Small greenhouse heating

[Aceetobe]

So I just got a small greenhouse from craigslist.

It is 4'x4'x5'

I live in San Diego, and so this greenhouse is going to be mostly for my warm growers (tolumnias, catasetinae, etc). I will need a little bit of heating for it, as our winter temps will drop down to 40F or so for a couple months. So I'm thinking for the most part I'll need about 20F night heating in 80 cubic feet. I would like it waterproof, because the greenhouse is square, all the racks are on the perimeter, and it doesn't have a standard "isle".

Anyone have any ideas?

[Aceetobe]

Couple quick ideas -> insane or not?

First one was that I could get a 30-50 gallon plastic tote, and run a combo fish tank heater/pump and place it in the middle. This is obviously waterproof, and has the added benefit of using the water as a thermal mass.

The other was something along those lines, but running soil warmers through gravel or something in the baselevel of the house.

[RonCo]

Assuming you want to heat your ghouse to 60f on a 40f night, it would take about 2300 btu per hour if the hosue is made of a single layer of glass or plastic.

Heating with electricity that would take about 675 watts per hour. You get 3.41 btu of heat per watt of electricity.

This is a good starting point for how much heat you need. Now the challenge is to find something that is safe to use in a wet environment.

Aquarium heaters would be safe if you can find one or several that are large enough.

Another thing that comes to mind is quartz work lights like they have at Lowes and Home Depot. You would have to shield them from any direct water spray with maybe a piece of sheetmetal but you would need to have good air circulation around them. A small muffin fan would help keep temps even.

I recently bought one of the oil filled Delonghi heaters from Lowes for my little greenhouse. It's rated at 1500 watts and works like a charm. It comes with a thermostat and has three heat ranges, 700 watts, 800 watts and 1500 watts. It was less than $40. It's fairly safe but you couldn't turn a sprayer on it.

Ron