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.

[Jess Shannon]

Sorry I forgot to check back on this! Here’s a drawing.

 

We’re renovating an old stone cottage with 50cm thick stone and rubble walls, and a small outbuilding of similar construction. The new extension will wrap around the outbuilding with a larger pitched roof, and a flat roof living room links to the original cottage.

 

The new slab foundation is Bed 2, both ensuites, utility and living room. I planned for the main manifold and hot water cylinder to be in the utility room. The ashp is over the other side though, it’s a corner out of the way that we wouldn’t otherwise use and is away from the bedrooms. I was going to run the pipes to it through the insulation under the slab and insulated through the ground at the last bit. It’s about 12-15m.

 

We want to have a small wood stove in the living room, mostly because it’s nice but possibly as an extra heat source if the ashp struggles at any point. So we’d run pipes through the slab for that. I’ve seen some cylinders that have separate ports for stove boilers, I guess that makes it easier to get lots of heat out of it without over heating the ashp or UFH? Such as for hot running water?

 

I was also thinking that during a power cut (common where we are) we could run the pump from a battery/generator and use the stove to heat everything.

 

The floors in the old cottage and possibly also Bed 1 might have to be poured separately to the rest of it so we don’t undermine the walls. We could put the main en-suite on another zone and run it outside the stone wall so it’s all in the new slab.

 

For the cottage maybe it makes the most sense to have a second manifold in the kitchen? I also wondered if it should be a separate mixer as it would have different thermal characteristics to the new slab. Could that be connected to the return from the ashp or would it take too much heat out before it gets to the main manifold?

 

Thanks for any and all advice!

 

(edit: we’re also putting in MVHR throughout)

Edited 18 hours ago by Jess Shannon

[JohnMo]

If you located the manifold on bedroom 2 / utility wall, you could takes pipes in to utility and terminate them on the manifold?

 

Are you using the wood stove/boiler just for cylinder heating or UFH as well?

 

Could you locate the ASHP nearer the utility? It looks to be on the south side of the house, which isn't ideal. Should be located out of the sun really.

[Jess Shannon]

25 minutes ago, JohnMo said:

 

If you located the manifold on bedroom 2 / utility wall, you could takes pipes in to utility and terminate them on the manifold?

 

Not sure what you mean. The manifold would be in the utility next to the hot water cylinder, to the right as entering the room, the wall straight ahead will have washer/dryer etc.

 

27 minutes ago, JohnMo said:

Are you using the wood stove/boiler just for cylinder heating or UFH as well?

Don’t know yet, depends on cost/complexity. It would only be for occasional use. So far my plan is to run pipes for it in the slab, and then figure out how we want it after spending a winter in there with just the ashp.

 

29 minutes ago, JohnMo said:

Could you locate the ASHP nearer the utility? It looks to be on the south side of the house, which isn't ideal. Should be located out of the sun really.

The north is facing the road and entrance into a courtyard area on the left. Where it is on the diagram is the most discrete place, could it be shade from direct sunlight with a screen, or should it really be on the north side?

[JohnMo]

21 minutes ago, Jess Shannon said:

Not sure what you mean.

Locate as shown, drill holes through wall from extension low down (piping level), and excavate area under manifold, connect UFH pipes, pressurise. Then no joints needed etc. cover manifold with some insulation to protect it from bangs and knocks.

 

21 minutes ago, Jess Shannon said:

occasional use.

Is it worth the hassle and increased expense to install boiler stove, piping and additional heat dump etc?

[Jess Shannon]

Ah sorry, that is all part of the new slab, shaded here in blue. The old floors that might need to be second phase are in red, and connecting points at the red squiggles

[dpmiller]

there are many complexities around linking a boiler stove into another scheme- will you have MVHR, will you be cooking on gas or electric/ do you want an extractor fan, and how big a hot tank have you room for? Even if you're only thinking about it, you better look at these things in advance. You may need e.g. a mains water supply going to stove for overheat protection etc etc

[Jess Shannon]

4 hours ago, dpmiller said:

there are many complexities around linking a boiler stove into another scheme- will you have MVHR, will you be cooking on gas or electric/ do you want an extractor fan, and how big a hot tank have you room for? Even if you're only thinking about it, you better look at these things in advance. You may need e.g. a mains water supply going to stove for overheat protection etc etc

Yes we’ll have MVHR. Cooking will be induction or possibly a multi hob with induction and gas. Extractor hood will be re-circulating. We should have plenty of room for a large tank, and only 2 people living there. Stove will have an external direct air intake and TAS safety valve.