Any idea what this is

Hey guys I’ve only been doing this a year so I haven’t come across one before. Any idea what this is? Expansion tank possibly? The house is heated with a boiler and radiators. What does it do how can I tell if it still works and how should I inspect it. I found it in the Crawl area of an attic in a home built in the 1920s

Looks like an expansion tank to me. Boiler systems have one. Did you see another one somewhere? Was it connected to anything?

you can ask Mr. Google for an explanation as to what it does and anything else you would like to know.

When you make an effort to find things out yourself you receive a much better understanding for the future.

You should also go to the top left of this page and click on the heading “control Panel” . Complete your profile including location, it helps us with answers. Scroll down to signature and enter your company contact info. It helps with SEO.


This is an expansion tank in the attic. Sometimes if the system is gravity versus pump the boiler water would rise up into the attic and feed back into the radiators below. I believe there is excellent information about this in the Advanced HVAC course available to members.

Could be an old boiler blow down tank.