Cheap & simple HERMS tank

skifast1 · 03-24-2007, 03:22 AM

A post a while ago pointed me to http://www.djlarrylive.com (<--now broken) for a simple HERMS setup, so to prove imitation is the sincerest form of flattery I'm building almost the same system. These are just some in-progress shots to get the same thing Larry did:

Parts you'll need:
> 3-gallon cooler
> 1500W water heater heating element (got mine at True Value, but Home Depot has them too)
> Mounting kit for the element (usually hanging right next to them)

Tools:
> 1.5" hole saw bit (& drill)
> Dremel w/ side-cutting bit OR sharp utility knife/X-acto

Step 1: Find basic 3-gal cooler. This one came from Target

Step 2: Take the hole saw bit and go up right through the bottom of that sucker. Center the mounting plate over the hole you made and trace the outside. Use a dremel or similar tool to cut out the outer shell only. Don't go too deep into the foam or you'll go through the inner shell and you'll have to pitch the cooler (or use it as a planter). Use a flat dull blade to scrape out all the foam in the square hole you just made.

Step 3: Find something stiff (hey now) and poke a hole in the foam, going sideways from the square hole you just made towards the side of the cooler. You're basically making a channel between the inner & outer shells of the cooler for the wiring. Take a small drill bit and carefully make a hole on the outside about where you'd expect the end of the channel to be. Be extra cautious because the inner shell is really close to this corner and it's easier than you'd think to ding it. I did it once with the dremel bit and thankfully just got a little scratch on the surface (whew)

Step 4: Mark and drill for the bolts to mount the heating element (don't forget the o-ring & gasket), and tighten carefully so you don't crack the plastic. Edit: You may need to widen the hole very slightly for the mounting bracket; I did so by running a sharpie around the rim of the 1.5" hole I made originally and very carefully removing the width of the mark with the Dremel

That's it - took all of about 45 minutes of careful marking & cutting. Only things left to do are put some rubber feet on the bottom of the cooler (the element sticks out a 1/2" or so), make a little cover for the square hole and wire it up. Drop in your recirculating coils and stir motor and you've got yourself a HERMS tank!

**JayC** · 09-28-2008, 07:40 PM

Did you have any problems with leaking? I tried to reproduce it, but it leaks like a sieve through the bolt holes. I tried gooping on some hi-temp silicone, and that slowed it, but didn't stop it. At this point I've got nothing to lose (except a trashed small cooler) so I'm going to just put some more silicone on.

skifast1 · 09-28-2008, 09:53 PM

Quote:

Originally Posted by JayC

Did you have any problems with leaking? I tried to reproduce it, but it leaks like a sieve through the bolt holes. I tried gooping on some hi-temp silicone, and that slowed it, but didn't stop it. At this point I've got nothing to lose (except a trashed small cooler) so I'm going to just put some more silicone on.

Definitely had some leaks to start, and had the same experience with the hi-temp silicone. I ended up putting a rubber washer on the inside and a small o-ring on the outside (and a new layer of silicone), did the trick

gtg644w · 09-29-2008, 02:09 AM

What materials are used in the resistance coil on your heating element ? Maybe a better question, what materials are safe to use with a system such as this?

I was hoping to build something similar.

Thanks,

David

**JVD_X** · 09-29-2008, 04:37 AM

Are you plugging it through a GFCI?

WBC · 09-29-2008, 04:52 AM

After reading and looking at the pictures I now see the problem. You need a stainless support washer on the inside of the cooler because the material the cooler is made of can not seal flat against the plastic as it is too weak (especially when heated). The support washer would have a large hole in the center and 4 mounting screw holes and should be 3/16 thick to 1/4 inch thick so it will give full support.

I would also use a ground fault relay as water and electricity do not mix.

**Orfy** · 09-29-2008, 05:17 AM

Quote:

Originally Posted by WBC

as water and electricity do not mix.

They mix VERY well. That's the problem!

I'd be tempted to use gasket material.

skifast1 · 09-29-2008, 10:44 AM

Quote:

Originally Posted by gtg644w

What materials are used in the resistance coil on your heating element ? Maybe a better question, what materials are safe to use with a system such as this?

I was hoping to build something similar.

Thanks,

David

It's a standard 1500w water heater element, any hardware store carries them along with a fitted gasket (which as I discovered, doesn't seal against the plastic as well as it should)

skifast1 · 09-29-2008, 10:50 AM

Quote:

Originally Posted by WBC

After reading and looking at the pictures I now see the problem. You need a stainless support washer on the inside of the cooler because the material the cooler is made of can not seal flat against the plastic as it is too weak (especially when heated). The support washer would have a large hole in the center and 4 mounting screw holes and should be 3/16 thick to 1/4 inch thick so it will give full support.

I would also use a ground fault relay as water and electricity do not mix.

Excellent suggestion on the washer/flange. You could also use a metal vessel for better structural support and wrap it with insulating material - maybe a cheap aluminum pot?

I absolutely use a GFI - see schematic of the system here