I've run into an H2K file that is not responding as expected when the BDT data is entered.  It's reporting higher gas consumption with a tighter house (the only change I made is to the  BDT data).  

If I enter in the ACH simply as an absolute Air Change Rate the gas looks good. 

Has anyone run into this problem and gone under the hood of H2K to figure out why this is happening?  And how to fix it?

I was going to say something similar to Angela. If you only input the ACH and use calculate it will be different. If you input the ACH and ELA from your BD test calcs it should match the same as if you inputted all the results into Hot2000. Have definitely seen cases though were the ACH is less in the post retrofit but the ELA is the same or higher and the home performs worse.