Author: Sam Myers, Retrotec

When pressurizing a building with a blower door, did you know that extra tubing must be added to the Channel B side of your gauge if you are not using a Retrotec DM32? If this tubing connection is neglected, you will have a reading that is approximately 20% high due to the open Channel B port that is referencing the indoor pressure of 50Pa instead of the outdoor pressure. Therefore, the extra tube is needed to connect that port on Channel B to the outside so that it is referencing the outside instead of the pressure induced by the blower door.

However, the Retrotec DM32 automatically removes the need to connect additional tubing by mathematically removing the additional pressure from the equation. The gauge knows to do this whenever a blower door is selected and the open input port on Channel A (blue) feels a positive pressure.

Below are some screenshots from both the TEC and Retrotec blower door manuals that show how each gauge should address positively pressurizing buildings:

Ch. 7 of TEC Blower Door Manual:


Ch. 10 of Retrotec Blower Door Manual:



As shown below, a blower door test was done on house with a Retrotec DM32 and a TEC DG-700 Pressure & Flow Gauge connected to the fan. The fan is set up to pressurize the house. Since the DG-700 can only work with TEC fans, a TEC Blower Door fan was used. The DM32 can read and control both Retrotec and TEC fans. The photo on the left has both gauges connected correctly, with the extra tubing (green in this case) connected to the reference port on Channel B of the DG-700. The photo on the right shows the same set-up with the additional tubing removed from Channel B. Notice the difference in readings on the DG-700 with the green tubing connected and disconnected. It is worth mentioning that the DG-700 used in this demonstration is passed its calibration date but is reading well enough to for this example.

In this test scenario, both the outside reference tubing (red) and tubing reading the fan pressure (yellow) are split using nylon T connectors so that both gauges can take readings at the same time. A Retrotec speed control adapter is installed so that the DM32 has full control of the TEC fan. This adapter converts the TEC stereo jack to the Retrotec ethernet outlet.


No matter what brand of equipment you use, it’s always important to ensure your gauges are set up correctly for each test scenario. Whether you are new to the industry or new to a certain test procedure, always refer to your manufacturer’s operation manual to make sure you are using your equipment correctly.

Retrotec focuses much of its attention on equipment design that helps speed up the equipment set up process and reduce user error by incorporating items such as color-coded pressure ports and tubing, removing the need for additional tubing when pressurizing buildings, removing the need to add a flow straightener when depressurizing ducts with a duct tester, etc. If you have any questions regarding your Retrotec equipment, please feel free to reach out to us at or visit our YouTube channel for instructional videos and webinars.