Thanks for getting me a diameter-measurement photo. It shows that your friend found a 3.67"-caliber Parrott shell, which most collectors call a "20-pounder" Parrott shell, because it was made for use in a "20-pounder" Parrott Rifled Cannon. The specific version your friend found, which has a short brass ring "sabot" encircling its flat iron base, saw its first combat use in early 1863. It was declared obsolete in the 1870s, due to the US Army's adoption of Breechloading cannons, which are superior to the civil war era Muzzleloading canoons.
I have to mention that contrary to your guess (25 pounds), that shell's empty-&-fuzeless weight is 17 pounds.
Factors which affect that shell's dollar-value:
1- It has a BRASS ring sabot, which is scarcer than the iron ring sabot version, so that's a "plus" for this shell's value.
2- Its brass ring sabot is in unfired condition, whereas most specimens which still exist are fired ones, so that's another "plus" for this shell's value.
3- Its iron body is is uncleaned condition, which can cause the iron to continue to corrode. That is a "minus" for its value.
4- Its fuzeplug is missing, which makes this shell an incomplete one. That is a "minus" for its value.
In summary, adding up those four factors produces a dollar-value of about $175-$200.
In the above comments, I mentioned that uncleaned iron will continue to corrode. So, let me recommend that your friend either learn how to do the Electrolysis rust-removal process, or pay somebody else to do it on that shell. I don't know anybody in Pennsylvania who does Electrolysis cleaning. I suggest you go to
www.bulletandshell.com and enter the Civil War Projectiles forum, go to the Artillery category, and post a request for the name of somebody in Pennsylania who does Electrolysis cleaning of relics. Or, perhaps one of our fellow TreasureNet members will know somebody in Pennsylvania who does it.
I do Electrolysis cleaning on iron relics, but I'm in the Richmond VA area, which means you'd have to mail the shell, or carry it to me. So I suggested first trying to find somebody more "local" to your friend.
By the way... I hope your friend hunted that old house-foundation diligently, because where you find one artillery shell there are usually more at the same location.