Harth / Free tools
Building performance
Four calculators for the first pass at how a building will perform: converting thermal resistance and transmittance between SI and US units, comparing steady-state heat loss for two envelope schemes, comparing the embodied carbon of material options using your own EPD factors, and estimating annual solar PV generation from system size and a documented specific yield.
4 building performance tools
Free export on every toolR-value / U-value converter
Convert thermal resistance and transmittance with explicit SI and US units, or sum a layer stack with surface resistances.
Interactive tool · Free exportEnvelope heat-loss comparison
Compare two envelope schemes by steady-state heat loss, annual degree-day energy and heating cost.
Interactive tool · Free exportMaterial embodied-carbon comparison
Compare material options using EPD factors or illustrative presets, per unit floor area, for A1–A3 or whole life.
Interactive tool · Free exportSolar PV yield estimator
Estimate annual and monthly PV output from capacity and a regional or documented specific yield, with savings and simple payback.
Interactive tool · Free exportAbout the building performance tools
The R-value and U-value converter uses the exact factors between m²·K/W and h·ft²·°F/Btu and makes clear when a product value, an assembly value and a surface resistance are different things. The heat-loss comparison sums area × U-value for each element, applies one temperature difference to both schemes and reports each scheme's heat loss, the difference and the percentage reduction. The embodied-carbon comparison multiplies quantities by carbon factors only when the lifecycle modules and units match, and asks you to record the factor source and date. The PV estimator multiplies capacity by the yield you supply.
Where inputs are dimensional the tools default to imperial with a metric switch, and every page states its formula, its assumptions and what it does not cover: no annual energy simulation, no thermal bridging or air leakage, no weather data, no full life-cycle assessment and no compliance checking.
Results and inputs export as PDF or CSV so the assumptions travel with the numbers.
Start with: R-value / U-value converter, Envelope heat-loss comparison, Solar PV yield estimator.
Popular questions
How do you convert R-value to U-value?
Divide 1 by the R-value, staying in one unit system. R-20 in US units gives U = 1 ÷ 20 = 0.05 Btu/h·ft²·°F, and RSI-3.5 gives U = 0.286 W/m²·K.
From the R-value / U-value converter
How do you calculate heat loss through a wall?
Multiply the wall's U-value by its area and by the indoor–outdoor temperature difference. A 1,000 ft² wall at U-0.05 with a 36 °F difference loses 1,000 × 0.05 × 36 = 1,800 Btu/h.
From the Envelope heat-loss comparison
What is embodied carbon?
Embodied carbon is the greenhouse gas emissions, in kg CO₂e, from making, transporting, installing, maintaining and disposing of building materials. Operational carbon, by contrast, comes from running the building.
From the Material embodied-carbon comparison
How much electricity does a 5 kW solar system produce?
Multiply 5 by the specific yield for your site. At an illustrative 1,200 kWh/kWp/year that is 6,000 kWh a year, about 16.4 kWh a day on average; look up your actual yield in PVWatts or PVGIS.
From the Solar PV yield estimator
How do you convert a US R-value to RSI?
Multiply by 0.1761. R-19 is about RSI-3.35 and R-30 is about RSI-5.28.
From the R-value / U-value converter
Other free tool categories
- Drawing & geometry7 tools
- BIM & files4 tools
- Materials & quantities10 tools
- Site & solar3 tools
- Documents & presentation5 tools
Browse all free tools or read the plain-text index.
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