Retrotec Residential Pressure & Air Leakage - Manual (Page 10)

Page 10 of 75
©Retrotec Inc. 2014
Another thing to notice when the wind is blowing is that it’s very difficult to establish and maintain the test
pressure. In windy conditions, the readings on the house/room gauge will fluctuate. For example, when trying
to establish 50 Pa, the wind will cause that pressure to go up to 55 Pa and down to 45 Pa, making it very difficult
to take a reading.
There are other reasons a large Bias or Baseline pressure can appear on the gauge and these should be
eliminated first before assuming wind is causing the problem. If the tube is being moved by the wind, a large
rapidly fluctuating pressure will appear but can easily be eliminated by taping or tying down the tube. Next, a
large and steady pressure of 10 to 70 Pa will appear if the tube end has touched water and a drop has sealed off
the end. Stepping on the tube, or pinching the tube will induce a Bias pressure, so ensure that tubes are not
pinched and are located away from walkways.
If air inside the exterior heats up due to the Sun shining on it and if the tube end is above or below the point
where it leaves the enclosure, a stack pressure will build up inside the tube that will create a steady pressure
that may increase as the tube gets hotter.
Wind velocity is always lower on the leeward side of the building. Moving pickup points away from the
windward side reduces the magnitude of wind induced pressures.
Wind velocity increases with height from the ground, so placing our pickup points at ground level reduces the
magnitude of fluctuations.
Covering the end of the tube without blocking it helps because the static pressure is reduced. Pop bottles or
other containers help. Some testers dig holes to place the tube in. All these methods work. Flat plates on the
ground work best because the openings face all directions, and the pickup point is low down. A T works well
too.
Combining these methods gives a list you can go by if Baseline pressures are above 2 Pa or you simply want to
increase repeatability. Your outdoor pressure pickup tube should:

Be 15 feet from the building

Terminate in a T

Have 2 pickup points at least 20 feet apart attached to either side of the T

Each point should be covered with a flat plate or box
These steps will reduce the magnitude and variation of the Baseline pressures your gauge will see. After that,
time averaging or long Baseline recordings will reduce the impact of these wind pressures.