Luckily I'd never take the pi$$.
It really is a "manual" stud finder. Magnet picks up on steel screws / nail heads. When it tilts perpendicular you're bang on the nail. Then pencil the two vees and in the middle is theoretically the centre of the stud. Assumes of course they originally banged the nails in on the centre line...
Stanley do something very similar.
If you are having an ASHP connect it direct to the UFH - if you get a reversible one you can cool the floors in the summer! You dont' need a battery or a buffer tank, although some have them but you do need to modulate the ASHP output so you need an inverter controlled one or you wont be able to tune for optimum COP.
Why would you have a stack in the house at all, rather than just AAVs? I'd think saving the roof penetration by keeping any needed stack outside would be well worthwhile.
Our builder (old school) built ours properly which has a full lead tray before roof to stop damp within the brickwork going around the flashing, just found this........https://www.labcwarranty.co.uk/blog/how-to-ensure-your-chimney-is-constructed-correctly/
Omg
as im sitting here bored I thought I would google RESTRAINT STRAPS well that turned up a few images I hadn’t thought I would see at 7.30 in the morning. ??