Two 100 watt heaters equals One 200 watt for 55 gallon???

cmid21

Hello all,

*I have a 55 gallon that I want to keep between 74-80 degrees. The recommended (depending on who you ask is around 200W, it varies but I will use this number). I would rather utilize two smaller heaters in case one decides to malfunction and stay on (small chance, but it does happen). That way individually, it won't have the capacity to cook my fish.

In general terms, if I purchased two ~100W heaters for a 55 gallon, is that equivalent to one 200W? Mathematically it checks out however, in real world terms does that hold true?
 

cmid21

Sorry for the new thread, this was moved to its own post from the similar thread posted previously.

Any thoughts are much appreciated.
 

Mongo75

For the most part, yes. Two heaters of the same wattage will be the same as a heater of twice the wattage. Three heaters of 1/3 the total wattage will be the same as one heater three times their wattage. Two 100 watt heaters are equivalent to one 200w heater. Three 75w heaters are the same as a 150w (oops, bad math) 225 w heater.

Each smaller heater will work less than a larger single wattage heater. They may even keep minor fluctuation from happening, or reduce them as well. A single heater may have a 1 or 2 degree fluctuation, meaning your water temp may fluctuate one degree either side of what you have the heater set to. With two heaters, one may be on while the other is off but the water will be closer to your set temp because the one that's on will be taking up the slack for the one that's off.

It also depends on what your ambient room temp is. The colder your ambient room temp is, the harder the heater(s) will have to work in order to maintain your set temp. If the difference is too great, the heater(s) will lose. They won't be able to generate enough heat to keep the water at your set temp.

Think of all of this in terms of a horse drawn wagon. If the wagon is too heavy, one horse might not be able to pull it, so two horses are used. Two can pull the wagon better than one. If the wagon gets too heavy, or if you're pulling the wagon up a grade, then it may get to where even two horses aren't enough. If it's a moderately laden wagon an level ground, one horse can pull it, but two horses will each be pulling 1/2 the total weight, and therefore each horse will be working half as hard to pull the same weight.

Now, back to your original question...two 100w heaters placed on opposite ends of your tank will do a bang-up job of keeping your temp where you want it, and the heated water will be more even throughout the tank. Redundancy is always good in case of a failure too.
 

WetRootsNH

Sorry for the new thread, this was moved to its own post from the similar thread posted previously.

Any thoughts are much appreciated.
I'm not sure about the mathification or physicals bout it. I will say that I run two 150w heaters on my 75 gallon and what has happened is that one just never turns on and the other is almost always on. So I'd say eventually I'm going to have 1 dead heater and one that's pretty much never been used.
 

cmid21

For the most part, yes. Two heaters of the same wattage will be the same as a heater of twice the wattage. Three heaters of 1/3 the total wattage will be the same as one heater three times their wattage. Two 100 watt heaters are equivalent to one 200w heater. Three 75w heaters are the same as a 150w heater.

Each smaller heater will work less than a larger single wattage heater. They may even keep minor fluctuation from happening, or reduce them as well. A single heater may have a 1 or 2 degree fluctuation, meaning your water temp may fluctuate one degree either side of what you have the heater set to. With two heaters, one may be on while the other is off but the water will be closer to your set temp because the one that's on will be taking up the slack for the one that's off.

It also depends on what your ambient room temp is. The colder your ambient room temp is, the harder the heater(s) will have to work in order to maintain your set temp. If the difference is too great, the heater(s) will lose. They won't be able to generate enough heat to keep the water at your set temp.

Think of all of this in terms of a horse drawn wagon. If the wagon is too heavy, one horse might not be able to pull it, so two horses are used. Two can pull the wagon better than one. If the wagon gets too heavy, or if you're pulling the wagon up a grade, then it may get to where even two horses aren't enough. If it's a moderately laden wagon an level ground, one horse can pull it, but two horses will each be pulling 1/2 the total weight, and therefore each horse will be working half as hard to pull the same weight.

Now, back to your original question...two 100w heaters placed on opposite ends of your tank will do a bang-up job of keeping your temp where you want it, and the heated water will be more even throughout the tank. Redundancy is always good in case of a failure too.
Wow, this is great information thank you!

I felt fairly stupid asking the question, as it seemed pretty obvious (100+100=200) but sometimes real world applications don't necessarily follow conventional sense.
 

kallililly1973

I just run a single 300W in my 55 keeps it perfect at 75-77
 

Mongo75

Wow, this is great information thank you!

I felt fairly stupid asking the question, as it seemed pretty obvious (100+100=200) but sometimes real world applications don't necessarily follow conventional sense.
That's why I said "For the most part...", lol. Real world can often fool us!
 

JenC

I remember a thread a few years back. I'd suggested getting two heaters totaling the desired wattage to produce more even heat and reduce the likelihood of boiling fish during a malfunction.

The response was that I was very wrong because didn't I know that watts don't add that way and two 50w heaters didn't equal a 100w heater?

I've been wanting to better understand how this works since then. I'm very interested to see the responses to this thread!
 

cmid21

I'm not sure about the mathification or physicals bout it. I will say that I run two 150w heaters on my 75 gallon and what has happened is that one just never turns on and the other is almost always on. So I'd say eventually I'm going to have 1 dead heater and one that's pretty much never been used.
That's odd! I wonder why that is the case. Maybe recalibrate the heaters so they both share the work load?

