I came across a problem with the Carrier HRVXXLHB HRV (Venmar/Vanee). There was water leaking from the insulated exhaust duct at the HRV. It turns out the manual shipped with the HRV called for the standard looped ptrap below the drain tee.
I found a revised HRVXXLHB manual - Here (http://www.hvactechgroup.com/files/Carrier%20HRVXXLHB%20Manual.pdf)
Page 8. now shows a modified ptrap that must loop above the drain tee. I attached the pic below.