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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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Good article. I'm toying with the idea of a hot water heater for my system. I think my water in my sump is pretty clean so I'll probably try an open system first. As for you restriction issue, you could split the water flow to two wort coolers and have 3/4" flow. Also is the 1/2" limit on the heater causing a problem?

I thought about using two wort coolers until I finally got a pump with enough head pressure to work with the one.  It's been remarkably stable setup since I've gotten it working, so I'll leave it alone.  

Just a warning.  I thought my water should've been clean enough but it wasn't.  

I went to Ebay and found the heater at a current bid of $109. I'm trying to find out the pressure of my pump to be sure I can use it. I really like the DC pump I'm using so I don't want to change it. Pumps all the water I can use up 10' on pump level 2 and it has 5 levels so I'm hopeful I can get enough pressure from it. If I want to keep my tank water at 80 can the heater be set at that low of a temp? I'm spending $100 a month to heat my water so I need to make a change.

The water temperature is actually controlled by the temperature you set on the Jehmco heater controller.  Based on the pond temperature, it'll turn on and off the water pump which turns on and off the water heater, so it's really kind of irrelevant what temperature comes out water heater itself.  I haven't measured but I assume the water coming out of the heater is in the 105 - 120 degree range.  Pond stays at 72 degrees exactly.

I know that there is used oil burning hot water tanks out there that can be used as well. A man that breeds koi here in thunder bay uses them to heat his pool sized ponds all winter long.


What is the make/model/flow rate of the pump you are using for your heating setup?

I intend to build a closed-loop heating system similar to the one James built using similar parts and equipment. I ordered the Excel heater and stainless coil from Ebay yesterday and the controller from Jehmco as suggsted.

I have a small system in an unheated part of a basement in Brooklyn, NY.  I have to heat approximately 400 gallons of water as follows:  1 x 100 gallon FT, 2 x 65 gallon FT, 1 x 100 gallon sump and my GB’s and totes I estimate hold close to another 100 gallons amongst them.  Currently, only the two 65 gallon FT’s are stocked with forty-five tilapia ranging between 2-5 inches.


Presently I have two 400w heaters, one in each of the 65 gallon tanks. The room temperature has been varying between the upper 50’s to the mid 60’s for most of the winter so far and the water temperature varies between 65°F-71°F (fish still active and eating). I figure the heaters are probably always on so I don’t trust them surviving very long. Then there is the issue of power usage with the heaters and all my lighting in the winter coming from T5’s.


The current outside temperature is 10°F going up to 20°F. We expect similar low temperatures for the next few days. I believe this will be the first time this season we will be have this long spell of consistently low temperatures. Until I build the heater, my backup will be a forced air electric heater.  I used it last night for the first time on a low setting and the room temperature was a steady 62°F and water temperature 71°F.


I will only use the forced air electric heater sparingly and when my grow lights are off so as not to overload my outlets.


I will update the forum on my progress.

I am in Michigan and my basement stays around 50-55 degrees. I have 2-45 gallon aquariums and another 75 gallon FT.

I use 300 watt heaters in each and they don't run continuously. I have 1" foam board around the larger tank. I did have it around one of the aquariums but don't any longer and it still stays warm.

James' system seems like overkill for a basement system but I am considering it for my GH as I primarily use the heat from the FT to heat the GH most of the time except extreme temps (like right now). I covered my 3 IBC GBs with a mylar low tunnel and between the grow lights on at night and the warm water running through the beds (2media and 1 DWC) they stay plenty warm but a more economical way to heat the water would definitely be nice. Right now I'm running a 1000watt heater 24/7 and it barely keeps up. I have a wood stove but it requires someone to keep it going. I also have a thermostatically controlled propane radiant heater but it uses a lot of gas so I don't use it as a rule. My GH is only 8 x 22.

Here are some of my goals and reasons for going with this system: 

  • Eliminate the use of the electrical heaters altogether.

  • Add more grow lights when I no longer use the electrical heaters.

  • Keep the room temperature in the mid-sixties and the water temperature in the mid-seventies at a minimum during the winter.

  • Grow my plants in the backyard earlier in the spring and later in the fall while maintaining a decent water temperature. 

 I started the system this past June and by early September, I had to stop growing outside because the water was getting too cold with just the two heaters I mentioned earlier.  

To lengthen your outside grow time just cover your plants in a low tunnel. Easy to build and cheap.

I really like this heater setup. I also live in Upstate south of Greenville.  Our greenhouse will be 14’ x 24’.

We have 550 gallon FT and 430 gallon sump tank. Sump tank is in the ground about 5’.

I just ordered the Excel Vent-Free copper heat exchanger off ebay.

I was thinking about getting the ½ beer wort cooler for better flow and less pump.

How is your setup still working? Thanks for sharing your setup.

As you are well aware, haven't quite needed it lately as it's been 96 degrees every day the past two weeks.  

I never did have any problems with it as long as it was on the timer.  It worked great and kept the water at a constant, even temperature.  Going to set it up so it's not in the way for this fall.  Too hot to do it now !  

Good Luck !

Yes we sure do not need heat right now. I am trying to keep my fish tank from getting to hot.

Thanks for the info.

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