Wednesday, July 29, 2020

Off Grid Hot Water

This last spring I had the plumbing in my house replaced.  The plumber used a product called pex pipe. Before this I have never heard of it. But I tell you what, uninsulated pex tubing in the attic this summer has picked up heat to the cold water line like you wouldn't believe.

When we turn on the cold water in the kitchen, it runs cold for a second or two, then starts warming up. And it gets probably 20°F hotter than the water heater does. It is actually hot enough to burn your hand, until it finally cools off from the incoming cold water.

So, this product would probably work well to make an offgrid water heater.  Build a box about 4x4, run this pex tubing in coils inside the box( it comes in coiled form already), paint it black, put a plastic cover on, and voila, hot water off grid. You could use this to be the inlet to the water heater. In winter i imagine you would have to remove and drain it though.

Have any of you made something like this before? How well does it work?


  1. I have heard about pex pipe. It's supposed to be very good as it is flexible, and can withstand freezing without bursting..rather important where it does get freezing temps in winter.
    When I had my 110 gal aquarium, I ran about 75' of a plastic tubing coiled inside one of those small refrigerators. One end of the coil attached to a 200 gph pump that cycled aquarium water through the chilled tubing inside the fridge. It wasn't plex, but was very efficient way to keep the tank water temp lower.
    Our pipes here are in the attic, and PVC. Yep, the water comes out very warm. We are on a well so even letting the water run a minute does not cool it down as the pressurized tank that holds the water is out in the wellhouse.
    Sounds like you wouldn't even have to paint the hose black, if it's already hotter than water heater water. Your attic gets very hot. You may consider some attic vents? or a flow through vents with a fan to drive the air through. Still, attics are hot in summer; especially in CA, I would guess. See what happens in the winter.

    1. Yep, I have been considering a solar powered attic fan on one or both ends of the house. I am also going to insulate the pex tubing, but I think that is going to wait until fall when it cools down a bit.