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Old 10-31-2008, 01:46 PM   #1
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Radiator Question


I have question regarding my cast iron radiator that was recently installed.

The radiator is a Top Bottom Same End (TBSE).

With this kind of radiator is it important that the hot water supply go into the Top and the return to leave out the bottom of the radiator?

If the reverse is the case will this affect the heat output of the radiator.

Thanks in advanced,
Andrew

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Old 10-31-2008, 07:58 PM   #2
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It's just a configuration issue. I have never installed one but have had to refurb many of these and can't see how it would make any difference.

In my opinion the TBOE are more efficient because of the water flow from one corner to the other.

Experience has shown me that they both heat just fine no matter how they are hooked up.

Water velocity will have more of an impact than entry and exit options especially on efficiency.

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Old 11-01-2008, 05:40 AM   #3
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On low flow rate applications, it will make a big difference.
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Old 11-01-2008, 09:52 AM   #4
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On low flow rate applications, it will make a big difference.
Thanks for the response. Can you expand on that? What is/are 'low flow rate applications'? I do find that the water is not flowing or returning very well to or from the radiator.
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Old 11-01-2008, 10:26 AM   #5
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It's just a configuration issue. I have never installed one but have had to refurb many of these and can't see how it would make any difference.

Experience has shown me that they both heat just fine no matter how they are hooked up.

Water velocity will have more of an impact than entry and exit options especially on efficiency.
Thanks for the reply. Is 'water velocity' the same as the amount of water flow? I've noticed that the water doesn't flow as quickly to 'this' radiator as the others and I've read that when the hot water flows into the top it eventually cools and falls to the bottom to meet the return.

This is all I could find, it was from Wiki-pedia:
"As it gives out heat the hot water cools and sinks to the bottom of the radiator and is forced out of a pipe at the other end."

I am pretty convinced that this is the right way to do it but I'm just trying to get a sense of how much this would affect flow or 'water velocity' (and whether it's worth it to call the plumber back and switch it - I'm sure he will say it doesn't have any impact on the flow and will want to charge me an insane amount to switch'em).

Thanks...
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Old 11-01-2008, 11:07 AM   #6
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Flow in a hot water heating system needs to be balanced for the system most often through the use of valves. Some people try to make that happen by zoning which is a lot of work and expense for minimal results and many times increased energy costs. There are ways to measure the delta T of the incoming and outgoing water to get the right flow for maximum heating but I have never seen anyone actually do that.

If the water flows too fast through the system then it doesn't have time to let the heat out before returning to the heating device. If this happens then you have a hot return and heating spaces that probably doesn't need to be heated. This makes for some inefficient heating.

If it moves too slow then it won't deliver the heat to the radiator as there will be heat loses on the way. Once the water gets to the radiator it stays in there too long and cools to the point where there is not enough warm water to heat the radiator.

Radiators require enough heat to overcome the natural tendency of the radiator to absorb the heat. Each radiator medium has a certain amount of heat needed to effectively radiate heat out to heat a room. Different mediums require different heat levels. Iron requires much more heat to be an effective radiator than pex or copper. That being said once an iron radiator is up to speed it is difficult to slow it down and will radiate a lot longer than pex or copper once the heat has been turned off.

Easiest way to test this is to put your hand on the incoming and then on the outgoing and see if there is a big difference. If it is hot coming in and cool going out then you probably don't have enough flow. If it is cool coming in then you have a supply problem.
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Last edited by Marvin Gardens; 11-01-2008 at 11:10 AM.
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Old 11-01-2008, 11:23 AM   #7
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Oncew you drop below .5 gallon a minute, your velocity drops fairly low, even in 1/2" pipe.

So when the hot water enters the bottom of the rad, it rises up through the first section more then going into the next sections.

You may also have a circulator problem.

A Taco 007, is not the right circ for most applications.
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Old 11-01-2008, 11:30 AM   #8
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A Taco 007, is not the right circ for most applications.
Unless it's for a solar hot water system which is just about right...

I actually have to slow it down to keep the water in the panels longer so the water can heat up. It would be nice if they made a Taco 003 (or a 001) or something like that.

I bought the 007 just because it was half the price of a 005 which really confuses me. Why is the 005 more than twice the price of a 007??? [rhetorical question].
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Old 11-01-2008, 11:37 AM   #9
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They make a 003. Almost 1GPM at 4' of head. Max head is 4'

A 006 may have worked for you also. 5GPM at 5' of head.
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Old 11-01-2008, 11:45 AM   #10
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They make a 003. Almost 1GPM at 4' of head. Max head is 4'

A 006 may have worked for you also. 5GPM at 5' of head.

I will have to look those up. My supplier never told me about those.

My head is level. It goes from the top of the panel to the heat exchanger and back to the bottom of the panels. Since the drop equals the rise I really don't have any head at all (my wife tells me this all the time).

