Heat Mat / Seedling Mat Questions

[estación seca]

Water bed heaters work well as under-mat heaters, and are designed to be somewhat moisture-resistant. A pan filled with sand can be placed over a mat to diffuse the heat to an area much larger than the original mat. I have put a heat mat under a metal oil drip pan, bought at an automobile parts store. I lined the pan with heavy-duty plastic (to prevent water corrosion of the pan) and filled it with sand. I set the plants on the sand.

For colder areas this can be enclosed in a topless and bottomless box built from a sheet of polystyrene house insulation. The foil side goes inside the help reflect light. A light can be suspended overhead. The top can be covered with clear landscape plastic to retain heat yet transmit light.

[twinofmunin]

Oh, and a tip -- don't be silly like me, and put your heating mat on a surface that'll heatsink all the warmth away. It took me a few days to figure out that I needed to put an insulating layer (in my case, cardboard) between the mat and my granite windowsill. Sometimes I am not so quick, ha. If your windowsill is wood or some other insulating material, you won't really have this issue.

[Diane56Victor]

Ive seen Youtube videos where a heating cable is laid under a bed of sand and plants placed on top of the sand. I guess watering the plants and sand would give a somewhat increased humidity.
This is a bit more involved than a plug in on a windowsill but as a greenhouse/shadehouse thing it might go some way to solve the heat/humidity issue.
Here is a link to one video.
How To Build A Heated Propagation Bench - YouTube

[fooferdoggie]

the heat pads are not expensive. I use mine with a Thermostat so it will not be on when not needed.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1