Location of Barometric and vent damper on Gas gun fired 380 boiler

The Steam Whisperer

I am laying out an installation of 2 Weil McLain 380 steam gas gun fired boilers feeding into a common supply which will be stage fired based on heating needs. I plan on using the Carlin 201 gas burners. Since steam from an on boiler will be condensing in the off boiler, we are looking at ways to reduce standby losses of the off boiler. Due to the load profile of the building ( a church) the second boiler will probably only need to be fired about 12 hours a week during the heating season.
We have a vent height limit of about 60 inches, so we are planning on using the back venting option on the boilers to increase our available working height.

I have 2 questions:

1) Is there any problem with putting the barometric damper on the horizontal outlet flue pipe of the boiler off a side tee.

2) Since the boilers are in a boiler room with its own outdoor air supply, I would prefer to install the stack dampers on the outlet of the boiler before the barometric damper to lock the heat in the boiler, rather that letting it dump out into the boiler room through the double acting gas barometric damper. This would be very similar to the vent damper installation used on commercial gas water heaters... the damper is installed below the draft hood opening. I expect installing the damper in this location would be more effective for this boiler installation and especially when the barometric is double acting.... the double acting will probably allow increased spillage of heat when compared to a single acting barometric used for oil.

If we install the damper directly on the boiler outlet the barometric could be moved to the vertical exhaust pipe going up to the common vent manifold.

captainco

Can you draw a picture of the barometric location?
You can use one barometric if the flue is the same size on the complete horizontal. Ten you have to set it for whichever boiler has the lower draft.
If facing the boilers and the flue goes to the left, you can install the barometric on the left end of the horizontal, again if the flue is not reduced.

EBEBRATT-Ed

I would go to the chimney twice 2 flues 2 barometrics if possible.

captainco

Sorry, I meant if the flue went to the right the barometric can go on the left. Two are always better when two can be used.

The Steam Whisperer

We are giving each boiler it's own barometric. I was discussing this with another member here and his belief is that installing the vent damper after the barometric would be best so you are not pulling cold boiler room air up the stack to cool the chimney. I talked to Field controls and they said to install the vent damper after the barometric too,so if you have a blocked flue the gases can dump out the double acting barometric and trip the spill switch. There was some confusion regarding the difference between atmospheric gas and power burner gas installations and regarding single acting and double acting barometric dampers.

captainco

You always use a double acting barometric on negative pressure flues and never use one on positive pressure flues. Once you get to the 10" size there will be 3 red stops that have to be removed to make it double acting.

The Steam Whisperer

Yes, the confusion was that I said it was a power burner boiler, so the tech immediately considered the flue as under pressure. That's not the case with the modern boilers that i have seen that are under positive pressure.... the damper at the boiler outlet provides the positive pressure in the boiler and then the flue goes to negative pressure due to chimney draft. Otherwise you would need a sealed venting system.