walk away and save yourself the aggravation.
First of all, its rusty, almost impossible to clean the inside of water jacket with cutting it apart. That just leads to problems down the road with heat exchangers and pumps.
Second my friend Jeff bought an Aquatherm new, so no rust issues at all. He built a brand new house very well insulated and built it with the knowledge he was going to put a boiler in. So, pex under the floors with tile, ect.
Now, look at design of Aquatherm boilers. Huge firebox with very little water around it and the chimney is right in the middle of the top of the firebox. Any heat escapes right out the top before it has much opportunity to soak into the metal. We've actually seen flame coming out of the chimney that was 16 feet tall!
It wore him out trying to keep that thing fed and he finally just gave up on the boiler. Plus, he is so disgusted that he won't even replace it with another because he felt so burned by the first one.