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Old 08-15-2014, 09:16 AM   #1
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Heater: So how much heat do I really need? Square vs Cube rule

I'm confused by heater sizing. I've got a 45G tank and a 100W heater and all is good, but frankly have no idea if it's running 95% of the time or 2%. Overkill is easy and cheap in that size.

I'm getting a 220G tall tank (72x24x30). I started looking at advice, and most advice seems volume related (e.g. I've heard 5 W per gallon = 1100W). While proportional to volume at initial fill, heat loss is proportional to the surface area not volume for loss into the room, so any guidance that is proportional to gallon-age seems wrong to me.

So I found this nice calculator:

Aquarium Heater Calculator

That says with even a whopping 15 degree difference I need 80W to break even; hugely different from 1100W (and at the more appropriate 5 degree difference break even is 26W).

When I look at Hydro (I liked their canister heater look at least) they don't quote anything larger than 80G and suggest 300W.

I've read several threads recommending as many as three 1000W heaters in similar size tanks.

I looked at Cobalt's sizing guide, and plotted gallons against wattage, and it is nearly completely linear, which just doesn't make sense with the square vs cube relationship of heat loss. Unless they are assuming people dump cold water in at water changes and it needs to heat fast? (Do people really do that?)

So what am I missing here? Do I really need a big honking heater for a (non-sump) 220G tank? Or is something like the Hydor ETH 300 (300w) much more than enough?

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Old 08-15-2014, 09:27 AM   #2
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Tank Heating

Hello Lin...

Figure on 5 watts for every gallon of tank size and you'll have enough.

Pretty simple.

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Old 08-15-2014, 09:36 AM   #3
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Hello Lin...

Figure on 5 watts for every gallon of tank size and you'll have enough.

Pretty simple.

B
Can you comment on why the advice is proportional to gallons rather than surface area of the tank?

I agree I'll have enough -- I don't want to have wildly too much. Besides cost, it seems safer to me to have a safety margin, but not have a heater so big that with a failure it will cook the fish (or at least not quickly).
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Old 08-15-2014, 09:52 AM   #4
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The way to avoid cooking fish is to have two or more heaters of lower wattage. I would say that 1000w seems excessive for a 220. Check the suggested wattage for Jagger heaters. They seem lower than other brands, which makes me think most ratings, such as 5 watts per gallon are too high. Unless the tank is in an exceptionally cold room, you may actually need less than you think. Ideally, a heater should never turn off. It is the constant on/off cycling that shortens their life. Sadly, it seems from reading all the cooked fish posts, heaters seem to fail in the on position more than in the off position.
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Old 08-15-2014, 10:09 AM   #5
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I run two 300 watt heaters in my 225 but my house never gets below 60 degrees. They are run by a temperature controller that will sound a alarm if the temperature goes above or below the set temperature by a few degrees. if your house gets colder then three heaters may be needed. Having two or more is a safeguard in case one fails. IME don't skimp on your heaters, it could fail and cook your tank. Good luck!


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Old 08-15-2014, 10:18 AM   #6
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I run two 300 watt heaters in my 225 but my house never gets below 60 degrees. ....

IME don't skimp on your heaters, it could fail and cook your tank. Good luck!
We are in SW Florida. Our house never gets below 74 degrees or so except a few days a year if my wife opens the door in really cool weather maybe 68. It's actually a bigger risk getting hot (AC failure).

The latter is my concern. Largely the fish would be OK if the heater failed off, but failing ON is an issue.

-----

In looking at that heat calculator I referenced above, I do not think it considers evaporation, which makes it pretty useless IMO.

I dug up this article

Feature Article: Heat Transfer in Aquariums Part 1 - Basic Theory ‚€” Advanced Aquarist | Aquarist Magazine and Blog

Near the bottom it gives a formula for heat loss due to evaporation that's parameterized by temps (well, indirectly through the tables to derive humidity ratio). If I plug in my house and tank, and assume 1 ft/sec air movement across the top (quite high) I get 276 watts from evaporative heat loss. That presumes the entire tank is uncovered. If I (as I do now) uncover about a quarter over surface agitation, it comes down proportionally to about 70 Watts.

