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Aquarium heaters

EdWhite

Members
Quick question... I was under the impression that a tank would need 3-5 watts per gallon. I've been keeping a 300w on my 75 and they kept dying on me. Luckily they'd just stop heating and I'd catch it and replace it.
After reading all of the reviews on here, I ordered a Eheim Jager 300w heater. The package states it's for 159-264 gallon tanks... Did I buy too much heater?


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jonclark96

Past CCA President
I think 300W is a lot for a 75. I use a 250W on my 120 with no issues. I'd be wary of having such a powerful heater on that sized tank.
 

EdWhite

Members
Aqueon 300w is rated for 75g
Top Fin 300w is rated for 65g

I guess eheim just has their stuff together. Do I order a 150w heater or just buy a big tank to match the heater, lol???


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Acpape0

Members
As long as it is big enough it will be fine ... They all have built in thermostats that will shut down heater on e desired temp is reached. one that has extra wattage will just heat water quicker.... The only worry is that if there is a malfunction with the thermostat and the heater stays on all the way and does not shut off once desired temp is reached it will heater your water faster giving you less time to catch the failure before you "boil" your live stock ....IMO you are fine


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I use a 100w aquatop on my 75 keeps my water 14º above room temp easily. My 125 has a 200w and I plan on replecing with a 150w. My experience is that 1w heats one gallon 8-10º above room temp. I think even that's a low estimate.

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Actually you can calculate your heater size requirements mathematically pretty easily.

1 watthour = 3.412 Btu,
1 Btu will heat one lb of water up 1 degree F.
1 gallon of water weighs 8.35 lbs.

Therefore,
to heat one gallon of water up 1 degree F we need 8.35 Btu or 2.45 watthours.

A 300 watt heater produces 1023.6 Btu, or enough energy to heat 122.58 gallons up one degree each hour.

Keep in mind that water has a high heat capacity. The larger the volume the more heat it retains. So once you get it up to temperature it will not take as much energy to maintain it.

Manufacturer heater ratings have more to do with marketing than actual science really. Although they aren't really incorrect. I do think Ebo's one is stretching it. It's better to be under than over.

Andy
 

blkmjk

Members
It actually is a bit more complicated than that Andy. But you are on the right track. If someone can link the last discussion we had about this subject that would be awesome. It would save me from repeating myself. But the aforementioned formula is partially correct.

1 gallon is 8.33 lbs and a btu is the amount of heat required to raise the gallon 1 degree. But heaters are sold in watts that are measured by the hour. So if you calculate the...
size of tank
desired over room temp tank temp and then you can size a heater more accurately.

So let's say it's 75 gallons
And the room temp is 70°F
And the desired tank temp is 80°F


The delta is 10°F multiply by gallons of tank
10 x 75= 750 btu
There are 3.412 btu per watt so divide 750 ÷ 3.412= 219 roughly
Now that is the watts you would need to raise the tank 10°F in 1 hour. When is the last time your tank temp dropped 10°F in 1 hour you needed it back up.??

Personally a 150 w is all a 75 gallon tank needs. But don't take my word for it. These calculations do not include surface area of water and evaporation nor the surface area of the glass or acrylic. Which effect the results greatly.


Drew
 
See thread
Calling all engineers....heater question.
Very detailed info on the thermodynamic physics of heating an aquarium efficiently.

Also keep I'm mind just cause it takes "x" watts "y" hours to heat a gallon of water doesn't mean you multiply "x" by gallons and go buy that size heater. Also keep in mind other equipment effects water temp. Technically anything with a motor creates heat. My 125 has an fx5 a magnum 350 and two koralia. Just this stuff raises the water temp a measurable amount. In the summer my room temp. Is about 72 and I don't use a heater at all tank stays at 78-80

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judtaaron

Members
just my two cents >>>>>no matter what you end up deciding to do . you should always divide the watts among multiple heaters . say you need 150 watts get two 75 watts .this will prevent the possible disaster of one heater shorting out and either the temp dropping or the heater super heating your tank ..
This may be rare but it happens and if you have ever come home and your tank is milky white and all your w/c fish are dead you will understand this is a simple easy way not to suffer a silly mistake of judgment .
 
Drew. Check your math. You made a mistake.

A BTU does not heat up 1 gallon of water 1 degree in an hour. It heats up 1 lb of water 1 degree in an hour.

If you have a Delta T of 10 degrees in a 75 gallon tank then you need.

10 x (75 x 8.35) = 6262.5 BTU or 1835.4 watthours. If you wished to get the water warm in 1 hour you would need 1835 watts. In two hours, 917.5 watts, in three hours, 612 watts, etc...

Of course that is in a perfect world where the aquarium is not losing any heat energy to evaporation or convection. The more or less the tank is insulated will affect the amount of energy required.

As to why you can use a smaller heater on a bigger tank it's because the range of precision of the heater thermostat is generally +/- 1-2 degrees. So you only have to apply energy (most of the time) to raise the water temperature 1 or 2 degrees.

Andy
 

Becca

Members
We used an eheim 300w on the 150 when it was at the old house and it was enough to heat the entire tank evenly. At the new place we had to add another heater, but the tank is now in a room with windows.
 
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