Calling all Engineers.....heater question.

[chriscoli]

Ok, I have a heater question for all of you smart people on our forum.

I understand the concept that X watts of heater will only raise the temp X degrees above whatever the temperature of the room is.

And if you have an underpowered heater, it'll run and run and run trying to keep up with the needs of the tank....

But is it also bad to have an overpowered heater in a tank? I was assuming (key word here...assuming) that an overpowered heater would just get the job done faster, maybe overshoot its target a bit, and then shut off till it was needed again. Perhaps a bit inefficient and perhaps some waste in having wider temp swings due to the overshooting of the target temp. But does it end up being grossly wasteful electricity-wise? I realize that I haven't quantified what I consider "grossly wasteful".... And that's because I don't know. But do any of you all have any thoughts on this besides "because that's what the box of the heater told me to do"?

 

[blkmjk]

I'm still at work ATM. But when I get a chance I will weigh in on this!

Drew

 

[chriscoli]

Please do!

 

[chriscoli]

Oh, and the back-story for why I'm asking.....I did a heater inventory this week to see what I had stuck behind my mattenfilters way back when I set things up. Well, the heater wattage is all over the place! I've got everything from 50 watt to 150 watt heaters behind the filters on a rack of 16, 10 and 15 gallon tanks. I'm wondering if I need to downgrade the big heaters......if I do, it needs to be worth the cost of replacing between five and seven heaters.

 

[cichlidaddicted]

I have found that there are several reasons its better to run either two small heaters or one that is a bit underrated for the tank. Keep in mind I'm not trying to heat water that starts any colder than 65-68º. Also there are some variables such as the length of the coils in different brand heaters- different surface areas being warmed in turn heating the water. If my starting temp was lower I would need higher wattage but no manufacturer specifies these key pieces of info(I wonder why) Perhaps a list of variables is needed
-starting temp
-volume to heat
-Surface area exposed to room temp
-Surface area of heater (length of coils)
-accuracy of thermostat (I have found it to be +- 3º at best no matter what they say)
-at what deviance from set temp it actually turns on and off
-placement
-water flow
-how fast the water is heated
I could go on but you get the point. That being said, this is what my experience has taught me.
1, two underrated heaters one on each side heat the water evenly eliminating the large temp. Swings
2, two heates eliminate the confusion of heat pockets causing heaters to turn on and off unnecessarily. (Also effected by poor flow)
3, two 100w heaters are more than capable of heating the same amount of water as a 300 watt given a fair starting temp. (Possibly due to surface area being heated)
4) heaters can only run at full power and often 300w isn't needed to heat the water a minimal amout.
5) maybe a larger heater would heat the water quicker but honestly who cares if your temp is set at 80 I don't care if it takes three hours to heat it from 78º-82º as long as it reaches that temp efficiently. I believe two heaters does it much more efficiently for reasons already stated.
I won't even go into the more obvious reasons such as malfunction and over heating. I think this a great experiment in the making. I would love to know if a 300w actaully gets hotter than say a 100w or if it just heats a longer coil the same temp? Or how long it would take two100w heaters vs. One 300w to warm 55g from 70º to 80º. Or let them both run an hour and see which warmed the water more.......all I know is that the charts on the box never make sense and are obvioulsy aimed at getting us to buy a bigger heater!
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[cichlidaddicted]

On a 30g or bellow anything over 100w is costing you more than it should. Hard to put in words but the water is always cooling at the same speed no matter how big the heater is so a 300 would run about the same amount of time as a 100. That doesn't make sense but the science behind this is beyond my explanational vocabulary!

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[ddavila06]

go heaterless

 

[cichlidaddicted]

Pardon my redundant posting but I just looked my 75 runs on a 100w my room temp is 69 and tank temp is 82.9 digital. Heaters off at the moment.

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[CichlidAddict]

The biggest hazard of having an over powered heater is that if the thermostat mel functions, you can cook the fish. More fish die from over heating than under heating. So it is OK to have over powered filtration, but never over power heating.

 

[chriscoli]

Dan, I think it was a previous comment that you made that got me to put two heaters on my big tank....so you've got some very sound advice there. I am also unimpressed by the total lack of precision on these heaters....as you point out. They vary widely and the temps on the dial seem to be merely a suggested starting point, which is a huge PITA with a rack of small tanks to be constantly adjusting them.

Since I have a rack of 16 small tanks (10 to 15 gallons each) and each needs a heater I can't do two per tank.

The room tends to vary from 68 to 70 in the winter and I'm ok running my tanks on the cooler side...I've been aiming for between 74 and 76 unless it's a species that can't tolerate that.

Also, before someone asks....no, I can't heat the room. If I could, I would love to. Unfortunately, if I did, we'd be walking around upstairs in tank tops all winter.

And Damian, I did try that and there were some very unhappy-looking fish. On the plus side, it got my White Clouds to spawn like crazy!

 

[chriscoli]

The biggest hazard of having an over powered heater is that if the thermostat mel functions, you can cook the fish. More fish die from over heating than under heating. So it is OK to have over powered filtration, but never over power heating.

I hear ya....I've had several near misses.

