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Have you had any luck connecting different size heat mats to the same controller? I have several small mats and one large mat and even tho the combined wattage is well within the spec, it just doesn't work right. Fortunately the small ones seem to provide just the right amount of heat without the controller, but it's one of those little things that just bug me. I love 'em anyway! Great article and timely. (Now where did I put those torenia seeds?)
Hmm, that's strange. Mine are the same size. I guess that wouldn't have occurred to me. I wonder if you could use it to your advantage, though, if you know which one runs warmer (as long as it's consistent).
If, for example, the little one runs at 80 degrees when the controller is monitoring set to 72 degrees with its sensor stuck into a pot on the big mat (I'm making up these numbers), you could put seeds that need an extra-warm start on the little mat and put all the seeds marked "germinate at 70-75 degrees F" on the big mat.
But I guess we've learned something... thanks!
Tip for anybody considering purchasing multiple heat mats and a controller: Get heat mats that are the same size!
One other thing I'd like to mention. The manufacturer of these heat mats, HydroFarm, stands behind their product 100%. The first mats I bought (the small ones) died after just one season. I contacted the mfr and they replaced all five of them with no question. Didn't even ask for a receipt. Apparently there had been a problem with a particular run of that size mat. They were very nice and I wouldn't hesitate to buy more.
Thanks Jill - this article spurred me to take the leap and purchase a 2nd mat and a thermostat yesterday!
The first mat is the ubiquitous HydroFarm 10x20 mat; the second one is coming from HarborFreight, so I don't know what brand it will be yet. I'm anxious to get them both set up and the thermostat in place - I don't know if I really need the thermostat since this room (my office) stays a fairly constant 65-70 degrees, but I suspect it'll come in handy as the days start to warm up and stronger afternoon sun will bring more warmth in here.
I've used heating cables in the past (mine are probably close to 20 years old, and I chose them over heat mats because of the cost.) A word to the wise for anyone who chooses cables: make sure the cable doesn't touch or cross itself anywhere because the heat can cause the cables to melt at the touchpoint. I recommend using regular masking or electrical tape to hold them down after you lay them out in the pattern you want.
So are you using the two mats one on top of the other in order to increase the heating capacity? My single mat seems to be too cool for my Palm seeds. Should I get another to layer on top of the other mat?
No, I'm using two mats side by side, to cover my 4 foot wide shelf.
I have no idea about the advisability, safety-wise, of layering 2 mats. Maybe you can find a spot with higher ambient temperature, so that the 10-20 degree increase from the heat mat will be sufficient? Try testing the actual temperature by sticking a thermometer into the potting mix around the seeds, so you know what's going on.
My problem tends to be more along the lines of not letting the soil temperatures get too high, since my basement light shelves aren't that cold. That's why I use a controller.
Jungleman, I can't guarantee that they're all like this, but the small mats I bought from Harbor Freight run quite a bit warmer than the HydroFarm small mats. I used them for starting corn in 3" peat pots last year and the extra heat worked out really well. For other seeds that didn't need so much heat, I rigged spacers between the mat and the tray. (I buy a LOT of thermometers!) :-)
