Offline mechanical-insulation calculator for HVAC engineers and contractors — condensation control, heat loss/gain, and safe-touch thickness. No subscription.
Have a question, found a bug, or want to request a feature? Reach out directly — every message is read by the developer.
Email duongnh@axalize.vnNo. The app is 100% offline — every calculation runs on your device, instantly, anywhere on a job site with no signal.
Condensation mode: enter the operating (pipe or surface) temperature, ambient air temperature and relative humidity, material, and jacket finish, and get the minimum insulation thickness that keeps the outer surface above the dew point — plus the computed dew point, the resulting surface temperature, and the margin above dew point. Heat mode: enter a thickness and get the heat loss or gain per unit length, the outer surface temperature, and a condensation-risk flag. Safe-Touch mode: find the minimum thickness that keeps the outer surface at or below a burn-safe limit (60 °C / 140 °F by default) for personnel protection.
The solver first finds the exact thickness that meets your target, then rounds up to the nearest standard nominal thickness — 13, 19, 25, 32, 40, 50 mm (½″, 1″, 1½″, 2″, 2½″, 3″) — so the answer is something you can actually buy and install. Above 50 mm it rounds up to the nearest millimetre, which in practice usually means a double-layer installation.
Because radiation at the outer surface is a large part of the heat balance, and it scales with the finish's emissivity. A bright aluminium jacket (ε ≈ 0.04) radiates far less than a painted, PVC, ASJ, or mastic finish (ε ≈ 0.9), which makes its surface run colder on a cold line — so a low-emissivity jacket typically needs more insulation to prevent condensation. This is why emissivity is a first-class input rather than a hidden constant. The default is 0.9, matching a typical painted/PVC/ASJ jacket.
Yes. Thermal conductivity (k) rises with mean temperature for essentially every insulation material, and using a single fixed k value is a common sizing error. InsulSizer evaluates k at the actual mean temperature of the insulation for each candidate thickness, and re-solves as the surface temperature converges.
Steady-state heat transfer following the ASTM C680 approach: series thermal resistances (cylindrical for pipe, planar for flat surfaces) with an outer film coefficient made up of a natural- or forced-convection term plus a radiation term. Because both the conductivity and the film coefficient depend on the unknown surface temperature, the surface temperature is solved iteratively to convergence, and the required thickness is then found by bisection. Dew point is computed from ambient temperature and relative humidity using the Magnus/ASHRAE saturation-vapour-pressure relation. The default condensation safety margin is 0.4 °C (0.75 °F) above dew point.
| Material | Typical use |
|---|---|
| Elastomeric / rubber | Chilled water, refrigerant (cold service) |
| Fiberglass | General HVAC pipe & duct |
| Mineral wool | Higher-temperature service |
| Polyisocyanurate (polyiso) | Cold and cryogenic service |
| Cellular glass | Cold service, below-ambient, high moisture resistance |
| Phenolic foam | Chilled water, low-conductivity applications |
| Calcium silicate | High-temperature / personnel protection |
| XPS / EPS | Optional, general-purpose |
Each material's conductivity-vs-temperature curve is taken from a published standard or a manufacturer's data sheet rather than a single textbook figure. Fiberglass follows ASTM C547 Type I, calcium silicate ASTM C533, cellular glass the Foamglas ASTM C552 data, polyisocyanurate the Dyplast ISO-C1 ASTM C591 table, and mineral wool the ROCKWOOL ProRox PS 960 pipe-section data measured to EN ISO 8497. Where a manufacturer publishes only a single reference value — as is common for phenolic foam, XPS and EPS — the app uses that value and interpolates conservatively around it, which is another reason to confirm against the specific product data sheet before finalising a specification.
Nominal pipe sizes from ½″ through 8″ NPS, using standard ASME B36.10M outside diameters. Since insulation wraps the outside of the pipe and the standard OD for a given NPS does not change with schedule, one OD table covers the usual piping materials. Flat surfaces (walls, ducts, equipment, tanks) are supported as a separate geometry.
Yes — Settings lets you pick temperature (°C, °F), thickness/length (mm, inch), thermal conductivity (W/m·K, Btu·in/h·ft²·°F), and heat flow (metric or Btu) independently, so you can work fully metric, fully imperial, or mixed. Heat flow is reported per unit length for pipe (W/m or Btu/h·ft) and per unit area for flat surfaces (W/m² or Btu/h·ft²). You can also set whether the app opens on pipe or flat geometry.
Yes — every result shows the thermal conductivity the solver converged on, evaluated at the mean insulation temperature for that result rather than at a fixed reference temperature. That makes it easy to sanity-check the answer against a manufacturer's published k-vs-temperature curve for the product you intend to install.
Yes — English, Español, 中文（简体）, Português (Brasil), 日本語, 한국어, and Tiếng Việt are all supported. Switch under Settings → Language.
No. InsulSizer is a one-time purchase. There are no subscriptions, no ads, and no in-app purchases beyond the initial download.
No — see the Privacy Policy for details.
Verify results before construction. InsulSizer is a calculation aid for preliminary sizing and field estimation. Published material properties vary between manufacturers, product lines, and production batches, and real installations are affected by joints, supports, jacket condition, moisture, air movement, and workmanship. Always confirm the final specification against the manufacturer's current published data for the exact product you are installing, and against the governing project specification and local code. The developer accepts no liability for decisions made on the basis of these results.