Riser sizing.

delcrossv · April 9

General, non system specific question:

Lets assume the minimum size is sufficient for installed EDR.

Is there an advantage to upsizing longer risers (like to a 3rd floor) for at least part of the way and then reducing to the radiator size towards the end of the run?

In this case, the risers would be insulated so more of a flow rate question.

Seems that for 2 pipe, for example, it would help to make most of the run in 1" or even 1-1/4, then drop to 3/4 near the end.

What say you?

mattmia2 · April 9

bigger pipes take more steam to heat so the steam progresses more slowly. 1 pipe needs certain minimum sizes so that steam and condensate can coexist.

EBEBRATT-Ed · April 9

The Burnham Heating Helper says for steam risers for example they say :

25edr for 1"

55 for 1 1/4

85 for 11/2

150 for 2"

It says if the horizontal distance from main to riser is more than 10' go up 1 size

For mains the pressure drop should not exceed 2 oz

so 2" pipe @100 ft=350EDR for 200' edr is 235

2 1/2" 100 ft 580 edr 200ft 335 EDR

The above is for 1 pipe

Each job is different

You have to consider pitch, condensate flowing with or against steam 1 pipe or 2 pipe etc etc

See attached:

Burnham Heating Helper .pdf

delcrossv · April 9

So, for 2 pipe, smaller is better just from a pipe heating angle? Makes sense

mattmia2 · April 9

It is also true for 1 pipe but you can go much smaller in 2 pipe before it is too small and causes other problems.

delcrossv · April 9

https://forum.heatinghelp.com/discussion/comment/1851722#Comment_1851722

"Other problems "? Condensate?

EBEBRATT-Ed · April 9

For two pipe "generally" you don't have condensate flowing against the steam so the pipe size can be reduced.

mattmia2 · April 9

Too much flow resistance if you go too small in 2 pipe as well.

delcrossv · April 9

https://forum.heatinghelp.com/discussion/comment/1851730#Comment_1851730

That's what I was getting at. Seems there's something to it.

"It says if the horizontal distance from main to riser is more than 10' go up 1 size

For mains the pressure drop should not exceed 2 oz"

So long risers should be somewhat larger?

ChrisJ · April 9

On my own single pipe system the horizontal runs appear to be kept larger even when the vertical runs are reduced. The vertical runs to radiators are a mixture of 1 1/4" and 1" but all of the horizontal runs are 1 1/4".

mattmia2 · April 9

https://forum.heatinghelp.com/discussion/comment/1851736#Comment_1851736

In one pipe the counterflow of the condensate will be more of an issue in laterals than risers.

delcrossv · April 9

And in 2 pipe?

mattmia2 · April 9

not sure. in 2 pipe there is still some condensate from the piping itself and it can connect in laterals, not really in risers. but that is an interesting question about what happens when small amounts of condensate and steam collide and how much cross sectional area is needed to make it a minor local disturbance vs water hammer.

ethicalpaul · April 9

not sure. in 2 pipe there is still some condensate from the piping itself and it can ~~connect~~ collect in laterals, not really in risers

From watching my glass headers I can say that it's likely that the fresh steam re-vaporizes a lot of condensate as it passes by.

If it's not able to re-vaporize all of it, yes it should collect where a lateral turns upward from being pushed by the flow of steam. Then it will get carried up to the radiator in the risers like how a coffee percolator works. It won't hammer because the condensate will be hot enough not to collapse the steam (contrary to popular opinion, hot condensate does not collapse steam. They co-exist). We see the same thing where there is a sag in a one-pipe system…after the steam heats up the water, the steam can pass through the water. And we also see it in a pot of boiling water, and in all of the boilers in the world.

Any water that makes it up to the radiator is then in good shape, as it will flow down to the trap with all the rest of the condensate from the radiator.

Any water that is still in a lateral at the end of a call for heat will counter-flow back to the boiler no problem.

All these statements are for more-or-less typical scenarios, not for crazy-a** s*** that might be out there.

mattmia2 · April 10

if there is a fitting transition that isn't exactly smooth or a little bit of sag that water will be there as the system is heating too, before it is steam hot.

EBEBRATT-Ed · April 10

In two pipe the rad is pitched the other way so the condensate goes down the return. Once the runout and the riser is hot there really is no condensate unless it is running through a really cold area or the run is extreamely long which it should not be.

ethicalpaul · April 10

https://forum.heatinghelp.com/discussion/comment/1851788#Comment_1851788

I don't think it's consequential. If it were we'd all be hearing pinging and small banging as the main heats up along all its fittings.

mattmia2 · April 10

https://forum.heatinghelp.com/discussion/comment/1851790#Comment_1851790

i think that comes in to pipe sizing, there needs to be a certain cross sectional area compared to the water pocket so that it can dissipate rather than propel a slug of water.

ethicalpaul · April 10

There is no slug of water. Every main in the world has condensate running in it along with steam and no slug of water is ever created. The tiny bit of water that might be sitting in the seam of a fitting surely isn't going to add up to a "slug"

Surging is I guess what people think "slug of water" is.

Unless you are talking about a sag that makes a big pond of water that can collapse steam when hammer actually happens, but I don't think we're talking about that here.

Riser sizing.

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