Things NOT to do on a Batch Water Heater

Batch water heaters are simple to build, and its easy to get the impression that you can just throw anything together and it will work.  But, batch heaters live in extreme temperatures (hot and cold), and you need to be a little careful about materials and construction:

 

Don't use plastic pipe:

Don't use CPVC or PEX pipe inside the batch enclosure or right near it.  The temperatures in batch heaters get to hot for these materials.

Use copper pipe at least inside the enclosure.

Be careful about the glazing:

Glass glazing is the best in terms of long life and temperature resistance.

Blemished panels, or sliding glass door panels that are being replaced can often be had cheap -- check with your local glass suppliers -- mine usually has something he is willing to (often very glad) to get rid of cheap.

For plastic glazing, polycarbonate with a UV protective coating is the only plastic glazing I know that will stand up to batch collector temperatures.  Acrylic, Plexiglas, PVC, ... will not.  Polycarbonates with a UV coating are readily available, and only a bit more expensive than the lower temperature plastics, so take the time to get the right stuff.

Plastics without a UV resistant coating will turn yellow with exposure to the sun.

Plastic glazing needs more support that glass to prevent warping as it heats up.

The Tank:

If using a used tank, be sure to pick the best one you can find.

Before spending effort on it, check it for leaks.

Clean it out well.

Sand and paint the outside with flat black paint.  Most paints are OK, but some use high temperature barbeque paint.

Be Careful About Insulation:

The common polystyrene insulation board (this is the "pink", "blue" and "white" stuff) will not hold up to much above 130F, and the batch enclosure temperatures will exceed this, and melt the insulation.

An example: http://www.builditsolar.com/Experimental/pinkfoam.htm

Polyisocyanurate insulation board works well, and comes with an alum reflective surface already installed.  Most lumber yards carry it, but may not know it by that name.  It is usually light brown and is typically faced with aluminum foil.

I've not tested the Reflectix reflective insulation, but I'm a bit skeptical that it will have a long life inside a batch collector.

Be Careful About Freezing:

Some people who have freezing winters just disconnect and drain the batch heater for the winter.  You just need to do this early enough in the season that you don't get pipe damage.  Insulation on the pipes will help protect them from a cold snap, and will also reduce heat loss.

Some batch heaters are designed to be used all winter.  They usually have some form of insulating cover that is closed when the sun is not on the collector.  These batch heaters must have very good insulation on the pipes, or the pipe will freeze for sure.

 

If you take a little more time and care with the construction, and use the right materials, the batch heater will last for many years, and need little attention.

 

Gary 10/1/06