About the only way you can find most of them...if they are all working ..is to find someone with a thermal imaging camera.
The loops will show up with a greater temperature differential ..the more the better.
Some heating companies carry them...some Home Inspectors(me)...and all fire departments that can afford them, but they don't lend them out usually, except to train someone.
If you do cut through one.....good luck with the repairs.