Building pressure and the effect of abandoned mains

Gateacre

I had the boiler replaced in a sprawling 1890s commercial property last year. It's a 10 section oil fired Weil Mclain. 2 pipe steam. Some areas of the building are unoccupied with no prospect of that changing due to modern fire egress code. There is no need to heat these spaces so the contractor sized the boiler accordingly (not that he did any edr calculations). He assured me that the easiest way to remove these areas from the system was to close the valves before the F&T traps at the ends of the mains that service these areas. Provided the valves hold, I see the logic. If air can't be pushed into the returns, steam can't enter the mains. This was much less costly and invasive than cutting and capping these lines nearer to the boiler, and while the abandoned mains don't get hot, I'm wondering if the air within them, being compressible, could be effecting the boiler's ability to build pressure.

We've recently been running on the low fire nozzle only while waiting on a part for the burner, but even with both burner stages working, I couldn't set the firing rate controller low enough to drop out of high fire.

I've installed a 0-3psi guage on the boiler and even after running (albeit unerfired) for 7 hrs continuously, the needle didn't budge.

Most of the building heats (slowly but this is partially a mains venting issue which I'm addressing currently) however in a few spots where I need enough pressure to lift condensate up about a foot, I'm having issues.

Long winded, I know. Real question, could abandoned mains full of air act like springs and reduce the boiler's ability to build pressure?

EBEBRATT-Ed

No. I don't think the abandoned mains will cause any issue as long as you don't get frozen pipes in unheated areas you should be ok.

But unheated stagnant condensate sitting in the old pipes may cause leaks down the road.

Jamie Hall

You mention a problem getting enough pressure to lift condensate a foot? I presume from an F&T trap? You will need a cutin pressure of at least 1 psig to do that. When you get the ability to run on high fire, this problem may solve itself. One hopes. If not, you may be in the rare situation where the boiler is undersized for the remaining radiation; if it is, it will never build enough pressure…

Gateacre

https://forum.heatinghelp.com/discussion/comment/1874786#Comment_1874786

Thanks Ed. No concerns on either score there.

Gateacre

https://forum.heatinghelp.com/discussion/comment/1874790#Comment_1874790

To be fair, the boiler hasn't run at high fire since I rebuilt all the traps in the building (most were shot) so I've probably got nothing to worry about. I've also got big box of mains vents to start installing and a pile of pipe insulating to do. I just wanted to sanity check the abandoned pipes theory I had.

Thanks

ethicalpaul

Can someone draw a picture of the situation where the boiler would have to build pressure in order to lift condensate? Where is it lifting it to? Away from the boiler?

EBEBRATT-Ed

It is never recommended to lift condensate with steam pressure but in the real world it is done quite often. 1 psi will lift about a foot. It should never be done in a place subject to freezing but it can be done with some risk of frozen steam coils.

@ethicalpaul

One place you see this done is in warehouses with steam unit heaters hung from the ceilings. They want to keep the steam and condensate up high because of forklifts etc. So they feed the steam into the unit heater from above. Come out with the condensate through a strainer, trap and check valve then rise straight up and dump the condensate into the top of the return line and run it back to the boiler room.

I did a job for Brooks Brothers with 2 high pressure steam boilers for about 35 various machines for making suits. All the machines were at floor level with steam and condensate overhead. When the machines were off and the steam was running you couldn't even here, they system run. The only thing you herd was the check valves faintly clicking. We had 100psi steam so no problem lifting condensate.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1874835#Comment_1874835

either the boiler or the return is above the emitter. i don't know the exact physics of how it works but it is common on commercial 2 pipe steam.

mattmia2

if you have shut off only the traps on the ends of the mains the emitters will still heat but more slowly. the air in the main will eventually vent through the return just like the emitters do.(unless i'm missing something)

if no one did the edr calculations you have no idea if the boiler is the right size or way too big or small.

Gateacre

https://forum.heatinghelp.com/discussion/comment/1874838#Comment_1874838

You're not missing anything. Radiator valves have been removed and supply lines capped off in these areas. And you're certainly correct that the sizing of the boiler was done by intuition not calculation. I was new to the property and knew relatively little about steam heating when the old boiler failed. Steam heat is extremely rare here and the contractor mainly deals with process steam.

Gateacre

https://forum.heatinghelp.com/discussion/comment/1874835#Comment_1874835

This building is long, not tall. At some point radiators were added at boiler level but a few hundred feet from it. They ran out of slope on the return and simply elbowed it up about a foot to restore pitch to an in floor return tank. So the section between the boiler and the rise backs up with condensate and without pressure to force it along the rads would stay half full of water and only drain by head pressure. They also need hefty vents on each rad (gorton d) because the traps are always at or before the water line. Trust me, I didn't design this, I just try to keep the tenant warm.

ethicalpaul

thanks! I didn’t mean to impugn you, I asked for my own knowledge

PS to address your question, I don’t see the air compressing to an extent that it would meaningfully affect the operation of your system

Gateacre

https://forum.heatinghelp.com/discussion/comment/1874866#Comment_1874866

Oh I didn't think you were😀. I'm as happy to share as I am to learn from this forum. Sadly my system offers precious few examples of what to do. Lots of cautionary tales though.