I just run a single 300W in my 55 keeps it perfect at 75-77
This was my initial plan. Just purchase the highest wattage as the difference in price was negligible. (talking about under a dollar difference between most of the heaters) However, I thought if that heater malfunctions, which does happen, this could easily heat my tank up to dangerous temperatures in a very short time, decreasing the time I would have for detection of the problem. So I have decided to split the work between two heaters. Plus I would anticipate having a more uniform temperature across the tank.
*Also, I already have a 100W heater, so that was a factor as well.
 

cmid21

JenC
Interesting. Do you happen to have a link to that discussion? I would be interested in giving that a read.
 

WetRootsNH

That's odd! I wonder why that is the case. Maybe recalibrate the heaters so they both share the work load?


This was my initial plan. Just purchase the highest wattage as the difference in price was negligible. (talking about under a dollar difference between most of the heaters) However, I thought if that heater malfunctions, which does happen, this could easily heat my tank up to dangerous temperatures in a very short time, decreasing the time I would have for detection of the problem. So I have decided to split the work between two heaters. Plus I would anticipate having a more uniform temperature across the tank.
*Also, I already have a 100W heater, so that was a factor as well.
Yeah, it's pretty unusual. I need to take a look at it this weekend. Maybe they are both dead and one is stuck on and the other is stuck off. No worries about it cooking my fish... we keep the house at 55 in the winter.
 

Mongo75

I have a 100w heater in my 20 gallon with a spare in the "spare parts bin". Two heaters are just too unsightly in my opinion. I worry more about someone forgetting to close the curtains and my tank getting direct sunlight than my heater failing. I also check my water temp throughout the day to make sure it's still where I want it.
 

WetRootsNH

Yes, I just found it here from last summer: Which Wattage Would Be Better? | Heaters 412444

It's actually been on my to do list to understand it better since then so I'm glad you raised the topic!
Very interesting read. Looks like things got rather, um... heated.

I think I agree more with the two heaters can provide more temp thing. I mean, they won't shut off till they reach the desired temp so it makes sense to me that they'll both keep heating till it gets there... so additive. Dunno, just my takeaway.
 

JenC

Looks like things got rather, um... heated.
I'd forgotten that happened. I just remember bookmarking the thread to come back to it later. Now I guess I'll have to read it properly.
 

cmid21

Yes, I just found it here from last summer: Which Wattage Would Be Better? | Heaters 412444

It's actually been on my to do list to understand it better since then so I'm glad you raised the topic!
Perfect thank you! This is great information.

Now I don't profess to understand all the science addressed, nor did I read the entire thread as of this time. After pondering your response about being told that several heaters do not equal the wattage in output; I was wondering how you would heat bigger aquariums. I skimmed the postings until I found someone that finally addressed my thoughts.

"Look, if this wasn't true, how could you possibly heat a 10,000 gallon aquarium? Do you imagine there's somebody out there making 50,000W heaters? The biggest single heater I've seen for the home market is 500W."
This is precisely why I think (my unprofessional opinion) there has to be validity to several heaters aside from the stability factor. (ie 100W+100W roughly will equal 200W)

That only makes sense to me.
 

Mongo75

Sorry for the back to back posts...

I remember a thread a few years back. I'd suggested getting two heaters totaling the desired wattage to produce more even heat and reduce the likelihood of boiling fish during a malfunction.

The response was that I was very wrong because didn't I know that watts don't add that way and two 50w heaters didn't equal a 100w heater?

I've been wanting to better understand how this works since then. I'm very interested to see the responses to this thread!
Yes, I just found it here from last summer: Which Wattage Would Be Better? | Heaters 412444

It's actually been on my to do list to understand it better since then so I'm glad you raised the topic!
Ok, I read the linked discussion(s), and I think what @Cichlidude is saying is on the mark. An individual heater has it's delta-t that it will be able to compensate for, but the heater doesn't shut off when it has reached it's limit. It will remain on, and continue to contribute to the overall heating of the water. I'm sure that if you put a heater in 40 degree water, it will not shut off because it can't heat the water to 75 degrees. It will stay on until it burns out, trying to heat the water.

Using a 15 degree delta-t as an example, if heater #1 can only raise the temp from 55 to 70, then by itself, the water will be 70. When you add heater #2, it's starting out with 70 degree water, so it will be able to heat that 70 degree water to say, 85 degrees. But since the combination of the two heaters are working in concert with each other, each in turn will be complementing the other, and together they will have the benefit of the other, and together they will be able to heat the water to a comfortable 78. At some point, they may not be able to increase the water to the desired temp based on ambient room temp, and the volume of water, but by working together, they will raise it beyond the limits of a single heater.

I have no science to back this, so it should be taken simply as an opinion.
 

Sorg67

I'm not sure about the mathification or physicals bout it. I will say that I run two 150w heaters on my 75 gallon and what has happened is that one just never turns on and the other is almost always on. So I'd say eventually I'm going to have 1 dead heater and one that's pretty much never been used.
It would seem that this would be the result of not having the heaters set to exactly the same temperature. Seems you could turn the temp up on the one that never comes on or turn the temp down on the one that is always on until you find the right balance.
 

WetRootsNH

It would seem that this would be the result of not having the heaters set to exactly the same temperature. Seems you could turn the temp up on the one that never comes on or turn the temp down on the one that is always on until you find the right balance.
Yeah, I have to play around with it a bit. Hopefully the one that never turns on is just set too low and not dead.
 

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