A question on heater size for you smart people

[DGonci]

Ok so I was thinking about heaters the other day and had a question for the smart people. I understand that there is a basic formula for determining tank size, watts per gallon, but I would like to question that logic. I think that may hold true if you are dropping heaters in the dispaly, but what if you have a sump. Say for example if I have a 30G sump with a return pump going at 700gph. Regardless of the display size, say either a 75G or 180G tank, I am going to have the exact same amount of water flow through the sump. Wouldnt it make more sense to base the heater size on the size of the sump and the flow throughput?

So take the 2 examples above and assume an average fo 4 wats per gallon:

75G tank would need 300W of heaters...

180G would need 720W of heaters...

If you were to place the heaters in the same sump, the higher wattage would obviously heat up the sump faster, but the water would travel into the display at the same rate. While I understand that if you have a 180G you will probably have a larger sump, but you could use any 2 tank sizes for comparison so long as the sump/return pump remain static. So what do you think? Does this make sense? or am i flawed? How would this change conventional thinking about heater size?

/Discuss...

 

[rickyrivera1]

Going to tag along...i need to figure this one out as i am running 4 250 watt heaters to heat about 300gal of water.

 

[naprestsleep]

I have thought of a couple things but cant explain them.

My thought is the higher wattage means warmer water is entering the DT, therefore after mixing with the DT tank water the less temperature change. If you had a smaller heater the temp in the sump area might be what you want but as soon as it hits the DT it would drop when mixed with the larger water volume.

 

[mr86mister]

Great view point and something to think about for sure. It would heat up the sump without an issue but I'm pretty sure not the entire system. The water will travel into the display than be dispersed throughout the entire tank and the water temperature would go up a fraction. While water is being pumped up into the display water is flowing down through and running into the heater which is cooler than the return water. This is a continuing process until all of the water in the aquarium is equal to the set temperature. Warmer water out of sump/Cooler water into sump until equalized. I hope that helps a bit.:hmm2:

 

[DGonci]

My thought is the higher wattage means warmer water is entering the DT, therefore after mixing with thBute DT tank water the less temperature change. If you had a smaller heater the temp in the sump area might be what you want but as soon as it hits the DT it would drop when mixed with the larger water volume.

The water wouldn't be any warmer since once the heaters hit their temp they would shut off. Higher wattage would just shut off sooner. With that being said it might even be cheaper to run a smaller heater, if my original post would be correct.

 

[DGonci]

Great view point and something to think about for sure. It would heat up the sump without an issue but I'm pretty sure not the entire system. The water will travel into the display than be dispersed throughout the entire tank and the water temperature would go up a fraction. While water is being pumped up into the display water is flowing down through and running into the heater which is cooler than the return water. This is a continuing process until all of the water in the aquarium is equal to the set temperature. Warmer water out of sump/Cooler water into sump until equalized. I hope that helps a bit.:hmm2:

With that you could drop a few larger heaters into the display initially to get it up, but maintain with just a smaller sump heater.

 

[mr86mister]

I also know that lower the wattage the longer it takes to heat the water completely with the possibility of the heater breaking, burning out and some cases exploding because of it overworking. The best is to also run two heaters unless one fails and the other one can try to keep up. We also have to remember that moving water cools faster than stagnant water.

 

[mr86mister]

With that you could drop a few larger heaters into the display initially to get it up, but maintain with just a smaller sump heater.

I couldn't tell you yes or no to that but I do hope a few others chime in on the topic and help out. There are a few guys on here that have been doing tanks since the 70's, I'm sure our main guy, Gary, will help out.

 

[naprestsleep]

The water wouldn't be any warmer since once the heaters hit their temp they would shut off. Higher wattage would just shut off sooner. With that being said it might even be cheaper to run a smaller heater, if my original post would be correct.

With a built in temp sensor you are right but if the heater is cooling it still putting off some heat and therefore could continue to warm the water(although the change is probably negligible).

What about people who use a controller or heater with remote temp sensors? In that case the sump would continue to heat until the display reached temp.

I am curious to about what your saying, just trying to play devils advocate.

Joe

 

[frofan]

On average 3 watts per gallon is good as long as the ambient temperature isn't more than 10 degrees lower than the desired water temperature. For every 10 degrees difference you need 3 watts per gallon. So, if you have a 100 gallon system and the sump is in a basement that is 20 degrees colder than the desired water temperature, you will need 600 watts of heat.

