You'll burn much more electricity trying to keep that big an area up to the right temp and might be tricky arranging your overhead lights. It takes much more electricity to heat all that water to the correct temp and keep it there than it does to just heat the bottom of a few seedling trays.

But if you have that many seedlings to make it worth it, yes it will work. You will still need a soil thermometer to check the temp in the soil cups - that's the advantage of just using the heating pad - it has its own thermometer attached you can just stick in the dirt. ;)

Dave

Use an electric blanket. It is a lot cheaper on electricity, and will warm a lot of plants. I use one for starting my pepper seeds and it works great. Peppers need 80 degree soil to germinate, nd I usually start about 1500 or so seeds. Hope this helps!