Pressure in gauge stays high after heating cycle ends

Ori

Now two units want steam radiator heat (used to be only for the 3rd floor), so I find that the the EG-50 with 446 steam sqft is somewhat undersized to the connected load of 536EDR, so it's about 17% undersized.
It does heat both units and few rads in the basement, but takes a while, about 1:45 hours per cycle, and some oversized radiators are not even fully hot (that's why there's no pressure in the 0-18oz gauge). An hour an 45 minutes seems long, doesn't it?

I can increase the gas pressure from 3.5"wc to 4", or, is there a way to add burners and essentially convert the boiler from EG-50 to EG-55? The later generates 521 sqft of steam, so it seems a match in load.
I understand that the physical dimensions of both models are the same, and same is for the chimney size, but not sure about the water volume though.

Jamie Hall

You are battling one of the (many) less desirable attributes of the Nest. Not much help for it -- other than swapping out for a nice Honeywell.

pedmec

You need to adjust the venting of your system. If the thermostat is satisfied and the room is not losing temperature then how you expect to heat the rest of the house. this is one of the issues with using a thermostat in one room to control a central steam heating system. your subject to temperatures of just that room which does not know what the hell is going on in the rest of the system.

I would bypass the thermostat by jumping the low voltage wires and let the system run. it will allow it to run to see if the boiler can heat the building. If you get steam everywhere (you might overheat some tenants) then your lucky because the boiler is making enough steam. if its doesn't then your boiler isn't big enough or your piping is not insulated. insulate exposed piping anyway. At the radiators that are getting start restricting venting. put adjustables and set them on the lowest setting.

Ori

Ok, I’ve reduced the connected EDR to match the boiler’s rating; it’s now very close to 446. 

I’ve lowered the vent sizes on most rads to be between #4-#5 (only two have larger orifice), and for the first time I can see pressure in the 0-18oz gauge. 

The pressure starts at about 4oz right from the start, even before the main vents close (again, there’s plenty of main venting), stabilizes at around 5oz, and climes up with time, as high as 9oz, where the vaporstat stops it. 

1) does having about 4oz of pressure right from the start seems normal, even before the mains close? Or it’s an indication of some obstruction? Please see video attached, where you can see the pressure at the start (towards the end of the video you can hear the air being pushed through the mains).

https://youtu.be/1WT6tvRqPhY

 

2) each heating cycle takes about and hour and fifteen minutes. Seems long to me but i don’t have a benchmark for comparison. 

Gas pressure at the manifold is 3.5”wc. 

At today’s weather of about 24°(f) each cycle was about an hours and fifteen minutes, with about 50 minutes between cycles. 

Seems excessive but I’m not sure. 

What do you think?