When I saw the plastic vent I thought it was a high-efficiency water heater. When I saw the compartment covering the burn chamber I thought it was sealed combustion. It’s not. When you open the compartment (no gasket/seal) you’re looking directly at a conventional burn chamber access cover, but with various other equipment.
As you can see from the energy label, it’s not even close to high-efficiency, so why does it have a plastic vent and all these other components in the compartment covering the burn chamber? Looks expensive. You could get this kind of performance from a conventional water heater.
Might the reason be be limited room for conventional venting?
The efficiency rating of water heaters is much lower than furnaces. The tip off for a high efficency water heater is the fan drive on the flue. When in doubt, check the manufacturer’s data sheet.
It may be your picture, but is the bottom of the TPR tube flush with the platform?
Standard, mid or high-efficiency models can be power-vented units that need electricity to operate. This type of heater is not usually affected by changes in the air pressure in the home but can contribute significantly to building depressurization, affecting other combustion appliances.