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What do I do if I can't reach 50?

If you were performing a One-Point Test and the Blower Door fan was unable to depressurize the building by approximately 50 Pascals because one of the Flow Rings was installed, remove the Ring and repeat the test (removing the Flow Ring will increase the maximum air flow available from the fan). If you were not able to depressurize the building by approximately 50 Pascals (with the "Open Fan" running at full speed) because the building is extremely leaky, use the following instructions:

  • For DG-700 Users: No adjustments to the test procedure above are necessary other than to make sure the gauge was in the PR/ FL @50 mode during the One-Point Test. If you can not achieve the target test pressure of 50 Pascals because the building is extremely leaky, a CFM50 leakage estimate will automatically be displayed on Channel B. The leakage estimate shown on Channel B is determined by continuously adjusting the measured air flow from the Blower Door fan to a test pressure of 50 Pascals, using the real-time Channel A building pressure reading and the Can’t Reach Fifty Factors shown in Table 2 below.
  • For DG-3 Users: Take your One-Point Test reading at the highest achievable building pressure. Now manually use Table 2 below to estimate the amount of air flow through the Blower Door fan it would take to reach the target pressure. To use Table 2, determine the flow required to maintain the highest achievable building pressure listed in the Table. Multiply this flow by the corresponding "Can't Reach Fifty (CRF) Factor" to estimate flow that would be required to maintain a 50 Pascal building pressure.

Table 2: Can't Reach Fifty Factors (See attached)

Example: With the fan running full speed, you are able to achieve a building pressure of 28 Pascals with a measured fan flow of 5,600 cfm. The corresponding CRF Factor for a building pressure of 28 Pascals is 1.46. The estimated flow needed to achieve the target pressure of 50 Pascals is 5,600 x 1.46 = 8,176 cfm.

Note: The TECTITE program automatically applies the CRF Factors to One-Point Test data.

Table 3 below show the potential errors in the One-Point CFM50 leakage estimates from using the CRF factors. (See attached)


There are two main sources of error:

  • The actual test pressure (Channel A) not being equal to the target pressure of 50 Pascals.
  • The actual exponent of the leaks being measured differing from the assumed exponent of 0.65.

Table 3: Error in One-Point Leakage Estimate from CRF factors (See attached)

For example, Table 3 shows that for a One-Point 50 Pa Blower Door building airtightness test, a 2.5% error would be introduced if the leakage estimate was determined at an actual test pressure of 30 Pa (Channel A), and the actual exponent of the leaks was 0.60 rather than the assumed value of 0.65.

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