Water heating versus space heating

Hi everyone, I was wondering if anyone could point me in the direction of any formal research comparing the outputs of Aquaponic Systems in cold / temperate climates when using solely water heating and / or solely space heating.

We have been experimenting with production outputs, growth rates etc with just passive solar space heating and electric heat pump water heating. We have noticed we still maintain reasonable production and good tasting produce even after whole plants freeze solid. I had expected to see the space heat not drop below freezing due to the thermal mass of the water temp being much higher. It appears this has a nominal effect, probably due to the rafts.

Nga mihi, (Thanks)
Aquaponics NZ



I haven´t read any specific document about the comparison of water or space heating. However, rather than looking at just “heating”, I advise you to considering “insulating” from the heat loss of your system. If you have massive heat losses (as it seems to be in your pictures) you will have a huge energy bill. If your goal is to maintain your plants under the sunlight but during the winter you need to spend loads of energy heating the water in a snowy landscape, you are probably expending much more than if you install artificial lighting and a well insulated greenhouse.



Thanks Ignacio. Yes its so hard trying to find the balance. We have 185mm (7.2 inches) of repurposed freezer room Polystyrene insulation panels lining the ground contact areas with an additonal 75mm (3 inch) wool fibre isulation on the sides. The actual water of the sytem is very well insulated so losses are negligible from the water mass. It is just the space above the rafts which is 2.5inch poly. Anecdotal evidence suggests that space heat, although when cold does effect growth by slowing, overall does not effect the quality or health of the plant. Maintaining the temperature in the rhizome has a more integral part, I believe, in the overall resilience and health of the plant…

Having said that, I will definitely be looking at ways to decrease the losses of space heating for next winter!

Nevertheless, it is probably a better option to heat the water. In this way the water flow moves the heat across the essential part of the system. If you try to heat the whole greenhouse, aside it is a bigger volume than the water (ie: you need more energy), you will have a much bigger surface of heat loss: anything that is not a part of your ecological system will absorve and conduct energy. The wood, the windows, the floor, etc. So heating the water is probably the best option.


I’m using geothermal loops in Arkansas maintains about 55^ F all year. Hardest part for us is the heat in the summertime. Since installing we have determined that we need more loop. Also remember that you need to be below the heat and frost lines to work.

in colorado I can tell you its much more efficient to heat the water. Me n robbie did a 50 x 30 x 18 greenhouse with only 83 lbs of propane thru the entire winter using a combination of solar water heaters and propane as a backup for bad weather. The trick is to get as much thermal mass as possible in the greenhouse so a water wall of drums heated and recirculating or your fish tanks in the ground under your beds like we did is the best way in colder climates. Throw in geothermal and you get it even lower but you will still need a backup heat source for prolonged cloudyness or cold nights. If you can get 80% or more of your top down floor footprint as water ie tanks or beds or walkways over tanks then you can get those kinds of insane climate control numbers.

Hi! Given the current structure of your system I’d recommend speaking to those guys and ask for their material https://www.kedergreenhouse.co.uk/ over your current structure - significant cost savings by better insulation and light diffusion also - Hope this helps!