 

[mchambers]

I guess that's right, but it also might be that an underpowered heater is more likely to malfunction. Don't know if that's true, but it's worth considering.

 

[cichlidaddicted]

I'm curious if they fail from switching on and off to many times or to often or if they fail from running longer and not switching as much. I would pay for a solid answer to that. The former sounds more logical to me but who knows.

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[npbarca]

Its ok for the heater to be overpowered as long as it has an accurate control of the temperature being produced, which means I would go for the higher quality controllable heaters if you want to overpower a tank. I have a Aqueon controllable 250w on my 75, and the temp it is set at is 79. Whenever I measure the temp anywhere in my tank, even next to the heart, the temp is always within 1 degree of 79.
So yes, you can use a bigger heater than needed, but make sure it is high quality and accurate to the temp it is set to produce.

 

[cichlidaddicted]

Its ok for the heater to be overpowered as long as it has an accurate control of the temperature being produced, which means I would go for the higher quality controllable heaters if you want to overpower a tank. I have a Aqueon controllable 250w on my 75, and the temp it is set at is 79. Whenever I measure the temp anywhere in my tank, even next to the heart, the temp is always within 1 degree of 79.
So yes, you can use a bigger heater than needed, but make sure it is high quality and accurate to the temp it is set to produce.

Do you mean digital control, or attached to a digital controller? I have an aqueon pro on my 125 with a dig thermometer the heater keeps the tank between 79-82º however the thermostat on the heater is set to 75. I have learned the hard way to never trust a heater, always atleast keep a thermometer in view and look at it everyday! And never ever trust a heater that is not adjustable. Just last week my 2 year kicked a ball under my fry tank didn't realize till the next day when I put my hand in to strip a fish and the water was 68º, heater came unplugged. I wish I could find a little digital thermometer just like the ones they make now but with an audible alarm just a few beeps when the temp is outside a set range.

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[Jmoore]

I wish I could find a little digital thermometer just like the ones they make now but with an audible alarm just a few beeps when the temp is outside a set range.

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Now that's a good idea



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[npbarca]

I have a digital and a stick, and the heater has the lights to indicate when it's heating and when it's not. When It's feeding time, I always do a routine check of equipment, it's a good habit to get into.

 

[cichlidaddicted]

I meant is the thermostat on the heater digital or is the heater plugged into a controller. By no means am I saying don't use a big heater. I'm actually looking for even one positive thing that can come out of using an overrated heater. Heater failure is one of the most dreaded events in the hobby and not coincidentally heaters are one of the easiest things to skimp on when setting up a tank. As previously stated its not the cold water that kills the fish.
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[CichlidAddict]

When a heater goes, it's typically the thermostat first before the heating element. A right size heater won't do much harm if it doesn't turn off, but an over sized heater will cook the fish.

I attended the the ACA convention last time it was in NJ over a decade ago. It was summer time and the air conditioned fish show room in the hotel was kept at mid 70s. None of the fish tanks had heaters except for a row of Discus show tanks. In the morning of the show, a number of prized Discus were cooked to death overnight because the heaters over shoot the temperature. The tanks were all 15 gal, so apparently, they didn't have heaters low powered enough to fit. I was there to witness the disaster. I could touch the surface of the tanks and felt the warmth. If they had used the right size heaters, it could not have raised the temperature by more than 10F above the room temperature and disaster could be avoided. An expesnisve lesson for the professional discus keepers.

 

[blkmjk]

Ok this subject is really to much to properly expand upon because it could go all the way into tuning PID loops. We don't need that for this discussion...

The best way to control the heat in your tank would be a modulated heat source. For the somewhat varying load you put on the tank while changing water and the rate of evaporation due to relative humidity fluctuations in your house. I would say this....

If you have one heater that runs 300W set at 80° and 2 150W heaters set at 80°they consume the same power and will experience the same swings because the setpoint and accuracy of the internal thermostat is the same. To reap the benefit of the two heater modulation you would have to set the heaters at different temperatures. Say 78°and 80° thus giving the first heater a chance to handle the load before heater number two comes on. The biggest problem is temp overshoot IMO as well as thermostat inaccuracy. The best way to control the temp of the tank us with as baby stages as possible or the most amount of small heaters that equal the max output you require. If that makes sense?

I could go on for hours but this is the long and short of it. I personally put the smallest heater possible for my tanks. Not based on the chart on the box.

Based on...
Surface area of the glass
Expected tank temp
Expected room temp
Volume of water

Remember it takes 1 btu to raise 1# of water 1 degreeF. I gallon = 8.33#
3.412 Watts per btu

So if I had a 100 gallons to raise the temp 1 degree in one hour I would need 833 btu or 244w introduced to the water over the period of one hour. Does that mean that I need a 250W heater???? No it doesn't. It just means that if I lower the temp in my tank one degree if i want the tank to come back to temp in one hour that is the heater I would need.


A large heater would bring the temp faster from the big loads that you put on the tank. Water changes mainly. But it will be overkill while operating regularly. Hourly this makes sense if not i could explain it better in person.

Drew

NO GOOD DEED SHALL GO UNPUNISHED!