Effect of elbows and sweeps on radiator supply/return

Scott_Mountain_View_CA

3 of my rads have connections on the bottom only, and my supply and return lines are from above. Assuming I use straight TRV's and shut off valves, I will need to redirect the 1/2" pex tubing 180 degrees within the wall stud cavity (16 o.c.) for both supply and return. Is this going to cause head/pressure loss problems? The only other solution would to use elbows but that seems even more restrictive. My total system GPM is less than 2, so should I assume that just about any pump I'd be using will overcome the resistance from the elbows or sweeps?

Maybe this isn't an issue at all. Floor radiant tubing makes a 180 degree bend at the end of each row....that's way more radical that what I'm dealing with.

I'm using Uponor propex expandable fittings on this job. Uponor 1/2" hePEX has a 3-3/4" min turning radius which might work, however Mr PEX oxygen barrier tubing has a 2-1/2" radius. They say they meet the ATSM 1966 standard which allows their tubing to work with Uponor ProPEX expandable fittings. Should I believe them? Anyone here have any experience using this combination?

hot_rod

They call him Mr Pex for a reason! It they say it is compatible, I would believe them. Mr Pex himself started this whole PE tube business under the Wirsbo name, now Uponor.

It's always better to make a sweep with the tube instead of tight turn fittings, you'll be fine. Now get to work, no more questions

Bob Bona_4

You really ought to look into a pex- aluminum -pex product for the rad piping. Uponor Multicor , Viega Fostapex, etc. This isn't really the best application for Hepex or other straight pex tubing. A lot of potential for expansion/chafing/noise. I think you'll be dismayed at what happens when things get hot.

Keep your 180 bends to a minimum, but don't stress over a couple in a loop.

Scott_Mountain_View_CA

You mentioned hePEX straight tubing. The hePEX I'm looking at SupplyHouse.com is coiled. This is confusing to me...could you clarify what you mean by "straight"? Is the coilded hePEX referred to as straight?

Scott_Mountain_View_CA

I guess I should call Uponor tomorrow morning to get a tutorial on their tubing. I already purchased the M12 expander tool from CPO but they said they'd issue a courtesy return at no cost to me...pretty good service.

Both Uponor hePEX and Mr PEX Barrier have an expansion coefficient of 1.1” per 10ºF per 100 feet. I don't know what that means.

My supply and return mains are running in an insulated soffit on the outside of exterior walls. The only tubing to enter the wall cavity is 1/2" radiator supply/return....12' each tube on average for each rad, embedded in R-13 insulation. Should I still be concerned about noise?

Mark Eatherton

Both Uponor hePEX and Mr PEX Barrier have an expansion coefficient of 1.1” per 10ºF per 100 feet. I don't know what that means.

My supply and return mains are running in an insulated soffit on the outside of exterior walls. The only tubing to enter the wall cavity is 1/2" radiator supply/return....12' each tube on average for each rad, embedded in R-13 insulation. Should I still be concerned about noise? END QUOTE

What that coefficient means is exactly as it say. So if you have a 30 foot run, and the water can go from say 70 to 180 degree F, then the tubing will literally "grow" as follows. 1.1 X 11 X .30= 3.63" on that run alone. Almost 4 inches of growth to contend with. PAP has an expansion factor similar to that of copper.

It can be dealt with if you manage the tubing. Anchor it in the middle, and leave room on the end/corners to allow it to expand without binding and sending the growth in a direction you didn't want and hadn't expected. The EVOH barrier is what causes the tubing to click and tick as it moves agains framing structures,

Leave enough space for branches to move freely horizontally (can be calculated using the same formula). The use of glides instead of 2 screw clamping suspension clamps will allow it to move quietly. The use of TRV's and the ODR will also significantly reduce the potential growth vs time function.

In other words, the net flow and subtle temperature change through the PEX branches is slow, so the expansion is slow too.

Don't forget to compensate for any contraction of the tubing as well, or it will tear itself out of the hangers.

BTW, 1.1" per 100' per 10 degree rise is the coefficient of expansion for all poly tubing, including PVC, CPVC and PE.

Hope this helps.

ME

Scott_Mountain_View_CA

Thanks Mark. On that expansion coefficient, I'd wanna know at what temp the tubing begins to expand as the temp rises. Is it 70 degrees or something higher? I'm guessing that the expansion is non-linear and that at some temperature the rate of expansion begins to slow. Cause I'm a curious type (ie anal) I'm gonna check that out.

I'm prepared to go with pex-al-pex to avoid all of the pitfalls you mentioned. I was really looking forward to using that cool M12 expansion tool and the propex fittings...it seemed dummy proof...lol.

Scott_Mountain_View_CA

Has anyone tried the Viega press PEX polymer fittings? They say they're new....not sure how long ago they were introduced.

Bob Bona_4

Yes, I use them exclusively, heat or potable. Brass has gotten obscene in price. They've been out 5 years now plus or minus. Extremely tough. From time to time, I'll give them the stress test (bending the pap on 2 sides of a 90, wrenching them around) on a job, have yet to snap one.

Scott_Mountain_View_CA

I'm working between 16 o.c. studs with 1/2" supply tubing that requires tight radius sweeps. Viega specs FostaPEX minimum bend radius at 3.5 times o.d. using their $350 (uh-uh) bending tool. Can I come close to that bending by hand? If it crimps do I have to cut and repair with 2 couplings?

