I live in a second floor condo. I want to replace my aging water heater (WH) with a hybrid, but there are some concerns. The current heater is in a closet outside, with door access from the balcony. My current concern is that there's no direct way to connect a condensate line from the hybrid water heater. My current WH does have a TPRV drain line that goes outside, I think, the building. My question is, can I use that one drain line for both the pressure release valve line and condensate line for the new hybrid WH?
Nope. The condensate drain can't share pipe with the TPRV. From the installation manual of my Rheem hybrid WH:
DO NOT connect any other plumbing to the T&P plumbing; it must go directly to a suitable open drain
The reasoning behind that is if the TPRV opens, the resulting water flow could be extreme and if any other plumbing is connected to that pipe, the discharge water could potentially back up into that. You don't want high pressure hot water shooting through the condensate tube back into the compressor housing and your ceiling.
I'm going to assume you don't have a floor drain in your water heater closet, otherwise that would be the best place to drop it in. Depending on local code and your local inspector's mood, you could potentially route the condensate out to drip on your balcony and evaporate away (provided your balcony isn't permeable). Other options include going down the outside of the building and dripping on the ground. Otherwise, you'll probably end up needing a condensate pump that outputs to another drain in the condo.