Waterproofing water heater closet

[Basilisk]

My 2 water heaters are sitting in a 3x5' closet in the garage, on a sheet of OSB that is the raised "floor". The closet is drywalled from the inside as well, and there are tons of gaps all around, so in case a leak happens outside of a drain pan, or if drain pans overflow, all the water would go straight into the house, which is obviously not great. I'd much rather have it go over the closet door threshold into the garage, where it will do a lot less damage, and can be reasonably contained. I'm about to replace both heaters, so this is probably the best time to do anything about it. What's my best bet to make the area at least somewhat water-resistant?
I'm ok with going a little overboard for an extra peace of mind. Or should I just caulk the perimeter and call it a day?

-B

 

[WorthFlorida]

Replace the drywall or cover it corner with DensShield® Tile Backer. You can get it a most Lowes or tile suppliers. It is nearly 100% water proof with a fiberglass like glass backside with fiberglass embed in the gypsum. You can take a small piece, place it in water and it will float and never absorb water. You'll still need to caulk the seams or what I did is I had cheap 4" tiles and placed them on the wall behind the water heater. You'll be nearly 100% water proof. Replace the OSB with 3/4 plywood.

Why two water heaters and what size? Replace both of them with one 65 gallon heater, install a mixing valve and set the WH at 140º. Use a thermostatic mixing valve to bring the outlet temperature to 120º. https://www.cashacme.com/us/en/thermostatic-mixing-valves/tank-booster-pro. You'll have an equivalent of about a 100 gallon water heater.

 

[Sponsor]

 

[John Gayewski]

Buy an oversized piece of linoleum and run it up the walls little ways on every side. Caulk the corners with np1 or something of quality. That's pretty easy and cheap. If you wanted you could put plastic base around the perimeter so the flooring isn't visible and caulk around that.

I own a home that has a second floor bathroom. That room can hold about 3 inches of water if the door were sealed.

 

[Terry]

I got a call one time where the assumption was that there was a plumbing leak in the kitchen. The wood floors had warped pretty badly. I went into the crawlspace looking for the leak, and found nothing.
Where are the water heaters located? Let's take a look. In the garage, there was a step up from the concrete where the main floor was framed in. The water heater was leaking badly, water was on the plywood subfloor, and was tracking toward the kitchen about 20 feet away inside. With wood flooring, there are gaps between the planks, plenty of space for water to travel through.

You will want to have pans for the water heaters, and pipe the pans somewhere safe.
A garage floor is sloped toward the garage doors, so that is better than letting them leak onto the plywood. It will drift toward the doors. Better of course would be to the outside. Or in some cases, to the crawlspace.
My Redmond home I had replaced the water heater and let the pan drain to the crawlspace. Fifteen years later my ex called me about a lack of hot water, the water heater had failed and was draining into the crawlspace. No harm there, but without the pan that was drained, it would have made a mess of the first floor carpeting in that home.