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# Take aways for screwed fittings

Member Posts: 28
Hi all,

I'm about to order some pipe for a new radiator run and wanted to double check my math. I found a good thread on this here: http://forum.heatinghelp.com/discussion/71116/how-much-do-you-guys-add-to-lenghts-for-threaded-pipe but it is now closed so i can't reply to it.

My run uses 1.25" pipe and consists of:
90* -> 9" ctc -> 45* -> 8" ctc -> 90* -> 10.75" center to bottom of valve

Nipple A: 9" center to center between a 90* and a 45*; (9") - (1 1/8") - (11/16") = 7 3/16"

Nipple B: 8" center to center between a 45* and a 90*; (8") - (11/16") - (1 1/8") = 6 3/16"

Nipple C: I don't know what the take away is for the radiator valve, but it can't be more than 3/4" before the pipe would interfere with the inside of the valve. So this measurement is the center of the 90* to the base of the radiator valve.

(10 3/4") - (1 1/8") + (3/4") = 10 3/8" ???

Overall, this doesn't see right to me because the results are much shorter than the center-to-center measurement which i think would be slightly closer since the pipe threads in almost to the center point. The results look to me like fitting-to-fitting measurements or the exposed visible pipe length.

Am i doing this right? Thanks!

• Member Posts: 11,021
I don't work with threaded pipe everyday, maybe once every 2 weeks. I seldom use the math you mentioned. I am lucky to have the 3 trays of all nipple sizes (66 or so in each).
Check your local supply house or big box store about their return policy.

So for the length between 2 45's, say it is somewhere around 9", I take 2 4" nipples with a coupling screwed up hand tight between them, then start one end into one 45 and while loosening the other out of the coupling start into the other 45. This gives me the alignment needed to connect those 2 fittings with their faces parallel. Then measure with allowances for bury (study some of your existing piping to see the bury involved) and that is the nipple length I need to cut. I dry fit from both ends of the project like this. Loose fit nipples as needed and then perhaps jump those each up 1/2" in length for the final tighten.

As mentioned I have access to all the sizes. In your case you could overbuy and return excess if allowed. Don't be shy about using couplings and for something like what you're doing I would probably include a union in the middle of things.
• Member Posts: 28
Hrmm i've seen charts that should allow me to hit this on the first try if the math is correct. That's the hope anyway.

Can someone please take a look? I hope to order parts tonight.

Thanks a lot!
• Member Posts: 11,021
Hopefully someone will help this HO out, my method is mainly trial and sometimes error. He doesn't have the 200 plus fittings/nipples available that I have at my disposal, and even then I might still have to chase after something quite often.

But can you buy nipples that are in fractions other than 1/2"?
I assume you are talking of custom cut pipe lengths which are maybe not returnable.
• Member Posts: 5,473
Maybe @ChrisJ can pipe in and tell us how he did his boiler install, I don't know if he was able to use niples or had to cut and thread some of his boiler piping..

Bob
Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
Vaporstat with a 12oz cut-out and 4oz cut-in
3PSI gauge
• Member Posts: 15,456
edited January 2016
My boiler install was mostly nipples with only four custom threaded.

My hardest was repiping the radiator to my son's bedroom which has an offset in the livingroom by the ceiling. I had to line up with a hole in the upstairs floor and a runout and it was tough. It's also part of the reason I bought my 65R-TC. It's not perfect, but it's as close as any of the originals.

The main problem is going to be figuring out how deep your stuff will thread together because many fittings vary and it seems all threaders vary. Not only that, the guy threading it can vary however he wants. After having many places thread stuff for me wrong, I gave in and bought my only manual threader. The pipe in the picture literally wasted my time at 5 places only to be disappointed.

If you need something within 1/2" or so any place can do it. If you need within 1/8" or so, forget it, you need to do it yourself.

