Heater physics question

[Liam]

In my quest for lower electric bill i am pondering this question on heaters.
Is it more efficent to use a larger heater than a smaller heater?
Personally i like to use 2 heaters for redundancy but i am interested if a larger heater that runs for a shorter time would be more efficient.
Or is the difference just negligable?
I'm sure there is some crazy complicated formula out there for calculating it,and if someone knows it great,lets see it but i just wondered what other folks thoughts and experiences are.

 

[smcnally]

IIRC, you will consume the same amount of electricity. The only time you will use more, IMO, is if the lower wattage heater is under powered for your size tank.

 

[RedTide]

In absence of knowledge of the frighteneing formula, I agree with Steve. Given the same volume of water and the same temperature change requirement, I would expect that the wattage required to do the same amount of work would be identical. If 500W of heat should maintain your system, at the desired temperature, then 500W should maintain the heat, regardless if it's from one 500W or 2- 400W. As Steve cautions, 2- 250W may not maintain that same temperature at the same elecrical usage.

 

[Gina McReeferson]

This is something I had just had on my mind yesterday.

Positioning of the tubes could play a role in the efficiency of heat transfer to the aquarium.

And, making it more complicated...

Would it be more efficient to run 2 x 250W heater tubes, or 1 x 500W tube (just example wattages)? It would at first seem to me that the 2 tube setup would result in more efficient heat transfer than the 1 tube due to the increased total surface area of the tubes. I realize a 500W tube is somewhat larger, but I would not think twice as large as far as surface area goes.

 

[Liam]

watch out for trying your tubes in different posistions.I tried that with near disasterous ramifications,but thats a story for another day

 

[Jim Tansey]

If this question had been asked about a different device other than a heater multiple units may well use more power than a larger single unit, such as using two pumps at 1/2 the desired flow rate as opposed one at the full flow. The efficiency of the two pumps would need to be compared with the one to know. Immersion heaters however are very efficient with almost all losses going to heat the water, so within reason multiple heaters could used with no loss of power.

Jim

 

[~Flighty~]

I don't think it would make any difference since heaters don't waste energy (like a light or pump wasting electricity through heat). I like having two smaller ones though so the tank can cope better with different conditions. My controller kicks one on at a certain temp, and the other on if that one can't cut it and the tank drops below a lower threshold.

 

[S Hunter]

watch out for trying your tubes in different posistions.I tried that with near disasterous ramifications,but thats a story for another day

talk about being lucky... not just the lose of that tank but the house as well... yes lady luck was with you on that day

 

[Liam]

talk about being lucky... not just the lose of that tank but the house as well... yes lady luck was with you on that day

the gfci's would save the house.It was me stood in the pool of water looking at bare wires dangling in my sump after i just RESET the gfci that was the worrying part.

 

[savyboy]

One benefit with two heaters is that if one dies it is not enough to overheat or cool the aq.

 

[savyboy]

They need to find a way to pipe water through the lighting, this would heat the water and cool the lights. =)

 

[Greg Hiller]

>I don't think it would make any difference since heaters don't waste energy (like a light or pump wasting electricity through heat).<

Exactly, use two, use three, use one. It matters not. All of the electricity that goes into a heater is converted to heat. This is different that an external water pump in which some of the electrical energy is converted to heat that excapes into air around the external part of the pump. Any water motion created by the pump eventually become heat as the water converts its kinetic energy into heat.

The only time efficiency would matter would be if you were using a single heater on tank and because there was little water motion around the heater the transfer of heat from the heater to the water would not be very effective. In this case the heater would likely be turning itself on and off because the water in the immediate vicinity was getting to a temp above the set point on the thermostat. That would mean that the tank as a whole might not stay as warm as you wanted it. In this case then it's possible that a single heater of say 300 watts would not work as well as a pair of 150 Watters. The pair of 150 watters might have a large surface area, and if placed far apart from each other they might be more likely to keep the tank warm.

Of course the simple solution is just to make sure that the heater is in a area of decent water motion. Then this problem would never come up.

 

[naturebatslast]

FWIW, I overheat (wattage-wise) with multiple heaters, assuming no one heater ever works harder than the others and redundant. Being redundant, with smaller, multiple heaters is probably the safest way to go.

 

[Fingolfin]

>>I don't think it would make any difference since heaters don't waste energy (like a light or pump wasting electricity through heat).<
Of course the simple solution is just to make sure that the heater is in a area of decent water motion. Then this problem would never come up.

