Richard,

Here is a write up on how it works. I hope it helps. Let me know if you have any questions.

Parts list:

Ecotemp L5 instant hot water kit: It comes with a 12vdc pump, heater unit and, strainer

55 gallon barrel

12vdc power supply

Dwyer TSW 160 or TSW 250 temperature controller.

100’ roll of 1/5” PEX tubing

6’ of dishwasher drain hose

Two ½” valves to isolate the PEX heat exchanger

Misc. hose fittings

The Ecotemp L5 is a 5 liter per minute water heater that uses propane from a standard BBQ grill tank. It starts heating when water flow is detected. I used the Dwyer temp controller to start and start the pump at the desired temp. The PEX tubing is a thin wall tubing that is rated for residential hot water distribution. It doesn’t have the same heat transfer as a stainless steel coil but is way cheaper and easier to get. I used the barrel as a reservoir for the heater and circulated the water through the heater, PEX and, back to the barrel. I think this helped with the heating because as the water in the barrel warmed up the heater output temp increased. This in turn allowed more heat to be transferred to the fish tank through the PEX.

The system works perfectly and was able to raise the temp of the three fish tanks from 57 degrees to 70 degrees in about 5 hours. It has easily maintained 73 degrees in the fish tanks when the greenhouse temp was in the high 30’s. I built mine on a two wheeled dolly so when not in use I could store it out of the way. It uses a standard 5 gallon propane tank per day when the temp is in the 30’s. My fish tanks are not insulated and the greenhouse is not heated yet. I think if they were I could probably get two days per tank. I also have the temp set a little high and could probably gain a half a day by lowering it to 65 degrees.

This whole system cost about $300.00. The only thing I didn’t have to buy was the barrel.

Don