It difficult to imagine something bad happening as a result of doing something we feel is so good. But here's what is bound to happen, at least a few times...

  1. A manual-j load calculation is produced by an HVAC contractor or third party.
  2. The default CFM values are left in place for the final report.
  3. This report is handed off to someone that sizes the ductwork in the field.
  4. They use the CFM numbers on the Manual-J report to size the ducts.
  5. Ducts are installed.
  6. Equipment is selected to meet the total cooling load, as shown on the Manual-J report.
  7. The equipment that is to be installed is the next available size.
  8. This system blows more air that what was represented on the Manual-J report.
  9. System is installed.
  10. Balancing report is completed for ESv3. Actual CFM numbers are quite a bit larger than the targets - more than the 20% difference allowed. 
  11. Ducts are too small for the system installed. Transfer grilles are too small. System performance is low, due to low airflow.

We need to make sure that our TARGET CFM #'s on the Manual-J reports are representative of the ACTUAL amount of air the system will be moving around the house. This means that the installing contractor may need to modify the CFM targets to match the installed equipment. If you're a rater, and you're working on a Version 3 ENERGY STAR project, be sure you keep these things in mind when you're measuring transfer grille sizes or critiquing a balancing report.

Here's a post I recently did on this topic. Check it out. I would love to hear your thoughts on the topic!

Tags: duct, manual-j, sizing

Views: 443

Videos

  • Add Videos
  • View All

Twitter

Latest Activity

Judy Rachel replied to Dean Kirkland 's discussion Im looking for a blower door / duct blaster / manometer rental in So Cal
"You can borrow the equipment from the Tool Lending Library maintained by SoCalEdison.  This is…"
3 hours ago
Profile IconSteve Last, Paul J Anzalone Jr, Jon Traudt and 1 more joined Home Energy Pros
17 hours ago
Jamie Medlin replied to angela stanzione's discussion Used Weatherization and auditing equipment for sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Please let me know if the flowhood  still for sale. jmedlin@archonenergysolutions.com"
yesterday
Jamie Medlin joined allen p tanner's group
Thumbnail

Energy Auditing Equipment for Sale, Trade or to Purchase

Discuss the pros and cons of the equipment you are interested in prior to purchase. Post equipment…See More
yesterday
Laurie DiDonato posted an event
Thumbnail

HERS Rater Training Discount: Register by 1/6/17 and Get $100 Off! at Energize CT Center, North Haven, CT

January 23, 2017 to February 3, 2017
Become a HERS Rater with the NEHERS Alliance!Online Component: January 23rd-February 3rd, 2017 -…See More
yesterday
angela stanzione replied to angela stanzione's discussion Used Weatherization and auditing equipment for sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Yes, I do. Pictures are above. I have a newer fan, I have a frame in a case and I have panels."
yesterday
Tom Phillips replied to Bruce Ceniceros's discussion How effective are whole house air cleaners?
"re: costs:  I suspect the added UV & PCO & ESP has a big price tag but no clear…"
Thursday
David Baerg replied to angela stanzione's discussion Used Weatherization and auditing equipment for sale in the group Energy Auditing Equipment for Sale, Trade or to Purchase
"Hi Angela, Do you have any fans left?  Frames?  Panels? Thanks, Dave"
Thursday

© 2016   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service