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Heaters Notes

Posted 08-30-2010 at 08:35 AM by NASAGeek
Updated 09-15-2010 at 06:16 AM by NASAGeek

Heaters… got have them but is there anything specific you need to know about them??

It seems that everything in the reef aquarium hobby has “more to the story”. This axiom holds true with heaters as well.

Let’s say that your average room temperature is 73 degrees. Let’s also assume you want to maintain your reef aquarium at 79 degrees plus or minus 1 degree. That’s a 6 degree differential… but not really. Before we go into heaters, let’s discuss a few other topics. Latent Heat Load. If the ambient air temperature was 73 degrees and there was no power to your tank, yes, the water temperature would trend to 73 degrees. But when there is power to your tank, several items other than heaters add heat to your tank. Most notable on this list are lights and submersible pumps. Most in-sump skimmers have a submersible pump. Return Pumps in sumps. Circulation pumps such as Koralias. All of these add latent heat load to your tank. A simple example. My tank is a 120 gallon display tank with a 40 gallon sump. I’ll estimate 100 gallons total water volume. I have 4 Koralia 1’s and 4 Koralia Eco1400’s in for circulation. I have 8x54W T5’s for lights. I have a Warner Marine K2 Skimmer with a Sicce PSK2500 pump. I also run a Mag 24 return pump. Finally, my refugium light is a Home Depot 6500K Compact Fluorescent. All of those contribute heat to my tank even before we talk about adding heaters.

The Mag 24 is 265 Watts. Sicce is 22W. Each Koralia 1 is 3.5W for a total of 14W. Each Koralia Evo1400 is 5.5W for a total of 22W. All that adds to 323W. That does not count the heat load from lights either. The latent heat load from items like these can easily raise the tank temperature 3-8 degrees. Thus, the ambient temperature of the water given the air temperature and the latent heat load ends up 76 to 81 degrees.

So while it is true that I “need” a heater, it isn’t on nearly as much as you would think. Typically, the difference is only a degree or two to get to my desired heat range of 78 to 80 degrees. Here’s the point…. You don’t necessarily need the big monster heater you might think you’d need.

Probably the most important thing to consider in heater is Failure modes…. Fail Off… Fail On… breakage. Fail Off and Fail On are thermostat failures. Fail Off is the thermostat fails to turn on when the temperature drops below your set point. Fail On is when the heater fails to turn off when the temperature rises above your set point. Both can be catastrophic to your tank. Both are easily remediated with some redundancy. Here is how I implemented my system.

Fail On has redundant protection in that even if the AC Jr is commanding the heaters on, the heater thermostats won’t kick the heater on if the water temperature is above 80 degrees. Fail Off is partially protected. If the AC Jr Temp Probe does not turn on the heaters, then the tank would get cold but if one of the heaters fails, the other heater would keep the aquarium warm. Breakage is something to be careful of when buying glass heaters. I prefer to buy non-glass heaters for that reason.

Another common question is "how big of a heater do I need?" Size doesn't really matter in this case. The reason is that ANY heater will raise the water temperature, it is just a question of how long it has to be on to accomplish the temperature change. Thus, size doesn't matter... to a point. Of course, a 100W heater in a 1000 gallon is just too great a difference. A general rule of thumb is 2-5W per gallon. I tend towards the small end of that range since I put two heaters in parallel. Thus the net effect of both heaters is on the high end of the range.

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