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Member Posts: 684
Im pretty sure it depends on the manufacturer. Not all have tappings in the same place.

The BTU ratings in most manufacturer literature I've seen is based on supplied water temp and designed delta T

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• Member Posts: 47
Piping panel radiator for max output

I'm sure this has been addressed before- but what is the best way to pipe panel radiators? I piped most of mine top in bottom out (on opposite ends, naturally) as the manufacturer (Myson) implied in their spec sheets that this would result in the highest BTU output.
I remember reading here years ago that bottom in bottom out (opposite ends) might be better. I might be moving some radiators and thought I might as well optimize while I'm at it...would be interested in hearing any explanations or theories.

Thanks,
Nathan
• Member Posts: 47
flow vs. convective currents

I think the difference in output is due to how the heat is distributed over the surface area of the radiator; i.e. you've got forced flow through the panel (trying to push the water through the path of least resistance) and you also have convective currents making the buoyant hot incoming water want to rise to the top of the panel.
Someone once posted a diagram and explanations here...it might not make a large difference in BTU output how it is piped, but it has to make some difference. I'm kicking myself for not remembering.

Anyone?
• Member Posts: 462
On a somewhat related note...

Does anyone make radiators (or baseboards) that pipe in and out of the same end?
• Member Posts: 97

Water should flow out the bottom because the cooler water is there. But it does not matter whether it goes in the top (diagonally opposite) or bottom, because hot water will rise either way.

There is no significant difference in BTU output between the two configurations you mentioned. Remember that the temperature difference between input and output is small, often ~20F. Installation convenience should determine how you do it.

But if you do want to worry about it, top in / bottom out is very marginally better, because the hottest water is delivered to the top which is where it wants to be. It does not have to rise to the top.
• Member Posts: 2,775
pipe in & out same end

Runtal has this option, I just finished 7 radiators in a basement new zone with this configuration. Runtal has every pipe option under the sun.
• Member Posts: 2,398
Runtal for one

gives options as noted by Tim Smith. The notion of supply in the top and return out the bottom does not necessarily apply because each has internal baffles which distributes the water optimally.

Runtal radiators do follow one precept I have noticed at least on their dual-bank (RF2 and RF3)styles: The supply connection is on the front panel/header facing the room. The return is against the wall.

I shot the radiator with my IR gun and their system works: The lowest of six tubes is the coolest and gets warmer as they progress to the top; ideal counterflow.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

• Member Posts: 47
I see

I see your point...if there's a worst case 20 degree difference over a small percentage of the surface area of the panel rad, it shouldn't make too large a difference in the output.
I went for top in opposite end bottom out due to Myson claiming that configuration produced highest output, and also on the logic that most car radiators are piped that way!
It's good to know that it's not critical. It's just interesting to speculate about this stuff from time to time.

Thanks,
Nathan
• Member Posts: 2,398
Just a wee bit more...

The counterflow principle:

Picture the coldest air entering the bottom of the radiator (assuming some convection capability of course).

If the hottest water entered here, it would give the air a boost of course, but as the air rises through successive fins and rows, the water conversely would cool, imparting less heat. Finally the leaving air sees the coldest water. What a drag....

Reverse this to the ideal: Cooler leaving air is still pretty warm compared to the 65 degree air coming off the floor. The leaving air at the top of the radiator sees the hottest water for a nice send-off.

The other part, the 20 degree delta-T: This is why average water temperatures are used when selecting radiators. The gains from the hottest balance the lesser gains from the coolest. This also illustrates why flow means less than temperature. Cut the flow in half on a 20-degree delta-T radiator and you have only cut the average water temperature ten degrees.... you still get about 90% of capacity from your radiator.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"