Duct Sizer: Size, Condensation

CFM, friction rate, dew point

Only for iPhone

Free · In‑App Purchases · Designed for iPhone. Not verified for macOS.

iPhone

A field calculator for duct size and insulation thickness. Enter the airflow and it gives the size you need; enter the size and it gives the airflow that size can carry. Enter the ambient air and the air inside the duct, and it tells you whether the duct will sweat and how many inches of insulation stop it. ■ There are two limits, not one The friction rate and the velocity. This app shows both, and says which one governs right now. Look at only one of them and you either get noise you did not want, or a duct that is larger than it needs to be. ■ How much insulation stops condensation From the ambient temperature and humidity and the temperature of the air in the duct, it works out the outer surface temperature and the dew point, then rounds up to a stocked thickness (1/2, 1, 1-1/2, 2, 2-1/2, 3, 4 in.). When no thickness can stop it, it says so, and separates the two reasons: - the dew point has reached the ambient air temperature (no thickness brings the outer surface below it) - the calculation gives an answer, but one thicker than stock ■ Rounding is always on the safe side Diameters round up to a standard size; the airflow a size can carry rounds down. Which way it rounded is printed directly under the answer. ■ Every number shows where it came from The formula it was solved from (Colebrook-White, solved directly), the absolute roughness of the duct wall, the Reynolds number, the friction factor, the direction of the rounding and the name of the source. All of it sits in the same block as the answer, so you can check it against your own standards. ■ Properties of the ambient air Dew point, wet-bulb temperature, humidity ratio, enthalpy and specific volume. Enter the site elevation and everything is recalculated at the local barometric pressure (calculating at sea level always makes the duct larger, which is conservative, and the cooling capacity higher, which is not). ■ Metric and Imperial Settings switches between Metric/SI (m3/h, Pa/m, mm, C) and Imperial/I-P (CFM, in.wg/100ft, in., F). Switching also swaps the standard sizes themselves: round duct snaps to US spiral diameters and insulation to US stocked thicknesses. You get a size you can actually buy, not a converted decimal. ■ Pro (one-time purchase, nothing renews) - Rectangular, flat oval and flexible duct in their own dimensions - Hold a friction rate for supply and for return at the same time - Change the jacket (surface film coefficient) and the dew-point margin - Return air mixed with outdoor air, the range of sensible heat ratios available, the apparatus dew point, the bypass factor and the cooling capacity Without Pro you still get the full answer for round duct: the size, both limits, pressure loss and velocity, the four assumptions behind them, the condensation verdict, the insulation thickness, and the ambient air properties. Results are never locked. ■ Privacy Every calculation stays on this device. The job conditions you enter and the results are never sent anywhere. Three things do go out: usage statistics (which screens you reached), crash records, and the text of a support message when you send one. The first two include an anonymous per-device identifier. No name, email address or location is collected. There is no advertising and no tracking across other apps or websites. The app uses no camera, photos, microphone, location or notifications. ■ What it does not do (said up front) - No fitting losses (elbows, branches, dampers), fan characteristics, sound attenuation or fire-rated construction - The final judgement is yours. Use these numbers as a reference

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The developer, RAINBOW TREE LLC, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .

  • Data Not Linked to You

    The following data may be collected but it is not linked to your identity:

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Information

Seller
RAINBOW TREE LLC
Size
11 MB
Category
Utilities
Compatibility
Requires iOS 17.0 or later.
  • iPhone
    Requires iOS 17.0 or later.
  • Mac
    Requires macOS 14.0 or later and a Mac with Apple M1 chip or later.
  • Apple Vision
    Requires visionOS 1.0 or later.
Languages
English and Japanese
Age Rating
4+
In-App Purchases
Yes
Copyright
© 2026 RAINBOW TREE LLC
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