Rev. of 4 brands of UTH locked

Note- Since this post was done in 2004, hermit crabs must have a night and day cycle to their lives to remain healthy.

This is meant as an informational post on the different types and varieties of under tank heaters available. I may illustrate some points about UTH's, but they are my opinion. Yours and other people's experience and opinions may vary from mine. Please do your own research and come to conclusions you are satisfied with about their use.

Before I list the different brands and info on them, I would like to comment that I was shocked to find little information available on the wattage and temperature put out by the different brands of UTH's. Out of the 4 different brands I will list here, only 2 of the four actually list the specific wattage of each size they offer, and only one brand reports the temperature output of their heater. One brand only lists the sizes and no wattage or temperature information:

They list only size, and no wattage or temperature (this one is referred to as a "mat", it does not stick on to the tank, but you can put it under the tank, space allowing or if you prop up the tank):

4"x5" Mini
6"x11" Small
11"x11" Medium
17"x11" Large
29"x11" Jumbo

ExoTerra? Heat Wave by Hagen (they list size and wattage, but not temperature output) This is a stick on UTH:

They have 2 lines, Desert and Rainforest:


4x5", 4 Watts
8x8", 8 Watts
10x11", 16 Watts
11x17", 25 Watts


8x8", 4 Watts
10x11", 8 Watts
11x17", 12 Watts

Reptitherm by ZooMed? (they list size and state only the wattage range from 4-24 watts and no temperature output. I have extrapolated what I believe to be the wattage of each size by looking at the progression of other brands, but I am not sure this is exact). Another stick on UTH:

4x5" (1-5 gallon), 4 Watts
6x8" (10-20 gallon), 8 Watts
8x12" (30/40 gallon), 16 Watts
8x18" (50/60 gallon), 24 watts

T-Rex? Cobra Heat Mats:
They list size, wattage and temperature output (another that is referred to as a mat):

4x5", 3 Watts
6x11" (10-20 gallon), 7 Watts
11x11" (30-40 gallon), 14 Watts
11x17" (50-60 gallon), 22 Watts
11x29 (60+ gallon), 38 Watts

T-Rex? reports these are all designed to operate at a constant 100 degrees fahrenheit.

Since T-Rex? is the only one to report temperature output, it is difficult to say exactly what the temperature output is of the other brands (I have written each manufacturer for this info and am awaiting responses). However, they all seem to have similar sizing and similar wattage for each of the sizes, with T-Rex? having about 1 watt lower for each size compared to some other brands that list wattage with size. It is not unreasonable to presume that the other brands with similar size and wattage will have similar temperature output compared to the T-Rex? models.

At the very least, not knowing the specific temperature output of most brands of under tank heaters, this should make clear the importance of monitoring the temperatures they produce at all levels of substrate from surface to bottom to ensure there is no danger of overheating hermit crabs that may burrow in over it. If you buy into the notion that since the others have similar sizes and wattages as the T-Rex? which reports to have 100 degree temperature output, it is not unreasonable to presume that the other brands are putting out similar temperature as well. 100 degrees fahrenheit is well out of the preferred or safe range for hermit crabs. There is significant potential for overheating of a hermit crab that burrows into substrate over or near the undertank heater. If they make it to the bottom, they can come in contact with at least 100 degree heat-- keep in mind, the deeper the substrate, the more heat becomes trapped near the bottom of the substrate, further increasing risk of overheating.

I feel this information is at least enough to warrant the recommendation that new crabbers (and experienced) that decide to heat with a UTH also purchase a good thermometer, preferably one with a probe and digital output to monitor the UTH. Radio Shack has several models around $15 or so, some even measure humidity as well. WalMart? and Home Depot also have digital probe thermometers and you can also check on eBay for a bargain in this area. If there is no access to purchasing a reptile thermostat, then it is possible to set the UTH on a timer (you can get one at Home Depot for about $5) to go on and off at pre-programmed intervals, or simply unplug and plug in the UTH periodically to guard against over heating, monitoring with a thermometer along the way to find an on/off cycle that produces your preferred temperature at the substrate bottom for safety. I personally don't let mine get above 85 degrees Fahrenheit at the bottom of the substrate because a number of my crabs do like to burrow, and pretty deep I might add.

