No vents, boiler replacement, possible vacuum system

WayneMech

Just looked at a boiler replacement candidate. Their gas consumption skyrocketed three years ago, and they had a hard time finding a contractor to deal with it. Local contractor thought it was hot water, but begged off when he found it was steam. Large tank above boiler looks like an old style expansion tank, but is a DHW tank (no heat exchanger) with (I believe) an immersed coil feeding it. The building cold water still passes through this, just before entering the upright water heater.
The boiler (Iron Fireman) has the sight glass inside the jacket, with a factory cutout for viewing, and an old red Hoffman water feeder (#4?). I am told it was originally coal fired. The house was built in 1911, by a rich family , in a small Midwest town. It has a really old Burks condensate pump and tank, that may be original. The radiators are all trapped. To their knowledge, nothing has ever been done to the traps. There are no vents, except the open condensate tank vent pipe.
I believe the last of the traps failed, leaving the heating, mostly, to the mains, which are completely uninsulated (this is what heats the basement). The lower water line of the new boiler leaves plenty of height for gravity return, and all the returns are in the basement ceiling. My question is this: Is it possible to eliminate the condensate tank, and just use the gravity return? I know that doing so would require piping in a vent (Hoffman # 75). What if I put a # 76 in? Could I transform this 106 year old, pumped return system, into a gravity return, vacuum system?
Please give me some guidance, guys.
Thanks,
-Dale

Steamhead

The short answer is, maybe. Where is this job located?

EBEBRATT-Ed

you need enough stacking height for the condensate to get back to the boiler with 1-2 psi in the boiler. Figure it out with a tape measure

MilanD

If the system is tight, maybe able to go to vacuum. You do need extra hight for dimension A at the drip (M on the attached pic), 24" for each inch of vacuum.

WayneMech

It is located near Peoria, IL. I have 40" between the steam main and the water line.

nicholas bonham-carter

There is certainly a need for height to accommodate pressure pushing up the water in the wet returns, (1.75 in/ounce of pressure), but I'm not sure I see the need for 24 inches of height per inch of vacuum.--NBC

MilanD

> @nicholas bonham-carter said:
> There is certainly a need for height to accommodate pressure pushing up the water in the wet returns, (1.75 in/ounce of pressure), but I'm not sure I see the need for 24 inches of height per inch of vacuum.--NBC

Maybe BC vacuum differential will be greater at the return side vs. in atmospheric pressure only setup, thus raising the water higher at the return side. Something like a Romaurie effect in an aquarium. Maybe?

clammy

First and foremost to get the skyrockets gas bills down would be to get the mains and runout insulated and insulated with a mimiun 1 inch wall thickness high denisty fiberglass insulation .You are most likely losing the bulk of heat to the basement .Then see how your system performs .I think i would pook about and see what rements of possible cross over traps in the mains and ends of the mains for possible removed air vents locations .peace and good luck clammy