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Discussion Starter · #1 ·
Only a few manufacturers have heaters rated for 180 gallons. But I've seen a couple threads where people recommend against having two heaters in the same tank but I don't recall the reasoning.

The Eheim 300 watt is rated for 264 gallons, but I've also seen recommendations to get a heater that's just barely enough rather than overly capable in case it sticks on. This makes sense to me because I'm not fond of boiled fish, I prefer baked or fried. ;^)

Plus that heater is 19" long and I think it would be easier to hide two shorter heaters than one giant one like that.

So what's the recommendation for heating large tanks?

Thanks.
 

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You have to also consider room temp. There's no way a manufacturer can accurately rate a heater without knowing that.

I don't recall the reasoning
The idea is that if one fails, the other will still be working. Or if it fails and sticks on, it won't cook your fish. I find the reasoning flawed since most end up using two heaters that can each cook your fish. So, just doubles the odds of a problem. Go with one properly sized heater. If it either fails by sticking on or not coming on at all, it won't kill your fish. The tank water would have to get down into the 60's before you had a problem. Between the room temp and water volume, very unlikely. If you want to use two undersized heaters, properly size them and then get them on a single controller. A properly sized heater will only take the tank water up to mid to upper 80's, no more.

Depending on room temp, I'd estimate you should use something between 200-250 watts. If the tank is a new setup, get one, install it and crank it up all the way. See what it takes the tank temp up to. Go from there. It may cost you $20-$30 to test this out, but better than losing a tank full of expensive fish 1-2 years from now.

HTH
 

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Discussion Starter · #3 ·
Thanks Tim! My room is my living room so it's kept at 68 in the winter and between 72 and 84 (the best my AC can do when it's nearly 100 outside) in the summer. I think I'll go with a single 250 watt, then crank it up overnight to see what it can do. Hopefully it won't over-do it.

Thanks for the help.
 

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With those seasonal variances, you may want to consider seasonal heaters. What you'll need at 68 in the winter will probably be able to overheat in the summer.
 

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The idea of using two heaters isn't flawed, but using to of maximum size is. In a tank the size of a 180, two heaters would probably keep the tank more evenly heated. It seems from reading numerous forums that heaters seem to fail in the on position frequently, with the result being cooked fish. This is more of a factor of an oversized heater than it failing. As mentioned above, a heater that can heat to mid eighties when the room is a 68 will go close to 100 in an 84 degree room. So, two inadequate (undersized) heaters provide a safety factor as it is unlikely that both will fail at once. As well, the more often a heater switches on and off the shorter it's life will be (generally speaking). The ideal situation would be a heater of the correct wattage that never shut off and maintained the temp you wanted. This of course is not a very practical solution.
 

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Discussion Starter · #6 ·
Hmmm... seasonal. That's a good idea.

but the more I think about it, two under-sized heaters makes more sense to me because It's very unlikely that both would stick on at the same time. And like I mentioned before one 19" long heater would be tough to hide. And though the tank will have UGJ and an FX5 it's probably true that two separate heaters would heat more evenly.

I've still got some time to think about it. I'm just building the stand this weekend.

thanks again for the input.
 

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two heaters would probably keep the tank more evenly heated
Not with any amount of current, which virtually all tanks have. That concern is unfounded. And if the current was so bad that you had mixed temps, it'd be stratifying in horizontal layers, not side to side. If someone has a variance of a degree to two from one area of the tank to another, the problem is lack of current, not a need for more heaters.

The ideal situation would be a heater of the correct wattage that never shut off and maintained the temp you wanted. This of course is not a very practical solution.
Also impossible since they're not designed to do this. They have a min and max. At min it kicks on until it reaches max (approx 1 degree variance) then kicks off.

Also, two heaters working on their own controllers just work against each other, not in tandem. You may find them kicking on and off much more often than a single one would.

If you can properly size one, it's enough. There's no gain to adding a second properly sized heater if the one alone won't cook the fish. And as the heated water from one reaches the other (which it will quickly with the 6-10X turnover rates commonly seen), it'll cause that one to kick off more quickly. If the thermostats aren't set properly, one may not come on at all. Just another thing to hide.

but the more I think about it, two under-sized heaters makes more sense to me because It's very unlikely that both would stick on at the same time.
One properly sized will do the same for you. How are you going to determine proper 'under sizing'?
 

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Discussion Starter · #8 ·
How are you going to determine proper 'under sizing'?
Find one that maxes out at 90 gallons and buy two for the 180 I guess.

How would you go about putting a single controller on two heaters?

The problem I'm finding is that none of the heaters I'm seeing are rated for right at 180 gallons.
 

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The problem I'm finding is that none of the heaters I'm seeing are rated for right at 180 gallons.
Forget the manufacturer's rating. They usually oversize anyway. I'd suggest starting with a 200 since we're into warmer temps. Just test it out as I said. Go from there. You're going to have to rate it yourself, since all tanks and room temp situations are a bit unique. Few do this, btw. But, on a semi regular basis someone posts about wiping out a tank due to a faulty heater.

