The extent of my experience with using a waterbed heater as a heat mat or soil heating device is what I've read over in the Greenhouse & Garden Structures forum ... and what I've read there is *don't do it* as it can be very dangerous and has been known to cause fires.

If others have been doing this with success, it would be important to know precisely how they are setting this up to avoid burns and/or fire.

Diane

....try reasoning with your homeowners insurance company if you should have a fire....I simply wouldn't consider this....

....as well as the safety of others who entrust a person's assessments and decisions....

Why not get a cheap waterbed mattress and set it on top of the heater, maybe only half full, and then put a smooth board over an old blanket on top to set your flats on. I'd only use something like that outside, and only with a ground fault interrupt switch at that. That way with the water in it and the gfci, even if it *does* catch fire, it's not likely to set the house on fire.

Lisa

well one must simply weigh it out...

I use a waterbed heater in the same way you would use heating coils as that's what a waterbed heater is, vinyl covered coils made to disperse it's heat to it's surroundings. Keep in mind that waterbed heaters usually sit on a plywood frame and are meant to reach temperatures of 100°. Not even close to the 72° I keep mine at. So here's how I did it.
I made a shallow framed box, lined it with vinyl and filled with a couple inches of sand. I put the temp probe in through the side of a soil filled flat like I use for sowing and set it on top of the sand. This is because I want the probe sensing the same soil evironment my seeds will be experiencing. I had it originally in the sand and quickly realized that the probe was sensing the direct heat and would turn off almost immediately, not enough to warm the soil in the seedling flats (duh). If you haven't got the skills or tools (luv my bandsaw!) to make a wooden frame, try one of those big under-the-bed plastic storage containers. It would have to be big enough for the heater to lie flat.
It's worked great for me so far. I made it back in Nov and it's warmed hundreds of little seeds. Not one of them has caught on fire!

Kris

I have used one in the same manner as Kris. Works great.............Tom

I don't know anything about waterbed heaters but this year I experimented with an old heating pad. Let me explain how I safetly used this. I usually start a tray of begonia tubers and caladiums and they are very slow to start. This year I got a permanest tray (one of the sturdy plastic trays, not the flimsy black plastic trays that are prone to developing holes) and put the heating pad under the tray on a GFI plug with a timer to run 6PM to 6AM when someone is home. There is no danger water can come in contact with the pad because with these tubers I only water them slightly once a week. I change the tray so it is completely dry after watering. So the tray and heating pad do not come in contact when water is present.

So far I can see that it has helped my begonias and caladiums start much quicker than other years. I thought I'd contribute what I've done for other people to try. Be sure to be safe in whatever you try. Remember, I would not recommend doing this with a cheap black plastic tray or in any situation where water is present when the pad is on.

enter variables: the integrity of used equiptment,knowledge pertaining to applicable areas of electrical devices as well as exceeding the design of a product....

....I don't know...this a hobby,I think...why do I sense issues are overlooked in our reasoning....

I shall suggest if higher media germination temperatures of the specific cultivar is required, work with the volume (container cell)and media selection....

Kris, I dont get this "I put the temp probe in through the side of a soil filled flat like I use for sowing and set it on top of the sand. This is because I want the probe sensing the same soil evironment my seeds will be experiencing"

What kind of flat, like a black bottom tray, one without cells. Do you bury the probe in the soil? What if the soil is damp?

Gloria