Best way to lay rad pipes through a wide chimney breast

It's an old nunnery with massive breasts! 3 floors and basement. Chimney had 6 fireplaces feeding it. As I am 1st floor (English)/2nd floor (USA) I have a wide breast with 2 blocked off fireplaces. The firepace flues from below run up through and into the flat above and on through the loft to the stack. I'd like to run 2x 15mm for rads through the breasts but it will be blind. Even if I were to take the panel out of the fireplace and unblock it, I would still not have access. Ripping it all out is not really an option because of the other flats.
Any ideas?

If you don’t know what is inside the wall - particularly if it is rubble filled - you really need to drill an oversized hole through the wall, duct it then run the pipes (insulated) through the duct.

If the wall is solid all the way through, you may be able to core drill it (circa 60mm diameter). If it is rubble filled, it probably needs to be drilled with a conventional hammer drill - the rubble will drop down as you drill through it, so maintaining a clear hole can be problematic.

Brambles said:

If you don’t know what is inside the wall - particularly if it is rubble filled - you really need to drill an oversized hole through the wall, duct it then run the pipes (insulated) through the duct.

If the wall is solid all the way through, you may be able to core drill it (circa 60mm diameter). If it is rubble filled, it probably needs to be drilled with a conventional hammer drill - the rubble will drop down as you drill through it, so maintaining a clear hole can be problematic.

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Thank you

1. If you breach any of the other flues you are going to have serious problem with products of combustion from any of the other properties still using (current or future owners) the fireplaces, and will compromise the fire integrity of the building.
2. I'd take a channel out at the base of the fire openings, removing the fire surrounds as necessary then re-cover. Still a risk, but at least you'd know if damage had been done, and be in a better position to fix it.

If this is a set of flats you are probably better off not attempting to take the direct route through. It's quite likely that the chimney itself is outside your property so you'll need permission from whoever does own it. (If I were the owner I would not give a flat owner permission for this sort of work. Lots of things could go wrong...)

I'd go with the @steadyon approach. My preference would be to avoid the problem entirely by using one larger radiator on the easily accessed side. If this isn't possible, I'd want to route the pipes carefully around the breast and box in neatly if necessary.