Rocket stove mass heater to keep Aquaponics water warm in winter?

Hi all,

I am planning my aquaponics setup. I am in Central Texas, where we do get a little cold in the winter, though intermittently. Occasionally (not this year, but last year), we had 3 days in a row where it did not get above freezing! Highs in the 20's, lows in the upper teens. I am planning to dig trenches about 2 feet deep, then build a ferrocement tank in which to grow Tilapia. I know they like it to be around 80 degrees. Being in ground will help keep the temperatures up, but I'm sure I will need additional heat, and I really don't want to run electric tank heaters. The whole setup will be contained in a hoop house, about 20 feet wide, 36 feet long. I'm toying with a couple ideas to heat the water in winter, and would love to hear your thoughts . . .

1) Build a solar water heater and have a temperature controlled valve to maintain 80 degrees. The problem with this idea is what would I do on cold, cloudy days? I've also seen quite a few DIY water heaters that get pretty warped if you use inexpensive materials (I would rather not use expensive materials for this project). Also, don't know if I could really get the temps up enough.

2) Build a rocket stove water heater like the one here: www.youtube.com/watch?v=YTnr8ua54Uw . Again, have a temp-controlled valve to maintain temp.

3) Build a rocket stove mass heater, where the stove pipe would be buried underneath the fish tank. Since the tank will be ferrocement, the bottom of the tank would be curved to cover the pipe, essentially encasing the pipe in cement. I like this idea, too, but since I've never had a rocket stove mass heater, I don't know if the stove pipe would get too hot for the fish. I certainly don't want to cook them in the tank! The tanks (2 of them) would be long tanks, about 24 feet, and about 750 gallons each, so that's a lot of mass to heat up. **Question: can I run a T off the rocket stove, then have 2 flue pipes? That way each tank will have a pipe underneath it, with a flue going to the outside on either side of the hoop house.

I'm fairly certain that the tanks will be cool enough in the summer, as they will be buried and the hoop house will have shade cloth rather than plastic, and plenty of side venting.

Eric

24 foot long, 2 foot deep, and only 750 gallons?? that is mighty skinny. I understand they fit in a tunnel floorplan really well, but that is a LOT of surface for the amount of water (cools quickly) and every ferrocement tank I have seen is round for strength.

Edit: I see you are in Texas, you can trench and gunnite foundation walls, nevermind on the strength problem.

You definitely do not want to T the flue--no way they would draw evenly and one would likely suck in COLD air when running.

Electric tank heaters are fine if you need them a couple nights a year MAYBE. After that you are right about wanting another source. But listen to Erica and Ernie's last podcast about all the problems with running a rocket stove in a greenhouse--they aren't little problems.

I still haven't figured out what I am going to do, I was planning the same thing but don't want to now. I will either pull heat from my house (I have a wood-fired water heater in the winter) or put a rig like Geoff's outside the greenhouse (If I can figure out how to make one freeze-proof).

Yeah, I guess long and skinny would make for a lot of surface area. I was thinking that might help regulate temps in the summer, but I guess it might make it very hard to keep warm enough in winter. Maybe I'll go for a single round tank of about 1500 gallons. Then, if I built in a heat exchange coil in to the tank and connected it to a RMH, perhaps that would work. Thanks for the advice on the T for the flue. Will not do that.

Summer regulation may be your bigger problem, so it isn't a bad plan (I didn't notice the TX location until after).

It would be relatively simple to build a heater like Geoff's and add a simple T-stat triggered pump that circulates it through pex coils in the tanks. One big thermal storage tank like from http://www.builditsolar.com

Eric Gerber wrote:Hi all,

I am planning my aquaponics setup. I am in Central Texas,

Eric

Why are you trying to fight nature? ALL Tilapia is illegal in Texas without a permit. It is a serious pest, and it doesn't like our weather (above ground tanks aren't subject to the geothermal cooling that lakes are, your water temperatures will rise to reach equilibrium as your air temperatures rise. )

Which brings me to my next point. Texas Perch, Bluegill, and Catfish. All of these fish are accustomed to living in the Texas heat and taste delicious. Not only that, but you can go out fishing and catch your tank stock.

If you absolutely insist on Tilapia and you get the permit, you could also geothermally maintain the temperature in your tanks. Dig down below the freeze line (rent a backhoe) and bury several water holding tanks with a volume greater than that of your fish tanks. These will make up your heat sink and cool/heat your water. (The temperature below the freeze line around here is 68 degrees year round) circulate water from this tank to your fish tanks to maintain water temperature. By controlling the flow, you can control the temperature and recreate the environment these fish can thrive in. Another advantage is that you can stock more fish in your above ground tank because the plants have more time to filter it.

Eric G, actually every buddy ! : Before I weigh in here I just wanted to send everyone to You Tube (10 points to everyone who flinched ). Its O.K. I'm sending you to one of
the best channels there. At U-Tube type in web4deb and attempt to scroll down to the Rocket Mass Heater Playlists, because Web4deb is so very interesting over 1/2 of you
will get lost on the way there, but thats alright you will learn a lot.

I may have something to add after you'all come back, if I can get a word in ! Big AL

For the good of the Crafts ! Be safe, keep warm ! As always, your comments/questions are solicited and Welcome ! Pyro AL

The simplest option, as mentioned above, is to raise a different kind of fish. Catfish are incredibly adaptable. Perch are pretty good. Or you could switch between trout (winter) and a warm weather fish (summer).

If you don't want to heat with electricity, I would recommend insulating and air sealing the heck out of your system. Especially air sealing, since evaporation will take all your heat .

2-4" of insulation on all sides of your system, include the top of your grow beds (let your plants sit in net pots in holes cut in the insulation) will do a lot. If you make the beds out of insulation with a wood structure and pond liner inside, that's a good option.

My website will have more ideas for you over time, but not there yet.