I recently measured disappointing bath fan flows at a project - both being below our program minimum of 50cfm. The builder had the installer come back to have a look and found nothing obvious but he did get a couple of new fan motors and swapped them out and also double checked that the damper flap wasn't stuck. There was a slight improvement to both but it was not enough, still both below 50.

These fans were routed - with a short run of duct - to soffit terminations which allowed us to look up inside and check for blockages but none were seen. 

Then the weirdness: I checked the flow coming from the terminations and both were about 90cfm, yet still only about 45 inside. How can this be? I've never seen this before, but that's because I never test at the outside. 

I hate to bash brands but these were Broan fans which I rarely see used around here. Most all of my contractors use Panasonics.

Views: 192

Reply to This

Replies to This Discussion

In my opinion venting into any soffit is a bad idea, it usually requires a sharp bend to get into the soffit, and reduces insulation value where it crosses the top plate. (significantly)  Better going through the sidewall or box/gable, nice straight run with an extra damper thrown in that doesn't put back pressure on vent pipe.  Additionally the hood damper seals much tighter (typically) then the inline damper that is provided with fan.

In my northeast climate (zone 5 & 6) adding damp air to roof edge in 0deg weather is asking for icing issues.

Never had issues getting fans up to needed CFM when running through wall.  Usually issue is related to air envelope tightness where the fan struggles due to lack of fresh air intake.  This can be detected by opening the bathroom window (or any window) while testing to see if it affects flow rate. (I've seen that it does)

RSS

Latest Activity

Brett Little posted an event
Thumbnail

Duct Optimization and Performance - Free CE Webinar at Webinar Online

October 31, 2018 from 12pm to 1:15pm
Good indoor air starts with proper duct design and installation. In residential ventilation…See More
13 hours ago
Nancy Hawkins is now a member of Home Energy Pros Forum
16 hours ago
John Nicholas replied to Jerry Needham's discussion Blower door test for small apartment building
"Thank You, Colin!  Those are very good points and processes to do some Zone Pressure…"
21 hours ago
Colin Genge replied to Jerry Needham's discussion Blower door test for small apartment building
"The way we'd normally do this is to mount one blower door in the hallway, then a duct tester…"
yesterday
Scott Katznelson replied to Jerry Needham's discussion Blower door test for small apartment building
"Most of the work I do is retrofit of older buildings. Marriage wall leakage is often significant,…"
yesterday
John Nicholas replied to Jerry Needham's discussion Blower door test for small apartment building
"Scott Katznelson   In 2013,  I had my HERS Field Review completed on a multi-family…"
yesterday
Sean Lintow Sr replied to Jerry Needham's discussion Blower door test for small apartment building
"Sorry but LMAO - one blower door for that small of a space gives you an accurate number for the…"
yesterday
Chris Davis posted a blog post
yesterday
Scott Katznelson replied to Jerry Needham's discussion Blower door test for small apartment building
"The most accurate way to accomplish this is to have 4 blower doors running at the same time, one…"
yesterday
Brett Little posted a discussion

Tour 2 IL New Built Homes - 1 LEED Silver - 1 Zero Energy Ready

During the IL Green Built Home Tour, we looked at 2 homes right down the road from each other to…See More
yesterday
Jan Green commented on Pearl Certification's blog post Two National Brands Join Forces Demonstrating Unity in Home Energy-Efficiency Rating Systems
"Congratulations to Pearl for innovative thinking and finding the right path to ensure these homes…"
yesterday

Photos

  • Add Photos
  • View All

© 2018   Created by Home Performance Coalition (HPC)   Powered by

Badges  |  Report an Issue  |  Terms of Service