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I have implemented a heating system for my 500 gallon partially inground tank that may be useful to some of you.  I've learned a lot reading these forums and appreciate when others have shared what they have figured out.

I live in the upstate of SC by the mountains and while we have a moderate climate temperatures often drop to the teens at night. If not heated, the water in the tank would drop to the low 50's which wasn't good.  I'm growing both catfish and tilapia in the pond.  

I debated using electric heaters, but I know how expensive they are to run as I've kept aquariums my entire life, so I came up with this method.  I also know my ability to screw stuff up and I visualized killing myself with a homemade heater.  

I've hacked this system together for this winter as I experimented with ways to make it work correctly and flawlessly.  Now that it's working without a hitch, I intend to rebuild it this summer/fall to get it out of the way and look better.  The current configuration has been working all winter without a single problem.

 I'm a terrible photographer, so I apologize for the bad quality of the pictures.

The key to the system is an Excel Vent-Free gas water heater available from Ebay which you can buy for $149.  They sell models for either Natural Gas or Propane.  Mine is the Natural Gas model.

Here's a picture of mine hooked up on the wall.  They're very small and can be placed directly on a combustible surface.  My greenhouse is a 16 x14 foot lean to against a storage shed at the back of our property.  I covered the wall of the shed with hardiboard sheets for ease of maintenance, so in my case it's not combustible.  

The way I looked at the gas heater was it runs at 100% efficiency.  If it's cold enough to warrant heating the water, any excess heat that doesn't heat the water will warm the greenhouse.  So far, the theory has worked out well.  I heat the greenhouse with a blue flame 20K Btu heater.  Between the blue flame heater and the excess heat from this unit, the greenhouse stays at a minimum of 65 degrees even on the coldest of nights.

At this temperature I've picked 6 tomatoes in the last two days and have bell pepper, green beans, lettuce, kale, and chines cabbage almost ready to pick.  It's a great joy on a cold, gloomy day to pick a fresh, ripe tomato!

Originally I tried to pump clean, filtered water from the pond through the heater and found that no matter how well I filtered the water, there was enough debris to clog the pipes in just a couple of days.  To clean the clog, I would have to connect a regular hose to the unit and blow it out under high pressure.  Therefore I decided on a closed loop system to heat the water.  

Also on Ebay, I found a beer wort cooler for about $75 which is made of 3/8" stainless steel tubing.  The current water container is just a temporary solution and holds about 20 gallons of water for circulating through the heater.  I was originally worried that the water returning via the red hose you can see under the pump would overheat the water in the container, but the cooler is very effective and the returning water is about 72 degrees which is the temperature of the pond water.  This summer I plan on replacing this container with a small, covered drum container and lid and re-position it out of the way near the water heater.

That's a normal sump pump from Lowes in the container.  Get one more powerful than you think you'll need.  The 3/8" piping in the water hoses, the beer wort cooler and in the heater itself really reduce the flow from the pump.  Look for a pump with a high head pressure.  It also takes a certain water pressure to activiate the heating mechanism of the heater.

The hoses you see are just washing machine hoses.  Don't really care for them as some of the 'brass' is rusting when it's submerged in water.  I'll probably replace with some hoses I make myself.  

The next part of this installation is a water heater thermostat controller from  Jehmco is a also a great place to buy Chloram-X for water treatment in bulk.  The controller defaults to Celsius, but you can change to view in Fahrenheit.   Mine is always on Celsius for a reason I'll explain in a minute.  This particular model cost me around $50 and is designed to handle a heater up to 800 watts.  In my case the sump pump is plugged into the control unit.  When the temperature drops, the controller activates the sump pump and pumps water from the container to the Excel heater which then activates the water heater.  The heated water travels through the 50 foot stainless coil in the pond and returns to the container.  The water temperature leaving the heater is about 105-120 degrees (I haven't really ever measured it).  When it returns to the container it has cooled down to the pond temperature.  

The last part of the puzzle is a timer that is set to turn on the controller every 30 minutes for 30 minutes.  The Excel heater has some type of internal safety control (not documented anywhere I could find) that turns if off after about 15 or 20 minutes.  It then will not come on again until you turn off the water supply and reactivate the heater by turning it on again.

Since the water temperature is below what's needed, the pump keeps pumping and the pond actually drops in temperature.  It took a few days to figure out what was happening.  To fix this problem, I installed this timer from home depot that cycles the thermostat on for 30 minutes and off for 30 minutes. I still get up to 12 hours a day of heating from the unit which is way more than sufficient for my situation.  If  you need more heating, you could go with a timer with shorter duration settings.


The problems I ran into that if you install this system you can avoid are:

1. Use 3/4" piping everywhere as it reduces the back pressure on the pump.  I originally used 1/2" pipe because the heater inlet/exits are 1/2", but I couldn't get the heater to reliably fire.  