I think this evaporative loss would be additive to the values in the calculator above.

It also means an open top tank is primarily losing heat from evaporation, which makes intuitive sense.

Still reading... thanks for input to day.
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Old 08-15-2014, 11:32 AM   #7
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You didn't mention if this is for a freshwater or saltwater tank. For a FW, you really want to try to keep the water temp as constant as possible. For marine inverts and most fish, a little fluctuation is not going to do as much damage. Having said that however, being where you are, a chiller may be more important than heater depending on what you are keeping. What's the average high temp you keep the house?
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Old 08-15-2014, 12:04 PM   #8
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Tank Heating

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Originally Posted by Linwood View Post
Can you comment on why the advice is proportional to gallons rather than surface area of the tank?

I agree I'll have enough -- I don't want to have wildly too much. Besides cost, it seems safer to me to have a safety margin, but not have a heater so big that with a failure it will cook the fish (or at least not quickly).
Hello again Lin...

This wattage will maintain a proper water temperature and not overwork the heater. This is the easiest way I know to explain it. A bit larger heater and multiple heaters will ensure the heat is distributed evenly and you'll have a backup if one fails. A bit larger heater won't come on as often, so isn't worked too much. It will last longer.

The heaters have dials on them, so a specific temperature can be set and the heater will maintain that setting until you change it. There's little or no chance of the heater cooking the fish.

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Old 08-15-2014, 01:09 PM   #9
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You didn't mention if this is for a freshwater or saltwater tank. For a FW, you really want to try to keep the water temp as constant as possible. ....Having said that however, being where you are, a chiller may be more important than heater depending on what you are keeping. What's the average high temp you keep the house?
Freshwater, low tech, planted. Haven't decided on stock.

Except for rare exceptions, our house stays at 74 degrees year round, 24x7. The exceptions are things like parties where one side of the great room is opened, but that usually only happens if the temp is within about 5 degrees of 74 anyway. Plus it doesn't stay open long.

I hate heat (don't ask why we are in SW Florida), and it's just so sunny here even when it's milder in winter that we use AC all the time.

The biggest heat risk is if the power is out for extended periods of time, but if ambient even went to 90 or so, it would take a while for the tank to heat. And I just did an Ich treatment at 88 degrees and everyone was healthy and happy (in fact I swear they were happier -- more active certainly). So I'm less worried about heat.
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Old 08-15-2014, 01:22 PM   #10
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Hello again Lin...

This wattage will maintain a proper water temperature and not overwork the heater. This is the easiest way I know to explain it. A bit larger heater and multiple heaters will ensure the heat is distributed evenly and you'll have a backup if one fails. A bit larger heater won't come on as often, so isn't worked too much. It will last longer.

The heaters have dials on them, so a specific temperature can be set and the heater will maintain that setting until you change it. There's little or no chance of the heater cooking the fish.

B
What a concept. You mean you can tell it the temperature, and it tries to maintain it? I assumed I would have to run around plugging it in when the fish were cold, and unplugging when they got hot.

To your point, however, I realize there may be little chance, but I've read too many posted horror stories. Could be fabricated (after all it's the internet), but it also makes sense.

In most if not all heaters there's going to be a relay, in fact that might be the only moving part in most (some might incorporate a bent metal thermostat). That relay arcs when it turns on and off. Going off the momentum is away from the contact, but going toward (turning on) it's a bit like a tiny arc welder. This is why the most common failure mode for relays is "stuck on"; the arc sort of welds the contact and the spring can't pull it away later.

And stuck on, absent some kind of fail safe, just runs all the time. Maybe they have fail safes, maybe they don't, not sure.

