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# Why closely spaced tees?

edited January 2020
Why closely spaced tees?

Primary-secondary piping systems call for the tees that go off to the secondary circuit to be close together, ideally not more than six inches apart.

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dan, i was once taught or read that the minimum spacing should be thought of as a function of pipe diameter so it was closer for smaller diameters. can't remember if that formula was maybe 6 times the diameter so 6" OK for 1" primary and probably not going to have primary smaller than that so good call for minimum spacing?
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I suggest a close nipple, regardless of pipe size. Even a 1" long section of pipe has some pressure drop, depending on gpm flowing thru it.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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Yes, the closer the better.
Retired and loving it.
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dan, i was once taught or read that the minimum spacing should be thought of as a function of pipe diameter so it was closer for smaller diameters. can't remember if that formula was maybe 6 times the diameter so 6" OK for 1" primary and probably not going to have primary smaller than that so good call for minimum spacing?

Honeywell's Gray Manual mentions the de-coupler in a pri / sec chilled water system being 6 - 7 times the inside diameter in length with the secondary coming off the bull of the T and the return running thru the T.
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Closely spaced tee's provide hydrolic separation between pumped systems. This is usually primary and secondary piping.

Pumps can interfere with each other if they are not separated hydrolically.
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I have a 1” pipe loop in my boiler room, with a set of close space tees heading off to another part of the basement (New radiant circuits), not too far (maybe 25’ one way). 1 x3/4 copper tees. 6” center to center. Dang thing leaches some flow without the pump on. Not a prob, if the heat is on the heat is on. if it really haunts me I’ll redo the loop someday. Guises I should have done 6 x 3/4 bit I was going 6 x 1.
Gary Wilson
Wilson Services, Inc
Northampton, MA
gary@wilsonph.com
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You have a flow check in that loop, right?
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@GW Don't know if you have any way to really estimate the flow or btus involved in that ghost circulation. As in long running discussions of Neutral to Earth Voltage in various electric education crowd sources, electricity does not travel the path of least resistance to ground, it travels all paths proportionate to resistance. Thus a bonded neutral leg with a nice ground rod affixed to the same bus will still show 7 volts to ground during times of high usage in our neighborhood (when the resistance of the neutral return to the substation is exacerbated by higher amperage).

By analogy, esp without a check, you are going to get some circulation in the secondary proportionate to pipe resistance which may be less in a short secondary tangent. As you also point out, it isn't the end of the world if it isn't enough to create uncomfortably warm zone with the actual btu's transmitted. While so far i'm a fan of LED lighting, it goes back to the reality that for 6 months of the year, incandescent lighting simply contributed to needed space heating so for that period it wasn't as inefficient as it appears relative to lumen production.

I would think your 6" figure was formulaically correct because it is the run diameter we're calculating, but that (relatively) low pipe friction in the secondary might have militated for an even shorter distance.

I just finished the piping from this project at 6" spacing on premanufactured 1 1/4" by 3/4" branch manifold and I don't have flow checks. I thought about it but decided I could throw one in a pump port if really needed/ There is one zone which is a short straight up 3/4" loop through a modine. With both the feed and return tees rising off equal temperature water and only 6" apart I figured thermosiphoning wouldn't be an issue but I think maybe all paths relative to resistance figures in and even 6" of pipe doesn't have zero resistance and i'm feeling a little heat in those pipes when the pump is not on. Here it is also largely irrelevant, other than in theoretical discussions after two 15 hour work sessions getting this together during a lull in cold temps, because if the modine fan is not on, the amount of btus transmitted is very little.

my 2 cents, or was that a nickle.

brian
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You need at least a check on the supply side, some times if it is piped vertical like this you need a check on both take-offs. Hot water can try to rise up the return leg if not checked.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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edited January 2020
Yes, this is inconsequential. Just making an observation. Sometimes I chuckle when people say “it won’t work, the tees aren’t close enough “ If there’s a circulator involved, the water is going to go with the circulator tells it to go.
Gary Wilson
Wilson Services, Inc
Northampton, MA
gary@wilsonph.com
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edited October 2021
Hot Rod, yes, in my case the three-quarter inch mini loop jumps up and to the Joist Bay about 5 or 6 inches, then 90°s and runs 20’ across the basement. Then down to the floor in the other room. Then back up, then back to the main loop. This is literally a loop off of the loop. There are two other radiant circuits pulling off of this mini loop. The mini loop will pull some flow, without the mini loop pump on.
Gary Wilson
Wilson Services, Inc
Northampton, MA
gary@wilsonph.com
• Member Posts: 22,694
Yes, we all agree the closer the better. I found with my T-drill I could get them very close, within inches even on a 2" primary loop..

How far apart before it causes issues really depends on a number of things, the flow rates, flow resistance between the tees, piping of the secondary, etc.

Undersized primary loops for example have more potential to induce in the tees when not required.
So as always, it depends

I don't like to see a ball valve between the tees, even a full port has about a foot of piping equivalent. Better to use a Webstone purge ball valve on the return side of the P/S
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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We've used the Weil-McLain "Easy-Fit Primary-Secondary Piping System" on our MBS Applications.
Can't find the website link to their Flyer C-716R1(103) and have requested it. Simple & straightforward.
Will post link when received (if they still do). Otherwise have .jpg & .pdf's on request.
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Taco makes this Tee ...The Tees are on the same plain so it has Virtually no Pressure Drop.