Wow, the inside of that box gets hot

The reason the pipe is a funny color is that it used to be painted black.

The heat not only made the paint and cement go away, it warped the pipe.

I’ve never seen that before. And I’m not at all confident the CPVC I brought home yesterday would survive inside the box any better than regular PVC did. Whoever suggested that the only way around this is copper with silver solder might really be right – and since that’s not going to happen, I’m going to change things up just a little: The black hose seems to be okay so far, so I’m going to pull the outlet end of the hose out of the box and connect it to the CPVC outside. That should keep the in-box heat from melting the cement.

About Joel

You shouldn't ask these questions of a paranoid recluse, you know.
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10 Responses to Wow, the inside of that box gets hot

  1. The Neon Madman says:

    It would be interesting to put your thermocouple inside the box and see what kind of a high temp you get.

    If you did go with copper (a couple of 60′ coils of 1/2″, maybe) I probably would suggest flared connections rather than solder.

  2. TK421a says:

    Please don’t take this the wrong way Joel, but I think your best bet is an indirect solar water heater verses the direct water heater you are making. You already have the majority of stuff you need and it will give you a lot less grief.

  3. Bear says:

    Joel, you’re over-thinking this.

    Get one of these water-bath canning pots.

    Fill it with water, bungee cord the lid down. Put it in the sun. Consider what your outdoor ambient temperatures run, then think of black metal in the sun. It should get plenty hot enough, and you don’t have to fight with silly fittings.

    If it doesn’t get warm enough, make one of these cardboard & aluminum foil solar cookers.

    Shoot, during Desert Shield, I got my MREs up to steaming temperature just by puttlng the pouch on a jerry can in the sun for a few minutes.

  4. Johanbz says:

    Hi Joel. My day job is doing terrible things to plastic pipe in the name of science. The CPVC will work for a little while, depending on how hot your box gets. Most CPVC is only rated to 155 degrees, but when we torture test it, it can spend six months at 189 F before is starts to get messed up. That being said, it will get messed up, and if your box gets hotter than that, it will fail faster. Copper is the way to go.

  5. terrapod says:

    Never fear. I have my scrounge antenna on for copper pipe at auction or scrapyard.

    I am pretty sure I have some 3/8 in a coil somewhere but think we need to hunt for 1/2 inch soft copper pipe. I am guessing about 75 or 100 feet worth and you don’t need to solder anything, just use compression fittings or flare the ends and use flare couplings. Keep an eye out for a smallish hot water tank being tossed due to a bad heating element, having a reservoir is not a bad idea.

  6. Jasonlj1911 says:

    Or just fill it up about an hour or so before you need it and keep it empty the rest of the time? KISS

  7. The Neon Madman says:


    That’s why I suggested a couple of coils of 1/2″. That would give 120 feet of copper. I’d also rather go with flare fittings than compression, due to the high/low temp extremes this will go thru. Between night in the winter and full sun in the summer I would not be surprised if there isn’t a 300 degree difference.

  8. The Neon Madman says:


    On further thought, I did what I should have done in the first place – run some rough calcs. 120 feet of 1/2 copper would give a volume of 282 cubic inches. I think that Joel is running 300 feet of 5/8 hose, that gives me about 4417 cubic inches. A gallon is 230 or so, which means the copper will only give about a gallon plus of capacity, but the hose should give about 20 gallons of hot water.

  9. Anonymous says:

    Too hot? Shade the glass and experiment til it doesn’t blow up

  10. john says:

    Copper would be best, for long term durability. The easiest thing, now, would be to plumb a pump into the system and circulate the hot water out of the hose into a holding tank, cooling the hose so it doesn’t melt. A system using hose and a thermosiphon layout would be cheapest, but you would have to install the holding tank above the collector so the hot water can naturally rise up into it and cool water flow down.

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