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Old 12-05-2008, 12:36 PM   #1
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Unexpected Heat Source

How long do you think it would take a bucket (5 gal) of water to warm to room temperature?

I'm wondering because I think I might have accidently stummbled across a way to heat the water in the tank without actually using a heater.

Backing up - I started a new fish tank (10gal) about two weeks ago (DS 'won' a goldfish as the school carnival). I'm doing daily water changes while the tank cycles. To reduce the change in water temperature during these PWC, I've been filling a 5 gallon bucket and letting it sit for a day to let it warm up to room temperature.

The thing I've been noticing is that the temperature of the water in the tank is definitely warmer than the water that's been sitting in the bucket. Since I'm using a floursent light positioned above a full tank cover, it would seem that the extra heat isn't comming from the light. But since the tank is covered, I am using an air stone to ensure the tank is getting enough oxygen. I'm thinking the extra heat is coming from the air that is likely being warmed from air compressor feeding the air stone.

It it's not the air stone, then the only other thing I can figure is that it's taking more than 24 hours for the bucket of water to warm to room temperature.

I guess it's time to buy a tank thermometer just to double check the temperature.
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Old 12-05-2008, 12:41 PM   #2
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Wouldn't come from the air pump. The air does get warm slightly as the pressure is increased, but it also cools back down as it returns to atmospheric pressure.

No, you're getting heat from the fluorescent fixture. Though they are much more efficient and run cooler than incandescents, they still get pretty warm.
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Old 12-05-2008, 12:54 PM   #3
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Quote:
How long do you think it would take a bucket (5 gal) of water to warm to room temperature?
That depends on the temp of the water to begin with and the air temp. 24 hrs should be enough time to let 5g raise to room temp.
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The thing I've been noticing is that the temperature of the water in the tank is definitely warmer than the water that's been sitting in the bucket.
I sure hope so. The lights give off heat. Any pump for a filter will give off heat. If you have a 50w pump on your filter, that is the same as running a 50w heater. The air will only warm the water if the air temp is higher than the water temp...and that increase would be miminal at best.
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Old 12-05-2008, 12:56 PM   #4
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Wouldn't come from the air pump. The air does get warm slightly as the pressure is increased, but it also cools back down as it returns to atmospheric pressure.
I wasn't thinking of the heat comming from the compression of the air by the air pump. I was thinking the heat was coming from the air effectively acting as a coolant for the pump's motar.

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No, you're getting heat from the fluorescent fixture. Though they are much more efficient and run cooler than incandescents, they still get pretty warm.
My first though is that that would seem impossible. The fluorescent isn't generating hardly any radiant heat. The bulk of the heat would be comming from the balast. But given that the balast is sitting just above the air pocket formed between the tank and the bulbs, that air pocket is going to be getting warmed by the balast, and some of that heat is going to get transmitted through the glass of the tank cover.

So for sure, the fluorescent must be contributing some (if not nearly all) the extra heat.

Of course the other thing the air stone would be doing is helping to at least bring the water up to room temperature. I guess I'd have to do some testing and compare the temperature of the bucket of water when first filled up, it's temperature after sitting in the room for a day, what difference it makes if I feed an air stone to the bucket of water for a day, compared to the average temperature of the fish tank.

Too back DS isn't a little farther along in school... sounds like an interesting science experiement.
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Old 12-05-2008, 01:03 PM   #5
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I wasn't thinking of the heat comming from the compression of the air by the air pump. I was thinking the heat was coming from the air effectively acting as a coolant for the pump's motar.
Open up that air pump. You'll notice the air doesn't really cool the motor. The air is drawn inside the housing and then just squirted through the orifice by a rubber diaphragm. Besides, most pumps only dissipate, at most, a couple of watts as heat - and most of that heat just goes off into the ambient air, not into the tank. So a watt or less isn't going to do much compared to the fluorescent bulb and ballast sitting above the tank dissipating 10-40 times that.
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Old 12-05-2008, 01:04 PM   #6
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The light itself is energy, which becomes heat when it hits things in the tank and is absorbed. When you say that a fluorescent bulb is efficient we really just mean that more of the electrical energy is being converted to light and less to heat, but the energy still gets output so even if you had a light that was 100% efficient and was always room temperature to the touch it would still warm the tank as that energy got absorbed in the water. It's just like going outside on a cool day and still feeling heat from the sun. That heat didn't come from the air, it was produced on your skin by the incident light.
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Old 12-05-2008, 01:10 PM   #7
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...If you have a 50w pump on your filter, that is the same as running a 50w heater...
Hadn't thought about the filter. I've got a Fluval 1 for filtration. It only uses 4.5 watts. Not much, but it is a heat source.

As for the air stone, it's being run by the Tetra Whisper Air Pump 10 (can't find a wattage for it online).
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Old 12-05-2008, 01:13 PM   #8
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Open up that air pump. You'll notice the air doesn't really cool the motor. The air is drawn inside the housing and then just squirted through the orifice by a rubber diaphragm. Besides, most pumps only dissipate, at most, a couple of watts as heat - and most of that heat just goes off into the ambient air, not into the tank. So a watt or less isn't going to do much compared to the fluorescent bulb and ballast sitting above the tank dissipating 10-40 times that.
Yea, I figured the room temperature air is providing most of the cooling for the air pump. But obviously the air going through the pump is going to aquire some of the heat from the pump. Not much, but some.
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Old 12-05-2008, 01:20 PM   #9
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The Whisper 10 consumes 1.5 watts total, only a tiny fraction of which would get imparted into the water.

The light is your major "extra" heat source.
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Old 12-05-2008, 01:23 PM   #10
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The light itself is energy, which becomes heat when it hits things in the tank and is absorbed. When you say that a fluorescent bulb is efficient we really just mean that more of the electrical energy is being converted to light and less to heat, but the energy still gets output so even if you had a light that was 100% efficient and was always room temperature to the touch it would still warm the tank as that energy got absorbed in the water. It's just like going outside on a cool day and still feeling heat from the sun. That heat didn't come from the air, it was produced on your skin by the incident light.
I'll admit that you're not totally off base, but it's unfair to compare a fluorescent light to what you feel from the sun. The sun is emmitting more than just visible light. It's also putting out radiant heat. In that regards, the sun is like an incandesent light bulb that puts out light AND heat (radiant heat). Otherwise, the light itself is listed as only 15 watts. But that light is going not only to the water, but it's lighting up the room itself.

So I don't think the light itself is a major contributor to the heat.

So far, I would say the source of the heat is a three way combination of the light's balast (conduction and convection), the filter (low wattage, but it's completely submerged), and the air stone.

WOW, this is getting to be an interesting science experiment. Any one have a child about to enter a science fair?
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Old 12-05-2008, 01:27 PM   #11
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The light itself is not a major heat contributor. The vast majority of it gets reflected out of the tank. Some small portion of it does get absorbed by the items in the tank, and indeed by the water itself, but it's not really going to be an awful lot.
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Old 12-06-2008, 12:29 AM   #12
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I would think the majority of the heat is from the light. Although the fluorescent is more efficient that the incandescent, it is only 65% or so. The rest is heat. My 4 T8's get quite warm in the canopy (and the electronic ballasts are hardly warm to the touch ... they are actually quite efficient).

Gzeiger - It is true that light is energy, but it is only converted into heat inside the tank if it is absorbed. The vast majority of the light produced is reflected so will not contribute to heat build up. <In the ocean, light is fully absorbed only after traveling hundreds of feet. In a 2' tank, the amount of light absorbed & transformed to heat would be low compared with the heat generated by the lightbulb itself.>
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