The best price I found on the Viega press flex tool was $179 for the 1/2" and $189 for the 3/4" (Amazon). I won't curse them for their prices since I'm sure everyone here has already covered that.

Bob Bona_4

You should have no problem bending by hand, although I have a rachet mandrel bender (yellow jacket/rems/all the same principle) I have yet to need it in all the crazy places I've piped. It only gets used to bend ACR copper. Your knee works well to form things, start the forming with the pipe long, then trim the ends to fit. I've used the chamfering tool as a hub to bend but grasp the body of the tool, don't chuck it up in a drill and use the drill as leverage- the hex shaft on the tool will bend. Then you've got an out of true wobbly "skinner" tool

Those prices aren't horrific, compare them to uponor if you want a real eye opener!

Jamie Hall

On the question of expansion -- within a very wide range of temperatures -- basically anything below actually melting -- the expansion is exactly linear. And the forces are very very large, so as folks have said you must make proper allowance.

Scott_Mountain_View_CA

r

hot_rod

Regular barrier pex works fine, just pay attention to the expansion details they show in the installation manuals. Millions of feet of it are in hydronic service across the globe.

The pros that work with pe products all the time like certain types and brands for the additional features and benefits. They all have pros and cons.

A few S bends as you drop down, insulate the tube in exterior walls and long covered runs, you will be fine.

Sort of like buying a new truck, lots of brands and styles to chose from, they all get you from A to B.

Scott_Mountain_View_CA

Attached is a schematic of a Runtal vertical wall panel radiator....three of the rads I'm installing are of this configuration. Notice there are bottom connections only. I'm using Danfus TRV angle valves which will put a 1/2" NPT female connection into the wall. What I've been trying to solve is how to bend the pex inside of a 3.5" wall cavity to make the connection using a brass adaptor on the end of the pex. That would require a 2.5" radius bend in the pex, which rules out pex-al-pex. The only barrier pex product that would work is Mr Pex oxy barrier which specs a 1/2" tube at 2.5" bend radius. But it would be tight, and I'd still have the expansion issue.

I just got off the phone with the head Runtal mechanical engineer and he told me that adding a brass 90 el would not cause any meaningful pressure drop, particularly on a parallel reverse return system requiring 1.8 GPM with a 6 GPM pump. Adding the 90 el to the TRV would point the connection upward which solves a couple of problems: 1) no worries about kinking bends, and 2) allows me to use pex-al-pex to eliminate any noise issues. The pex drops down from above directly into the brass with minimal tube flex.

hot_rod

Is the stud bay open or are you trying to drop the pex down a finished wall?

If it is open, at least some of it, the pex detail looks like this. Rough into two FIP ells, finish the wall and hang the radiator. Provide backing for the hanger brackets also.

Use a 1/2 pex barb to 1/2 FIP ell, fasten to a block of wood at the appropriate spacing. With a threaded nipple the angle valve screws into the ell below the rad.

If it is a retro fit, you will still need to open some wall to get the tube out and into the radiator, possibly some backing to hold the weight of the radiator.

It's the little, but crucial details like this that brings out the value of an experienced installer, it might be worth spending some $$ at least for a jobsite consultation from a pro?

Bob Bona_4

Ah, ok, I get what you're saying Re the bends. Going from vertical down wall to horizontal stubouts. What HR said is a great transition. Most of my panel rads have been Buderus, using floor stub out to either diverters or in/out fittings.

Scott_Mountain_View_CA

hot rod said:

Is the stud bay open or are you trying to drop the pex down a finished wall?

If it is open, at least some of it, the pex detail looks like this. Rough into two FIP ells, finish the wall and hang the radiator. Provide backing for the hanger brackets also.

Use a 1/2 pex barb to 1/2 FIP ell, fasten to a block of wood at the appropriate spacing. With a threaded nipple the angle valve screws into the ell below the rad.

If it is a retro fit, you will still need to open some wall to get the tube out and into the radiator, possibly some backing to hold the weight of the radiator.

It's the little, but crucial details like this that brings out the value of an experienced installer, it might be worth spending some $$ at least for a jobsite consultation from a pro?

LOL...I'm a builder with plenty of plumbing experience....just an idiot on hydronics and fluid dynamics. Not a retrofit, walls are open, and yes I plan to use a brass 90 el off the angle valve to get the threads pointed upward rather than horizontal. I was trying to avoid that because several pros here suggested an el might be a bad idea due to pressure loss. Turns out it's not an issue. I guess I've run out of excuses to not begin work.

Scott_Mountain_View_CA

Bob Bona said:

Ah, ok, I get what you're saying Re the bends. Going from vertical down wall to horizontal stubouts. What HR said is a great transition. Most of my panel rads have been Buderus, using floor stub out to either diverters or in/out fittings.

Bingo. I'm on a slab so supply has to come down from above and in my area 2x4 exterior walls are standard. I'm guessing that most of the pros here are in cold country and probably have 2 x 6 exterior walls, and maybe even some double wall construction.

Bob Bona_4

It's only 4 PM out your way...get going on that rough in!

Scott_Mountain_View_CA

Ordered 1/2" and 3/4" Viega press tools, fosta pex, and fittings.