As an example, here's a picture of 3 nipples I had done, one at a time to go through the second floor. The top one was first from Lowes, the second one was supposed to be a little longer from Lowes (it's the same), and the bottom one was done by a local plumbing supply, was also supposed to be longer but he was off by an inch from my measurement. Guess he had the weekend on his mind because he left before I could go back.

Also, from my experience, brass radiator valves tend to thread on further than steel / cast iron fittings. That's why my last nipple ended up a hair short in the first place.
Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
• Member Posts: 28

You cannot purchase pipe nipples in lengths that are accurate to 1/16". 1/2" is the best you are going to do.

Any hope of success requires both the shorter and the longer nipple for the attempt. Understand that it might be possible that neither one works unless the piping can move somewhat.

Yes, you are forgetting the insertion depth of the 1.25" threads. That value is .71" maximum. It could be a bit less (and probably will be) due to manufacturing tolerances. I would estimate .65 as a realistic length.

Ahh, now things are making sense. I'm thinking that the chart i referenced only gave you the additional "length" provided by the fitting itself? That would be subtracted from the nipple length.

But then! i need to add length to account for the threaded nipple length that will go inside of the fitting. So another 2 x .71" per nipple?

So i believe i take the nipple lengths i calculated above and add 1.42" each. Please confirm.

And yes, through supplyhouse or in stock at Lowes/HD, i can only get 1/2" increments. I'm hoping i can round one up, one down, etc and get things about right. If not, i'll go for a custom pipe from Home Depot.

Thanks again, all.

• Member Posts: 5,699
When I piped my boiler I did a complete layout based on theoretical thread insertions. I used all off the shelf nipples and didn't need to custom cut and thread any pipe at all. It's possible to do, but unless you have the software and know how to use it, it's typically not feasible for most. Also the thread insertion varies by the pipe size.
1" - .6609"
1 1/4" - .6809"
1 1/2" - .6809"
2" - .6969"
2 1/2" - .9320"
3" - 1.016"
2014 Weil Mclain EG-40
Boiler pictures updated 2/21/15
• Member Posts: 15,456
KC_Jones said:

When I piped my boiler I did a complete layout based on theoretical thread insertions. I used all off the shelf nipples and didn't need to custom cut and thread any pipe at all. It's possible to do, but unless you have the software and know how to use it, it's typically not feasible for most. Also the thread insertion varies by the pipe size.
1" - .6609"
1 1/4" - .6809"
1 1/2" - .6809"
2" - .6969"
2 1/2" - .9320"
3" - 1.016"

I'm confused.
Why aren't 1", 1 1/4", 1 1/2" and 2" all the same? They use the same exact thread pitch.
Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
• Member Posts: 5,699
Can't answer that one @ChrisJ I didn't make up the standards, but I would guess it's the pipe diameter that factors into it somehow. If you look at the specs the only variation is in the hand tight engagement, it increases with the size. the wrench makeup is the same for all 4 of those.
2014 Weil Mclain EG-40
Boiler pictures updated 2/21/15
• Member Posts: 28
edited January 2016
Thanks again, all.

My run uses 1.25" pipe and consists of:
90* -> 9" ctc -> 45* -> 8" ctc -> 90* -> 10.75" center to bottom of valve

Nipple A: 9" center to center between a 90* and a 45*; (9") - (1 1/8") - (11/16") + (2*.65) ~= 8 1/2"

Nipple B: 8" center to center between a 45* and a 90*; (8") - (11/16") - (1 1/8") + (2*.65) ~= 7 1/2"

Nipple C: 10 3/4" form the center of the 90* to the base of the radiator valve so i subtract the 90* take away and add two thread insertions

(10 3/4") - (1 1/8") + (2*.65) ~= 11 1/2"

These are rounded to the nearest 1/2", but they actually came out fairly close by luck.
• Member Posts: 28
I just placed an order for an 7.5", 8", 8.5", 11", and 11.5".

Here's to hoping! (Worst case i run to Home Depot)