Estimated Heating and Cooling Loads
Complete the form, then calculate the design estimate.
Load Breakdown
| Component | Cooling Sensible | Cooling Latent | Heating Effect |
|---|---|---|---|
| Total after safety factor | — | — | — |
Design Load Plot
This planning tool provides preliminary estimates. Use local design weather, equipment data, duct losses, moisture sources, and applicable codes before final equipment selection.
Advanced Load Inputs
Use consistent imperial units. Fields marked with an asterisk are required.
Example Data Table
| Input group | Example value | Why it matters |
|---|---|---|
| Conditioned area | 1,800 ft² | Sets lighting and building volume calculations. |
| Wall, roof, and window U-factors | 0.06, 0.03, 0.35 | Controls conductive heat transfer. |
| Summer design temperatures | 95°F outdoors, 75°F indoors | Creates a 20°F sensible cooling difference. |
| Winter design temperatures | 20°F outdoors, 70°F indoors | Creates a 50°F heating difference. |
| Airflow values | 120 CFM ventilation, 0.35 ACH infiltration | Adds sensible and latent air exchange loads. |
| Internal gains | 8 people, 1.10 W/ft² lighting, 1,600 W equipment | Raises cooling demand and offsets some heating loss. |
Formula Used
Conduction and Solar Gain
Conductive load = U × Area × Temperature Difference
The calculator applies this formula to walls, roof areas, and windows. Window solar gain is estimated with Window Area × Solar Factor × SHGC.
Air Exchange and Internal Gains
Sensible air load = 1.08 × CFM × Temperature Difference
Latent air load = 0.68 × CFM × Humidity Difference
Infiltration CFM equals Building Volume × ACH ÷ 60. Lighting and equipment watts are converted using 1 W = 3.412 Btu/h.
How to Use This Calculator
- Enter the conditioned area, height, envelope areas, and window area.
- Use known assembly U-factors and local outdoor design temperatures.
- Add realistic occupancy, lighting, equipment, ventilation, and infiltration values.
- Set a moderate safety factor, then select Calculate Loads.
- Review the total, breakdown, and plot. Export records when needed.
Heating and Cooling Planning Guide
Begin With the Thermal Boundary
Heating and cooling equipment should match the building load. Start with the conditioned floor area. Then identify the walls, roof, windows, and doors that separate indoor air from outdoor conditions. Each surface transfers heat at a different rate. A low U-factor resists heat flow better. Accurate areas matter because small errors can grow across large roofs and window groups. Exclude window area from opaque wall area. Use whole-window U-factors whenever possible. They account for frames, spacers, and glass together.
Use Local Design Conditions
Design temperatures are not daily averages. They represent demanding outdoor conditions used for equipment planning. Choose summer and winter values that fit the project location. Keep indoor targets realistic. A very low cooling setting increases energy use and capacity needs. A high heating setting does the same during winter. The difference between outdoor and indoor temperatures drives conductive heat transfer. Larger differences create larger loads. Solar gain also matters. South, west, and unshaded glass can add major cooling demand during sunny hours.
Include Air and Internal Loads
Ventilation and infiltration bring outdoor air into the building. That air needs cooling, heating, and sometimes dehumidification. The calculator estimates infiltration from building volume and air changes per hour. Tight buildings usually have lower infiltration. Ventilation still remains necessary for indoor air quality. People, lighting, appliances, and electronics add sensible heat. People and outdoor air can also add latent moisture. Ignoring latent load may produce a system that cools air but controls humidity poorly.
Read the Estimate Carefully
The cooling result combines sensible and latent loads. The heating result begins with envelope and air losses. It then credits useful internal sensible gains. A modest safety factor addresses uncertainty. Large factors can cause oversized equipment, short cycling, weaker moisture control, and uneven comfort. Use the chart to see the dominant contributors. Improve insulation, shading, glazing, air sealing, or ventilation recovery where it gives meaningful savings. This calculator supports early planning. Final selections should include duct losses, zoning, part-load performance, local codes, and professional design review.
Keep Project Records
Save each estimate with assumptions, dates, and weather data. Compare upgrades using the same inputs. This makes insulation, glazing, air sealing, and equipment decisions easier to explain. Repeat the process whenever layouts, schedules, occupancy, or construction details change.
Frequently Asked Questions
1. What does this calculator estimate?
It estimates preliminary peak cooling and heating loads from envelope losses, solar gain, ventilation, infiltration, people, lighting, equipment, humidity difference, and a safety factor.
2. Is this a replacement for a full HVAC design?
No. It is an early planning tool. Final design should use verified site data, local design weather, construction details, duct losses, humidity conditions, ventilation requirements, and equipment performance information.
3. Why is the cooling load split into sensible and latent values?
Sensible load changes air temperature. Latent load removes moisture. A system must address both loads to maintain temperature and indoor humidity during demanding weather.
4. What is a U-factor?
A U-factor measures heat transfer through an assembly. Lower values indicate better resistance to heat flow. U-factor is the reciprocal of R-value for simple assemblies.
5. What solar factor should I enter?
Use a project-specific value when available. It should reflect window orientation, season, exterior shading, nearby obstructions, and local solar conditions. The example value is only a planning assumption.
6. How is infiltration airflow calculated?
The tool multiplies floor area by ceiling height, then multiplies by ACH and divides by 60. The result is estimated infiltration airflow in cubic feet per minute.
7. Why do people add both sensible and latent load?
Occupants release body heat and moisture. Sensible gain affects temperature. Latent gain affects humidity. Both values increase cooling capacity requirements in occupied spaces.
8. Does the heating load include internal gains?
Yes. The calculator subtracts useful sensible gains from people, lighting, and equipment from gross heating loss. It never reduces the net heating result below zero.
9. What safety factor should I use?
A modest factor, often near five to ten percent, can address uncertainty. Avoid large factors because excessive capacity can cause short cycling and poorer humidity control.
10. Why can an oversized cooling unit cause problems?
An oversized unit may satisfy the thermostat quickly, then stop before removing enough moisture. Frequent cycling can reduce comfort, efficiency, and equipment life.
11. Can I export the calculation?
Yes. After calculating, use the CSV button for spreadsheet data or the PDF button for a downloadable summary. The print button provides a paper-friendly version.