I looked into doing this back when I was a new fishkeeper and had bettas in one-gallon bowls. I gave up on the idea because couldn't figure out how to keep the temperature steady (and when I was able, moved the betta into a tank w/a regular heater). It might work going on/off at regular intervals, if your room temp doesn't fluctuate? sounds like you have tested that part out.

I doubt it would crack the glass, as you're not drastically changing the temperature suddenly- but let somebody more knowledgeable chime in on that.

 

I think you could get it to work, but after your all done you would still have a real kluge of wires and so on.

Something to consider would be to setup a sump for all the tanks, and plumb that as a filtration and circulation system. You'd ideally want to fit each tank with a small overflow. Here is an example of a bulkhead overflow kit - Bulkhead Kit Assembly, sch. 40 by Pentair Aquatics - AquaCave.com

As you can see these would require drilling the tanks. Here is an example of the glass drill needed - 38mm, 1.5 Diamond Coated Glass Drill Bit / Hole Saw for 3/4 sch. 40 Bulkheads - AquaCave.com and you might want the guide device - Diamond Glass Bit Guide with Suction Holder - AquaCave.com

Now I know this is not at all what your planning, but think of the advantages. All the tanks have the same water, and can be heated with a single heater in the sump and you have a lot less in the way of filters to maintain.

Drilling tanks isn't too difficult if you take your time and are careful. Practice a couple of times on some scrap glass first,

 

Dave's idea sounds like your best bet to consolidate so many individual tanks. It will require a bit of planning and work on the front end, but in the long term, heating, filtering, water changes, etc, can all be done in the sump tank instead of doing 14 individual tanks with 14 individual heaters and whatever else equipment you would have.

Maybe head out to your local PetSmart or Petco or LFS and ask how they provide filtration for all of their tanks to get an idea of how it is done, then scale it down at home.

 

I would not recommend heat directly on glass. The heat seems like a minimum but that is more due to the total size being small rather than the heating wires not getting hot. First check how hot the individual spots on the pad will get?
Hot enough to not want to hold them and I would expect it to very quite close to breaking the glass when one small portion tries to expand unevenly.
Perhaps consider an option?
How about placing the pad inside a raised area under the tanks where it will not be smashed by the weight and will heat the airspace. The air can then heat the tanks above much more evenly. I'm thinking of something like a ring built out of 1X material to raise the tanks, heat pad inside the space with a temperature controller with probe to go out to one of the tanks to monitor the temp and control it as the ambient temp changes.
I built something of this sort but used lightbulbs under a plastic tank. The bulbs would have been too hot directly on the plastic but the heated air spread the temp around and worked much better. In fact, a cheap way might be to use some of the older large Christmas lights using 4 watt bulbs if they are handy. Just watch out for too much heat in one spot but give them more airspace to spread it?

 

Hi, I'm back with another terrible idea. Hopefully, not as bad as my other thread

Funny. :grin2:
Other threads could benefit from the same preface. LOL