Enter Building and Design Inputs
Default temperatures are planning assumptions for Bonita, California. Replace them with approved local design conditions when available.
Formula Used
Cooling and heating transfer through an assembly follows Q = U × A × ΔT. Q is load in Btu/h. U is the assembly U-factor. A is area. ΔT is the design temperature difference.
Window solar gain uses Qsolar = A × SHGC × solar factor. The solar factor is editable because orientation, shading, and glazing exposure change the result.
Air sensible load uses Qsensible = 1.08 × CFM × ΔT. Air latent load uses Qlatent = 0.68 × CFM × grain difference. Infiltration CFM equals building volume × ACH ÷ 60.
Internal electrical gain uses watts × 3.412 × diversity factor. Cooling and heating subtotals are adjusted for duct loss and the selected planning allowance.
How to Use This Calculator
- Measure conditioned floor area, ceiling height, and exterior perimeter.
- Enter assembly U-factors from plans, insulation details, or manufacturer data.
- Add window area, U-factor, SHGC, doors, and realistic shading assumptions.
- Review summer and winter design temperatures for the exact project location.
- Set infiltration and ventilation values based on testing and ventilation design.
- Enter people, appliances, ducts, then calculate the planning loads.
- Compare results with certified equipment performance at actual design conditions.
Example Planning Data
| Input | Example | Why It Matters |
|---|---|---|
| Conditioned area | 2,200 sq ft | Sets floor and roof exposure. |
| Window area | 280 sq ft | Controls solar and conduction gains. |
| Infiltration | 0.35 ACH | Estimates outdoor air entering the home. |
| Ventilation | 55 CFM | Adds required fresh-air load. |
| Duct allowance | 8% | Accounts for distribution losses. |
Bonita Load Planning Basics
A Manual J calculation estimates how much heating and cooling a home needs during design weather. It is the starting point for sensible equipment sizing. A useful estimate begins with accurate home geometry. Measure conditioned floor area, ceiling height, perimeter, windows, and exterior doors. Do not use total lot size. Include only spaces served by the system.
Envelope values strongly affect the result. Wall, roof, floor, window, and door U-factors describe heat flow. Lower U-factors usually reduce conductive load. Window area also changes solar gain. Glass facing different directions receives different sunlight. Exterior overhangs, screens, trees, and interior shades can reduce peak solar exposure. Use realistic values rather than optimistic assumptions.
Bonita homes may experience mild coastal influence, inland warming, and daily temperature swings. Therefore, editable outdoor conditions are important. The calculator begins with planning values. A final design should use approved weather data for the actual address and elevation. Indoor targets also matter. A lower cooling setpoint raises cooling demand. A higher heating setpoint raises heating demand.
Air leakage and mechanical ventilation should not be ignored. Leakage adds sensible load when outdoor temperatures differ. It also adds latent cooling load when outside air carries more moisture. Blower-door data provides a better infiltration estimate than guesses. Balanced ventilation can improve indoor air quality. It still needs load treatment because fresh air must be conditioned.
Internal gains come from occupants, lights, cooking, electronics, and appliances. These gains are usually more important during cooling. The calculator uses editable sensible and latent people loads. It also converts appliance watts to Btu per hour. Diversity factors prevent every device from being counted at full output simultaneously.
Duct losses can be material when ducts pass through unconditioned attics or garages. Sealed, insulated ducts reduce this penalty. A small planning allowance can address early uncertainty. Large safety factors often cause oversizing. Oversized cooling equipment can short-cycle, reduce humidity control, and lower comfort. Select equipment using manufacturer data at the calculated design conditions.
This calculator is best used for preliminary decisions, remodel comparisons, and option testing. Use a room-by-room professional procedure before permit submission or equipment installation. Verify ducts, zoning, return airflow, ventilation, and electrical requirements. Good measurements create better comfort, capacity, and operating costs. Record each assumption in project notes for future checking. Keep revisions dated.
Frequently Asked Questions
1. Is this a certified Manual J report?
No. It is a detailed planning calculator. A certified report needs room-by-room construction data, approved weather data, and professional review. Use this estimate to understand inputs and compare options before formal HVAC design.
2. Why are Bonita design temperatures editable?
Microclimates, elevation, nearby terrain, and project requirements can change design conditions. Editable fields let you use the design temperatures required by the authority, engineer, or HVAC designer.
3. What is a U-factor?
A U-factor describes heat flow through an assembly. Lower values generally mean better insulation performance. Use the whole-assembly U-factor when possible, not only the insulation label.
4. How does window SHGC affect cooling?
Solar heat gain coefficient measures how much solar energy passes through glazing. A lower SHGC usually reduces solar cooling load. Orientation and exterior shading remain important.
5. Should I include garages?
Usually no. Include only conditioned spaces served by the HVAC system. Add a garage only when it is intentionally conditioned and part of the design scope.
6. What ACH should I enter?
Use measured or documented infiltration when available. Blower-door testing is best. For early planning, choose a conservative value that reflects the home’s age, sealing quality, and construction details.
7. Why does ventilation add both sensible and latent load?
Outdoor air may be warmer or cooler than indoor air, creating sensible load. It can also carry a different moisture content, creating latent cooling load.
8. Why do ducts increase the required capacity?
Ducts can lose heat or gain heat outside the conditioned envelope. Leakage and poor insulation increase losses. Well-sealed, insulated ducts keep the allowance lower.
9. Does a higher safety factor improve comfort?
Not always. Excess capacity can short-cycle and lower moisture removal. Use a modest allowance only for genuine uncertainty. Resolve unknowns with better measurements whenever possible.
10. Can I size equipment from cooling tons alone?
No. Check sensible capacity, latent performance, heating capacity, airflow, duct design, electrical limits, and manufacturer performance tables at the project conditions.
11. When should a professional review be required?
Get professional review for permits, new systems, additions, major envelope changes, duct redesigns, zoning, unusual geometry, or any equipment purchase decision.