Sizing Steam Mains With And Without Insulation

New England SteamWorks

I've just spent a few hours pulling my hair out. I know I read (almost certainly from Dan) somewhere how much larger steam mains would need to have been specified if they were to be installed without insulation (it was quite a bit), which is why they were always insulated. But I've searched and searched and now cannot find the reference. Can anyone help, or am I destined to go bald?

Thanks!

Erin Holohan Haskell

https://heatinghelp.com/systems-help-center/why-you-should-insulate-steam-pipes/

New England SteamWorks

Thanks Erin, that's where I thought it was too, -but it's not. Not in TLAOSH either...

EBEBRATT-Ed

I don't recall that the pipes need to be larger. I seem to remember that I think he suggested upping the pick up factor from 1.33 to I think 1.5

But I could certainly be wrong

New England SteamWorks

It was along the lines of the pipe would make too much condensation without insulation, and so would have to be larger to avoid banging.

DanHolohan

I don't recall writing about the pipes needing to be larger if they weren't insulated. The boiler would certainly need to be larger.

New England SteamWorks

It could be that I am mis-remembering.

But.

Mains and run-outs were sized so that the steam and condensate can co-exist without banging, right? If we remove the insulation we have more condensate, right?

Jamie Hall

I've never seen it in Dan's writing -- but there is a certain logic to it: if the steam main is uninsulated, there will be more condensate formed during startup. This raises a number of considerations: first, one will need to increase the pickup factor to account for it (which is undesirable during later stages of heating); second, steam will take much longer to reach the ends of the mains, as more of it will be consumed heating the pipes (this is an often overlooked factor in getting even heating, but a very important one; third, you have that extra condensate. On that last point, if the mains are sloped parallel, it may not be a problem -- but if they are sloped counterflow, you will need to increase the pipe diameter to reduce the steam velocity, to avoid picking that condensate up and creating water hammer.

Bottom line: insulate the pipes...

DanHolohan

Yes, but how much would depend on the ambient temperature in the space around the pipes. Tough to call.

AnthraciteEnergetics

If it was counterflow I could see it maybe if there was a lot of connected load on the main. Bigger pipes then make more condensate (more surface area), but surface area/cross-sectional area ratio does go down as size goes up. I've been in places where it was evident that the main was designed to be a heat emitter in a finished basement. If you figure in the EDR of the bare pipes for the boiler and pipe sizing, it should be fine.

EBEBRATT-Ed

The first inch of insulation is the most important. The thicker the better I guess but you get more ban for the buck with the first inch, less with the second and even less after that.

Good insulation is worth it but is sure is pricy now

New England SteamWorks

I just remember Dan writing something like "So the engineer had a choice. He could specify 2" pipe with insulation, or he would have to specify (fill in the blank) inch pipe. Naturally, he chose the 2" pipe with the insulation".

AMservices

How many systems have we all see with no insulation and yet, they don't bang?
I'm sorry to say this @New England SteamWorks
In this business, your destined to go bald.
If thinking about mechanical problems doesn't do it to you, wrapping your head around what other people do or dealing with customers will

EBEBRATT-Ed

@AMservices , don't forget the manufacturers that won't stand behind their junk equipment.

SeymourCates

The amount of condensate produced from a given boiler is identical whether the steam condenses in the mains or in the radiators. You get about 87 lb/hr of condensate for a 100K boiler (output). Doesn't matter if it condenses in the mains or the rads (the rads are preferable).

87 lb. is about 10 gallons which, in practice, is negligible for a 2" pipe.

clammy

i would have to agree on increased pick up on uninsulated mains but i really try to size my replacements to the edr w a mimiun pick up usually less then 1.33and as for up sizing of piping ,never heard of that but i would say that it s a total waste of fuel from my experences .That downside of uninsulaed steam piping is a uneven heat hard to balance system thats piping will surcome to groving in the piping and leaking of the thinest piping mostly at the joints and of course finding some one to repair those leaks without causing other leaks in the process .When ever im faced with uninsulated steam mains and repairs i explain it all to the HO and let them decide being i don t mind the repair work $ and usually in some cases they use to heat the basement but thats ok keeps me busy repairing . As for fuel savings and better comfort insulate those mains and near boiler piping or save money to pay for pipe repairs and higher then should be fuel bills. As for banging on uninsulated its all relative to cold system start up and ambient temps i have had them bang so bad nearly pooped my self and lets not forget shut down on lwco till all the extra condenstae makes it way back home oo the water feed fills her and floods when t stat is satisfyed .To myself uninsulted steams pipe sare a no no and jobs where they dont want to do anything except complain about noise and fuel cost is a sure sign for some one to hood wink them and i give the HO and number a of flat rater to continue to rip them off w BS instead of doing whats right . peace and good luck clammy

mikeg2015

I'd be careful going much above 1.33 on pickup. Once the header and run outs are heated, even insulated header won't lose as much heat as you think if you do the math. Especially if you consider that a header at a basements ceiling once heated will be surrounded by 85F air, and have a lot less radiation than a radiator near the floor and outside wall with 65F air moving across it with the same surface area.

I still think when sized right, the system should run continuously without building significant pressure once all radiators are heated. Heating all that metal can take a long time on a bigger system from a cold start, probably over 1 hour.

ChrisJ

@Dan Holohan Where the very early steam systems insulated?

I didn't think asbestos insulation started catching on until the 1920s-1930s?

j a_2

EBEBRATT-Ed said:

I don't recall that the pipes need to be larger. I seem to remember that I think he suggested upping the pick up factor from 1.33 to I think 1.5

But I could certainly be wrong

Very very seldom did I come across a properly insulated system, I pretty much always used the 1.5 factor...but seldom did it change the number of sections on a gas boiler .... oh no!!!

EBEBRATT-Ed

@mikeg2015 said:

"I still think when sized right, the system should run continuously without building significant pressure once all radiators are heated. Heating all that metal can take a long time on a bigger system from a cold start, probably over 1 hour"

I certainly agree with this 100%. Too much pick up will give you an oversized short cycling mess.

In most cases when you pick a boiler the 1.33 pick-up is already figured in the boiler rating. The boiler selection seldom falls on the exact #. My thought is that when it's cold out the boiler is cycling often enough the piping doesn't get much chance to cool off. In warmer weather the boiler doesn't cycle as much but the piping has more time to cool, but you have extra capacity.

Still need to fill all the pipe with steam to keep the system in balance

mikeg2015

All the pipe, yes. Why would that be a challenge. Assuming it’s hot it only represents maybe 10% capacity at most. Another 5% for the boiler jacket. But what happens when everything is hot and now you have an extra 10-15%? I think we get away with it because EDR is a little conservative.

Let me add this observation. Is my boiler is oversized at 1.75 and I’m not seeing any pressure increase until the radiators are full but it heats up so quickly that it overshoots (never short cycles). I don’t see how it would become unbalanced if it fill the radiators slower so long as my main is generously vented. Further I could use even smaller vents to control it tighter.

Steam takes path of least resistance so long as your boiler achieves a minimum size to fill the main and your venting is controlled enough. I think the mistake is that the combined venting rate becomes too high and far exceeds the peak rate of steam expansion which is the moment the main is heated. Maybe this only holds for vapor systems. If my main was 1 size smaller, I would operate at 8oz instead of <0.5 and the system would probably be harder to control.