Anyway... I'm new to this hobby, so perhaps I shouldn't sound like I am arguing with good advice; sorry. But I am not new to engineering. To me the reason for trying not to get too large a heater are:

- One sized correctly runs at a higher duty cycle, which means more even heating reducing hot spots (think cooking on a stove on low heat for 20 minutes, vs cooking on a stove on high heat for 5 seconds out of every minute). (I realize you suggest the opposite is an advantage, a lower duty cycle; I just do not see why that's good).

- A stock-on heater will take longer to do damage and might be noticed before it does.

Obviously getting one too small with either allow tank fluctuations, or will take too long to make tank changes (e.g. if you did have to add water significantly colder).

Trust me, I tend to be a "more power is better" type, a la Tim Taylor in the old Tool Time show. But sometimes it isn't. Consider Heat pumps for houses -- it's quite bad actually to get one that is way over capacity, uses more energy.

This just feels like one of those cases were "way too much" may not be good. Maybe i'm wrong, will keep reading and listening, thanks for the input.
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Old 08-17-2014, 01:03 AM   #11
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Freshwater, low tech, planted. Haven't decided on stock.

Except for rare exceptions, our house stays at 74 degrees year round, 24x7. The exceptions are things like parties where one side of the great room is opened, but that usually only happens if the temp is within about 5 degrees of 74 anyway. Plus it doesn't stay open long.

I hate heat (don't ask why we are in SW Florida), and it's just so sunny here even when it's milder in winter that we use AC all the time.

The biggest heat risk is if the power is out for extended periods of time, but if ambient even went to 90 or so, it would take a while for the tank to heat. And I just did an Ich treatment at 88 degrees and everyone was healthy and happy (in fact I swear they were happier -- more active certainly). So I'm less worried about heat.
I have to laugh, sorry. If you think Cape Coral is hot, you should come to my neck of the woods. My tanks are outside so they do get hot enough that my Angelfish stop spawning and my Betta's eggs were hatching so fast that the fry were deformed and under developed. Heat, is not always a good thing.

I understand the difficulties in understanding the mechanics of the system but try not to over think it. These thermostatically controlled heaters will shut off if the temp is above the set temp. ( All my heaters are still plugged in and turned on and set to last winter's temps. I don't see them on because the air temp is hotter so their water is hotter.) If you are using a non submersible type heater ( such as the old Supreme heaters like I am using) you can periodically take them apart and clean the contact points to prevent them from sticking. If you are using a sealed type, such as a submersible, you are just going to have to trust that they work as planned by the manufacturer. Most often, these type heaters fail by not turning on, NOT from staying on and cooking the fish. Yes, if they do get stuck in the on position, you "should" have time to catch it in a larger aquarium but that is not usually the case. Using the "Murphy's Law" principle ( my favorite when it comes to fish keeping ), it will happen, if it happens, when you are not available or not there to see it or stop it from happening. That's just "fish keeping" through my 50 years of keeping them. While the odds are in your favor by picking the right machines and inhabitants, in reality, it is still a crap shoot. Things happen. Not everything is preventable.

One thing to consider is that at 74 degrees, your tank is not really best suited for many tropical type fish. It's a bit too cold. It's a good goldfish temp or maybe for some of the cooler water loaches, rainbowfishes or catfish as well but most tropical fish are best kept at 78-80+ degrees. This could swing the whole heater debate back to a necessity rather than a luxury ( depending on what you are going to stock) and as such, if going with more tropical fish, I think you would be better off with multiple heaters placed in different areas of the tank or all within the sump (if you are using one) to make sure the water going back into the tank is at the proper tamp. Temperature consistency is a key element to keeping fish from getting sick. If a tank keeps jumping more than 2 degrees in either direction, fish are more prone to ICH infestations.

