Advanced Room Load Calculator

Room Load Input Form

Room Length (ft)

Room Width (ft)

Room Height (ft)

Effective Wall Area (ft²)

Roof Area (ft²)

Glass Area (ft²)

Wall U-Value

Roof U-Value

Glass U-Value

SHGC

Solar Gain Factor

Air Changes per Hour

Outdoor Temperature (°F)

Indoor Temperature (°F)

Outdoor Relative Humidity (%)

Indoor Relative Humidity (%)

Mechanical Ventilation (CFM)

Occupants

Occupant Sensible Gain (BTU/h each)

Occupant Latent Gain (BTU/h each)

Lighting Load (W)

Equipment Load (W)

Equipment Use Factor

Duct / Miscellaneous Gain (BTU/h)

Safety Factor (%)

Target Sensible Heat Ratio

Example Data Table

Use these sample engineering inputs to test the calculator before entering project-specific values.

Input	Example Value	Notes
Room Size	20 ft × 15 ft × 10 ft	3,000 cubic feet total volume
Wall / Roof / Glass Areas	350 / 300 / 60 ft²	Effective exposed surfaces only
Outdoor / Indoor Conditions	95°F, 60% RH / 75°F, 50% RH	Peak summer cooling design case
Ventilation and Infiltration	80 CFM and 0.70 ACH	Combined outside-air source
Internal Gains	4 people, 900 W lights, 1,200 W equipment	Office-style occupancy profile
Safety Factor	8%	Planning margin for selection

Formula Used

These equations estimate a practical cooling load by combining envelope, solar, occupancy, equipment, and outdoor-air effects.

Wall Load = Uwall × Wall Area × ΔT

Roof Load = Uroof × Roof Area × ΔT

Glass Conduction = Uglass × Glass Area × ΔT

Glass Solar Gain = Glass Area × SHGC × Solar Factor

Infiltration CFM = (ACH × Room Volume) ÷ 60

Ventilation Sensible = 1.08 × Outdoor CFM × ΔT

Ventilation Latent = 0.68 × Outdoor CFM × ΔGrains

Lighting Load = Lighting Watts × 3.412

Equipment Load = Equipment Watts × 3.412 × Use Factor

Grand Total = (Sensible + Latent) × (1 + Safety Factor)

Capacity is also converted into refrigeration tons and kW for equipment selection review.

How to Use This Calculator

Enter room geometry and exposed surface areas.
Fill in U-values, SHGC, and solar factor assumptions.
Provide outdoor and indoor design temperature with relative humidity.
Add air changes, mechanical ventilation, and internal heat sources.
Set a reasonable safety factor and target sensible heat ratio.
Press calculate to view the result above the form.
Review total load, airflow, SHR, and component breakdown.
Use CSV or PDF export for design notes or client review.

Frequently Asked Questions

1. What does room load mean?

Room load is the cooling energy needed to remove sensible and latent heat from a space under selected design conditions.

2. Does this calculator include humidity effects?

Yes. It estimates humidity impact through latent load using outdoor airflow and the difference in moisture content between outdoor and indoor air.

3. Why are both sensible and latent loads shown?

Sensible load changes dry-bulb temperature, while latent load removes moisture. HVAC selection works better when both values are checked separately.

4. Should I include internal partitions?

Usually no, unless partitions border hotter unconditioned spaces. Most projects use only exposed walls, roof, glass, and internal heat sources.

5. What is a good safety factor?

Many early-stage estimates use about 5% to 10%. Oversizing too much can reduce dehumidification performance and increase equipment cycling.

6. Can I use this for heating calculations?

No. This page is arranged for cooling load estimation. Heating design needs separate assumptions for winter conditions and transmission losses.

7. How accurate is the solar glass estimate?

It is a planning-level approximation. Detailed glazing analysis should also consider orientation, shading, glass type, hourly sun angle, and local climate data.

8. What unit system does this calculator use?

The form uses imperial units: feet, square feet, Fahrenheit, CFM, watts, BTU per hour, refrigeration tons, and kilowatts.