Analyze envelope losses with flexible thermal options. See breakdowns infiltration impact charts and energy cost. Plan upgrades confidently with practical outputs for real projects.
Use this page to estimate conductive and infiltration heat leak, compare envelope components, project energy usage, and export results as CSV or PDF.
The layout stays single-column overall, while the form fields use three columns on large screens, two on smaller screens, and one on mobile.
This example uses metric units, U-values, 20°C temperature difference, 12 operating hours daily, 30 days, 90% system efficiency, and 0.15 cost per kWh.
| Component | Area (m²) | U-Value (W/m²·K) | Heat Leak (W) |
|---|---|---|---|
| Walls | 120 | 0.35 | 840.00 |
| Roof | 90 | 0.22 | 396.00 |
| Floor | 90 | 0.28 | 504.00 |
| Windows | 22 | 2.40 | 1056.00 |
| Doors | 4 | 1.80 | 144.00 |
| Infiltration | 250 m³ volume | ACH 0.60 | 990.00 |
| Total Heat Leak | 3930.00 W | ||
| Daily Energy | 47.16 kWh/day | ||
| Estimated 30-Day Cost | $235.80 | ||
Q = U × A × ΔT × (1 + bridge factor)
Q is heat leak in watts, U is thermal transmittance, A is area, and ΔT is the indoor-outdoor temperature difference.
U = 1 / R
When you enter R-values, the page converts them to U-values first, then calculates heat leak for every building element.
Qinf = 0.33 × ACH × Volume × ΔT
This estimates the heat loss caused by air exchange. ACH is air changes per hour and volume is the enclosed room space.
Energy = (Q × hours × days) / 1000
Purchased Energy = Load Energy / Efficiency
Cost = Purchased Energy × Rate
It estimates how much heat escapes through walls, roofs, floors, windows, doors, and air leakage. The result helps you size insulation upgrades, compare assemblies, and estimate energy demand.
U-value measures how quickly heat passes through an assembly. R-value measures resistance to heat flow. A lower U-value or a higher R-value usually means better thermal performance.
Windows commonly have much higher U-values than insulated walls or roofs. Even smaller window areas can create noticeable heat loss when the temperature difference is large.
Yes, especially for real buildings. Air leakage can be a major part of total heat loss. Including ACH and room volume gives a more practical estimate than conduction alone.
It increases conductive heat loss to account for framing, fasteners, slab edges, and other paths where heat bypasses insulation. This makes the estimate more realistic for field conditions.
Yes. The calculator accepts both systems. It converts everything internally so the final outputs stay consistent, including watts, kWh, and Btu per hour.
It is a planning estimate based on your energy rate, operating hours, analysis days, and system efficiency. Actual bills can vary with weather, schedules, controls, and equipment behavior.
Yes. Change one assembly value at a time, such as roof or wall U-value, and compare the new heat leak, energy demand, and cost. That makes upgrade decisions easier.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.