Hope this helps
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Old 08-17-2014, 01:54 AM   #12
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Although you may not need it, redundancy is a good thing. I would suggest 2 fluval e300's. Living in fla with a near constant temperature of 74 indoors, your heaters just wont be working that hard. The fluval e series have built in thermometers so you will be able to see how hard they are working to maintain trmperature.

You say you will be doing a planted tank, unless you are using LED's, you will be adding more heat to the tank from the lighting.

You probably only need one, but I like to be redundant. The tank will never get cooler than 74, and that is with an extended period without light and heat. Plus the tank will cool slowly, so the fish wouldn't notice a wide temperature swing. Not ideal, but not really harmful for a short amount of time.


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Old 08-17-2014, 08:56 AM   #13
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You say you will be doing a planted tank, unless you are using LED's, you will be adding more heat to the tank from the lighting.
I am still working out which, but I am definitely using LED's. Home or whatever, I'm glad to see the end of the incandescent or florescent bulbs.

So I'm probably going to see a net loss at the top of the tank from evaporation not heat gain.
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Old 08-17-2014, 09:02 AM   #14
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I have to laugh, sorry. If you think Cape Coral is hot, you should come to my neck of the woods. My tanks are outside so they do get hot enough that my Angelfish stop spawning and my Betta's eggs were hatching so fast that the fry were deformed and under developed. Heat, is not always a good thing.
Ah come on, Lake Wells is way up north! I bet you even turn your house heat on in the winter, put on long pants and real shoes, and probably have a coat somewhere a closet!

But more seriously-- you keep them outside? Like on a Lanai?

How do you deal with too much light? (Or are they more in shade)?

I make RODI water in the shade on our Lanai. This summer the water has averaged about 91-93 degrees, a combination of high tap water temperature and time sitting (in the shade!) at mid-90's in a bucket while it makes. So I have to make water a day ahead and let it cool to use it.

I just assumed living in that heat would be very bad for fish, and the light for 16 hours (maybe 6 direct) would cause a lot of algae?
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Old 08-18-2014, 03:51 AM   #15
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3x 200w Cobalt neo-therms, not glass, visual thermometer, digital setting so no fiddling with 3 dials, 3 year warranty and if one does "break" in the on position 200w isn't enough to boil ur tank.

If thats to rich for you, 3 of any 200w heater would work weather it be Jagers or Aqueons from petsmart, or 2x 300w's but then 1 going bad could over heat your tank.
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Old 08-18-2014, 03:55 AM   #16
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Although you may not need it, redundancy is a good thing. I would suggest 2 fluval e300's. Living in fla with a near constant temperature of 74 indoors, your heaters just wont be working that hard. The fluval e series have built in thermometers so you will be able to see how hard they are working to maintain trmperature.

You say you will be doing a planted tank, unless you are using LED's, you will be adding more heat to the tank from the lighting.

You probably only need one, but I like to be redundant. The tank will never get cooler than 74, and that is with an extended period without light and heat. Plus the tank will cool slowly, so the fish wouldn't notice a wide temperature swing. Not ideal, but not really harmful for a short amount of time.


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I like the E series too but they do wacky things when not in flow or in to much or when not heating a lot. Mine was perfect, now I put on a canister filter and a 300gph pump on for hillstreams and it says low flow... like wat?

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I am still working out which, but I am definitely using LED's. Home or whatever, I'm glad to see the end of the incandescent or florescent bulbs.

So I'm probably going to see a net loss at the top of the tank from evaporation not heat gain.
Lol why do you hate on Florescent so much? T5's are bomb.
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Old 08-18-2014, 08:50 AM   #17
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3x 200w Cobalt neo-therms....
If I use in-tank I absolutely would use them. This question was more about how much than which.

I bought a 200W Neo-therm, it had a small problem (one dead LED). Cobalt was so incredibly nice about replacing it that I am now a huge fan of the company, plus it's inconspicuous profile and solid-slab design are nice.

