While a proportional thermostat (helix, herpstat, etc.) with a backup on/off thermostat (ranco, johnson controls, etc.) is usually best for any herp setup not everyone wants to go down that path or has the money to do so.
Alot of times I see new keepers with entry level on/off thermostats that alone in my opinion just aren't enough piece of mind for your animal(s) and vary temps too much as the heating source is either fully ON or fully OFF, no happy medium. Also on/off thermostats or proportional thermostats can fail in the on position, hence the need for redundancy by having a backup. If you ONLY have a proportional thermostat or one on/off thermostat you run the risk of the unit failing and potentially harming your collection no matter what brand they are. They all run the risk of failing. So always have a backup.
For an affordable and reliable alternative to two on/off thermostats or a proportional thermostat and on/off thermostat backup, you can use a rheostat with an on/off thermostat as a backup.
The most affordable and what I would consider bare minimum for anyone keeping herps is a rheostat/dimmer in combination with a lower end on/off thermostat (500r, bah-1000, etc.). This setup to me is safer than a proportional (helix, etc) or on/off (ranco,etc.) alone.
With this setup the easiest rheostat to use is at your local Walmart or almost any superstore for around $10. A in-line dimmer switch:
Entry level on/off thermostats can be found at a number of herp stores such as Big Apple Herp, Bean Farm, or even at reptile shows for around $30. (I apologize that I don't have a pic as I use Rancos or Johnson Controls on/off thermostats only)
Setup is fairly simple. Using just the dimmer set the temp to a couple degrees warmer than your desired temp. Think of this as the MAX temp you ever want your heat tape/rope to get for your herps. Then connect the dimmer to your on/off thermostat and then set the on/off thermostat to your desired temp. If either one should fail in the ON position the other is the backup and in most situations due to how they are structured the rheostat doesn't fail in the ON position.
Keep in mind the rheostat is setting the maximum amount of heat provided on the tape or heat rope. So if for instance you set it in the summer when the room is warm when winter comes and the room cools down you might need to adjust the dimmer to hit your desired temp.
Now something a bit more complicated. What if you have a rack system and ALOT of flexwatt or heat rope connected to an on/off thermostat and you want to use a dimmer with your on/off thermostat?
I personally like using an on/off in combination with a rheostat for all my hatchlings and subadults. The rheostat makes for a smoother temperature curve and also helps to keep my electircal bills down as the heat tape isn't going fully ON when the on/off kicks in, thus using less electricity.
The problem with the dimmer model above is that most models are limited to 300w. While this really corresponds to quite a bit of heat rope/flexwatt sometimes more is needed for a full rack system.
For situations like this I personally like to spend a few dollars more and make my own dimmer/rheostat.
Most items can be picked up at your local Lowes or Home Depot and putting it together is easier than you might think.
Here is what you'll need.
Supplies:
single gang work box <$1
work box cover <$1
single pole dimmer switch(600w is common but 1000w is also available) <$10
6ft extension cord <$2 (grounded versions cost ~$8)
Total = $14 ($20 grounded)
Tools:
wire cutter/stripper
philips screwdriver
3 electrical caps (usually come with the dimmer)
utility knife (or a razor blade)
electrical tape
First cut the extension cord in 1/2.
Then pop two inlets into the work box using the screwdriver and thread in the wire.
Using the utility knife separate the wires.
Find the "hot" wires connected to the wider plug (polarized) end of both the female and male ends and strip the wires. (note: the wires usually have some indicator to denote one from the other, usually markings or ridges)
Using the wire caps and the dimmer connect one lead on the dimmer to one wire and the other lead to the other on the dimmer. Essentially causing the "hot" wire to pass through the dimmer.
Next strip the other two "neutral" wires.
Connect the "neutral" wires to each other with the 3rd wire cap. Essentially connecting them back together.
It should now look like this:
If you are using an extension cord with a ground wire you would connect the two grounds to the ground on the dimmer with a wire cap. After all caps are in place secure the caps and the ground wire (if left bare) with electrical tape.
Next pull some of the wire back through the work box and put the dimmer in the box.
Screw it in place with the included screws with the dimmer.
Lastly put the face plate over the dimmer to give it a nice clean look.
After getting everything together plug a light into the dimmer to be sure that it can turn the light off and on as well as dim the light using the dimmer. If it works you are all set.
Here is a pic of a grounded version I made. The extension cord is slightly more expensive but well worth it for working with grounded on/off thermostats.
I hope all of this information helps. If anything to get people to use backups because no matter how much you spend on a thermostat without redundancy there is a chance it could fail and harm your animals.
Thanks for reading!
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