Water doesn't hold a great deal of heat. (not talking about phase change)
One cubic feet = 62 lbs.
1 BTU = one lb of water rising one degree F.
a 1,500 watt heater will give you over 5,000 BTUs per hour.

Water feature in a greenhouse? great idea!

dcarch

Hi
Have a 3x6 x3 foot deep pool in the shadehouse as well as a 150 gallon aquarium and a marsh garden,. These are all attached to the outside 5x10 water lily pool. Heated with aquarium heates mainly for the fish but added a waterfall
last March hopefully to provide some heat .
I think I'm going to remove the 3x6 for several reason.. It takes up way too much floor space,is too shaded to grow water plants well and of course it's almost impossible to view into it. The aquarium has worked very well, not only provides warm water but allows growing submerged plants and very easy to view the interior.
I use it for the resevoir for the waterfall which is7x10 feet. It drains into the marsh area which acts as a channel to return to the lily pool. The main problem there has been unbelieveable growth !! lol Way too much shade for the submerged plants. Another is gardening with a ladder lol.
very inconvenient, I made the waterfall from expanding foam painted with acrylic paint. Got a huge "rock" wall with very little weight and low price.
This also functions as a semi-hydroponic "seep" wall for epiphytes mostly orchids.
All things considered , I'm rather pleased with it but there have been some problems. Have no idea how it works as a climate moderator as it's been too warm for a test.
I wouldn't make a pool that deep ,way too hard to clean,somehow everything that falls goes in the drink lol.
Above ground is far more useful. gary

Water is great as a thermal mass compared to air.
A deep pond will stay at around ground temperature, where a shallow pond will be much cooler.

Gary, would love to see your wall if you have pics?!

Hi
Looks like i might get a test of the water heating system lol. May get a frost tomorrow night. In any event
it'll be the coldest since installing the system.. I feel certain that it will be frost proof and keeping the water temps up will be no problem. but there will be cold pockets and I have plants rated at 60's lol. Will give me some idea of what really happens.
root I took pix while making the wall but none came out. It is still not completely planted and there are still large areas of styrofoam showing. I planted whatever i had leftover on the wall to see what works. Not too exciting to look at yet but it's getting there lol Hope my heating system works!!!! gary

I have a pond across the end of my 6 x 8 HFGH but built it to grow tropical plants, not to heat greenhouse. It does not heat the greenhouse.

I have multiple other ponds, would not be without water features. Love them.

buyorsell888, do you have any pictures of that? What else do you use to heat the greenhouse there?