In slab UFH with phased slab pours, connecting pipes between them.

[Jess Shannon]

We're planning a full renovation of an old stone cottage, with a new large extension.

 

We'll have in-slab UFH throughout, and for the extension the concrete slab will be the finished floor. Because of the way the extension wraps around two sides of the cottage, it might be too risky to dig out both sides of the stone walls, even with underpinning. It would be much safer to pour the extension slab and inside floor separately.

 

Would it be possible leave the pipes sticking out of the slab edge at the opening to the cottage, and then attach more pipe with couplers when completing the cottage floor and bury them in concrete. I'm worried that the connection is a failure point, some of the couplers say they are not to be buried.

Would it be better to have the whole pipe loop sticking out of the slab, and then lay it down after digging out the old concrete and rubble floor. Then I'd be worried about it getting damaged.

The other option I can think of is to dig out a small part of the floor to where the couplers could be hidden in an access hatch under a kitchen cupboard, or maybe slightly up the wall to be connected above ground?

[JohnMo]

10 minutes ago, Jess Shannon said:

and then attach more pipe with couplers when completing the cottage floor and bury them in concrete. I'm worried that the connection is a failure point, some of the couplers say they are not to be buried

I wouldn't do that. Use a coupler in an emergency, but wouldn't plan to do it.

 

Couldn't you decide where the manifold is going and make the connections to the manifold. Then pressurise the loop and add mechanical protection as needed. 

[Nickfromwales]

1 hour ago, JohnMo said:

I wouldn't do that. Use a coupler in an emergency, but wouldn't plan to do it.

 

Couldn't you decide where the manifold is going and make the connections to the manifold. Then pressurise the loop and add mechanical protection as needed. 

For a sanity check here, the 16mm couplers I have used a good number of times to do repairs (which have all been buried and covered over) are still A1 today.

 

If these are made off carefully then there is no more reason for these to fail as the ones made off to the manifold; difference being the ones in the slab are never going to be subject to mechanical damage (being hit or pressed up against etc).

 

You absolutely can do this, if it’s the only option.

 

If you lift these out of the floor somewhere where you can then connect to them later on, you’ll have to make those upstands off so they are T’s with air bleed (vents) as this will be a trap for air. UFH pumps around very slowly, so these would airlock if you don’t have provision to routinely vent them (or you can fit automatic air vents which do this whenever air is caught).

 

The pressure in the UFH circuits will never see more than 3bar, and the normal operating pressure is 1-1.5bar, so these don’t have the same as cold mains pressure or higher to deal with.

 

How far is it from the break in the floor to the manifold location? You could fit flexible conduits and do more loops of a smaller (12mm) pipe which would easily pull through 25mm flexible conduit if you lay them sympathetically. 

 

[-rick-]

Ideas to consider:

1. Don't split any loop between areas, put separate loops.

2. For routing the pipes for the loops for the second phase, either use conduit as @Nickfromwales to allow you to install the pipes when you are doing the second phase, or look to see if you can route pipes in walls/ceilings between areas.

3. Maybe it makes sense to have two manifolds, one for phase 1 and one for phase 2. Then you just have to route 2 (bigger) pipes between the two locations.*

 

* Some nuances here that needs careful thought but worth considering if other options difficult.

[Nickfromwales]

The kicker with leaving pipes exposed to connect to later down the line is preserving their condition. So add that to the list of reason not to go for the joints under the slab / screed option.

 

But it is an option. 

[JohnMo]

A drawing of what you're doing and where you propose to locate the manifold and boiler/ASHP would actually help. We're all guessing otherwise.