Enter Room Conditions
Add up to twenty rooms. Use design temperatures and conservative inputs for early planning.
Example Data Table
| Room | Size | Windows | Occupants | Typical Purpose |
|---|---|---|---|---|
| Living Room | 18 ft × 14 ft | 42 sq ft, west | 4 | Main daytime space |
| Kitchen | 14 ft × 12 ft | 18 sq ft, south | 2 | Appliance heat present |
| Bedroom | 14 ft × 12 ft | 24 sq ft, east | 2 | Evening occupancy |
Formula Used
This calculator estimates sensible and latent gains for each room. It then applies your room-level safety factor.
Room volume = Area × Ceiling Height
Transmission gain = Surface Area × U-Value × Temperature Difference
Solar window gain = Window Area × Orientation Solar Factor
Infiltration CFM = Air Changes per Hour × Room Volume ÷ 60
Infiltration sensible gain = 1.08 × CFM × Temperature Difference
Infiltration latent gain = 0.68 × CFM × Grains Difference
Design load = (Sensible Gain + Latent Gain) × (1 + Safety Factor)
One ton of cooling equals 12,000 BTU/h. Estimated airflow uses 400 CFM per ton as a preliminary target.
How to Use This Calculator
- Enter each room’s name and measured dimensions.
- Set outdoor and indoor design temperatures for your location.
- Enter glass area and select its main orientation.
- Use realistic U-values for walls, roof, and windows.
- Add people, lighting, appliance, and equipment heat.
- Set air changes and moisture difference for infiltration.
- Apply a modest safety factor, then calculate the total.
- Review unusual room results before selecting equipment.
Room-by-Room Cooling Load Planning
Central cooling equipment must meet the building peak load. South-facing rooms often receive more solar heat. Kitchens also add appliance loads. Bedrooms can need greater evening airflow. A room-by-room calculation reveals these differences before equipment is selected.
Start with room dimensions. Length and width give floor area. Ceiling height gives room volume. Higher rooms contain more air. Enter window area. Glass can be a major heat path. Use the facing direction to apply a reasonable solar allowance. East and west glass often need special attention.
The calculator separates sensible and latent heat. Sensible heat changes air temperature. Latent heat represents moisture removal. People, air leakage, and humid outdoor air add latent load. Lighting and equipment mainly add sensible load. The report combines both values into a design load. It also shows cooling tons for simple equipment comparisons.
Envelope values matter. U-values describe heat flow through walls, roofs, and windows. Smaller U-values mean better resistance to heat transfer. Use values from the actual assemblies where possible. Avoid using marketing R-values directly. Convert resistance to U-value first. For estimates, use conservative defaults and document every assumption.
Air changes per hour estimate infiltration. Tight construction needs a smaller value. Older construction may need a larger value. Duct leakage can also raise the effective outdoor-air load. The calculator uses room volume, air-change rate, temperature difference, and moisture difference. This approach is useful for preliminary sizing. Detailed HVAC design needs local weather data and measured ventilation rates.
Review every room result. Large differences deserve another check. A room with heavy glass may need shading. A kitchen may need a dedicated airflow path. An upstairs room may need duct balancing. Use the total load to select nominal equipment capacity. Then review sensible heat ratio, airflow, duct friction, and manufacturer performance data. Do not select equipment from tonnage alone.
The safety factor is a planning allowance. It can cover unknowns. It should not hide missing inputs. Large allowances can cause oversizing. Oversized systems may short cycle. They can remove less moisture and reduce comfort. Keep the allowance modest. Compare the result with a professional load calculation before procurement.
This calculator supports clear early decisions. Record assumptions with every estimate. Update dimensions, insulation, windows, and occupancy when plans change. Use final equipment selections after professional verification and commissioning.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates preliminary sensible, latent, and total cooling loads for individual rooms. It combines dimensions, envelope heat transfer, glass exposure, occupants, internal gains, and infiltration.
2. Is the result suitable for final equipment selection?
No. Use it for early planning and comparison. Final equipment selection should include local design weather, duct losses, ventilation requirements, system performance data, and professional review.
3. Why are sensible and latent loads separated?
Sensible load changes air temperature. Latent load removes moisture. A system must handle both loads to deliver comfort, especially in humid climates.
4. What U-value should I enter?
Use the U-value for the complete assembly, not only insulation. Lower values indicate less heat transfer. Product data, plans, and energy documents can help identify realistic values.
5. How should I choose the window orientation?
Select the direction the largest glass area faces. East and west glass often receives strong low-angle sun. Use separate room entries when one room has major glass on several sides.
6. What is air changes per hour?
Air changes per hour describes how often outdoor air leakage replaces room air in one hour. Tight, sealed buildings usually have lower values than older or leaky buildings.
7. Why does ceiling height affect the calculation?
Ceiling height changes room volume and wall surface area. Those changes affect infiltration and envelope heat transfer. Tall rooms can need more cooling than equal floor areas with lower ceilings.
8. How much safety factor should I use?
A modest factor, such as five to ten percent, can cover minor uncertainty. Very large factors may oversize equipment and reduce moisture control.
9. Does lighting add cooling load?
Yes. Nearly all electrical power used by interior lighting becomes heat inside the room. Enter the expected operating watts during the cooling peak.
10. Why is estimated airflow included?
Airflow helps compare room loads with duct planning. The estimate uses 400 CFM per ton. Actual airflow can differ due to equipment type, humidity targets, and duct design.
11. What information should I keep with the estimate?
Keep room plans, design temperatures, U-values, glass assumptions, occupancy, internal loads, infiltration choices, and the calculation date. This record makes later updates easier.