows, walls, roof, infiltration, people)
• Latent loads (people, cooking, showers, infiltration)

Output includes:

• Total cooling (BTU/hr)
• Sensible cooling (BTU/hr)
• Required SHR

Equipment selection: Match equipment SHR to calculated SHR within 0.05.

Improving Low SHR (Too Much Dehumidification)

Symptoms: Room feels cold and dry. Humidity below 30%.

Solutions:

• Add a humidifier
• Reduce AC runtime (increase thermostat)
• Use a higher SHR AC

Improving High SHR (Not Enough Dehumidification)

Symptoms: Room feels cool but clammy. Humidity above 60%.

Solutions:

• Add a dehumidifier
• Reduce AC airflow (lower CFM)
• Use a lower SHR AC
• Two-stage or variable-speed AC

Final Thoughts

Sensible Heat Ratio is critical for comfort in humid climates.

My Sensible Heat Ratio Calculator gives you:

• SHR from heat values
• SHR from temperatures and CFM
• Climate-based recommendations
• Visual meter

Bookmark this page. Use it for AC sizing and troubleshooting.

The next time your AC cools but does not dehumidify, you will know why. Your SHR is too high.

Disclaimer: This is an educational tool. For HVAC design, consult a professional engineer.

External Links (Authority Backlinks):

1. Wikipedia – Sensible heat{:target=”_blank” rel=”noopener noreferrer”}
2. Wikipedia – Latent heat{:target=”_blank” rel=”noopener noreferrer”}
3. Wikipedia – Psychrometrics{:target=”_blank” rel=”noopener noreferrer”}

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