2. Make your own hoses for connections since washing machine hoses are really 3/8" or 1/2" inch at best.  

3. I had to tinker with the two controls on the heater a whole lot to come up with a happy medium.  One controls the flow of water and the other controls the flow of gas (how hot the exit water is).  Mine is set to fairly low gas (exit water is cooler) with a high flow rate.  Now that it works, I never change the settings.  

4. Buy a powerful pump with a lot of head pressure.  It took me three pumps to finally get one that worked each and every time.

5. Learn Celsius.  The timer when the power resets always goes back to Celsius, so I've learned enough to handle the needed pond temperatures.

6. Plan to do a lot of tinkering to get your unique situation working well.  In my situation, now that it's setup, it runs without me having to touch it.

Hope people find this useful and I look forward to seeing how people can improvise and improve on this setup !



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Glad to see this discussion pop back up. Reminded me what I was going to be building this summer. I usually wait til November then throw something together.

I was thinking about doing more of a completely closed loop system with an air bleeder and a expiation tank.

Most tanks startup off so much water flow but I just got a install doc from them and they say the tank needs 20 psi to startup.

Similar to this but with a ½ 50’ beer wort cooler heat exchanger and the controller above.

I guess a combination of both systems.

Do you know how much it cost to run this each month in the winter?

I have the hot water tank, controller, pump and expansion tank.

Excellent info. I have just purchased a "portable" on demand propane unit from Home Depot. I am planning to set it up this weekend. Your post will save me a TON of time. Thank you.


I read your replys about building an on demand water heater. I live in the northeast and I have been searching for a solution to my problem of heating the greenhouse and heating the fish tank water in an economical way. Could you send me a little more info on how you built your on demand setup? I friend requested you if that makes it easier to exchange information.


Rich K

Don Cole said:

Excellent info. I have just purchased a "portable" on demand propane unit from Home Depot. I am planning to set it up this weekend. Your post will save me a TON of time. Thank you.


 I have been following this discussion and was going to set something up like this until I saw how much water pressure is needed to make it work. I live in Michigan and suffered last year (as did everyone) trying to heat my greenhouse.  My 1000 watt bucket heater ran 24/7 and barely kept up. This year I am doing some things differently.  First I made sure there are absolutely no/or minimal air leaks from the outside. I insulated he roof over the fish tank on the north end of the greenhouse and all of the walls since we have limited sun in the winter. The trade off makes sense. I have 3 400 watt grow lights that I run alternately at night to utilize the heat they put off. I have a wood stove that I run in the evenings and morning before I leave for work. There's also a thermostatically controlled propane radiant heater that maintains a minimum of 55 degrees when needed. My bucket heater only runs 7 hours a day in the fish tank. What all this is doing is keeping the temps up in the GH so the FT doesn't loose so much heat at the same time keeping the GH warm enough to grow a variety of plants. It has cut my energy cost for the GH more than half.

Here's an update.  I'm out of town or I would post a few pictures.  

I'm still using the setup.  It's still working great.  It keeps the water in the tank at a constant temperature. I did upgrade to a 40 gallon closed drum as the container.  

The only problems I've had are

 - some type of slime algae enjoys living in the pex tubing and slowly blocks the flow.  I blow it out by connecting to the faucet and it's good for another month or two.  I could put some copper in the water since it's a closed system, but haven't done it yet.  

- after a big ice/snow storm, we lost power for a couple days.  The water temperature quickly dropped to upper 50's.  After debating pulling extension cords down to greenhouse from the generator I realized I just could run the faucet to activate the system.  worked great. I still have the problem where the unit cuts off after run 10 minutes or so.  So, I just had to keep turning the water on an off for a while.


Thanks for the update James. I am going to set up a closed loop system with a portable on demand water heater. I am going to use 50 gallon closed drum as the water reservoir and 100ft of stainless steel coiled tubing as the heat exchanger for the 300 gallon fish tank. I figure that I will put the 50 gallon drum inside the greenhouse to act as a heat exchanger to keep the greenhouse from freezing. I will be insulating the greenhouse and the fish tank to try to prevent heat loss.

Thanks to all for posting this thread!

Rich K

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.


If I'm reading this correctly and you're using a 20 lb. tank a day you're talking about $300 a month in propane. Did I miss something here?

Don Cole said: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.

No, you read it correctly. My greenhouse is not insulated and neither are the fish tanks (900 gal.). The heater only runs when the water temp drops below the set temp (currently 73degrees). Now this is the first run with this unit and I have been testing it out. That being said If I lower the the temp set point to something more reasonable like 65 degrees and do the insulating I pretty sure I can cut the gas usage down by half or two thirds. I live in Phoenix, Arizona so we dont really have long cold spells. So far this winter it has been really mild with about a week and a half of 30 to 40 degree nights and low to mid 50's days. 


My 300 gallon tank runs between 65-70 degrees with a couple of different heating tools. Do you do any winter growing?

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