 

[DGonci]

What about people who use a controller or heater with remote temp sensors? In that case the sump would continue to heat until the display reached temp.

Thats a good point. And with that you would be correct that the heater would be on until the display gets warm enough. It would be interesting to see the temperature in the sump while the heater is on compared to teh display.

 

[DGonci]

On average 3 watts per gallon is good as long as the ambient temperature isn't more than 10 degrees lower than the desired water temperature. For every 10 degrees difference you need 3 watts per gallon. So, if you have a 100 gallon system and the sump is in a basement that is 20 degrees colder than the desired water temperature, you will need 600 watts of heat.

I understand the watts per gallon, but what I am saying is that it is flawed because you are heating up the sump, not the display. I think the watts per gallon is practical back before sumps became fairly standard and the heaters were in the display.

 

[dreaminmel]

For what it's worth, I have two 300w heaters in my sump in the basement. Total water volume is 150g. Temp in display and sump are both constantly the same.

 

[mr86mister]

I understand the watts per gallon, but what I am saying is that it is flawed because you are heating up the sump, not the display. I think the watts per gallon is practical back before sumps became fairly standard and the heaters were in the display.

I see where you are coming from but you are heating up both the sump and display, as long as they are connected. Your goal is to heat the entire system. I have to heat roughly 160 gallons for my system. One 100w heater will heat my sump system but won't heat my entire system enough to bring it to the correct temperature. It would cool back down to fast to the ambient temperature before it would be able to heat the entire system to the desired level. Basically you have the water at a constant to be the same temperature as the surrounding atmosphere. If it is warmer on the outside it will soak up the heat and warm to that temp and if it's lower it will loose heat.

I'm trying to say it clearly but it's actually pretty hard...lol.:lmao:

 

[DGonci]

However how fast you heat up your diplay would be related to how high your flow up to the display is. With a larger return pump you would pump warmer water up faster, therefore keeping the display warmer, however it would be in teh sump a shorter period of time to heat it up.

So say if you had 800 watts in a sump but a return pump of only 400gph going up to a 180 Gallon tank, it would have a harder time keeping the tank warm, since you are only pushing up 400 gph. This is not to say it wouldnt work, but is the system working efficiently?

I guess my overall point is the heater size needs to be related to pump flow/ sump size as compared to overall tank size.

 

[pascal32]

The wattage of the heater is a reflection of the amount of heat it can provide. The bigger the tank the more heat loss, accordingly the more heat needs to be put in.

Take your 30 gallon sump and use it to heat a pool. It would never work as the heater doesn't put enough heat (energy) to overcome the loss.

Flow rate from the sump could be an issue, though you would need some major heat loss to stand a chance against a five to ten time turnover on a typical sump.

 

[DGonci]

I understand heaters, dont get me wrong....Im just tossing out a question against the normal conventional wisdom.

While you couldnt use a 30G sump to heat a pool, you could do the same thing with a pool but the "sump" would need to be somewhat more proportionate to the pool?

So would you think 200w would be enough to heat a 120G tank with a 30G Sump?

Overall I think this could be a pertinent question when you are talking about energy use/cost. Why use 600W of electricity to do a job that 200 could do?

 

[Gary Majchrzak]

Why use 600W of electricity to do a job that 200 could do?

the only way that a 200w heater can acheive the same temp. that a 600w heater can is if it's given more time.

Whether using a 600w heater or a 200w heater (to warm the same given body of water) the end result of energy consumption will be the same.

To simplify: it will take a 200 watt heater more time to accomplish what a 600watt heater can. The same amount of joules (units of measure/ heat energy) will need to transferred.

 

[DGonci]

My question Gary is do you need to heat the sump size or the display tank? After all 200W would heat up the sump size fairly quickly in a 30G. WIth the same flow rate I think the difference wouldnt be that much in time to heat it up.

 

[pascal32]

the only way that a 200w heater can acheive the same temp. that a 600w heater can is if it's given more time.

Whether using a 600w heater or a 200w heater (to warm the same given body of water) the end result of energy consumption will be the same.

To simplify: it will take a 200 watt heater more time to accomplish what a 600watt heater can. The same amount of joules (units of measure/ heat energy) will need to transferred.

+1. Energy usage is measured in wats per time (hours). Not to say the correlation is perfect, but in the ballpark