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Old 12-01-2020, 10:37 PM   #1
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Heater Question

This is the first time I've set up a large tank (normally hang with the 20-30 gal range). I'm doing a 55 gallon tank and I know the formula for determining the wattage I need. The coldest the house will get is 68 degrees (at night), target temp is 76-78 degrees and I should be looking at 300w heaters for that.

Now...I've heard long ago that instead of doing a single large heater, use two half powered heaters. In my case, a pair of 150w heaters.

The reason I was told was that having two half powered heaters protects me if one fails to turn off or if one just dies. The water won't get too hot nor too cold.

Now the only thing I can find is "It's not a bad idea to have two heaters" but nothing on the ideas I've heard years ago.

So...suggestions? Thoughts?
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Old 12-01-2020, 10:46 PM   #2
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Several of my bigger tanks I have 2 heaters. Mainly cuz I would need a 500 or 600 watt, which I've never seen. So I just double up the smaller ones. The backup plan/ idea for having 2 is just an added coincidental bonus. I think your plan would work fine ime
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Old 12-02-2020, 04:26 AM   #3
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You need a 150 watt heater to raise the temp 10f. No need for 2 heaters in a 55g if you get the correct heater.

Running too large a heater is a risk, if the thermostat fails and sticks the heater on a large heater will very quickly raise the temperature in your tank and possibly kill your fish before you notice what is going on.Click image for larger version

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Old 12-02-2020, 06:15 AM   #4
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Originally Posted by Aiken Drum View Post
You need a 150 watt heater to raise the temp 10f. No need for 2 heaters in a 55g if you get the correct heater.

Running too large a heater is a risk, if the thermostat fails and sticks the heater on a large heater will very quickly raise the temperature in your tank and possibly kill your fish before you notice what is going on.Attachment 318802
Good point. All of the heaters on the market, irregardless of price point, have the same reviews and ratings about failing and shocking, and over hearing etc
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Old 12-02-2020, 06:16 AM   #5
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*heating
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Old 12-02-2020, 06:26 AM   #6
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Running 2 heaters would mitigate the risk of overheating if 1 should fail and have the thermostat keep the heater on. Its unlikely 2 would fail in the same way at the same time.

However i think 2 heaters in a 55g is a bit OTT, but if you are particularly risk averse then go with 2 x 75w heaters. Takes up a bit too much real estate in my opinion.
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Old 12-02-2020, 08:14 AM   #7
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Running 2 heaters would mitigate the risk of overheating if 1 should fail and have the thermostat keep the heater on. Its unlikely 2 would fail in the same way at the same time.

However i think 2 heaters in a 55g is a bit OTT, but if you are particularly risk averse then go with 2 x 75w heaters. Takes up a bit too much real estate in my opinion.
I'm sorry, but according to your chart above, one 75w heater would barley heat a 20 gallon tank. If that is true how would a second 75 watt heater heat any higher than the first? Let alone two in a 55 gallon.
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Old 12-02-2020, 08:56 AM   #8
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150 watts (2 75) will raise the temp 10f in a 55g. The chart clearly shows this.
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Old 12-02-2020, 09:10 AM   #9
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150 watts (2 75) will raise the temp 10f in a 55g. The chart clearly shows this.
I see no mention of 2 heaters. If one heater can only raise the temperature to a max of 70 degrees and shuts off, it is perfeclty matched for 70 degrees. If you put in an identical heater it can only raise the tempurature to a max of 70 degrees also and it shuts off because it can't heat any higher (since the water is already at 70 degrees). What you are saying is if you have two pots of 100 degree water and you combine them, you now have 200 degree water, but the water is still only 100 degrees. That's really not how thermodynamics work.
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Old 12-02-2020, 09:44 AM   #10
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No im saying 150 watts power will raise the temperature 10f in a 55g tank. It doesnt matter whether that wattage comes from 1 or 2 or 15 heaters, as long as the heater is capable of raising its own temperature above the desired temperature and passing that temperature into the water. Temperature is different to power.
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Old 12-02-2020, 09:48 AM   #11
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No im saying 150 watts power will raise the temperature 10f in a 55g tank. It doesnt matter whether that wattage comes from 1 or 2 or 15 heaters, as long as the heater is capable of raising its own temperature above the desired temperature and passing that temperature into the water. Temperature is different to power.
Yes, but two 75w heaters don't make a 150w heater as seen above. The heaters are independent of each other and have no idea the other is in the tank. They only know the tank water temperature.
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Old 12-02-2020, 09:56 AM   #12
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Power is power, they dont have to know about each other. 2 tractors will be able to pull twice the load because they have twice the power. By your arguement if 1 tractor isnt capable of pulling a load then adding a 2nd (or more) wont make any difference.
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Old 12-02-2020, 10:26 AM   #13
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Power is power, they dont have to know about each other. 2 tractors will be able to pull twice the load because they have twice the power. By your arguement if 1 tractor isnt capable of pulling a load then adding a 2nd (or more) wont make any difference.
We are not talking torque, we are talking thermodynamics which is just a little bit different. Your tractors are connected to the same load. Heaters are not connected together they are independent.

Using your argument above, let's look at a failure of one tractor. If one fails, the other will NOT be able to pull twice the weight, right? So it stops dead.

Same thing in a fish tank. If one of the smaller heaters fail you now have a 50% reduction in energy. This will not keep the temperature stable.