Find one that maxes out at 90 gallons and buy two for the 180 I guess.
You mean the manufacturer's rating? Like I said, don't trust it. If you truly want to use two, I'd get two truly undersized and do some testing with them. Try two 100's or 150's. Get the ones that have some type of indicator lights so you can see on/off cycles. Compare the on/off cycle to a single 200. It's a perfect time to do this testing, and once you do, you'll come to your own conclusions and know what will work for you. I took the time myself and found the results not what I expected. I think few do this testing and many make some assumptions that just don't hold up.

Check out this pageon temperature controllers. Be sure to scroll down to the bottom and read what they have to say about using multiple heaters without one.
 

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Sorry to bring more confusion to an already complicated decision but there are other things that will change the ideal heater size. How is the tank covered and lit? If it is covered well with little air circulation, there will be less evaporation and cooling. How dry is the room air? Is there a heat/AC duct blowing on it? Does the tank set next to a wall heated by the sun or a wall frozen by the North wind. You can see where this is going, I think. There is no way that I can see for choosing an exactly right heater before you try some. Even then it will never be exactly right because the heat needed is constantly changing. Even small things like changing from a filter which has the motor setting in the water to one which has the motor outside the tank will change how much heat is needed.
Since there is no way to calculate all these things, I go for a heater somewhat smaller than the specs show and then add more if needed. I find no problems with using two heaters if needed. One can be the primary heat and then if it can't get the job done and the temp drops a couple, the second also comes online. One sticks on, the other will shut off.
 

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PfunMo said:
Sorry to bring more confusion to an already complicated decision but there are other things that will change the ideal heater size. How is the tank covered and lit? If it is covered well with little air circulation, there will be less evaporation and cooling. How dry is the room air? Is there a heat/AC duct blowing on it? Does the tank set next to a wall heated by the sun or a wall frozen by the North wind. You can see where this is going, I think. There is no way that I can see for choosing an exactly right heater before you try some. Even then it will never be exactly right because the heat needed is constantly changing. Even small things like changing from a filter which has the motor setting in the water to one which has the motor outside the tank will change how much heat is needed.
Since there is no way to calculate all these things, I go for a heater somewhat smaller than the specs show and then add more if needed. I find no problems with using two heaters if needed. One can be the primary heat and then if it can't get the job done and the temp drops a couple, the second also comes online. One sticks on, the other will shut off.
All good points. And many more good reasons why manufactures cannot begin to accurately size heaters for us.

He also points out the one good way to use a second heater as a fail safe heater. Set one a bit lower so it only comes on if the first one fails to come one. But, probably only needed in cold rooms where the tank water could get dangerously low if the main failed.
 

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Discussion Starter · #13 ·
All good points. And stuff I've honestly never considered even after 15 years or so of having fish. I appreciate it.
 

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I have a hard enough time trying to hide one heater which I why I decided against using two but I see on different foums quite often in which people recommend having two undersized heaters in case one gets stuck in the on position. This thread totally makes me rethink the dual heater theory which I had come to accept as a good idea.
 

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One my 180 gal tank i have 3 Visi-Therm 300w heaters. I used to use 1 800w but when it broke I did not have anything heating the water so I will never rely on just one heater.
 

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smitty said:
One my 180 gal tank i have 3 Visi-Therm 300w heaters. I used to use 1 800w but when it broke I did not have anything heating the water so I will never rely on just one heater.
800w is way too much for a 180 unless it's a cold, unheated space or something. Even a single 300 could probably raise temps to dangerous or lethal levels. If that's the case, you've tripled your chances for a tank wipeout. I had a heater fail on my 180 one time, didn't come on, and the temp dropped to 74 or something. You couldn't tell by the fish's behavior. I don't know how many days it wasn't working. The real danger is in a heater that's too powerful sticking on.
 

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I like to tear things down after they fail and see why. When I look at heaters, I see why they fail by sticking on more often then not heating. Older guys who worked on cars before electronic ignitions will recognize what happens when contacts open and close. They arc! Each time they arc, the contacts get a bit rougher and the rougher the contact, the more arc you get. At some point, the arcing works like a welder and the contacts are welded together. The heater stays on until unplugged.
 

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It is not hard to do but it is sometimes not worth the effort. One has to slide the insides out and get to the contacts. Sometimes that is tough. Then you may find the contacts were so tiny that there is not much left to file down to smooth. Once smooth, they are also uncoated so tend to wear and burn quicker the second time. When they overheated the first time, did it distort the spring they ride on? Once you are happy with the contacts, you have to get it back in the tube and deal with sealing it. I am pretty tight but find the process not worth the effort as I am then left with a heater I can't trust as it is less quality than when new. Since it failed me once and is now lesser quality, do I want to trust it again? I use them in my reserve water but not my tanks with fish.
I now buy heaters with contacts outside the tank so that those type contacts are avoided.
 
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