Cooling Load Calculator
Free Cooling load Calculator for hvac & plumbing projects. Enter dimensions to get material lists and cost estimates. Get results you can export or share.
Formula
Total Load = Wall + Roof + Solar + Window + People + Lights + Equipment + Infiltration
Each component is calculated separately. Transmission loads use Q = U x A x Delta-T where U is the heat transfer coefficient, A is area, and Delta-T is the temperature difference. Solar gain uses SHGC x window area x solar intensity. Internal gains are estimated from occupancy and power density. All components are summed for total cooling load in BTU/hr.
Worked Examples
Example 1: Residential Home Cooling Load
Problem: A 1,500 sq ft home with 9 ft ceilings, 200 sq ft of windows, outdoor 95F and indoor 72F.
Solution: Wall load + Roof load + Solar gain + Window conduction + People + Lights + Equipment + Infiltration\nTotal calculated from each component using standard U-values and solar factors
Result: Approximately 30,000 to 40,000 BTU/hr (2.5 to 3.3 tons)
Example 2: Small Office Cooling Load
Problem: A 500 sq ft office with 8 ft ceilings, 60 sq ft windows, outdoor 90F, indoor 74F.
Solution: Smaller area but higher internal gains from computers and lighting\nDelta-T = 90 - 74 = 16F\nInternal loads from 4 people, lights, and equipment dominate
Result: Approximately 12,000 to 18,000 BTU/hr (1 to 1.5 tons)
Frequently Asked Questions
What is a cooling load calculation?
A cooling load calculation determines the total amount of heat that must be removed from a building to maintain the desired indoor temperature. It accounts for heat entering through walls, roof, windows, and infiltration, plus heat generated internally by people, lights, and equipment. The result, measured in BTU per hour or tons of cooling, is used to properly size air conditioning equipment. An accurate load calculation prevents over- or under-sizing.
What are the main components of cooling load?
Cooling load has two categories: external and internal. External loads include solar radiation through windows, heat conduction through walls and roof, and air infiltration through gaps and openings. Internal loads come from occupants (body heat), lighting, cooking appliances, computers, and other equipment. In commercial buildings, internal loads often dominate, while residential buildings are more affected by external loads due to larger window-to-wall ratios.
What is the difference between cooling load and heat gain?
Heat gain is the instantaneous rate of heat entering the space from all sources at a specific time. Cooling load is the rate at which heat must be removed to maintain the setpoint temperature. They differ because building materials absorb and store heat, creating a time delay between when heat enters and when it affects the space temperature. This thermal lag means peak cooling load often occurs later than peak heat gain, which is why accurate calculations use time-of-day factors.
How accurate is a simplified cooling load estimate?
Simplified methods like Cooling Load Calculator provide estimates within 15 to 25 percent of detailed Manual J calculations. They are useful for preliminary sizing and budget planning. For final equipment selection, use ACCA Manual J or similar detailed methods that account for specific construction materials, window types, orientation, local climate data, and duct losses. Professional HVAC contractors use these detailed calculations to guarantee proper system performance.
How do I calculate the load-bearing capacity of a beam?
Beam capacity depends on material, cross-section dimensions, span length, and support conditions. For a simple rectangular wood beam, bending strength = (F_b x b x d^2) / 6, where F_b is allowable stress, b is width, and d is depth. Always consult a structural engineer for critical applications.
What formula does Cooling Load Calculator use?
The formula used is described in the Formula section on this page. It is based on widely accepted standards in the relevant field. If you need a specific reference or citation, the References section provides links to authoritative sources.