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HVAC Duct Tools app icon

US · Manual D methods

Duct numbers you can defend, in seconds.

Size a run, check total static, or catch an undersized duct right on the truck. Before the homeowner asks why the back bedroom is hot.

  • Free field tools
  • iPhone & iPad
  • Works offline
  • No sign-in, no tracking
Coming soon to the App Store

Who it’s for

Built for the call, not the office.

Service and install techs. If you carry a manometer and argue about duct sizes, this is yours. No account, no cloud, no signal needed in a crawlspace. Punch in what you can measure and screenshot the verdict.

  • Quick Size. Enter CFM, get the round size. About ten seconds, with velocity and which limit governed the answer.
  • Real materials, not chart guesses. Galvanized, duct board, lined, or flex with actual compression. 15 percent field sag is the default, because that is what flex does.
  • Rectangular too. Boxed into a joist bay? Fix one side and it solves the other, with the equivalent round shown.
  • Static pressure verdict. Supply plus return against the equipment’s rated max. Total, headroom, and which side is eating your static.
  • Duct Check. Existing size plus airflow tells you if that run was ever big enough. Undersized, oversized, or fine, judged against the Manual D velocity limit for its role.
  • Honest math. Every result states what it assumed, so a defaulted 0.10 friction rate never hides in the fine print. Bad inputs read as “check your inputs,” not a confident wrong answer.
  • Nothing leaves your phone. Fully offline. No sign-in, no tracking, no analytics.
  • Design a System: coming soon. Full Manual D trunk-and-branch sizing, from static-pressure budget to duct schedule. In the app today as a preview card, shipping next.

The numbers behind the numbers

Equation-derived, stocked-size honest.

  • Method: Manual D friction-rate approach; design friction rate = ASP × 100 ÷ TEL, target band 0.06 to 0.12 in. w.c. per 100 ft, default field rate 0.10 and editable.
  • Velocity limits from Manual D targets: 900 fpm supply trunk, 600 supply branch, 700 return trunk, 300 at the filter grille.
  • Stocked sizes only: rounds snap to 4 through 16 inch, skipping 11 and 13, because your supply house does too.
  • Engine: Darcy-Weisbach with Altshul-Tsal friction, not a scanned chart. Altitude correction to 6,000 ft.
  • Flex penalty: sized per diameter from LBNL compression research, capped at 30 percent where flex starts to bulge.
  • Sanity checks: TESP totals over 2.0 inches flag as probable misreads, and a verdict that rests on an assumed 0.50 inch rating says so out loud.

Get it

Free. The ductulator stays in the truck.

HVAC Duct Tools is headed to the App Store now. Check back shortly, or grab one of the other apps in the meantime.

Coming soon to the App Store