Low down on heating an aquarium

[andrewh]

Typed this up for one of our members and thought yawl'd like it as well enjoy!!!

Well maybe this will help some understand what's going on a little better (or might just bore the heck outta ya - sorry if that's the case).

You've probably heard of BTUs (British Thermal Units) which is a measurement of heat transfer. It takes 1 BTU to heat one pound of water 1*F. There are approximately 8 pound of water in 1 gallon of water. So it takes 8 BTUs to raise 1 gallon of water by 1*F.

1 watt = 3.42 BTUs, so you need 0.29 (call it .3) watts per gallon per 1*F increase.

As an example take a 100 gallon tank. Going from 75*F (room temp) to 80*F (desired water temp) would required: 5*F @ 100 gallons = 100g X .3w X 5*F = 150 watts or about 1.5 watts per gallon. If you start out at 72*F you would require: .3w X 8*F X 100G = 240 watts or 2.4 watts per gallon. Even 10*F increase would require 300 watts or 3.0 watts per gallon.

Now that is the "best case scenario" where the heater is 100% efficient and there's no "wind" blowing across the surface of the water nor over the sided of the glass (like a ceiling fan or AC vent). Generally you can double the number you get to account for heater inefficiencies and other factors that will increase the wattage to reach the desired water temp.

There are a lot of factors when it comes to Thermal Dynamics so having a "do this exact thing and you'll be covered" is pretty difficult.

Going off your exact setup - 300 gallon going to 78*F from say 74*F (assumed room temp) you'd need 360 watts or about 1 watt per gallon.

Hope that helps explain the science and math behind the scenes a bit (as in explains where the 3-5 watts per gallon comes from and why it's a very general rule). In extreme cases - room temp is say 68*F and you want your tank to be 88*F you're looking at 6 watts per gallon minimum.

[jeebus]

Outstanding! :emt_thumbs:

[schance]

much appreciated

[Zulaab]

Now I will say this.. what you are asking is that the heater be a massive heater and your are looking at wanting that mass amount of water to heat up quick. I use 200w heaters in all three of my tanks, the 58/70/110 -- and they stay consistent in a house that steady at around 71-72 (roomate loves it cold and he pays the electric bill)
When I get the 180 in place I am going to use a 200 again. It might take longer to heat up a tank and it would be a lot quicker to use a massive heater.. but my answer is this.. my Marineland stealth's works fine :)

[andrewh]

EDIT:

Crap, I hate when I do this...

Math is wrong above... here is the correction:

3.42 BTUs = 1 watt
1 BTU = 1# water ^ 1*F
8# = 1 gallon = 8 BTU
2.34 watts per 1 gallon of water
(here's the error )
forgot about the time frame = 24 hours)

100 gallon from 75*F to 80*F = 100 gal X 5*F X 2.34 watts per gal / 24 hours = 97 watts

(FYI watts are really watts per hour and BTUs are also BTUs per hour)

Now with 100% more attachments

[andrewh]

Outstanding! :emt_thumbs:

much appreciated

TYVM!!! Hope it helps someone.

Now I will say this.. what you are asking is that the heater be a massive heater and your are looking at wanting that mass amount of water to heat up quick. I use 200w heaters in all three of my tanks, the 58/70/110 -- and they stay consistent in a house that steady at around 71-72 (roomate loves it cold and he pays the electric bill)
When I get the 180 in place I am going to use a 200 again. It might take longer to heat up a tank and it would be a lot quicker to use a massive heater.. but my answer is this.. my Marineland stealth's works fine :)

What temp do you keep the tank(s)?

Seems a 175 watt (if it existed) would work to get you to 80*F in a 180 gal from 71*F room temp, but I'd bet it'd be on almost all the time. There are ways to help make the heater more efficient.

Well you also have to take into account the efficiencies which are involved.

One heater brand/design vs. another may have a huge advantage in heating a tank. Plus the heater's placement within the tank (near water movement = more efficient away from water movement = less efficient). Plus the way you mount the heater. Vertical will be less efficient while horizontal or even 45* might lend to heating the tank better.

