The 2 half size heaters experiment

[Clownfish2]

I recently set up a 20 gallon QT. For the heater set up, I have been curious. Often, I read of reefers using 2 half size wattage heaters in their tanks to prevent overheating a tank. But does this really prevent a temperature hot enough to kill your inhabitants? It depends.

Before adding fish to this QT, I tested this theory with two 50 watt Eheim Jager heaters. Both heater thermostats were set to 78 which gave me a desired tank temperature of 78.7
Ambient temperature in my house is 70.2.

So I simulated one heater failing in the OFF position while the other staying ON with a setting of 78. Excellent, the temperature reduced to and maintained 78. But what if that one heater failed in the ON position?

While one heater was set to 78, I set the other heater to the maximum of 93 for 24 hours. At the end of 24 hours, the tank temperature had increased to 80.4. The house temp was 70.2. So essentially, this QT tank would reach 10 degrees warmer than my house temp with a stuck heater.

A max temp reached of 80.4 is certainly not enough to kill the tank, but the max temp reached will depend on the ambient temp of your house. Wattage per gallon plays a role too. So with one 50 watt stuck ON in a 20 gal equates to 2.5 Watts per gallon. I’m not sure how you keep your house temperature, but I tend to maintain a house temp of 65-70 in winter and 74-76 in the warm season. I believe if my house was 75 and the QT heater stuck ON, the QT would peak to 85. 85 tank water is not too hot, but I’m not confident every inhabitant would survive.

I think for 2 half size heaters to really prevent an overheat condition, the ambient temperature in the room would have to remain absolutely constant throughout the year. Another idea is to further reduce the heating wattage below 2.5 watts per gallon. Example, use two 25 watts in a 20 gallon and one of them fails ON.

 

[don_chuwish]

I like the idea, thanks for fleshing it out.

 

[m3rcfh]

That's a valid and good point, here in Michigan temperature varies a lot throughout the year... my house goes from 64 during the night on winter to 75+ sometimes during summer. I have been thinking in using 4 heatters of 1/4 of the wattage needed and use a industrial-grade temperature controler to reduce the impact even more when one of them gets stuck turned ON - BeanAnimal has a nice writeup about this subject on his website

 

[Davy Jones]

Although it may not prevent it completely, say you had a single 100 watt heater in that tank, stuck on to 93 degrees. The tank surely would have hit more than the 10 degrees above ambient temp. With the same 2.5 watts per gallon the seprate heaters produce

 

[ca1ore]

Of course! Any heater, or cooler, has a certain total energy it can add or subtract from a body of water (usually stated in terms of BTUs). An unregulated 100 watt heater, for example, may be able to maintain 20 gallons of water at 10 degrees above ambient. If your room is 70 degrees, then you're good; if your room is 75 degrees then you may not be. Years ago I had a large tank crash because the heating system in my house failed and my total aquarium heating capacity was only enough to maintain about 15 degrees above ambient. When the house dropped to 40 degrees my tank was a goner. The idea behind multiple, smaller heaters is that if any one sticks on, it's going to do less cumulative damage than if a single, large one sticks on. But during the hottest days of the year, even a smaller heater stuck on can be problematic (which is why I usually disable them). All other times of the year, multiple, smaller heaters is a sensible practice.

 

[Radman73]

I kind of got experience with this since Florida participated in winter this year. Well, sort of. We did get below freezing lol! I could only find low wattage heaters locally for my QT tanks so I'd have 2-3 in each one. None failed, on or off, but I played around with them too to see how many were needed to at least maintain temp.

 

[MaiReef]

I agree
two just over half sized heaters with an Inkbird should do it it fine with both set just above the inkbird in the event the ink bird fails.

 

[Allen752]

Great Idea.

 

[Clownfish2]

Experiment #2: The purpose is to determine how hot a tank would get with a heater stuck ON using 1.25 watts per gallon. Prior to starting this experiment, I heated the water to 78 degrees (common tank temp) with a different higher wattage heater and then pulled that heater out and then plugged in the 50 watt Jager heater to its max thermostat setting of 93.

At 1.25 watts per gallon, using 40 gallons of water and a 50 watt heater, ambient room temperature 67.7, the temperature initially decreased to 74.4 but it held this temp for a couple days. With the heater ON continuously, the max temp was 74.4, that’s only 6.7 degrees warmer than ambient.

This means even during the warmest time of the year, using 1.25 watts per gallon will greatly reduce your chances of a tank overheat if the heater fails ON.

 

[[Cameron]]

Keep in mind each additional heater is its own extra failure point as heaters can fail in ways other than being stuck on or off such as stray voltage. Each new item added to a tank has to be weighed against its potential to fail in unexpected ways. Also undersized heaters will wear out much quicker and often struggle to maintain accurate temperatures.

IMO two properly sized heaters with built in temp controllers paired with two different external controllers each calibrated with the "ice water" method is a solid balance of risk vs performance. One temp controller is set to 76, the other to 78. The 76 degree controller's heater is set to 79 while the 78 heater is set to 80. Adjust those temps according to your needs. The total cost for a small tank is around $100 and near bulletproof operation.

 

[ca1ore]

No bigger red herring in this hobby than stray voltage. OK, the more heaters you use, the greater the chance of physical breakage of the glass tube (at which point the voltage isn't 'stray' anymore; thus use of GFCI), but in almost 40 years of aquarium keeping I've not had one shatter yet.