GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Why are we measuring a pressure (in Pa) for the fan, when we are really interested in knowing the flow rate of air through fan?

Iqra Khan | Posted in General Questions on

The question relates to blower door testing and the Tectite system.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    We use a manometer to measure the pressure difference. Knowing the pressure difference and the diameter of the round opening or duct, we can thereby deduce the air flow rate.

    There are lots of ways to measure air flow rates -- you can use an aenomometer or a hot-wire probe that detects temperature changes, for example -- but using a manometer to measure a pressure difference is a fairly accurate method. The bottom line is that you have to measure something to deduce the air flow rate, and measuring a pressure difference works.

    For more information on methods used to measure air flow rates, see this article: Is Your Ventilation System Working?

  2. Paul Morin | | #2

    Iqra Khan's question relates to blower door testing using The Energy Conservatory TECTITE software. When using TECTITE, you have the option of performing an automated test or manualing entering the data. When you are manualing entering the data you can choose between entering the fan pressure or the flow. Most people will choose to enter the blower door flow and that is the default setting in the software.

    The pressure and flow gauge is always reading a fan pressure and converting it to flow, but that happens in the background. Most techs do not know that is happening and do not need to be concerned about it.

    Paul Morin
    The Energy Conservatory

  3. GBA Editor
    Martin Holladay | | #3

    Thanks for the clarification. Iqra's question was more specific than I realized. I'm glad you could help.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |