There is no doubt that the mats with thermostats work far better as they keep the temperature constant based on the soil temp, not the air temp, so don't over heat the soil. And thermostats are available to add to any mat set up if interested.

But with what you have you can't use one mat for both crops as their needs are so different. The pelargoniums will germinate fine with your normal air temps so use the mat just for the beppers and have it on just at night when the temps are so low. That will give them approx. enough heat to germinate but it will just take them longer to do so.

There are many other steps you can take to control the temp in the immediate germination area - tenting around it to restrict air flow, even a cardboard box lined with foil and a small incandescent bulb can help - less air to heat means warmer temps so no need to try to control the temp in the entire garage.

Here is a link to many of the previous discussions here on "how to use a heat mat": http://www.gardenweb.com/gardenweb/query/using-heat-mat/topic=seed

You'll also want to do some reading on the problems using a dome can create and how to prevent them.

Dave

What counts is the soil temperature. If you bury a thermometer in moist soil in the planned sprouting area, what is the temp without the mat? The temp of solids fluctuates less than air temps.

Tips for more even temps: Place the mat on insulation - a thick sheet of packing styrofoam, for example, or several layers of cardboard - with some "thermal mass" above it. "Thermal mass" can be anything dense that will warm and cool slowly, such as a couple of inches of sand or aquarium gravel in a tray, stone or ceramic tiles. Insulate around the edges of the whole stack with more styrofoam.

Place the seeds, dome and tray on top of the stack and under the lights if you are using them.

Run it with everything - minus the seeds - to figure out how long you need to have it on.

Thanks, I ended up purchasing a thermostat, found a pretty decently priced one! I set it at 73 degrees and it's doing a good job at keeping the soil even for my pelergoniums.