Exactly what I was trying to convey!
The only reason ask Steve is because the plastic piping (pex) "* looks like it attached to copper/brass* and then the galv" the picture i just not that clear so therfore a valid point. Dielectric fittings would be necessary if that were the case.
Brass fittings are allowed in place of dielectric unions when joining galvanized to copper. But this is plastic pipe. There is no need for any type of union.
Thanx for noting that Joe. I thought it wasn’t ok either. I guess my assumption was due to everyone here uses CPVC or copper for HW TPRV drain lines. 
10-4 Steve…
Another question. That doesn’t look like a high efficiency water heater. Why do you say it is. Too blurry to read label.