Calculator Inputs
Enter project values. San Diego defaults are editable.
Formula Used
The calculator uses common residential cooling load relationships.
ΔT = Outdoor design temperature - Indoor design temperatureConduction load = U-factor × Area × ΔTSolar glass load = Area × SHGC × Shade × Solar factor × OrientationInfiltration CFM = ACH × Volume ÷ 60Sensible air load = 1.08 × CFM × ΔTLatent air load = 0.68 × CFM × Grain differenceWatts to heat = Watts × 3.412Final load = Diversified load × Duct factor × Safety factorTons = Final BTU/h ÷ 12,000
This tool supports design review. It does not replace certified calculations.
How to Use This Calculator
- Measure the conditioned area and average ceiling height.
- Enter San Diego indoor and outdoor design temperatures.
- Add wall roof window door and skylight areas.
- Enter U-factors from plans or product labels.
- Adjust SHGC shade orientation and solar values.
- Enter infiltration ventilation humidity and occupant data.
- Add lighting equipment appliance and duct allowances.
- Press the calculate button to view results above.
- Export the result as CSV or save a PDF.
San Diego Cooling Load Planning Guide
Local Climate Context
San Diego cooling design is usually mild but detailed. Coastal air can reduce dry bulb load. Inland neighborhoods can create higher afternoon peaks. A Manual J style review helps separate sensible heat from latent heat. It also prevents oversized cooling equipment. Oversizing can cause short cycling. Short cycling reduces humidity control. It can also raise operating costs.
Envelope Details Matter
Cooling load begins with envelope heat gain. Walls, roofs, glass, doors, and skylights each transfer heat. U-factor shows how fast heat moves through assemblies. Lower U-factors usually reduce load. Roof load can dominate single story homes. Attic insulation and radiant barriers can help. Window loads depend on size and orientation. West glass often adds severe late day heat. Exterior shading can greatly reduce solar gain.
Air Leakage and Moisture
San Diego projects still need infiltration checks. Older homes may leak more outdoor air. Ventilation systems can also add load. Sensible air load comes from temperature difference. Latent load comes from moisture difference. Grain values help estimate moisture heat. A tight home may need planned ventilation. A leaky home may need air sealing first.
Internal Loads and Ducts
People, lights, appliances, and equipment add heat indoors. Modern electronics can be important. Kitchens can create strong intermittent gains. Ducts also affect final capacity. Ducts in hot attics increase losses. Sealed ducts near conditioned space reduce penalties. The calculator lets you apply a duct percentage. It also lets you apply diversity. Diversity recognizes that every load rarely peaks together.
Verification Notes
Check plans before entering values. Confirm room additions and ceiling changes. Count only conditioned spaces. Separate garages from living areas. Use real window labels when available. Note large overhangs and exterior shutters. Review ducts before choosing final tonnage. Ask the installer for airflow readings. Keep assumptions with the project file. Update values after weatherization or glazing upgrades.
Sizing Judgment
The result shows BTU per hour and cooling tons. One ton equals twelve thousand BTU per hour. Use the suggested size as a review point. Do not select equipment only by floor area. Confirm orientation, insulation, leakage, and glazing data. Also compare sensible heat ratio with local humidity needs. Smaller accurate systems often run longer cycles. Longer cycles improve comfort and dehumidification. Final equipment choices should follow local professional review.
Example Data Table
| Input | Example value | Reason |
|---|---|---|
| Floor area | 1,800 sq ft | Medium San Diego residence. |
| Outdoor design temperature | 84°F | Mild coastal cooling condition. |
| Indoor design temperature | 75°F | Common comfort target. |
| Window SHGC | 0.28 | Low solar gain glazing. |
| Infiltration | 0.35 ACH | Moderate leakage estimate. |
| Duct allowance | 8% | Typical allowance for imperfect ducts. |
Frequently Asked Questions
Is this a true Manual J report?
No. It is a Manual J style calculator. It helps estimate loads. A certified report needs approved software and verified field data.
Why does San Diego need special inputs?
San Diego has coastal and inland microclimates. Outdoor temperature, solar exposure, and humidity can vary. Editable inputs keep the estimate flexible.
What is SHGC?
SHGC means solar heat gain coefficient. It shows how much solar heat passes through glass. Lower values usually reduce cooling loads.
What is a U-factor?
A U-factor shows heat transfer through materials. Lower values indicate better insulation. Use tested product data when possible.
Why include latent cooling load?
Latent load represents moisture removal. Even mild climates can have humidity. Ignoring latent load can reduce comfort and control.
What does duct loss percentage mean?
It estimates cooling lost through ducts. Leaky or hot attic ducts need higher allowances. Sealed ducts may need less.
Can I size equipment by square footage?
Square footage alone is weak. Orientation, glass, insulation, leakage, and ducts matter. Detailed inputs produce better sizing guidance.
What airflow should I expect per ton?
The tool estimates 400 CFM per ton. Actual airflow depends on equipment, ducts, filters, and humidity control targets.
Why use a diversity factor?
Diversity accounts for noncoincident peaks. People, appliances, and solar loads may not peak together. Use conservative values carefully.
Should I add a large safety factor?
Large safety factors can oversize equipment. Use small factors only for uncertainty. Better data is usually safer than padding.
Can this help with permit review?
It can support early planning and discussion. Permit submittals may need official forms. Check local requirements before selecting final cooling equipment sizes.