This is my tank heater

UPDATE:
2013/01/18
Several months ago I built this heater with a stainless steel element. Its actually refered to as an Incoloy type water heater element  (120-1500-ELD.

You can purchase them online here at http://www.plumbingsupply.com/elements.html

This heater now floats in the sump tank.  Its very important to add something buoyant at the end opposite the cord so that air bubbles leaving the element do not get caught in the small area where the element screws into the plastic housing.  Even this very small amount of exposure will burn out the element.

 


Previous Designs


 2012/03/19
Today I made the mistake of unplugging my pump while the heater was on.  PVC smoke quickly filled the room and the element died.
.
Here is my new design.  Its made of 1" galvanized pipe, but the element will still self destruct withing seconds if its run dry so I have moved it to a position below the level of the sump tank.  The outlet is above the fish tank so it will not draw a siphon but the water level will drop to the level in the sump tank.
If I should loose the pump the water will boil inside the pipe, but this galvanized pipe will not burn.
The thermostat can not operate at boiling temperature, and will still burn and self destruct within seconds if the water is not flowing.  At least this will prevent heating galvanized pipe. - Just looking for a bright spot to an unpleasant situation...

I will not be using the Honeywell Thermostat because the water changes so slowly that I can regulate it as I wish by flipping the switch on and off.  The temperature changes by about 4F per day.
 
If I ever choose to hook up the thermostat I think I may be able the use the high cut off temp as a safety.
But there has simply been too much to do.

My plan is to use an 1-1/2" PVC elbow to cover the electrical connections.

Original Post:
This is my heater. It uses two 1500W elements in series to drop the current down below 8A which is the max amperage my Honeywell 675 thermostat will handle.  In this picture I am using only one element without the thermostat in order to deliver more heat.
Its an inline flow through heater. It works very well and should last for many years. As long as water flows through the heater it will not over heat.  I would like to add a relay that will only allow the heater to be on when the pump is on and water is flowing.
The elements are rated at 1500W, but measurements indicate only 1300 W are actually being used when only one element is used, and when placed in series 750 W is drawn.  I attribute the difference to line loss even though the building is wired with 12 gauge.

The elements screw into 1" female adapters.  The housing is made of 2" PVC.  When I put my hand on the heater, I can just barely feel the heat, but over time it will maintain my 1000 gallon system which is well insulated.

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