My GPM needs to be 3 max.
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Old 11-02-2008, 12:45 PM   #11
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I believe you are confused. The amount of head has nothing to do with height. It is resistance to flow. Everything the water passes througth has a resistance to flow. See the resistance of the panels. It will be listed as ft head or psi drop.
Than add the piping and fittings and radiator.
By the way. If you are talking about a standard cast iron radiator and you are piping the same side you may loose about 20% output. If it is cast iron baseboard depending on the length you may lose upto 40% output.
As flow drops btu output drops unless as stated above you are way too fast. The rule within the limits of pipe size and amount of radiation is speed water up get more heat slow water down get less heat.
The rule for heat producers speed flow up get less heat and slow flow get more heat......Confused yet?
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Old 11-02-2008, 01:07 PM   #12
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LOL...

I did a cast iron baseboard on the same side once, only half of it gave off heat.

I had to dig out the crawlspace, to get a line to the other side of it.
Big PITA.
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Old 11-02-2008, 01:20 PM   #13
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I believe you are confused. The amount of head has nothing to do with height. It is resistance to flow. Everything
Your correct as far as the heigth per say has no bearing on head.
The water basically weights the same in both directions.
It would just be the increase in pipe length that adds restriction that would add head on a vertical difference.

Depending on his panel set set up, he could easily be under 6' of head.

A panel that has 5' of head at 2GPM, is only about 1' of head at .5GPM.
So depending how many panels, his head could be very low.

A Taco 007, is about 3GPM at roughly 9.5' of head.
If he had to slow his current 007's flow down by adding head. Then his set up is under 9 foot of head.
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Old 11-02-2008, 01:30 PM   #14
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Originally Posted by tk03 View Post
I believe you are confused. The amount of head has nothing to do with height. It is resistance to flow. Everything the water passes througth has a resistance to flow. See the resistance of the panels. It will be listed as ft head or psi drop.
Than add the piping and fittings and radiator.
By the way. If you are talking about a standard cast iron radiator and you are piping the same side you may loose about 20% output. If it is cast iron baseboard depending on the length you may lose upto 40% output.
As flow drops btu output drops unless as stated above you are way too fast. The rule within the limits of pipe size and amount of radiation is speed water up get more heat slow water down get less heat.
The rule for heat producers speed flow up get less heat and slow flow get more heat......Confused yet?
Head and resistance to flow (friction loss) are two different things.

Head is the vertical distance from opening to opening and is a constant when at rest with consideration to the medium, altitude, barometric pressure and temperature. Head does not change with configuration of the system. There is pressure head (at rest) and hydraulic head (in motion).

Friction loss is the increased resistance to a pressurized medium in motion due to non laminar flow within a system. A smaller vessel will have much more resistance than a larger vessel at the same operating pressure. There is no friction loss when the medium is at rest but there is still head pressure.

Friction loss is increased by things that cause non laminar flow like 90's, curve pipe, the diameter of the pipe, the surface of the interior of the pipe or anything else that disrupts flow.

More pressure will increase resistance and less pressure will decrease flow.

For years my life depended on friction loss. Not enough flow if water and I died. I appreciated the increase of water going from a a 1 1/2" attack line to a 1 3/4" attack line. Lots more water for little extra weight. The extra flow saved my life more times that I care to think about.

When a pump is rated for so many gpm's at a set height that is the ability to pump against gravity (or head).

My solar setup is over kill for anything that will put out more than a few GPM. It is all level. The highest point is 6 feet above the lowest level. It is all connected in a closed system.

This allows water that it going downward to decrease pressure on the upward side. Since my water is flowing at a very slow rate since it has to stay in the solar panels to heat up (I have them set up in a combination of series and parallel) I don't need speed in they system. Then when it is in the heat exchanger it has to move slowly to give off as much heat as it can. I have the differential set at 15 degrees since there is a declining heat transfer rate below that.

So moving heat in a fluid is different for different situations.

I don't think I am confused.
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Old 11-02-2008, 02:11 PM   #15
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LOL...

I did a cast iron baseboard on the same side once, only half of it gave off heat.

I had to dig out the crawlspace, to get a line to the other side of it.
Big PITA.
Been there done that.

I had a radiator that wouldn't put out any heat. I traced it to a rusty valve I had to replace. Figured that I had is solved and told the home owner that it was just a matter of time.

Filled the system and nothing.

Started all over again and traced the line again. This time I found the output line of the radiator that was buried in the wall and was capped off. They had removed the pipe when they put in the new wall and had capped off both ends.

I could get water into the radiator when I bled it but there was no flow once the bleeder was closed.

After draining the system AGAIN, I fixed it an had heat, imagine that....

Boy, did I feel stupid.

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