Subscribe or Renew Membership Subscribe Renew

Insulating Outdoor Tankless Water Heater

delpi's picture

I've recently installed a Paloma PH-28 tankless water heater on the outside wall of my home in Atlanta. the heater has its own internal heater to keep it freeze proof.

But I need to insulate the supply lines as we will have several hard freezes each winter.

I will buils a box (about 14X24X10 to surround the pipes. Is typical foam pipe insulation going to protect these 3/4 copper supply lines or will I need more insulation?

I'm thinking of simply stuffing the box with fiberglass insulation, but I wounder what will happen if it gets wet.

I've also considered slicing a 4" pvc pipe in hals putting it around the supply pipes and filling it with foam insulation.

And/or - I have a thermostat that will power up at 38 degrees and power down at 50 degrees. I've thought about just putting a 100 watt lightbulb in there.

Heat tape won't work because I only have about 30 inches total of pipe that is exposed and the tapes say "do not install on pipes less than tape length"

Any suggestions, experiences are welcome.


(post #113498, reply #1 of 11)

Mac- I have the same issue, and also in ATL. I bought a self-regulating heat tape from McMaster-Carr (item 3580k22). It's probably a little longer than I need, and I havent' read the package yet to see what it says about installation. So I'm not sure if there are similar caveats as what you've read.

Our Noritz has a pipe cover (which really is only cosmetic). And I've been wondering what type of insulation to use.  I believe the foam stuff you see at HD isn't for outdoor use. There's jacketed fiberglass- but again, I don't know if the paper jacketed stuff will hold up. I'm used to seeing aluminum jacketing in industrial installations, but that's overkill and probably wouldn't fit in the tight space, anyway.

(post #113498, reply #2 of 11)


Thanks. I just looked up the product you bought and found this "To prevent burnout, rope must not be overlapped and must be in full contact with the surface being heated." which leads me to believe that it would not suit my needs.

I'm thinking I'll just use the foam strips and wrap them with duct tape. then enclose all of that it a small box which I will attempt to make weatherproof/waterproof. I'm planning to build the box out of a "Hardie Plank" 4X8 sheet and seal it with silicone and use some sheet foam insulation on the inside. Then I'll put some sort of small heating device in the box and hope for the best.

I've also thought about changing to PEX pipe for the outdoor portion. Aparrently it won't burst if it freezes.

Of course the simplest solution is just to have the wife get up every hour and run a bit of water through the system.


(post #113498, reply #3 of 11)

You read the description for the pipe protection heat cable, not the self-regulating heat cable, which states that it can be safely overlapped (makes sense, since it lowers heat output as the temperature increases). Like I said, I need to go read the info on the package, but I feel pretty confident that what I picked will work.

(post #113498, reply #4 of 11)

MrSludge -

You're right, I didn't bother to look at the part number, I just looked at the first item on the page.

I'm going to order a 6 foot length of the self-regulating cable and give it a try.

Let me know if you have any problems and I'll do the same.


(post #113498, reply #5 of 11)

FYI, I grabbed the package and it's a Raychem Gardian W51-6P.  McMaster's easy b/c they have everything on the planet, but once you know what the product is, it might be easier/cheaper to find somewhere else.  And make sure you don't get burned on shipping across town (their whse is on Fulton Industrial near Camp Creek Pkwy).  The default shipping option used to be "Best Method," which meant $20 express courier to them.

(post #113498, reply #6 of 11)

Slightly off topic, but you need to check your facts. I used to live near Atlanta and we did lots of business with McMaster-Carr. On orders placed before 11 AM, they delivered same day via courier, but shipping charges were billed at the UPS-Ground rate. There was no extra cost for this same-day service.

Now we're 900 miles from their Chicago warehouse. They ship orders to us via FedEx standard overnight, and still bill us at the UPS ground rate!

McMaster-Carr is one fantastic company.

(post #113498, reply #9 of 11)

I ordered from Mcmaster on a Tuesday and the package was at my door on Wednesday. Four dollars shipping to Fayettevile, GA.

(post #113498, reply #10 of 11)

Good deal. I ordered insulation and misc stuff to put it all on yesterday. Also from McMaster.

I revise my earlier statement- I had a couple of things 4 years ago or so that the shipping was out of hand. That was back when "Best Method" was a shipping option, and it meant "spare no expense and break any laws to get it there real quick."  Just kidding about the breaking laws part.  But all my recent stuff has been very quick and at ground rates.

(post #113498, reply #11 of 11)

The fiberglass pipe insulation has lighter weight PVC jacketing that won't be as expensive as the aluminum variety. It uses peel and stick tape for installing - you can add some silicone caulk to the seams as well. This is an all in one version:

(post #113498, reply #7 of 11)

Rather than install the heatintg tape parallel to the pipe why not wrap the pipe with the heating tape, in a spiral fashion, then all portions of the tape will be in contact with the pipe and your problem is solved.

(post #113498, reply #8 of 11)

The product sold by Lowe's and HD specifically says "do not wrap product around pipe".

The self limiting tape from McMaster allows wrapping. That's what I did, but working in a tight space, it is very difficult. It is approximately as stiff as, and the same size as, 14-2WG Romex and is very difficult to get it to stay tight around the pipe.