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Old 04-06-2012, 07:26 AM   #1
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heating a large reef tank with gas




Is this a place I could get assistance heating 800+ gallons of water with gas? I'm considering a small tankless water heater connected to PEX. The PEX would coil in the sump as a heat exchanger. Maybe a Ranco controlling the pump. So all I have is a general idea. Is this workable?

Joe



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Old 04-06-2012, 09:39 AM   #2
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heating a large reef tank with gas


I don't think that would give you enough heat exchange. You may be able to do it with a titanium heat exchanger.

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Old 04-06-2012, 09:45 AM   #3
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heating a large reef tank with gas


800 gallons.. hhhhmmmm why not a gas fired spa heater???? just a thought....
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Old 04-06-2012, 10:15 AM   #4
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heating a large reef tank with gas


Plastic is not a good conductor and wouldn't yeild very good results.

To what temperature are you trying to heat the water to?

Is the 800 gallon tank insulated?

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Old 04-06-2012, 11:34 AM   #5
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heating a large reef tank with gas


Hpex would work fine.
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Old 04-06-2012, 11:36 AM   #6
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heating a large reef tank with gas


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Hpex would work fine.
Would it work, sure, would it work efficiently, no.
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Old 04-06-2012, 12:17 PM   #7
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heating a large reef tank with gas


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Would it work, sure, would it work efficiently, no.
And why not?
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Old 04-06-2012, 02:25 PM   #8
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heating a large reef tank with gas


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Originally Posted by Jackofall1 View Post
Plastic is not a good conductor and wouldn't yeild very good results.

To what temperature are you trying to heat the water to?

Is the 800 gallon tank insulated?

Mark
The water will be heated to the the mid to high 70s F. The tank is not insulated, but is in a heated area.

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Would it work, sure, would it work efficiently, no.
While PEX does not conduct heat nearly as well as metal, I plan to compensate by using 50'-100' coil of PEX. So in terms of efficiency, I can't see why using a long PEX coil would require any more gas than a short metal coil.
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Old 04-06-2012, 05:21 PM   #9
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heating a large reef tank with gas


Heres the difference if you are interested

Polypropylene heat transfer = .06 Btu/ft2/hour/DegF differential
Copper Heat transfer = 232 BTu/ft2/Hr/DegF differential.

So you will wait a real long time to heat it, and while waiting you lose efficiency keeping an 80% efficient heater running for so very much longer to achieve the same task.

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Old 04-06-2012, 05:21 PM   #10
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heating a large reef tank with gas


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And why not?
Read post #9

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Old 04-06-2012, 05:52 PM   #11
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heating a large reef tank with gas


Quote:
Originally Posted by Jackofall1 View Post
Heres the difference if you are interested

Polypropylene heat transfer = .06 Btu/ft2/hour/DegF differential
Copper Heat transfer = 232 BTu/ft2/Hr/DegF differential.

Mark
Wow and Wow! That would be a lot of heat up the chimney. I had no idea the difference was so great. Then let's say a short titanium coil heat exchanger.

How would the water in the system be topped off? Would some sort of sight glass to monitor water level be good?
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Old 04-06-2012, 07:03 PM   #12
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heating a large reef tank with gas


Quote:
Originally Posted by Jackofall1 View Post
Heres the difference if you are interested

Polypropylene heat transfer = .06 Btu/ft2/hour/DegF differential
Copper Heat transfer = 232 BTu/ft2/Hr/DegF differential.

So you will wait a real long time to heat it, and while waiting you lose efficiency keeping an 80% efficient heater running for so very much longer to achieve the same task.

Mark
Cite your source. Copper doesn't transfer 232 BTUs per sq ft per degree F difference.

I think you'll find you BTU is low for pex piping also.
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Old 04-06-2012, 07:12 PM   #13
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heating a large reef tank with gas


Quote:
Originally Posted by salty joe View Post
Wow and Wow! That would be a lot of heat up the chimney. I had no idea the difference was so great. Then let's say a short titanium coil heat exchanger.

How would the water in the system be topped off? Would some sort of sight glass to monitor water level be good?
A 4" copper pipe only loses 111 BTUs per linear foot per hour, at a 40F temp difference. A 4" copper pipe 1 foot long, is 150.72 sq inches of copper, which is just over 1 sq ft.

The temp difference would have to be 99F to have a 241 BTU an hour per sq ft heat transfer.
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Old 04-06-2012, 10:30 PM   #14
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heating a large reef tank with gas


Quote:
Originally Posted by beenthere View Post
Cite your source. Copper doesn't transfer 232 BTUs per sq ft per degree F difference.

I think you'll find you BTU is low for pex piping also.
I didn't pull this from a dark piece of anatomy----

http://www.engineeringtoolbox.com/th...als-d_858.html

Pex is suited for water distribution due to its insulation qualities this is why they use it, that and its resistance to corrosion when used as in slab radiant heat, copper doesn't do well corrosion wise encapsulated in concrete.

If they were anywhere remotely the same conductivity wise, you could use Pex for wiring, would love to see that, after all conductivity of both heat and electrical energy are similar when talking about materials.
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Old 04-06-2012, 11:16 PM   #15
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heating a large reef tank with gas


Thanks for that link Jackofall. Titanium is the only metal I would consider using. It has a (Btu/(hr oF ft)) of 11-13 at 68 F, according to that link. Way, way lower than copper. Plus titanium is quite pricey. If PEX is 0.06 (Btu/(hr oF ft)), it would take 200' of PEX to transfer the heat of 1' of titanium of the same diameter. Which is hard to believe-but what do I know.

Doesn't PEX used in heating applications have aluminum under the plastic to improve heat transfer?

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