Well, the classic is a solar heater with a sky-facing panel, a water tank, and a small pump. Even a small one would be more than adequate for a greenhouse, but likely more elaborate then you are looking for.

Another would be geothermal heat, but the drill rig required to get that deep would destroy the greenhouse, your back yard, and probably the house too. So that's out.

The Kandle Heater sounds like it burns candles?

Dennis

P.S. In a greenhouse, you might consider some thermal ballast, like a flat water tank painted black. It would function like the solar heater but without the separate panel and circulating pump. Prospective problems: it might not be enough, and it could occupy quite a bit of internal space.

I have a couple of containers filled with water that radiate heat during the winter and I use bubblewrap on the back wall only. I do not use a heater since it is always hotter in there than outside.

Our winters also do not get super cold so it is not really necessary (Im in CA).

If you can find a nice compact solar heater that would collect the energy during the day and run at night when cold, that would be the way to go. I am just not sure there is one that is reasonably priced (at least I have not seen one in my searches).

This post was edited by RonnyB123 on Sun, Aug 17, 14 at 12:13

Dennis, yes, Kandle Heeter is the trademark name for a system using candles, either wax or oil based along with a series of terracotta pots and an iron core to provide and preserve the heat energy from the fire, and dispense it over time.

I guess it is based on the ceramic tile stove concept. It looks like it make sense, though I have never tried it. You can serach Kandle Heeter, to see what I am talking about.

I am also thinking that that CO2 released in the burning might be beneficial for the peppers, from what I understand the Carbon Monoxide should not harm plants, and would actually convert to CO2 relatively soon after I open the door in the morning....

Again, I am talking about a 5 x 7 ft greenhouse, and would bring the plants inside the house whenever temps were going under 25f.