Blower Doors Don’t Need to Be So Confusing w/ Genry Garcia

Genry Garcia returns to the podcast to talk about blower doors and why ACH50 may needlessly complicate efforts to tighten a building envelope.

A large element of indoor comfort comes down to controlling the load, especially the latent load. Even though we can control indoor humidity sources, we may also deal with infiltration, which contributes to a high latent load and decreases comfort. The blower door test comes in when we can no longer control the load and need to determine how much infiltration is happening.

When using blower doors, we would typically use an ACH50 test, which takes the CFM50 (cubic feet per minute that the blower door moves to get the house up or down to 50 Pascals) and translates it to air changes per hour at 50 Pa. To do that, you would need to find the volume of the space, which adds hurdles that the HVAC technician needs to deal with.

However, Genry prefers using the CFM50 and factoring in the square footage and LAIR (leakage area infiltration ratio) to determine how tight a house is; he doesn’t focus on the building’s volume. To decrease the leakage, it’s best to stay focused on the CFM50 the entire time; worrying about the ACH50 just adds an extra step that we don’t necessarily use.

Genry and Bryan also discuss:

  • Connecting design and execution
  • Attic encapsulation
  • How to use LAIR
  • Ceiling height and stack effect
  • Blower door testing for code compliance vs. comfort consultation/diagnostics
  • Common duct problems in new constructions
  • Balancing supply ducts
  • Automation of communicating controls
  • IAQ products and dehumidification


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