Try not to be controversial. Not 100% electricity is turned into heat. A small fraction of the electricity is turned into magnetic field, which is generated by time-varient electric field, i.e. AC current, going through the coil inside the heater. The high resistance inside the coil then dampens the electric current to generate very weak magnetic field. Nonetheless, it's there.

Heater controllers are designed to have certain hysteresis. For example, if you set the temperature @77 degrees, the heater would probably turn on @ 76.5 then turn off @ 77.5 degrees. It gives you +/- 0.5 degree as the hysteresis. The hysteresis overcomes the local temperature perturbation so it doesn't respond to it by turning on or off constantly. The problem I can see from the most of the integrated single unit heaters in the market today is that the controller is on the top of the coil. Without decent water circulation, the heater generates a thermal distribution localized around the heater. Once the temperature adjacent to the controller hits the hysteresis setting, it shuts off the heater. In the meantime, the thermal gradient slowly moves the water around then eventually brings down the temperature to the point that the temperature hits the lower end of the hysteresis then it turns on the heater again. It goes through the cycle over and over again until the thermal gradient around the heater disappears. There's nothing wrong with it. It's just very inefficient time-wise.

To enhance the efficiency, you would be better off placing the heater and sensor at different locations and increasing the circulation in the tank. By separating the heater sensor/controller from the heater, the sensor won't be affected by the localized thermal distribution when the heater is on; by increasing the circulation, the thermal distribution profile can be changed drastically to speed up the heating process.

 

[Liam]

FWIW, I overheat (wattage-wise) with multiple heaters, assuming no one heater ever works harder than the others and redundant. Being redundant, with smaller, multiple heaters is probably the safest way to go.

until one of your large heaters sticks on

 

[~Flighty~]

Put your heater sideways to mostly eliminate the local heating effecting the temp sensor. That being said, I don't rely on any of the temp sensors built into heaters. They are too likely to fail on. I want a system that if it fails will fail off which seems to be the way the finnex ones go if they do fail.

 

[Fingolfin]

Put your heater sideways to mostly eliminate the local heating effecting the temp sensor. That being said, I don't rely on any of the temp sensors built into heaters. They are too likely to fail on. I want a system that if it fails will fail off which seems to be the way the finnex ones go if they do fail.

Gravity can certainly affect the thermal distribution profile. As long as the sensor is a few inches away, the heater is still affecting the sensor no matter how you position the heater.

Just think it as a feedback loop. As long as the sensor is adjacent to the heater, you will always have a small loop, which is subject to variations outside the loop. The key is to make it a large feedback loop that includes many variables: remote sensor and circulation.

 

[maurod]

This is something I had just had on my mind yesterday.

Positioning of the tubes could play a role in the efficiency of heat transfer to the aquarium.

And, making it more complicated...

Would it be more efficient to run 2 x 250W heater tubes, or 1 x 500W tube (just example wattages)? It would at first seem to me that the 2 tube setup would result in more efficient heat transfer than the 1 tube due to the increased total surface area of the tubes. I realize a 500W tube is somewhat larger, but I would not think twice as large as far as surface area goes.

^ I think David hits the key points here. 2 tubes will probably provide some small increase in surface area that would increase efficiency. That said, I'd be willing to bet the TI heaters are far more efficient than plastic or glass due to heat transfering out of metal far more easily than plastic/glass.

M.

 

[MarkO]

I'm the king of cheap (ok, maybe Dong is, but I'm a close second) Dong, that's a compliment, btw
So I say screw the heaters all together. Lower your lights and have your lights heat the tank. On the down side, you will have a bigger fluctuation in tank temp (mine runs 74 in AM, 78-79 at lights out). I do have a heater in wintertime, but the temp is set at 72 and rarely (if ever) comes on. Also, my heater is only a 300W (200 gal. of water). So if it ever got stuck "on" I don't believe it would take the tank temp too high.

 

[Fingolfin]

^ I think David hits the key points here. 2 tubes will probably provide some small increase in surface area that would increase efficiency. That said, I'd be willing to bet the TI heaters are far more efficient than plastic or glass due to heat transfering out of metal far more easily than plastic/glass.

M.

The surface area is indeed important, however, smaller heaters generate very different thermal profile than the larger ones. Eventually, it may be a wash in terms of total wattages.

And I agree that Titanium case transfers heat much faster than the glass/ceremic ones. However, the difference is in the order of seconds, not minutes. And for Titanium, you will always worry about the oxidation.