A free platform for architects, engineers, and homeowners to calculate BTU, OTTV, and CLTD, estimate cost, and optimize the building envelope — all in real time.
Move a slider — watch OTTV drop, savings climb, and the heat breakdown shift. No reload, no waiting.
Simplified illustration. The full app uses the complete ASHRAE CLTD/CLF engine.
We model heat flow through every part of the envelope and surface the highest-impact upgrades first — so every unit of build cost moves the needle.
Average savings on a first model vs. an ASHRAE 90.1 reference baseline.
Both are completely free. Pick Standard for a single room, or Pro for a whole building.
For homeowners and quick renovations. Improve one room at a time with simple inputs and instant results.
For professionals designing entire buildings. Full envelope analysis, optimization sliders, charts, and PDF reports.
Good buildings start with good design decisions. We put engineering-level calculation into the hands of every designer.
Buildings consume around 40% of electricity. Optimizing the envelope with the right materials can reduce cooling load by up to ~70%.
ASHRAE CLTD/CLF formulas and OTTV standards, ready to use instantly — no programming or spreadsheets required.
Adjust a parameter and see the result immediately. No waiting for simulations — save hours on every design.
Location, room type, area, orientation, wall and glass areas, plus internal loads from people, equipment, and lighting.
See total BTU, OTTV (W/m²), tons of cooling, and a real-time breakdown of where heat comes from.
Move sliders for wall/glass R-value, shading coefficient, and roof R-value to see BTU, annual cost, and % savings update live.
Use the R-Value layer calculator to design wall/roof layers precisely, then bring the value back into the main tool.
Understand the core inputs so you can read and interpret results with confidence.
Higher is better insulation.
Lower is better insulation (the inverse of R).
Share of solar heat passing through glass vs plain clear glass.
Common conversions used throughout the tools.
Formulas and data reference recognized engineering standards and official agencies.
From the ASHRAE Handbook of Fundamentals, adjusted for ~15°N tropical latitude.
Building envelope criteria for controlled buildings, aligned with regional energy codes.
Enter your own rate and currency for accurate, location-independent cost estimates.
Outdoor design dry-bulb temperatures per location, from ASHRAE climatic data.