You need room to service all the pipes and to clean and descale the burners. Any such cabinet would need to be relatively large to allow those activities to occur. And to supply enough air flow to not trigger error codes.

A photo would help a lot.

If it has outside air intake you only really need to worry about servicing.

My hope is to build a large cabinet around it.

Perhaps you could build a cabinet above the washer/dryer that would extend from the wall with the entry door to the light switch. The right-hand portion would hide the water heater (behind a properly-vented door). The left-hand portion would contain shelves onto which you could put stuff like that sitting on top of the dryer. -- amateur

It's gas. Can see the gas line and the vent.

Are you wanting the cabinet to be useful at all for storage, or just for decorative purposes?

If decorative,. You could build a wood cabinet that has slotted vents on the front doors, sides, bottom, and possibly top (basically however many needed for adequate airflow), and cut outs around the plumbing. You can use french cleats to hang the cabinet on the wall over the tankless water heater, essentially hiding it with a box hung on the wall. The cabinet would then be fairly easy to lift up slightly and remove from the wall to service, but would allow some good airflow for it to operate. You would want the cabinet box to be as light as possible since it would have to be lifted up for servicing. Fairly easy to go lightweight if it's only decorative. Be sure to check with the manufacturer to see how much clearance and airflow is required. This may not work depending on what they say and what your space is around the unit now. Good luck and post some follow up if you come up with a solution, other people will be interested in this question over the next couple years.

Thanks Jake!

Thanks everyone. It is an older water heater, so it will likely need to be replaced in a few years. When that happens we plan to remodel the whole space and hide as much as possible.

Hi Robin P.
Did you come up with a solution to hide your tankless water heater? I wi be facing the same challenge soon. Thank you.

Wow! This looks a lot like our laundry area. I’d love to see what you came up with. I’m looking to disguise ours as well, but it’s over the utility sink so I feel like a cabinet would be a bit intrusive, if not “in your face” while using the sink. Ours was added as part of a reno/addition and the wall it’s mounted on, and the bathroom/ shower surround behind it were not part of the reno, so running the duct work etc in the wall was not really an option without a big budget hike.

I have this same situation at the moment! Years later. Hopefully I come up with something nice and post it later!

try using a privacy screen (nice ones on overstock), curtain system, or room divider