Minimum 1/2” loop lengths

Rod Kotiga

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? 

Rod K

Mosherd1

I’m thinking of doing the same in my crawl space. I know I don’t have the room to work with 250 feet of pex runs under there, my nose touches the bottom of the floor joists in parts while I’m laying on my back, but if I can do a full loop per joist space and do a reverse return I should think it would work as I’m just using it for floor warming not my primary heat source.

Zman

If you use an uncoiler and pull the loops through the bays one at a time, 250' is not difficult to work with. I am not sure why you would want to add all those connections...

EdTheHeaterMan

You are correct, That will work just fine.

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.

Solid_Fuel_Man

I dont think there is a minimum. You could even use smaller then 1/2" if you can get the plates. May be no advantage other than being the most workable. 

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. 

Solid_Fuel_Man

This is a small basement radiant job, needed very little heat. Customer couldnt be happier.  

Dave H_2

Think of it this way, the main reason you are running a radiant floor system with pex is because of it's flexibility and lack of connections. Every connection you make is a threat leakpoint.
If it's the flexibility you are looking for, consider running 3/8" instead, night and day difference

Dave H

Jamie Hall

@EdTheHeaterMan has a good point about purging. It will be almost impossible with multiple short loops. However, there is another problem even more fundamental: the resistance to flow in a loop is inversely proportional to effective loop length. The effective loop length is the length of the pipe, true -- plus all the miscellaneous losses along the way from bends, Ts, elbows, kinks, etc. etc. As the length of pipe gets shorter, those miscellaneous losses get greater; on very short loops they will become dominant. As has been noted, water is lazy. I those multiple loops are piped in parallel, some will get far more low than others, and the heating across the floor will become patchy.

hot_rod

Yes it would work fine with reverse return, I too would go with 3./8 purge with city water pressure and you will get an adequate purge.
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

TAG

I just did the great room of my current project -- 1000sf room --- using extruded plates and 3/8 pex. It went very well and the 3/8 pex is so much easier to work with. The loops are 160' -- 11 loops to the manifold. Remote manifold piped with 1.25 copper.

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

EdTheHeaterMan

All good stuff to think about. Aren't you glad you posted here so you can get this valuable info @Rod Kotiga?

TAG

BTW -- I had never used 3/8 pex with the plates prior to getting advise and recommendation here on the forum .... had used it for a house where we did wet bed tile and did not want to have the floor too thick --- but not retrofit plates.

EdTheHeaterMan

Rethinking my radiant system. I believe I used 3/8" PEX with aluminum plates. Me and a helper. We made 200 to 250 ft loops and fed 4 to 5 joist bays at a time... in a crawl space... It was not that difficult once we got a system going. 1400 Sq Ft of hardwood floor above us and we got it done in 2 days.

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!

hot_rod

EdTheHeaterMan said:

Rethinking my radiant system. I believe I used 3/8" PEX with aluminum plates. Me and a helper. We made 200 to 250 ft loops and fed 4 to 5 joist bays at a time... in a crawl space... It was not that difficult once we got a system going. 1400 Sq Ft of hardwood floor above us and we got it done in 2 days. 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!

It’s hard to live with any other heat system once you experience properly installed and controlled radiant 

Solid_Fuel_Man

I built my house as a heated slab on grade. Here in the far northeast everyone has a full basement. I have hard ledge everywhere, and didnt want to bla$t. 

I would absolutely do it again, just takes planning before the pour to have all mechanical stubs in the correct locations. 

motoguy128

Solid_Fuel_Man said:

I built my house as a heated slab on grade. Here in the far northeast everyone has a full basement. I have hard ledge everywhere, and didnt want to bla$t. 

I would absolutely do it again, just takes planning before the pour to have all mechanical stubs in the correct locations. 

2/3rds of the new construction in my mostly rural area is slab on grade even though most typical homes have basements (SE Iowa, 5F design). I really like the concept. Downside is you lose storage space without a basement so you need a good garage attic area with pull down stairs. Most customers also build vaults as well as a storm shelter (tornado country) and for their guns, of course.

hot_rod

motoguy128 said:

Solid_Fuel_Man said:

I built my house as a heated slab on grade. Here in the far northeast everyone has a full basement. I have hard ledge everywhere, and didnt want to bla$t. 

I would absolutely do it again, just takes planning before the pour to have all mechanical stubs in the correct locations. 

2/3rds of the new construction in my mostly rural area is slab on grade even though most typical homes have basements (SE Iowa, 5F design). I really like the concept. Downside is you lose storage space without a basement so you need a good garage attic area with pull down stairs. Most customers also build vaults as well as a storm shelter (tornado country) and for their guns, of course.

Scaredy (sp) holes is what we call those dual purpose rooms here in Missouri. A builder friend of mine found an old bank vault door for his concrete room.

Rod Kotiga

What hotrod said 👌
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.