heating - submersible vs external pump

daven · 08/21/2007, 01:13 PM

In another thread I had a discussion concerning heating caused by submersible/internal pumps versus external pumps. The contention was that they were equivalent. That didn't seem right to me since with an external pump I could feel it radiate heat, heat that wasn't going into the water.

Being curious I ran a test. Using a 21x20x18 spare acrylic sump (approx 32 gallons) and a mag 12 I ran a couple tests.

1. Internal pump. Starting temp of water was 78 degrees. Room temp 78 degrees. Pump was placed in sump and pumped water up a piece of 3' spaflex and back into the sump. Return was underwater and there was little to no surface disturbance. Ran for 18 hours (when it seemed to be stable). Final temperature - 87.6

2. External pump. Starting temp of water was 78 degrees. Room temp 78 degrees. Pump was placed outside sump. Return was through the same spaflex and was underwater, no ripples. After 18 hours the water temp stabilized at 84.5.

3. I turned off the pump and the water returned to 78 after a couple hours.

Ran both tests twice, same results.

Now there are a lot of other variables we could consider such as different pumps, the amount of the water being pumped, whether evaporative cooling on a larger tank would keep temps down, etc.

In this test it seems that there was approximately 30% less heating (6.5 degrees versus 9.6).

I wanted to do the tests with a kill-a-watt to see if there was a difference in energy consumption but it's taking too long for my meter to arrive. Perhaps I can update this.

For what it's worth.

cdbias2 · 08/21/2007, 01:15 PM

I've always agreed with what you are finding.
External = cooler!

daven · 08/21/2007, 01:17 PM

I made that assumption but when challenged realized I had nothing to back it up. Frankly, I expected more of a differential. Still, its enought to make me glad that I engineered my 180 with no submersible pumps or powerheads.

RichConley · 08/21/2007, 01:40 PM

Thats funny, we just did the same tests with the same pump, and got EXACTLY the same temperature on both setups.

let me see if I can find the thread.

rickh · 08/21/2007, 02:32 PM

When you us a submersible pump externally it still transfers most of it's heat to the water. A most "real" external pumps have cooling fins and fan blades on the shaft. I spoke to Danner, the Mag manufacture and they recommended placing the Mag pumps into a bucker of water to act as a heat sink when they are used externally. I have used Mag 5 and 7s externally without a problem, but they still heat the tank. R

daven · 08/21/2007, 03:54 PM

Yes, I agree. That's exactly what my testing showed. THey still head the tank when external but not as much as if they were submerged.

I can think of several other tests I want to run but the wife says its time to tear it down and return the use of the tub :-)

08/21/2007, 01:13 PM	#1
daven Registered Member Join Date: Jul 2006 Location: Jacksonville, FL Posts: 283	heating - submersible vs external pump In another thread I had a discussion concerning heating caused by submersible/internal pumps versus external pumps. The contention was that they were equivalent. That didn't seem right to me since with an external pump I could feel it radiate heat, heat that wasn't going into the water. Being curious I ran a test. Using a 21x20x18 spare acrylic sump (approx 32 gallons) and a mag 12 I ran a couple tests. 1. Internal pump. Starting temp of water was 78 degrees. Room temp 78 degrees. Pump was placed in sump and pumped water up a piece of 3' spaflex and back into the sump. Return was underwater and there was little to no surface disturbance. Ran for 18 hours (when it seemed to be stable). Final temperature - 87.6 2. External pump. Starting temp of water was 78 degrees. Room temp 78 degrees. Pump was placed outside sump. Return was through the same spaflex and was underwater, no ripples. After 18 hours the water temp stabilized at 84.5. 3. I turned off the pump and the water returned to 78 after a couple hours. Ran both tests twice, same results. Now there are a lot of other variables we could consider such as different pumps, the amount of the water being pumped, whether evaporative cooling on a larger tank would keep temps down, etc. In this test it seems that there was approximately 30% less heating (6.5 degrees versus 9.6). I wanted to do the tests with a kill-a-watt to see if there was a difference in energy consumption but it's taking too long for my meter to arrive. Perhaps I can update this. For what it's worth.

08/21/2007, 01:40 PM	#4
RichConley Registered Member Join Date: Sep 2004 Location: Bostonian in Chicago going to DC Posts: 9,908	Thats funny, we just did the same tests with the same pump, and got EXACTLY the same temperature on both setups. let me see if I can find the thread. __________________ NO TANKS!!!

08/21/2007, 01:15 PM	#2
cdbias2 Appalachian Reef Society Join Date: Mar 2004 Location: Alum Creek, WV (No more) Posts: 1,433	I've always agreed with what you are finding. External = cooler!

08/21/2007, 01:17 PM	#3
daven Registered Member Join Date: Jul 2006 Location: Jacksonville, FL Posts: 283	I made that assumption but when challenged realized I had nothing to back it up. Frankly, I expected more of a differential. Still, its enought to make me glad that I engineered my 180 with no submersible pumps or powerheads.

08/21/2007, 02:32 PM	#5
rickh Registered Member Join Date: Aug 2005 Location: Lost_in_Michigan Posts: 1,306	When you us a submersible pump externally it still transfers most of it's heat to the water. A most "real" external pumps have cooling fins and fan blades on the shaft. I spoke to Danner, the Mag manufacture and they recommended placing the Mag pumps into a bucker of water to act as a heat sink when they are used externally. I have used Mag 5 and 7s externally without a problem, but they still heat the tank. R

08/21/2007, 03:54 PM	#6
daven Registered Member Join Date: Jul 2006 Location: Jacksonville, FL Posts: 283	Yes, I agree. That's exactly what my testing showed. THey still head the tank when external but not as much as if they were submerged. I can think of several other tests I want to run but the wife says its time to tear it down and return the use of the tub :-)