What’s Wrong with Thermostats

Mostly we don’t need them —

Most every care sheet you read will instruct you to incorporate a thermostat of some sort into your vivarium design. So maybe its surprising to read here that I think they are often worthless and even dangerous.

Probably because there was no such thing during the first 20 years of my herp keeping career, we had no choice but to live without them. And when they first showed up on the scene I thought of them mostly as more pet store junk. Later I realized just how dangerous they were!

There is almost no scenario that I can imagine that would require a thermostat. I even asked others to provide examples of when and why they thought thermostats were actually important to herp care. Most of the replies were kind of crazy – like “what if your air conditioner goes out but your heat lights stay on and then the animals bake?”

Like that has ever happened. But the only scenarios that made a thermostat even arguably useful were these totally unpredictable equipment failures, and they were far fetched at best. If your A/C failed, the temperature in your home would very gradually increase over many hours. The situation would be corrected before any actual damage would be done.

Heat waves happen. And they are predicted days in advance. Hardly likely that a heat wave would ever create a problem for our animals, since we could simply unplug one or all of the heating elements in any cage in an unconditioned space.

But that leaves two considerations: How to set up the heating elements for a cage and how to control those elements once in place.

The best primary heat source for reptiles and amphibians is incandescent light bulbs. (Halogens are a type of incandescent which are hotter per watt, and a good choice for many setups). For most cages use flood bulbs for their wider, gentler beam. Do not use the mini-halogens sold at pet stores, which concentrate a small, very hot beam that can easily burn your pet.

Incandescent flood bulbs can still be bought at the Home stores in much of the US. When the US ban goes into effect, as it has in California and many European countries, we will have to by the pet store bulbs – which are expensive and sometimes dangerous – or search out other sources of specialty bulbs. The US ban states that “general use” light bulbs that use a lot of energy to produce few lumens will be banned. This leaves “specialty bulbs” like those branded for the pet or plant / horticulture industry.

Other common heating elements like radiant heat panels and ceramic heat emitters are not suitable for primary heat. (See: The Problem with Ceramic Heat emitters and Radiant Heat Panels) In the unlikely situation where ambient or overnight temps fall into the 60s, these technologies may be useful. But they are not to be used as your primary heating elements.

Deep heat projectors (DHPs) provide infrared B and some IR-A, so they do radiate heat down into the cage. These can be a good choice for overnight heat for some species. Because they produce almost no light and are directional they can be used to establish a thermal gradient even at night.

Under tank heat pads get a bad rap, but usually because they are used wrong. Like the CHEs and RHPs, UTHs can also be useful to boost ambient temps under certain circumstances. It is true that reptiles and amphibians instinctively go to the ground and under the ground to find cooler, more humid conditions. So a warm substrate may not be a good choice for terrestrial species. But for other species like arboreal lizards or snakes or tree frogs, gentle heat from below may be fine. Just don’t set the tank or cage or anything heavy on the power cord – that can cause an electrical fire.

So to provide the right temperatures with our overhead bulbs we have to start with an educated guess. How many bulbs and how many watts? If you are just starting out you may have to learn by trial and error. (Make sure you dont accidentally buy LED bulbs which produce no useful heat) Common wattage for bulbs are 45, 65, 75, 90 100 and 120. The right wattage and the number of bulbs will depend on your cage shape, ventilation, whether the bulbs are inside or out, and the species you are keeping, to name a few of the variables.

Thats why no one can answer the commonly asked question, “What lights do I need for my cage?” Obviously you need to start by asking what temps does my species need. This means what range of temps – since I know you will want to create a good thermal gradient – and also what night temps as well as day temps.

If, for example, you are housing a new corn snake in a 20 gallon long tank with a screen lid (See: Why Aquarium Tanks Make Such Great Herp Housing) you may want to create a warm side basking area of 88-90F (31-32c). So try a 75 watt flood bulb in a 10 inch reflector sold for baby chicks at the farm store. Use a $3.00 thermometer (also from the farm store) or a temp gun to measure the surface temperatures the 75 watt bulb creates. If it hits your target temps you are done.

If the basking area is still too cool, simply try the 90 watt bulb. Or better, leave the 75 watt and get another 10 inch reflector for a 45 watt or 65 watt bulb. I say better because with two reflectors and bulbs you will create a munch bigger warm area and you’ll also have more leeway to tweak temperatures: Two 65 watt bulbs, or a 75 and 45, etc. You can use two bulbs to create more gradual temperature gradients.

And as always, exactly what you want will be informed by the animal you are keeping! Is it avoiding the warm area? If so, why? Does it rarely leave the warm area? The animal’s behavior will be a good teacher if you are a good student!

I have found it often beneficial to use a dimmer in conjunction with adjusting the wattage of the bulbs. The manual slider type dimmers can work, but many keepers are finding the digital, wi-if dimmer / timers to be valuable here. These marvelous little devices solve a host of issues and allow the keeper to really fine tune their enclosure environment.

Here is a link to the digital dimmer / timers I use:
https://www.amazon.com/dp/B0BXP8QL52

For some sensitive species like baby emerald tree boas I have both the halogens and the night DHP on their own dimmer / timer. with these I can control exactly when they come on and their intensity once on. After a couple days I can dial in the exact temperatures and illumination I want.

Almost all lights and heaters, including UTHs and CHEs are dimmable now, but it is worth double checking before buying. And remember CHEs and RHPs are NOT what we want as primary heat sources.

So why are Thermostats Dangerous?

Hopefully we’ve learned how simple it is to create great thermal and visual radiation scenarios for our animals. So we know now that thermostats are not necessary at all. But are they really dangerous?

Thermostats are introduce a complexity (and a cost) that can easily be avoided. The more complex a system is, the more likely it is to fail. And I have seen animals’ lives endangered by failed thermostats, and failed implementation of thermostats, way too many times.

First, the equipment itself can fail. It seems like half of what we buy these days is cheap crap that fails shortly after we unwrap it. Many thermostats sold today are no exception. And when they fail they can allow the once dimmed lamps or heating elements to switch to full power, potentially lethally over heating the caged animals.

But its more likely the thermostats will fail due to keeper error. The probe is placed in the wrong place, for example, or it’s placed correctly but the animal dislodges it. Suddenly it is way down in the shadows of the cage, which it will now try to heat to basking temperature!

So, in balance, the keeper and the kept will both be better off without this expensive and unnecessary addition to our vivarium design. Try to design without them – as many of us did for decades – and see how easy and safe life without thermostats can be!