Can low flow velocity be bad ??

Brian_18

Thanks for the replys. I re-used the supply & returns and hooked up to the manifold last night. (DIY'er) When I re-configured my system 2 years ago with a mod-con, P/S, & VS Injection I took the wise advise and "pumped away", and installed a spirovent. My system has never been so "air free" as it is now. So, if the only real concern is not carrying air bubbles back due to low velocity, I'll purge like there's no tomorrow, and see how it reacts. That will be tonight's objective. Thanks again

Brian_18

Can low flow velocity be bad ??

I've converted another portion of my home from fintube to infloor radiant. I'm in the process now of hooking up the manifold, and would like to re-use the old copper supply & returns from the previous fintube era. For whatever reason, (maybe that's what they had on the truck) the return is 1" copper. My calculations of headloss for this new zone says even 3/4" is oversized and not needed. My question becomes, what's the consequence of using the grossly oversized 1" return?

Brad White

That is not grossly over-sized.

If you needed only 3/4" copper but had 3-inch instead, I would tear it out, sell it for scrap and retire.

The only risk you run is hitting a point of laminar flow but that is not so horrible. Just lower output. Most manufacturers rate their fin-tube at 3 FPS and it drops off below that. Not appreciably until you get to about 0.25 FPS. Even so you still get about 90.5% of capacity.

The other concern would be the ability to carry along air to the vents. A good purge can take care of this during start-up but normal operation can leave some air behind. Not enough to hurt anyone if you have high point vents.

But one-inch pipe? Hardly extravagant.

Glenn Sossin_2

Robert Bean

just had a webcast on this subject. One of his points, if the water moves too slowly, dirt and air can separate in the piping. Sediment can build up over time in a particular spot and eventually create a flow restriction. Brad hit on the other one - moving air along to the vents.

Steamhead (in transit)

Interesting

but in old converted gravity systems, with their oh-so-gentle low-velocity flow, I've never seen either of those problems.

Of course, I pump them away. And in Brian's case, pumping away should take care of the air. If there's so much sediment in the system that it collects and causes a blockage, I'd say we have other issues.

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