Whole-Home Load Inputs
Use measured areas, local design conditions, and documented product values whenever possible. Default values are only starting assumptions.
Example Data Table
These example inputs show a possible detached-home estimate. They are not design recommendations.
| Input | Example Value | Reason for Review |
|---|---|---|
| Conditioned area | 2,200 ft² | Defines the project scale. |
| Wall U-value | 0.060 | Represents thermal transmission. |
| Window SHGC | 0.250 | Controls solar heat admission. |
| Combined outdoor air | 100 CFM | Affects sensible and latent loads. |
| Duct allowance | 8% | Allows for distribution losses. |
Formula Used
This estimator uses transparent screening equations. A full ACCA Manual J process includes more detailed procedures, location data, construction classifications, room-by-room analysis, and approved calculation methods.
Cooling totals combine sensible and latent components. Nominal tons equal total cooling load divided by 12,000 BTU/h. Sensible heat ratio equals sensible cooling divided by total cooling.
How to Use This Calculator
- Collect conditioned areas and enclosure measurements from drawings or field checks.
- Enter realistic indoor settings and local outdoor design temperatures.
- Use documented U-values, SHGC values, and outdoor-air estimates.
- Apply a weighted solar factor for the window mix and shading condition.
- Review heating, sensible cooling, latent cooling, and total cooling separately.
- Export the estimate for discussion with a qualified HVAC designer.
- Use compliant procedures and manufacturer data before selecting equipment.
Understanding Residential Load Estimates
Why whole-home loads matter
Heating and cooling equipment should match the building. A load estimate starts with the home, not the old unit. Floor area alone cannot describe comfort needs. Two similar homes can have very different loads. Window area changes solar gain. Insulation changes conductive transfer. Air leakage changes both heating and cooling demand. Outdoor air also adds moisture during cooling seasons. A whole-home review creates a starting point. It helps teams discuss capacity with better evidence.
Envelope details drive results
The enclosure separates conditioned space from outdoor conditions. Walls, roofs, floors, glass, and doors all transfer heat. Their effect depends on area, U-value, and temperature difference. Lower U-values reduce conductive transfer. Window data needs special attention. Glass carries conduction and solar gain. SHGC measures the solar portion that enters the space. Orientation and exterior shading change that result. Enter net opaque wall area. Do not count the same window area twice. Better envelope inputs usually improve the estimate more than added safety factors.
Cooling needs two load types
Sensible load changes air temperature. Sun, walls, appliances, people, and outdoor air create sensible heat. Latent load is moisture removal. Ventilation, infiltration, and occupants can add latent load. These loads behave differently at the equipment coil. A system may satisfy sensible demand while removing too little moisture. Review both values before discussing equipment. The sensible heat ratio shows their balance. A lower ratio means latent demand is more important. Accurate design conditions therefore matter.
Use estimates with discipline
This calculator gives an understandable preliminary number. It does not replace a room-by-room design report. Manual J calculations consider more than a few summary fields. They use approved methods and detailed adjustment procedures. The final system also depends on equipment performance at design conditions. Duct design matters. Air distribution matters. Controls matter. A qualified professional should verify inputs and choose equipment with manufacturer data. Avoid selecting capacity from square footage rules. Avoid large margins that encourage oversizing. Keep the calculation record with the project documents.
Review assumptions before construction
Recalculate when the plan changes. New glazing, insulation, shading, duct routes, or ventilation systems can alter demand. Confirm that inputs describe the finished building. Compare outputs with room-level needs. Use a compliant load calculation for permits, final selection, and design responsibility. This page supports early planning conversations. It does not certify code compliance. Careful measurements support better comfort, lower cycling, and clearer decisions.
Frequently Asked Questions
No. This page is a preliminary estimator. A compliant calculation needs the applicable ACCA procedures, detailed project inputs, and approved methods or software.
BTU/h means British thermal units per hour. It expresses the rate of heat loss or heat gain that the HVAC system must address.
They use different outdoor conditions and heat sources. Cooling also includes solar gain, internal gains, and moisture removal. Heating mainly reflects heat loss through the enclosure and outdoor air.
SHGC indicates how much solar heat enters through glass. Lower values generally reduce solar cooling gain. Orientation and shading still affect the final window load.
A U-value measures heat transfer through an assembly. Lower U-values indicate better thermal resistance and usually lower conductive heating and cooling loads.
Sensible heat ratio is sensible cooling divided by total cooling. It helps show the relative share of temperature reduction versus moisture removal.
Usually no. Large arbitrary margins can encourage oversizing. Verify assumptions first, then use applicable selection procedures and manufacturer performance data.
Use measured blower-door data when available. Otherwise, use a defensible estimate based on the building enclosure, construction quality, and applicable design guidance.
No. Duct sizing requires airflow targets, pressure calculations, fittings, geometry, and equipment data. This page only applies a simple duct-loss allowance.
Not by itself. Equipment capacity varies with outdoor temperature, airflow, and indoor conditions. Review sensible and latent capacity using manufacturer data and proper selection procedures.
Update the analysis after changes to glass, insulation, air sealing, ventilation, duct routing, occupancy assumptions, or indoor design conditions.
Accurate inputs support safer, quieter, more comfortable homes today.