# Duct Sizer: Size, Condensation — CFM, friction rate, dew point

> CFM, friction rate, dew point (iPhone/iPad app by RAINBOW TREE LLC.)

- Source: https://appshunter.io/ios/app/duct-sizer-size-condensation/id6813524453 (this page in markdown: same URL + `.md`)
- Developer: [RAINBOW TREE LLC](https://appshunter.io/developer/1619997282)
- Category: Utilities, Productivity
- Price: Free with in-app purchases
- Age rating: 4+
- Requires: iOS 17.0 · 10 MB
- Languages: American English, Japanese
- Released: 2026-09-22
- Data updated: 2026-09-24
- User reviews in markdown: https://appshunter.io/ios/app/duct-sizer-size-condensation/id6813524453/reviews.md

## What is Duct Sizer?

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

## Pricing and in-app purchases

Base price: Free.

**One-time purchases**

| Purchase | Price | Type |
| --- | --- | --- |
| Duct Sizer Pro | $9.99 | one-time |



## Version history (last 1 release)

### 1.0 — 2026-09-23

No release notes.

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All apps by RAINBOW TREE LLC: https://appshunter.io/developer/1619997282

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-09-24.*