as in: for a loop system or not I suppose:
visiting our text version of this document.
... Q. What are the main components of an underfloor ... A. All the buried pipework in underfloor
heating systems should be ... The flow and return from each loop of pipe ...
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... depending on the injection and return method used ... temperature migration from the
main primary circuit ... the various types of underfloor heating system temperature ...
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... Hunting Gate Construction plc were Main Contractors for the ... it with return water
from the underfloor heating loops to ... temperature of 43 o C (38 o C return). ...
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Note added at 12 mins (2004-10-19 18:05:24 GMT)
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barreau is a bar...but I don\'t get how that it part of this system..

anyway, main return bar...whatever that may mean...I thought underfloor heating was with loops...

Well, the 'axe' part seems logical enough to me, but the 'barreau' is, as Jane says, a bit of a puzzle.

If this is a water-based system (I presume?), then the pipes are probably connected back to some sort of common rail (as in diesel injection engines!), which, in the absence of brighter inspiration, I'd think of in terms of 'header'. So how do we get 'header' from barreau? Well, it IS only a guess, but given that the more usual word for a header would be 'rampe' (or maybe more often 'collecteur'), maybe there's some kind of analogy there? After all, in other terms a 'rampe' is a bar of steel! And I know that 'headers' are often referred to (in certain narrow contexts) as 'rails' too.

OK, OK, I know none of this holds water linguistically, but it's just 'stream of consciousness' stuff, which might just possibly lead somewhere in the end...

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Note added at 56 mins (2004-10-19 18:49:03 GMT)
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Could this be electrical? I note that the famous \'barreau de retour\' is 0.5 m above the underfloor level --- that seems rather high for plumbing, unless the screed is VERY thick! So might it be a rail or busbar for electrical connections? The similarity between \'barreau\' and \'barrette\' makes one wonder. Again, \'branchement\' wouldn\'t be inconsistent with electricity -- though sadly, \'retour\' probably would be! As ever, more context from Asker would help...

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Note added at 59 mins (2004-10-19 18:52:02 GMT)
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Well, in the light of your next question, which mentions \'tubes\', I have to assume that it is indeed water, and so my electrical idea is a non-starter. Pity!

French term (edited): axe de la barre de retour

I think there is a mistake.It's not "barreau" but barre, which means the return pipe of the loop. "axe da la barre de retour" = axis of the return pipe of the loop.

Since your previous question about "plot" implied that you area dealing with raised flooring, I wonder if your underfloor heating is not the type where electrical elements (heating cables) or hot water pipes are embedded in the concrete floor slab, but rather a system of ducted hot air routed through the floor void. In this case the hot air is distributed through grates in the floor and returned through more grates at other locations (one of my parents' houses in NZ had such a system - great for obtaining that "Marilyn Monroe" look!). In which case your "barreau" could, collectively, be the bar(s)of the return grille. Still, 50cm seems like an awfully high raised floor, though I guess if you are fitting large-diameter ducts in the plenum you want all the space you can get.

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Note added at 4 hrs 53 mins (2004-10-19 22:45:56 GMT)
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I see from Robert\'s site, which contains your very words, that it is not a hot-air but a hot-water system. I see it also gives some insight into what might be meant by \"dalles droites\", which raises further questions about \"dalles à plots\".