Tee-ing in a Radiator: Wondering about restriction

NewPlumber

Currently in the process of plumbing in a loop of Stelrad radiators. We are using Direct Return System with TRVs on each rad. The supply and return are 3/4" Pex. The radiators were to be connected via 3/4" x 3/4" x 1/2" tees. However, the installers are having a hard time fitting in the tees due to tightness of the runs. (the supply and return lines were fitted into the walls, pipe sections were cut and overlapped at each connection to ensure adequate available pipe (as opposed to running a continuous piece and then cutting in for each tee)).



One solution offered was to cut back the 3/4" Pex and install a 1/2" x 1/2" x 1/2" tee for supply and return at each rad. The reason being the 1/2" tees and pipe were easier to work with withing the cavities. The 1/2" tees would then be  re-connected to the 3/4" lines with 1/2" Pex and 1/2" x 3/4" adaptors.



My argument against was that 1) restrictions are being introduced into the supply and return lines where the 3/4" goes to 1/2" and 2)  four additional joints are being made at each tee.

icesailor

Radiator Teeing:

First of all, if what you are saying is that you are using a direct return AND TRV's, you may or will end up with a very unbalanced system that could be extremely hard to balance. And you running a lot of 1/2" and 3/4" PEX (and using 1/2" PEX in place of 3/4" for piping convenience) may end up in you trying to overcome your problems with a bigger circulator, like the current fix-all of bad designs, the Taco 010 or equivalent. With a direct return, first out, first back, the water takes the easiest route back home. With a reverse return, first out, last back, the pressure is always equal in every circuit.

Hydronic piping is hard to screw up. Mostly, it is forgiving and will take a lot of abuse. When you really step over the line, it can really be a problem.

Its like the old story about little boys and girls and what they say about little boys. "When they are good, they are very, very good. And when they are bad, they are awful."

NewPlumber

Clarification (maybe)

Thanks for your reply icesailor. Perhaps I misspoke. Each radiator has it's own thermostat valve (Herz) fitted to the inlet. This loop is also zoned from the other loops in the house.  The Direct Return system was set up according to a generic schematic from Stelrad radiator supplier (these are flat panel wall mount h/w rads). I would have preferred the Reverse Return but the quantity of pipe and routing requirements made this very difficult. It's a retro-fit in a very old house.



That being said, a similar DR loop was set up on the 1st floor and works extremely well.



I don't want to mix any 3/4 and 1/2" on the two manifolds. The whole purpose of running the 3/4" supply and returns was to ensure adequate supply to each radiator which use 1/2" inlets and outlets. The guys that are actually fitting the system want to insert the 1/2" x 1/2" x 1/2" take off tees and 1/2" "pigtails" (for lack of a better term) to join in to the 3/4" system pipes. I think this is a big mistake but I lack the experience to make the arguement.



I will leave the question of the circulator for a later thread as I don't want to side track this one I really need some advice on this one soon.

icesailor

Restrictions:

You have to work with what you work with. If a Direct Return is what you have to work with, then you don't have much choice. I decided long ago that if a unit has 1/2" connections but needs 3/4" to get the rated output, to pipe 3/4" to the units. The more 1/2" in the loop, the more flow restriction.

Whenever I add anything to an existing system, I always do it as a new zone. That way, I don't fall victim to someone Else's bad piping practices. Piping practices from years ago that I learned are no longer true. Like 15,000 BTU to a 1/2" pipe and 35,000 BTU's to a 3/4" pipe. No longer apply. But when I see 50' of baseboard  series looped with 3/4" PEX (5/8" ID) and it isn't heating properly, I know why it isn't working properly when it is cold. And I see a 40 degree drop in temperature.

You sound like you really know what you are doing. Just don't fall into the trap that the last guy knew what he was doing.

With the increase in "Green Builders" installing "Green Systems" bought from Internet Supply Houses, and not working, you may own someone Else's mistake.

Being a Plumber and Heater, I've been in a lot of new houses being built where there was no place to put plumbing. They designed a house where you basically can't put plumbing in it? How do you run a 3" PVC soil stack to the second floor when there are only 2X4 partitions and the one that is supposed to line up is 2" off and no one wants to pad out the wall. Or, the only place to run a full sized soil/vent stack has a heating duct run in it?  3" PVC needs a minimum of a 4" hole. "Oh can't you put that coupling above the plate so we can get the Sheetrock around it? If you leave that coupling there the sheet rocker will bend the Sheetrock around the coupling and there will be a bump in the wall." Like that's MY fault.

I just worried about the connection of 1/2"X1/2"X1/2" Tees connecting units. It sounds like you have another house like I am only too familiar with where some designer NOT A LICENSED ARCHITECT, has designed their dream (your nightmare) and expects YOU, for very short money, to make their dream come true. And they want you to be the lowest bidder too.

Mark Eatherton

Got pictures or drawings??

I'm trying to look into your minds eye, but I keep coming back with blanks... :-)



Reducing the mains to 1/2" through the branch connections is not the greatest idea, but it will work. The most important thing you have to worry about is the velocity of the fluid through the congested intersections. Send water through the 1/2" tees too fast and you will be able to hear them (think HISSSSSS), and its related compounded pressure drop. Did I mention Hydraulic Erosion Corrosion? THe best example of that is the Grand Canyon.



Pressure drop can be accommodated for in pump sizing, but keeping the pipes larger will result in less resistance (head) and less parasitic cost of operation.



As for parallel direct return piping, due to the fact that you will have TRVs on the radiators, it will self balance the circuits.



The "issues" you are telling us about as it pertains to the PEX fittings and available space have been an issue every since PEX came out. No room to get the required crimping tools into the space. When I was actively installing panel radiators, we ALWAYS made the radiator risers out of copper to avoid aesthetics and the possibility of an irate teenager running the vacuum cleaner into the riser...



WIth that said, the branch tees don't HAVE to be directly below the radiator risers. In fact, they could be 1 joist bay over, thereby allowing plenty of elbow (tee) room for making connections, and then use 1/2" PEX to make the run to the radiator connection, leaving plenty of excess 1/2" tubing to compensate for expansion/contraction and ease of access.



The other alternative is to NOT use PEX, but use copper instead. Do it and be done with it and move on to the next project. Sometimes, the alleged labor savings of using these new materials doesn't always work out to our advantage...



As it pertains to reductions in a main line, in our minds eye, we think that the 1/2" restriction is going to be what the pump "sees" for the pipes full length, when in reality, the pump sees the restrictions as bumps in the road, and not full length lane restrictions. But still, as it pertains to the overall energy required to move the fluid through the circuits, the less restrictions, the better. Ironically, the copper tubing manufacturers have discovered,a nd are exploiting the fact that the fittings used in PEX piping systems are so restrictive that they are the equivaient of running one pipe size smaller than is actually being installed. So for your 3/4" PEX run, if you ran it in 1/2" copper, you'd see about the same pressure drops, or at least that is what THEY are saying. I can see it in my minds eye. The friction through some of these PEX connectors looks pretty choked down.



I experienced this phenomena recently on a home that was newly built. The plumbers ran 3/4" PEX throughout the home. The 1 man 5 woman Jacuzzi soaking tub took 1 hour to fill... at FULL FLOW. Unfortunately, that house burned to the ground. Fortunately, the new house will be built with 1" mains. Fortunately, only the family Parrot perished in the blaze, along with many years of memories, nostalgia and memorabilia, that can NEVER be replaced...



But I digress...



Got drawings?



ME