Replies

1. 
   Kopper37 | Mar 06, 2011 04:17pm | #1

   Some quick Googling turned up this chart. It lists Omaha, NE:

   http://www.captiveaire.com/CATALOGCONTENT/FANS/SUP_MPU/doc/Winter_Summer_Design_Temps_US.pdf

   It shows -2 F and 91 F for your location.

   What % frequency does your HVAC tech claim to use? Some like to use the more conservative 0.4% / 99.6% value, and this can affect your system sizing if you're on the edge. In Manual J, you are supposed to use the 1% value for cooling, 99% value for heating.

   You can also call your local building department for that type of information. You probably should.

   Here's another link on the subject:

   http://www.energycodes.gov/events/energycodes/presentations/ECodes10_Rossmiller_HVAC_Handout1.pdf

2. Expert Member
   CARL SEVILLE | Mar 06, 2011 04:23pm | #2

   Design temperatures are listed in the Manual J Book, and you can get them for any zip code in RemRate and other energy modeling programs.
   Manual J lists the following temps for Omaha:
   Omaha AP: Winter 99% dry bulb -2; Cooling 1% dry bulb 92
   Omaha WSO: -2; 90

   Make sure that they get the infiltration right, your report lists construction as "average". If it is a new home that is well sealed, this should be "tight:. Also check the window U factors and wall, ceiling, and floor R values to make sure they are correct. More often than not, the person doing the load calcs uses defaults and doesn't input the actual values for the home.

3. 
   mapnerd | Mar 09, 2011 01:07am | #3

   Is there a resource out there where I could find a consultant to run a Manual J and D for me? My local HVA contractors may be honest, but "tight building enclosures" is a new concept in our area, so I'm afraid they may not use the right inputs into the calculation.