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Lol why do you hate on Florescent so much? T5's are bomb.
Nothing to do with aquariums. LED's are SO much more energy efficient, I felt like there was a decade or so we lost out, and the whole CFL tangent (with its mercury-laden waste) was such a wasteful dead end (but that we are still going down). Not really relevant to the conversation I guess, just a lament.
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Old 08-18-2014, 12:28 PM   #18
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If I use in-tank I absolutely would use them. This question was more about how much than which.

I bought a 200W Neo-therm, it had a small problem (one dead LED). Cobalt was so incredibly nice about replacing it that I am now a huge fan of the company, plus it's inconspicuous profile and solid-slab design are nice.
Oh haha I didn't even know that was you, yeah I would say 2 300w or 3 200w heaters. You could even go 3 250w heaters, if you go with eheim or other glass heaters the difference in price between size's is almost nothing, also get something with a ON indicator LED, most have this, at night you can also see if the heating element is glowing or not. A 300w is suppose to be good up to 90g but 1 heats my 150g just fine, but I will be replacing it with 2 200w neo-therms.



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Nothing to do with aquariums. LED's are SO much more energy efficient, I felt like there was a decade or so we lost out, and the whole CFL tangent (with its mercury-laden waste) was such a wasteful dead end (but that we are still going down). Not really relevant to the conversation I guess, just a lament.
Oh haha I was just wondering, they are more efficient but the house bulbs I have scene I wasn't to exited out (directional light with a huge heatsink), they for sure rock in flashlights.
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Old 08-18-2014, 10:58 PM   #19
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Ah come on, Lake Wells is way up north! I bet you even turn your house heat on in the winter, put on long pants and real shoes, and probably have a coat somewhere a closet!

But more seriously-- you keep them outside? Like on a Lanai?

How do you deal with too much light? (Or are they more in shade)?

I make RODI water in the shade on our Lanai. This summer the water has averaged about 91-93 degrees, a combination of high tap water temperature and time sitting (in the shade!) at mid-90's in a bucket while it makes. So I have to make water a day ahead and let it cool to use it.

I just assumed living in that heat would be very bad for fish, and the light for 16 hours (maybe 6 direct) would cause a lot of algae?
Okay, for starters,
Yes, I have used the house's heat in the winter along with long pants but no shoes. I work barefoot. ( okay, I use socks in the winter too. )
Actually, I am only about a 2 hour drive Northeast of you so I am not that far away. Being in the center of the state however, it is very hot and humid during the summer. The avg temp this past week was 94 degrees on my porch where some of the fish are. I have tanks on an open porch and my 2 screened in porches. I keep the fish well oxygenated in the summers with a lot of bubblers going. Thankfully, I've not lost any tanks due to overheating. I've even had to encapsulate the tanks in styro the past 3 winters just to keep the air temps from overtaxing the heaters. But again, I didn;t lose any fish from temp issues. Proper fish selection helps. My neighbor is a Koi farmer and he uses no heaters at all. His fish are in pools or ponds so they can adjust to whatever temp is most comfortable for them.

Yes, algae is a problem. Thankfully that problem is almost over. I'm having a climate controlled building being put up on my property to house the fish so I shouldn;t have a temp or algae problem anymore. About 1 more month before it's all done.

So as for keeping fish in the heat, it all depends on what you keep. Most tropical fish prefer a temp of 78-82 degrees with some fish, like Discus, liking it even hotter. It's why FL is one of the fish breeding capitols of the world. The temps and water are so right for it. The colder water fish are bred indoors.

Hopefully you'll get your heater issue taken cared of. As I said before, don;t over think it. Fish keeping, while a science, does not always follow the basic rules of science. It's sometimes is still trial and error.

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Old 08-19-2014, 08:39 AM   #20
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It's sometimes is still trial and error.
Indeed, that's why the internet is helpful. If you can sort through the crap, you can then benefit from other people's errors.

What's the saying, we learn from experience, but usually only the painful ones.
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