Another point to be made on the efficiency of UTH's is that if these things are putting out about 100 degree heat at the contact point, then why do so many crabbers have a hard time getting temperature up, especially in cold homes? UTH's heat by thermal contact only, with very little radiation to the air and other areas of the substrate. Incandescent bulbs (day or night) and ceramic heaters heat through radiation they reach air and substrate more efficiently. Now, the same warnings with regard to wattage need to be applied if you try overhead radiant heat. Don't go using a 50 watt bulb to heat a 5 gallon tank. I have seen wattages of day and night incandescent bulbs in 15, 25, 30, 40, 50, 60, 75, 100, 150 and 250 watts. I have seen ceramic infrared heaters in 25, 40, 60, 80, 100, 150 and 250 watts in different brands. Obviously care must be taken to select the aprropriate size bulb or heater to produce the preferred temperature for your set up in your house. I am not the only crabber using overhead radiant heat. There are others who have used various iterations of over head heating with good success. At the end of this article there is a template so people can share their heating methods with others. Hopefully you will see someone witha similar setup (i.e.e tank size, house temp) and yo ucan ask them what they did and how they did it. There will be some trial and error involved no method is perfect. You will need to possibly test a few different wattages of bulb or ceramic heater before you find one that produces the temperature you desire night and day. The larger the tank you have, the more you may find a need to use some type of radiant overhead heat to either supplement or replace that provided by a UTH. Humidity is also an important consideration and should be monitored carefully, especially after you make any changes to your heating methods.

Please do not take this post as a complete bash of UTH's. They have been tried and true by a lot of crabbers. I use one myself, though it is modulated by a thermostat so it does not get too warm. Just please be aware that if you choose a UTH as your main or only heating source that there will be pros, cons and some pitfalls. There have been reports of crabs that have died burrowed in over a UTH that was not modulated. Also, my suster is an exotics veterinarian in Florida, she is well published and has lectured around the wrold. She has several case reports of heat and burn injuries from UTH's in various animals, with documented deaths as well. Please don't take this the wrong way-- I am not trying to scare people off using UTH's. Just keep in mind that these put out significant heat at contact point and the potential does exist for overheating a hermit crab that burrows in.

In the absence of a modulator like a thermostat or rheostat, and if you are unable to unplug/replug the UTH to modulate it during the day, you may want to consider the Rainforest line by ExoTerra? (Hagen). They put out half the wattage of the other UTH brands, and may represent an alternative to having to modulate them. I have no direct experience with this particular heater (the ExoTerra? Rainforest line), so at the very least temperature should be monitored closely if you try this model to see if it too needs to be modulated.

In my opinion it is pretty clear that UTH's need to be monitored and in a lot of cases modulated in some way so as to reduce the risk of overheating a burrowed hermit crab. This poses a new problem-- many already have lower temps than they would like even with their UTH on full all the time. This leaves them with cooler air temps than they would like in their tank and also the possibility that with the UTH full on all the time, it could overheat a burrowed crab. In my opinion, this leaves the door open for the exploration of other methods of heating to meet the temperature needs of hermit crabs, which by most reliable sources is in a range from 75-84 degrees, preferably with a gradient where there is a warm end and a cool end in that range during the day, with slightly cooler temps at night time as it cools off naturally in the wild. I am wide open for suggestions on how to address this problem. I think this is a good jumping off point for people to write what methods they use and the success they have heating their tank. Here is a template that might be helpful. I'll fill in my answers to start:

Tank size (in gallons, or dimensions if other than aquarium): 75 gallons, 48"x18"x22"

House temp day/night: 70 all the time

Main heating method: Daytime- I have 2 48" fluorescent bulbs, 40 watts each, and a UTH (25 watt 11x17 from Hagen) modulated by a thermostat to keep temp 85 or under at substrate bottom. Night- The fluorescents go off and a 40 watt ceramic heater goes on.

Auxilliary heating method(s): 40 watt ceramic on at night when dual 40 watt fluorescents go off

Tank temperature: 78-80 daytime (82-84 warmest area on second level, 72-74 in some of the subterranean caves I have landscaped in). 75 night time (ambient air temps for both)

Tank Humidity: 70-80%

Tank cover type: Glass with 2-3" gap under fluorescent strip

Use of thermostat or rheostat yes/no (if yes which and what kind?): Thermostat, Alife 3 outlet model

Use of day light for day/night cycles (yes/no): yes

Overall satisfaction and/or success with your method (i.e. are you happy with the results, or do you feel there is something more you can do?): I may hook up the ceramic heater to a thermostat for use around the clock now that it is getting a lot colder. Even though my house is set at 70, the temp in their area gets a little cooler due to the room it is in. Otherwise, I have the tank at the temperature and humidity I want virtually all the time with little adjustment being made.

Any comments or suggestions you have with regard to the implementation of your method for someone else with a similar set up to yours: e-mail me at bill at kazabee dot com if you have a large tank and I can tell you exactly how I did some of the things I listed.

If anyone has information on any other UTH's, or additional info or experience with the ones I listed in this article, please, by all means share it so we can all learn more about them!

Copyright 2004, Kazabee, Inc.

Created by ladybug15057. Last Modification: Thursday 12 of June, 2008 22:26:14 CDT by ladybug15057.
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WhizKidsMom, 17:28 CST, Tue 01 of Jan., 2013: Happy 2013
ladybug15057, 15:37 CDT, Tue 19 of June, 2012: How time flies! June 17th was our 12 year hermit crab anniversary! Yepper, same hermit crabs too!!
ladybug15057, 16:01 CDT, Mon 28 of May, 2012: WOW has it been super hot and humid the last few days....
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