Reptile Thermostats Explained

By Tony Jones
9th June 2009.

Carpet Python 1
Temperature control is one of the most important aspects of reptile husbandry.   Before the introduction of solid state electronic thermostats in the late 1980’s, innovative herpers were forced to adopt and adapt technologies from other fields in an attempt to control the micro-climate inside their vivariums.  Thankfully there are now several different types of reliable and effective thermostats to do the job to in a variety of applications.

The On/Off Stat.

These stats are the most basic budget option available to the herper and are the minimum standard I would hope to see in any vivarium set up.

Approximate Retail Price: £35

How they work:
These basic stats control temperature by switching the heat source on and off.  If the unit senses a temperature in the vivarium that is too cool it switches the heater on.  When the temperature reaches the upper level of tolerance it switches the heater off.
•    They are the best value thermostat available and so there is no excuse to have an uncontrolled heater in your vivarium.
•    They can be used with any type of heater.
Whilst having any type of thermostatic control by far preferable to having none, the ON/OFF nature of these stats raises several issues.
•    As heat sources are either fully on or completely off, this can create a noticeable fluctuation of temperature between the two phases,
•    When the heater is fully on it will be generating a great deal of heat which therefore increases the risk of burns, particularly if the heater is unprotected.
•    As most vivariums are heated using spotlight bulbs, the intermittent switching on and off of the light can prove stressful to both the vivarium inhabitant and to humans trying to watch TV or sleep in the same room.
•    The constant switching on and off will mean that bulbs will blow more often and need to be replaced.

The Dimming Thermostat.

A much more effective thermostat option is the dimmer stat and it is no surprise that these are the most popular stat by far, despite costing a little more.

Approximate Retail Price: £55

How they work:
Dimmer stats control temperature by supplying power to the heater incrementally.  The easiest way to explain it would be to assume the heater source to be a spotlight bulb.  If the temperature in the vivarium is too warm it supplies less power to the bulb and so the light will dim.  Conversely, if the temperature is too cool it will supply more power, therefore brightening the bulb to provide more heat.  They work in exactly the same fashion with other heaters too, such as heat mats and ceramics.
•    Dimmer stats are much more accurate than on/off stats. The constant feedback and adjustment keeps the temperature stable and effectively eliminates fluctuations, making them the preferred option for most herpers.
•    In addition to eliminating temperature fluctuations the dimmer stat negates every one of the other negative points of on/off stats too, i.e. less burn risk from ferocious heat sources, less blown bulbs to replace and less flashing lights stress.
•    Dimmer stats are exceptionally versatile and can be used in any application with any animal and with any heating equipment.
•    None to speak of, although in some applications there is a marginally cheaper stat that will do an equally effective job.  See below.

Box Out:

When setting up a vivarium with a dimmer stat and spotlight bulb it is important to use the correct wattage heater.   If the spotlight bulb is very bright or very dim it could indicate a problem.  A constantly bright light indicates that the bulb and stat are working too hard to keep the temperature at the desired level.  A higher wattage bulb will more easily achieve the temperature and will function at a safer ‘half dimmed’ level.  A constantly dim bulb indicates the wattage is too high and is kicking out so much heat that the stat needs to keep it very dim to hold the temperature in check.  It is far better to choose a wattage that operates in the centre of its range, not too bright, not too dim.  This allows the thermostat enough scope to increase or decrease the heat if necessary and means the vivarium is lit for viewing without increasing the risk of burns from ferociously hot bulbs.

Unexpected and unusual changes in brightness should always be investigated too as this could also indicate a fault such as an inadvertently nudged temperature dial or unit breakdown.

Pulse Thermotats.

Despite being less versatile than dimmers, pulse stats are often used in more advanced vivarium set ups because of their specialism.  Being exceptionally good at the job they do at a cheaper price than a dimmer makes them a hit with the more discerning herper.

Approximate Retail Price: £45

How they work:
Pulse stats regulate power to the heater by pulsing at differing intensities.  If the temperature is too low it pulses quicker at a higher intensity; when too cool it pulses slower and less intensely.
•    As with the dimmer stat the feedback and power supply are on a constant loop giving immediate temperature adjustments and minimum temperature fluctuations.
•    They are slightly cheaper than a dimmer stat.
•    Because of the pulsing nature by which they supply power, these stats can only be used with non-light emitting heat sources such as heat mats and ceramic heaters and cannot be used with spotlight bulbs.

So why are Pulse Stats so popular?
Most hobbyists will justifiably content themselves with coloured bulbs to minimise the effects of heater spotlights remaining on at night.  However, accurate photoperiod management (or the amount of light and dark your reptile sees) is another important aspect of reptile husbandry, particularly for breeders.  In advanced and breeding vivarium set ups, spotlights are often replaced with non-light emitting ceramic heaters which enable keepers to regulate the photoperiods more effectively, utilizing only natural light or fluorescent tubes for viewing. Pulse stats can control ceramic heaters perfectly well and so these are a good choice for this type of set up.

Optional Extras.
The three units outlined above are the most popular thermostats in use today but there are a handful of different varieties, variations and enhancements available too.  Some manufacturers offer thermostats that sit inside the vivarium rather than mounted on the outside.  Whilst this feature disposes of the need for separate temperature sensor cables it does also increase the risk of the temperature dial being turned by the inhabitant. (Although some brands solve this problem with dials that require adjustment using a screw-driver.)  Another downside is that these types of internally housed thermostats are less easily cleaned with water if the animal craps on it.
Another optional feature is an automatic night-time temperature drop option.  This can be activated with a timer unit, but some stats even incorporate a light sensitive ‘magic eye’ that triggers the drop when ambient light drops below a certain level.  The most advanced thermostats have the ability to manage temperatures in several vivariums at once, some using computer link ups to monitor and adjust each temperature separately.

Belt and Braces.
When thermostats fail the results can be disastrous.  Reptiles can tolerate relatively low temperatures for quite extended periods of time but temperatures even a few degrees above optimum can kill if the reptile is not able to escape.  Some thermostat manufacturers use components that (in most cases) ensure that should the unit fail it will default to the OFF position thus helping to avoid deadly overheating should the heater be stuck ON.
Another way to avoid this rare but devastating problem is to utilize a trip switch device which will kill all power to the heater should an upper temperature level be reached.  Fan units are also available to extract excess heat and kick in at a pre-set temperature level.  Both of these items of equipment can be ordered from your reptile supplier.


~ by Tony's Desk on September 13, 2009.

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