I recently installed a Takagi Flash TK-jr tankless water heater. Let me first say that I absolutely love it, it performs flawlessly, and I've already seen a decrease in my gas bill.
That said, I removed the old tank unit and drain pan, and I did install a pressure relief valve on the new unit, complete with 3/4" copper drain line. The old copper drain line emptied into the pan, but it seems like a complete waste to install a huge round drain pan under this new, very small, tankless unit.
The UPC requires a watertight pan in attics, where it is, with a minimum 3/4" drain that terminates to the outside.
My question is.... what have others done for the tankless units? What kind of drain pan arrangement have you used?