Feeding new radiator in extension

[djaychela]

I'm slowly building a ground floor extension, and where the original house wall was (which is coming out) there was a large radiator, with pipes coming up through the concrete floor (1970s build, if that helps). This is now capped off temporarily, but I need to feed a new radiator in the extension. My original idea was to extend from these pipes in the new screed floor (in some sort of duct), but from what I've read that's not a great idea. There is the option to take a feed from the upstairs radiator feed into the new extension and down from that, but I believe that I'll need to provide provision to bleed air from that, but it will mean there's less chance of having a problem as there won't be a pipe buried in the floor.
If this is the way to go, what's the best way to approach it?
What's the best way to cap off the original pipes (which currently stick out of the floor, and have some movement in them, so I'm imagining that I can carefully chip away the old floor around them to get access to cut them off below the floor level to do whatever's needed)?

 

[Justin Passing]

All the above are possible. Surface pipes look rough. Dead ends under a floor aren't a good idea. you shouldn't have a problem with quantity of water flow from the existing pipes as you've removed one probably near the same rating, assuming 15mm. Ducting isn't difficult. Don't just wrap the pipe in hemp rubbish and bury it in screed, the cement WILL almost certainly get it eventually.
Be careful to not compromise damp proofing,
Something like this.