closely spaced tees

PM Home and Cabin Services

Question about closely spaced tees: is it ok to have larger spacing than the rule of 4XD or no more than 12" on closely spaced tees for primary/ secondary piping connections.
Existing : 3" primary and 2.5" secondary pipe and the tees are 15.5" center to center.
Long story short, I am working on getting prices together for replacing 25 yr old boilers and correct nearby piping (which I thought was incorrect due to spacing ). I asked the distributor (who will supply equipment) to come look at the job and piping (they like to be involved with planning of large jobs) and it blew my mind when the hydronic specialist from the distributor tells me that 15.5" spacing is fine and can be reused and not necessary to correct.
So I hit the books again, and could find nothing other than 4XD no more than 12" (Caleffi, taco, and Dan H. reference materials). Everything I have done, learned and was taught has made it difficult for me to accept that 15.5" space between tees is correct with no negative affect.
Can closely spaced tees be spaced further and how much is too far (especially if 12" is supposed to be max).
Thanks in advance

Gordy

Is this copper.or iron piping? How much space is between the actual t fittings?

hot_rod

It is all about keeping the pressure drop between the tees as low as possible. It can never be 0, even 1" length of pipe has some pressure drop, depending on flow rate.

Even with the tees close nippled together you would probably have 10"? branch to branch. 4D on 3" pipe is 12".

Usually the secondary branches have a pump and a check, and I would add a check on the return also. So I doubt a few extra inches between the tees will cause problems.

PM Home and Cabin Services

Thanks for the fast replies
Piping is iron.
It is a relief to hear others agree a few inches should not be a problem, makes for a simpler project.

EBEBRATT-Ed

It will be fine. A few inches seldom matters

Tinman

The smaller the gap, the better. Keep'm as close as possible.

GW

Many (15 or so) years ago it was 6x, then I’ve been seeing 4x for the last 5 or so years. Did someone move the cheese? Regardless it all works, unless you’re doing big and small gpm. Similar gpm seems like it won’t matter much

Tinman

hot_rod

GW said:

Many (15 or so) years ago it was 6x, then I’ve been seeing 4x for the last 5 or so years. Did someone move the cheese? Regardless it all works, unless you’re doing big and small gpm. Similar gpm seems like it won’t matter much

Good point! Without running complicated calculations on every job I doubt we will reach a one dimension fits all answer.

Putting ones hands on the take offs is a good indicator of how well the separation function is working.

Checks are cheap and easy and near 100% assurance.

Tinman

Siggy's first book came out about 20 years ago, didn't it?

Gordy

Always knew the 4 pipe diameters, 12” max. Never the 6pipe diameters. I suppose it depends on how the primary, secondary flows behave is the bottom line,

GW

Ok I guess I dreamed it

Gordy

NOT saying you dreamed it just didn’t remember coming a crossed it.