What is a cooling load calculation?

A cooling load calculation determines how much heat must be removed from a building per hour (BTU/hr or kW) to maintain a comfortable indoor temperature during peak summer conditions. It accounts for heat gain through the building envelope, solar radiation through windows, internal gains from people and equipment, and outdoor air ventilation.

What is the difference between sensible and latent cooling load?

Sensible cooling load refers to heat that raises air temperature — from sun, walls, people's body heat, and equipment. Latent cooling load refers to moisture that must be removed from the air — from occupants, cooking, outdoor humid air, and infiltration. Air conditioners must handle both. The ratio of sensible to total load is the Sensible Heat Ratio (SHR).

What is SHGC in window cooling loads?

SHGC stands for Solar Heat Gain Coefficient. It represents the fraction of solar radiation that passes through a window as heat. A SHGC of 0.25 means 25% of solar energy becomes heat indoors. Lower SHGC reduces cooling loads. South and west-facing windows with high SHGC are a major driver of peak cooling loads in summer.

How is commercial cooling load different from residential?

Commercial cooling loads have much higher internal gains from lighting, computers, equipment, and high occupancy. They also have larger outdoor air ventilation requirements per ASHRAE 62.1. Commercial buildings often have simultaneous heating and cooling zones, requiring zone-by-zone analysis. This calculator handles both residential and commercial scenarios.

❄ Load Calculations

Cooling Load Calculator

Calculate peak summer HVAC cooling loads for residential and commercial buildings. Separates sensible and latent heat gains across envelope, solar, occupants, lighting, equipment, and ventilation — following ASHRAE fundamentals.

Unit System:

🌡 Design Conditions

Indoor Cooling Setpoint * i

°F

Outdoor Summer Design DB * i

°F

Look up design temp →

Outdoor Summer Design WB i

°F

Calculate wet-bulb →

Indoor RH Target i

%RH

Floor Area *

ft²

Ceiling Height *

▢ Envelope Heat Gain

Gross Wall Area *

ft²

Wall U-Factor * i

BTU/hr·ft²·°F

U = 1/R. R-20 wall → U-0.050

Wall Color / Absorptance i

Window Area by Orientation i

↑ North

Area

ft²

SHGC

↓ South

Area

ft²

SHGC

← East

Area

ft²

SHGC

→ West

Area

ft²

SHGC

Window U-Factor (all) i

BTU/hr·ft²·°F

External Shading Factor i

Roof/Ceiling Area *

ft²

Roof U-Factor * i

BTU/hr·ft²·°F

Roof Color / Solar Absorptance i

👥 Internal Heat Gains

Occupants i

people

Occupant Activity i

Lighting Power Density i

W/ft²

Residential: 0.5. Office: 0.8–1.2. Retail: 1.5+

Equipment / Plug Load Density i

W/ft²

Kitchen / Cooking Load i

BTU/hr

Motor / Mechanical Load i

BTU/hr

🌫 Infiltration & Ventilation

Infiltration ACH i

ACH

Outdoor Air Ventilation i

CFM

Calculate required OA →

ERV/HRV Efficiency i

❄ Cooling Load Results

BTU/hr

Sensible Heat Ratio (SHR)

—

SHR

Sensible Load —

Latent Load —

Total Cooling Load —

Equipment recommendation: —

Heat Gain by Component

📊 Sensible vs. Latent Breakdown

Detailed Results Table

Component	Sensible (BTU/hr)	Latent (BTU/hr)	Total (BTU/hr)	% of Total

Export:

How to Use the Cooling Load Calculator

Enter Summer Design Conditions

Use the ASHRAE 1% summer dry-bulb and coincident wet-bulb design temperatures for your city. The design temperature lookup provides these values. For the wet-bulb, use our wet-bulb calculator if only dry-bulb and RH are known.

Enter Envelope Data with Window Orientations

This calculator separates windows by orientation because solar heat gain peaks at different times: east windows peak in the morning, west in the afternoon, south at midday. Enter area and SHGC for each orientation. Use a lower SHGC (0.20–0.25) for south and west glazing to minimize cooling loads.

Enter Internal Gains Accurately

Internal gains are often the largest cooling load component in commercial buildings. For residential, lighting and equipment at 1.0–1.5 W/ft² total is typical. For commercial offices, use 0.8 W/ft² lighting + 1.5–2.0 W/ft² equipment. Each occupant adds both sensible and latent heat — select the appropriate activity level.

Review Sensible Heat Ratio (SHR)

The SHR indicates what fraction of your total cooling load is sensible vs. latent. A low SHR (below 0.75) means significant dehumidification is needed — you must select equipment with a low SHR rating. Most standard AC equipment has SHR around 0.75–0.80. For a more detailed analysis, see the SHR calculator and dew point calculator.