The only reason to use two heaters in a tank is for temperature stability and redundancy.
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Old 12-02-2020, 12:55 PM   #14
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I'm sorry, but according to your chart above, one 75w heater would barley heat a 20 gallon tank. If that is true how would a second 75 watt heater heat any higher than the first? Let alone two in a 55 gallon.
I'm not sure where ya'll are seeing 75 watt on that chart anyway. But I know i have 2 300's on my 150g, and 2 400's on my 215g and they keep it optimal. Of course where I live on the gulf coast, if it's in the 40's it's like the north pole to us, lol
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Old 12-03-2020, 09:20 AM   #15
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I'm not sure where ya'll are seeing 75 watt on that chart anyway. But I know i have 2 300's on my 150g, and 2 400's on my 215g and they keep it optimal. Of course where I live on the gulf coast, if it's in the 40's it's like the north pole to us, lol
You are doing it right. Just one of your heaters is sized right for each tank for a 15 degree delta in temperature. Using two of the SAME correctly sized heaters insures you have temperature stability and if one heater fails, the remaining heater can maintain the correct temperature.

Here is a more accurate guide than one from a heater manufacturer.
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Old 12-05-2020, 05:44 PM   #16
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Running too large a heater is a risk, if the thermostat fails and sticks the heater on a large heater will very quickly raise the temperature in your tank and possibly kill your fish before you notice what is going on.Attachment 318802
I've never heard of this before. I looked up the fail-over procedures my unit takes if there's a problem of some sort. A nice finnex tech told me that a heater based fish boil is unlikely due to their engineers having lots of room to over-design the thermostat (mounted dry on the outside of the tank). Either way, thanks Aiken for giving me 1 more thing to be paranoid about.
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Old 12-05-2020, 06:08 PM   #17
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I've never heard of this before. I looked up the fail-over procedures my unit takes if there's a problem of some sort. A nice finnex tech told me that a heater based fish boil is unlikely due to their engineers having lots of room to over-design the thermostat (mounted dry on the outside of the tank). Either way, thanks Aiken for giving me 1 more thing to be paranoid about.
Hah!! I've cooked fish. It happens.. Finnex heaters are trash anyways. Running heaters in tandem will not match the output of a single heater in effectiveness, numbers aside. Instead of a 200 watt single heater, I'm running duel 150's. Depending on the fish, most tropical fish in a healthy tank will not suffer greatly if your heater fails and the tank goes down to 66 for a night or two. All of my many tanks are heated by a single heater rated for the gallon age. My 90 gallon discus tank has 2-300 watt heaters. Cant let them get to cold. They can handle 90 for a day too. I check the temp twice a day. I've had heaters fail in all other tanks, never lost a fish immediately from this. All depends on what's in the tank and how massive temp swing will affect them.
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Old 12-05-2020, 08:02 PM   #18
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Hah!! I've cooked fish. It happens.. Finnex heaters are trash anyways. Running heaters in tandem will not match the output of a single heater in effectiveness, numbers aside. Instead of a 200 watt single heater, I'm running duel 150's. Depending on the fish, most tropical fish in a healthy tank will not suffer greatly if your heater fails and the tank goes down to 66 for a night or two. All of my many tanks are heated by a single heater rated for the gallon age. My 90 gallon discus tank has 2-300 watt heaters. Cant let them get to cold. They can handle 90 for a day too. I check the temp twice a day. I've had heaters fail in all other tanks, never lost a fish immediately from this. All depends on what's in the tank and how massive temp swing will affect them.
Thanks for the Finnex shout-down, Brook. Prompted by this I took a detailed look at the positive and negative Amazon reiews. My first 800w died after about a year. Without an extended warranty, Amazon replaced it in a day. That unit has been online for nearly 24-months. It still freaks me after reading that it might electrocute my fish under the right circumstances.

I've got two cobalt 200w units as backup, so I'm good there. The only reason I went with the 800w was the idea that it would heat my 125g easily and quickly without having it snap on/off all the time. It works in that role quite well. I've even watched my surviving pleco clean the plastic shield while the unit was powered, and not floating belly up to the surface afterwards completly boiled. In spite of these positive outcomes I'll start to look for two lower wattage units that meet my requirements (including my tech ego), hopefully with WiFi support.

I've tried to balance my fish's thermal requirments to be about 79 degrees actual.
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Old 12-05-2020, 08:08 PM   #19
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In all honesty, I've tried all the heaters. The aqueon pros used to be the best but I heard manufacturing standards had shifted and the quality was not there. New aqueon pros fail fast and glass stick. The mirror finish fluval are my go to. They have yet to let me down. I understand nothing lasts forever but I'd like atleast 2 years out of $40 heater.
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Old 12-05-2020, 08:13 PM   #20
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Thanks for the Finnex shout-down, Brook. Prompted by this I took a detailed look at the positive and negative Amazon reiews. My first 800w died after about a year. Without an extended warranty, Amazon replaced it in a day. That unit has been online for nearly 24-months. It still freaks me after reading that it might electrocute my fish under the right circumstances.

I've got two cobalt 200w units as backup, so I'm good there. The only reason I went with the 800w was the idea that it would heat my 125g easily and quickly without having it snap on/off all the time. It works in that role quite well. I've even watched my surviving pleco clean the plastic shield while the unit was powered, and not floating belly up to the surface afterwards completly boiled. In spite of these positive outcomes I'll start to look for two lower wattage units that meet my requirements (including my tech ego), hopefully with WiFi support.

I've tried to balance my fish's thermal requirments to be about 79 degrees actual.
I have a finnex, it was recommended for its ability to hold at 82-84 f. It did for a week and than didnt. I use it in a smaller tank to hold 75-77, it does. Actual temp vs dial setting is 5* off.
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