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Minimum 1/2” loop lengths

Over the years I’ve seen many posts about Maximum loop lengths of different pex sizes but never a minimum.
For example, What if you have a staple up system with plates of course but your thinking about just running a supply and return main to pick up each joist space run separately. I know some might think that’s a lot of tees but plastic tees aren’t that expensive and as long as all the loop lengths are equal what’s the downside?
For example, What if you have a staple up system with plates of course but your thinking about just running a supply and return main to pick up each joist space run separately. I know some might think that’s a lot of tees but plastic tees aren’t that expensive and as long as all the loop lengths are equal what’s the downside?
Rod K
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Comments
Albert Einstein
I have one question. How are you going to purge the air from each individual loop? Are you climbing under the floor in the crawlspace and have a purge valve on each joist bay?
That air will be purged based on the principles of physics. The water will take the path of least resistance. Once one or two of the loops are air-free, the rest of the loops will have more resistance and resist purging the air.
When I did my last home, I put the manifolds in the wall cavity so I would not need to go in the crawl space ever to purge the loops.
Retired HVAC Contractor from So. Jersey Shore.
Cleaned & services first oil heating system at age 16
Specialized in Oil Heat and Hydronics where the competition did Gas Warm Air
If you make an expensive repair and the same problem happens, What will you check next?
I've done several radiant jobs with nothing more than a ball valve per loop and a bunch of reducing Tee's. Purges fine, and simple reverse return. That way you just need one purge station, do 3 or 4 loops at a time. Never had any air issues.
Pump toward the loops (after the mixing device) and all works wonderfully.
If it's the flexibility you are looking for, consider running 3/8" instead, night and day difference
Dave H
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
A Dahl ball valve with pex adapter would be nice on each loop for somem adjustability and purge ease.
I have seen a few jobs where copper headers ran the length of the crawlspace with short loops. The pex connections properly done should not be a problem, most pex plumbing systems in homes have hundreds of pex connections, under much higher pressure.
https://www.pmmag.com/articles/88420-extended-thinking-br-john-siegenthaler-pe
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
We used a bluefin manifold -- you can't use the 3/8 bluefin fittings w/ viega brand pipe .... they leak. I got other fitting and it working great ... we power flushed it
Retired HVAC Contractor from So. Jersey Shore.
Cleaned & services first oil heating system at age 16
Specialized in Oil Heat and Hydronics where the competition did Gas Warm Air
If you make an expensive repair and the same problem happens, What will you check next?
A year later I was able to have another of my technicians do the manifold piping and install the boiler. 3 years prior we installed an addition that was a Slab on grade. 2" foam board on the ground and the perimeter before the pour with 6 loops of 1/2" PEX left idol in the crawlspace. (I left a 20 PSI pressure on the tubing for the 3 years and it held the whole time.) Once the staple up was completed I had Spray Foam insulation applied to all the floor joist spaces.
Loved that heat! Sorry I had to leave it.
Oh well, it is what it is!
Yours truly,
Mr.Ed
P.S. Damn, My feet are cold!
Retired HVAC Contractor from So. Jersey Shore.
Cleaned & services first oil heating system at age 16
Specialized in Oil Heat and Hydronics where the competition did Gas Warm Air
If you make an expensive repair and the same problem happens, What will you check next?
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
I would absolutely do it again, just takes planning before the pour to have all mechanical stubs in the correct locations.
trainer for Caleffi NA
The magic is in hydronics, and hydronics is in me
Also not trying to pick a fight but I thought design temp is - 3.
Also I’ve done several staple ups doing the 250’ loop length thing.
but sometimes there’s a lot of obstacles in a crawl space ( even one that’s 4’ deep) and as in some cases your fighting a little with the coil and that’s what’ll make you think about a long supply and return main and be done with it.
Being a plumber as well we all put a ton of pex fittings in the crawl and in the wall at higher pressures than radiant so more connections is not a worry as it’s all tested anyway.