Size Equipment from Results

Use the total cooling load to size your AC system with the AC sizing calculator or mini-split sizing calculator. For commercial projects, also run the heat load calculator to compare and size for both seasons.

HVAC Cooling Load Calculations — Complete Guide

A cooling load calculation determines the peak rate of heat gain a building experiences during summer, measured in BTU/hr or kW. Unlike heating load (which is primarily conduction-driven), cooling loads involve multiple simultaneous heat sources that peak at different times of day, making the calculation considerably more complex.

The Six Sources of Cooling Load

This calculator accounts for all six recognized sources of cooling heat gain per ASHRAE fundamentals:

Solar heat gain through windows: The dominant cooling load component in most buildings. Use low-SHGC glazing and external shading to reduce it. The solar heat gain calculator provides detailed orientation analysis.
Conduction through walls and roof: Driven by the outdoor-indoor temperature difference, wall color (solar absorptance), and U-value. Dark roofs are a major contributor — cool roofs can reduce this by 50–70%.
Internal gains from occupants: Each person produces sensible body heat (raising air temperature) and latent heat (moisture). Activity level matters — a gym occupant generates 3× more latent heat than a seated office worker.
Lighting and equipment: All electrical energy consumed inside the conditioned space eventually becomes heat. LED lighting has reduced this significantly vs. fluorescent, but computing equipment loads continue to grow.
Ventilation — outdoor air: Hot humid summer air brought in for ventilation must be cooled and dehumidified. This adds both sensible and latent load, partially recoverable with an ERV.
Infiltration: Uncontrolled air leakage adds sensible and latent load proportional to the humidity difference between indoors and outdoors.

Sensible vs. Latent Cooling — Why It Matters for Equipment Selection

Sensible cooling lowers air temperature. Latent cooling removes moisture (dehumidification). The Sensible Heat Ratio (SHR) is the fraction of total cooling that is sensible. Most standard residential AC equipment is rated at SHR 0.75–0.80. If your space has a very low SHR (below 0.70) — due to high occupancy, cooking, or humid climate — you need equipment with a matching low SHR or a dedicated dehumidifier. The psychrometric calculator and dew point calculator help analyze moisture conditions in detail.

Peak vs. Average Cooling Loads

Cooling loads fluctuate throughout the day. West-facing windows peak in the late afternoon. East-facing windows peak in the morning. Internal gains from people and lighting peak during occupancy hours. This calculator uses simultaneous peak assumptions — a conservative approach suitable for equipment sizing. For energy analysis (annual energy use), proceed to the energy savings estimator which uses hourly profiles.

Next Steps After Your Cooling Load

Size your AC: AC Sizing Calculator or Mini-Split Sizing Calculator
Compare with heating: Heat Load Calculator and Heat Pump Sizing
Design air distribution: CFM Calculator and Duct Sizing Calculator
Analyze moisture: Psychrometric Calculator and Dew Point Calculator
Evaluate energy: SEER Calculator and Payback Period Calculator

Frequently Asked Questions

Heat gain is the total rate of heat entering a space. Cooling load is the rate at which the HVAC system must remove heat. They differ because buildings have thermal mass that stores heat — so the actual cooling load lags behind the instantaneous heat gain. This calculator uses the simplified simultaneous peak approach (conservative for equipment sizing). ASHRAE's Radiant Time Series method is more precise for design.

SHGC (Solar Heat Gain Coefficient) is the fraction of solar energy that passes through a window as heat gain. For cooling load reduction: south and west windows should have SHGC ≤ 0.25. North windows have minimal solar gain so SHGC matters less. East windows benefit from low SHGC in hot climates. Energy Star requires SHGC ≤ 0.40 for most Canadian climate zones. High-performance triple-pane windows can achieve SHGC of 0.15–0.20. The solar gain calculator analyzes this in detail by month.

The most impactful measures in order of typical savings: (1) External window shading — overhangs, awnings, exterior blinds (20–40% reduction in solar gain). (2) Low-SHGC glazing (15–30% reduction). (3) Cool roof coating (10–20% reduction in roof heat gain). (4) Increased ceiling/roof insulation (5–15% reduction). (5) LED lighting to replace fluorescent (5–10% internal gain reduction). (6) ERV to pre-cool ventilation air (5–15% ventilation load reduction). Use the load comparison tool to quantify savings before and after improvements.

Yes, this is very common in Canada. A well-insulated home in Toronto may have a heating load of 60,000 BTU/hr but only 24,000 BTU/hr of cooling load — a 2.5:1 ratio. The heating load is driven by a large temperature differential (up to 50°C ΔT in winter) while the summer cooling differential is much smaller. This is why many Canadian homes are adequately served by 2-ton AC systems despite requiring 80,000+ BTU furnaces. When selecting a heat pump, always size for the larger (heating) load.