Near by window or door drafts will affect it too.

If you're having trouble keeping/holding a temp you might try moving or adjusting the mounting or location within the tank to see if that helps.

Any of the "in-line" heaters should be superior to one that simply sits there. Simple as more water exposed to the heater within a give time frame. In-line should be pretty steady output, and be more accurate.

[Zulaab]

I keep all of my tanks at 80.... I find it to be a good temp for all of my tanganyikan fish.

[Brownsnoutuk]

You would only need to get the tank upto temperature once. Maintaining the temperature is different from getting to that temperature.

[andrewh]

Good point, but maintaining a 80*F water temp in a 70*F house is what the number are based on.

There's a constant 10*F maintenance which the heater has to compensate for the entire volume of the tank.

[andrewh]

(trying to make things a little more clear)

Watts = Watts per hour
BTUs = BTUs per hour

The 'per hour' part is understood, so a 1 hour time framed is assumed within the formulas and math.

Any time you see watts (like on a light bulb package) it's actually watts per hour. So a 100 watt light bulb consumes 100 watts per hour. Same with kilowatt. The time frame is still 1 hour, so the electric company sends you a bill measured in kilowatt-hours. The 1 hour time frame is a standard to make conversions and comparisons easier.

Same with BTUs... 300 BTUs is 300 BTUs per hour.

see edit reason below

[screename]

Andrew, that 33 gallon is amazing!!!! I love the dimensions on it!

[blacksmith37]

As far as efficiency; electric resistance heating of water is as close to 100% efficient as anything in the real world. You also pick up about 100% of all the heat (wattage) from any submerged motors in filters. And a fair amount of heat from lights.
It is rare that one is increasing the temperature of an aquarium ; usually we are maintaining the temperature. But the heat wattage factors provide some idea of the factors.
To calculate the power required to maintain aquarium temperature would require some seriously difficult heat transfer/radiant loss/conduction loss/convection losses calculations :Likely worth a masters thesis in p.chem.

[PhishPhreek]

Heat Transfer

Great Post. Thanks

It's been 40 years since I took heat transfer in college so can someone refresh my memory on how to calculate the rate of heat transfer from 80f water through 3/8" glass to 75f air per square foot of surface area ?

[CichlidFan]

Great Post. Thanks

It's been 40 years since I took heat transfer in college so can someone refresh my memory on how to calculate the rate of heat transfer from 80f water through 3/8" glass to 75f air per square foot of surface area ?

PP....


Here's what I think...

It would seem to me that there would be so many variables to consider. Your formula in a classic research or lab type environment would be fairly easy to assertain if you had no fluckuations.

But in the common household, there is always minute changes in the air/room tempetures, i.e. televisions, ovens, a/c or heating...etc...

A significant volume of water such as a 75 gallon tank that has been heated to a tempeture of say 80 degrees, might fall to 75 degrees in 8 hours in a labratory, but in a average household, it may never get to 75 due to outside influences??

That was my long winded version of I DONT KNOW....

CF

[wesleydnunder]

(trying to make things a little more clear)

Watts = Watts per hour
BTUs = BTUs per hour

The 'per hour' part is understood, so a 1 hour time framed is assumed within the formulas and math.

Any time you see watts (like on a light bulb package) it's actually watts per hour. So a 100 watt light bulb consumes 100 watts per hour. Same with kilowatt. The time frame is still 1 hour, so the electric company sends you a bill measured in kilowatt-hours. The 1 hour time frame is a standard to make conversions and comparisons easier.

Same with BTUs... 300 BTUs is 300 BTUs per hour.

This is misleading. A 100 watt lamp is using 100 watts all the time...it's not cumulative over time. When it uses 100 watts for an hour, it uses 100 watt/hrs. Watt is the product of volts x amps, P = I x E. A 60 watt lamp operating at 120 volts has 1/2 amp current flowing through the element. It's using 60 watts all the time. Watt-hrs is also a product of watts used for time used.

Mark