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Discussion Starter #1
Had a fan tech flex 100 HRV installed
Testing with manometer to balance gives exhaust of 92 pa and intake of 99 pa regular speed and 66 pa exhaust and 69 pa intake on reduced speed
With 4” ducts my calculations seem to convert this to cfm of
Regular ex 213 cfm in 221 cfm
Reduced ex 180 cfm in 185 cfm

despite the machine being rated at 100pa=122 cfm by the brochure

can anyone explain or assist with this please
Tks
 

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I have a 155 Max Lifebreath and sell them. You need to take the readings on the door if it has ports otherwise you need a special pitot tube probe and put it in a horizontal area away from elbows.

It is critical where you take the readings and I suspect you are getting wrong placement readings. The install manual may show you where to take them.
 

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Discussion Starter #3
Had to put the probe in the 5” duct 18” clear span
So center Ed it on a 4’ section and am getting these high calcs
Need some insight
Calc used is changing Pascals to inh2o then multplying that by 4005 and multiplying that by the area of the duct in sq/ft to get cfm
 

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I use a chart that is in the LIfebreath manual and the newer ones have test ports on the door by the cells. The reading gets changed into CFMs by that chart.

I did some with a pitot tube which then gives you CFM but you have to be very careful where and how you take the reading with them.

I am not sure what your issue is.
 

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Are you using a pitot tube? If not, then your applying a velocity formula incorrectly.

The 4005 is multiplied by the sq root of the velocity pressure, not the static pressure.
 

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Okay, what was the velocity pressure.
 
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