Residential HVAC screening
Enter Design Inputs
Use local design conditions and verified building data whenever possible. Fields are grouped for a practical preliminary estimate.
Example values
Example Data Table
| Input | Sample value | Reason |
|---|---|---|
| Conditioned floor area | 2,000 ft² | Sets floor exposure and building volume. |
| Ceiling height | 8 ft | Helps estimate infiltration airflow from ACH. |
| Window U-factor | 0.32 | Represents window conductive heat transfer. |
| Window SHGC | 0.30 | Represents transmitted solar heat gain. |
| Infiltration rate | 0.35 ACH | Provides a preliminary outdoor-air leakage estimate. |
| Duct allowance | 10% | Adds a transparent preliminary distribution allowance. |
Calculation method
Formula Used
This tool uses transparent heat-transfer and airflow relationships. It simplifies the detailed CLF and CLTD procedures used in formal Manual J work.
U = 1 ÷ R
Heating load = [Σ(U × A) × ΔT + 1.08 × CFM × ΔT] × (1 + duct allowance)
Sensible cooling = [Σ(U × A) × ΔT + window area × SHGC × solar factor × shade + 230 × occupants + 1.08 × CFM × ΔT] × (1 + duct allowance)
Latent cooling = [200 × occupants + 0.68 × CFM × grain difference] × (1 + duct allowance)
Approximate airflow = sensible cooling ÷ [1.08 × supply-air temperature difference]
A is area, U is conductance, ΔT is temperature difference, and CFM is outdoor airflow. Humidity difference is calculated from entered dry-bulb temperatures and relative humidity.
Practical steps
How to Use This Calculator
- Enter conditioned floor area and the average ceiling height.
- Use local outdoor design values rather than daily weather observations.
- Enter envelope areas, assembly R-values, window U-factor, and SHGC.
- Estimate infiltration and add planned mechanical ventilation airflow.
- Enter occupants, shading, solar, duct, and supply-air assumptions.
- Calculate, then review heating, sensible, latent, total cooling, and CFM separately.
- Test upgrades one variable at a time before selecting equipment.
Planning guidance
Understanding Simple Residential Load Estimates
A residential heating and cooling estimate starts with the building envelope. Walls, windows, roofs, floors, and air leakage all move heat. Each surface needs measured area and insulation data. Windows also need a U-factor and solar heat gain coefficient. Those values affect peak cooling more than floor area alone.
This page provides a transparent screening method. It separates sensible cooling from latent cooling. Sensible load changes air temperature. Latent load removes moisture. It also shows heating loss, ventilation airflow, duct allowance, and an approximate supply airflow target. The results help organize early project conversations.
A simple result is not a substitute for a complete design. Design weather varies by location. Orientation changes solar exposure. Window shading changes by season and time. Construction layers create thermal bridges. Appliances, lighting, cooking, and occupancy schedules add internal gains. Ducts outside conditioned space add further losses. A detailed survey captures these items.
Use measured values where possible. Check plans, insulation labels, window schedules, and manufacturer data. Estimate infiltration cautiously. Older homes can have large leakage paths. Newer homes can be tight, but mechanical ventilation may add airflow. Include both in the total outdoor-air flow.
Review the outputs as separate components. A large solar value may indicate unshaded glass. A large latent value may indicate humid outdoor air or high ventilation. A large heating loss may show weak insulation or extensive glazing. Correcting the building issue can reduce equipment demand.
Do not select equipment from tons alone. Compare the sensible and latent cooling totals with manufacturer performance at design conditions. Compare heating output at the local winter condition. Then check duct design, airflow, controls, and room balance. A qualified designer should complete formal calculations when permits, contracts, or equipment selection require them.
Use this calculator during feasibility work, renovation planning, and insulation comparisons. Run a baseline estimate first. Change one assumption at a time. Save the results as a project record. This approach makes tradeoffs visible before costly decisions are made.
Compare several design options without changing the weather inputs. Test window upgrades, attic insulation, shading, sealing, and ventilation rates. Record every assumption. Small input changes can move the calculated load significantly. Clear assumptions make review easier for owners, contractors, and building officials before materials and equipment are ordered for projects with fewer avoidable surprises.
Common questions
FAQs
1. What does this calculator estimate?
It estimates heating loss, sensible cooling, latent cooling, total cooling, preliminary airflow, and several load components. It is designed for early planning and comparison work.
2. Is this an official Manual J calculation?
No. It is a simplified educational screening tool. Formal projects should use the complete procedure, documented inputs, and suitable approved software when compliance is required.
3. Why are sensible and latent cooling separated?
Sensible cooling lowers air temperature. Latent cooling removes moisture. Equipment must satisfy both demands, especially in humid climates or homes with meaningful outdoor-air ventilation.
4. Which outdoor temperatures should I enter?
Use local summer and winter design temperatures. Do not use a recent daily high or low. Published design data is more useful for peak-load planning.
5. How should I estimate infiltration?
Use measured blower-door information when available. Otherwise, choose a cautious ACH estimate based on home age, air sealing, construction quality, and leakage observations.
6. Should gross wall area include windows?
Yes. Enter gross exterior wall area, including openings. The calculator subtracts the entered window area before applying the wall R-value.
7. What does SHGC change?
Solar heat gain coefficient estimates how much solar energy passes through glazing. A lower value reduces the simple solar-gain estimate when the other assumptions remain unchanged.
8. What does the duct allowance represent?
It adds a planning allowance for distribution losses. Actual duct performance depends on leakage, insulation, location, design, and installation quality.
9. Can this tool size individual rooms?
Not reliably. This page produces a whole-home screening estimate. Room-by-room loads need separate areas, orientations, exposures, windows, internal gains, and airflow details.
10. Does cooling tons select equipment?
No. The ton value is a load reference only. Compare design loads with manufacturer capacity data at the stated design conditions before making equipment decisions.
11. Can I use this page for a permit submission?
Usually not. Permit jurisdictions may require a formal residential load calculation and supporting documentation. Confirm local requirements with the authority having jurisdiction.
Verify results before selecting HVAC equipment for lasting comfort.