Can anyone tell me what the tank is in this attic picture? 100 year old house.

Can anyone tell me what the tank is in this attic picture?
The house is a 1900 house.
It appears the tank is attached to a wet drain in the attic.


Craig Barger



Old Heating Boilers (steam or hot water) may have No Relief Valve at All - Check the Attic**
Some very old heating boilers may not have a relief valve installed.
These systems used a pressure relieving overflow tank located high in the building, above any upper floor radiators or baseboards, often in the building attic.
The attic pressure tank was open to the atmosphere and often itself included an overflow pipe which would permit any excess water (or pressure) to flow out of the tank and out of the building, perhaps through a building wall to the outdoors.
While these attic systems for boiler pressure relief safety worked well for decades, placing a temperature relief valve right on or very close to the heating boiler is a safer installation.

Looks like an old boiler expansion tank.

And this

Q: What does an expansion tank look like?
A: A typical one looked like this. LINK

 **Q: Where did the expansion tank go?** 

A: Typically, at the high point of the system. You’ll usually find them in the attic. The tank gives the expanding and contracting water a place to rise and fall.
Q: Suppose I put too much water into the system when I first fill it up. What will happen?
A: It will overflow from the tank through its vent and wind up on the roof.
Q: Can this do any harm?
A: Not to the system. It might leave some rust stains on the roof if the system is old, but that’s about it.
Q: How much water should I put into the tank when I’m first filling the system?
A: Normally, you should maintain the tank at one-third full when the water is cold (there’s often a gauge glass on the side of the tank so you can see what you’re doing). As the water heats and expands, it will rise into the upper two-thirds of the tank and stop before spilling over onto the roof.

Nice. Thanks guys.
Appreciate it.


These were called “open systems” up here. Have only seen 2 in my 26 years of inspecting. Last one, the tank was mounted over the bath vanity with the drain going up into the attic and out to the eaves. The original cast iron boiler was still operating but with an efficiency of only 62-63% (I test furnace/boiler efficiency as part of my inspections).

Steam Boiler head pressure tank.

Nice call Mike. Took a few of them out back when I first started working. The great thing I remember is how wonderfully light and easy to get down the stairs they were.

Agreed, they are an expansion tank, but not a pressure tank, “open system” is what I would call it.



Aw come on. You guys never seen a bootleggers attic? Obviously the original owner was makin’ shine!

Such an arrangement worked well because the operating pressure of those old boilers was very low (could not be greater that the weight of the water in the system up to the discharge). If you were operating a ‘boiler’ at such a pressure today that would still be a very effective ‘overpressure’ arrangement.