Can a slab be too thick to have UFH pipes in it?

[Thorfun]

if I may carry on with this thread and ask another question somewhat related...

 

the A393 rebar that the SE has specified in our slab has a 200mm spacing between the 10mm wires. if I'm not mistaken I've read on here that the UFH pipes are better off being supported by following the runs of rebar so I'd be looking at 200mm spacing for the UFH pipes.

 

I've spoken to Wunda and their response was:

 

"As you will be having a heat pump, I would advise against taking the pipe spacings to 200mm.  Having a heat pump would mean the heat outputs are naturally less than they would be with a boiler and by spacing the pipe further apart would make it less again, meaning you would most likely need a supplementary form of heating alongside the underfloor heating."

 

obviously, Wunda are not aware of our planned insulation or airtightness levels as they don't have the SAP calculations (nor did they ask for them), so this could be a stock response from them.

 

This isn't a financial decision for me as the extra cost for 150mm spacing would be negligible in the grand scheme of things it's more about 200mm centres will be better protected during the slab pour.

 

Anyone able to comment or advise on this? I have posed the question to the suppliers/designers of our ASHP system but while I wait for that response I thought I'd ask the collective mind on here.

[jack]

3 minutes ago, Thorfun said:

Anyone able to comment or advise on this? I have posed the question to the suppliers/designers of our ASHP system but while I wait for that response I thought I'd ask the collective mind on here.

 

You're right that Wunda is thinking about spacing for a normal building regs (at best) house.

 

I believe just about everyone (including me) on here with an MBC slab has 200mm spacing, and I don't recall any complaints.

[Thorfun]

39 minutes ago, jack said:

 

You're right that Wunda is thinking about spacing for a normal building regs (at best) house.

 

I believe just about everyone (including me) on here with an MBC slab has 200mm spacing, and I don't recall any complaints.

thank you @jack. puts my mind at ease.

 

I also asked for them to just make it all one zone after reading on here. I think with a slab this thick the response times will be so slow there's no point of having individual zones and we'll just keep the whole basement at a constant temperature, assuming we even need to turn it on for most of the year that is!

[Dan F]

5 hours ago, Thorfun said:

thank you @jack. puts my mind at ease.

 

I also asked for them to just make it all one zone after reading on here. I think with a slab this thick the response times will be so slow there's no point of having individual zones and we'll just keep the whole basement at a constant temperature, assuming we even need to turn it on for most of the year that is!

 

If in doubt about spacing, download a LoopCAD free trial which lets you design UFH and simulate it using your floor makeup and heat loss figures.  I did this, and 200mm was absolutely fine and only needed very low temperature.  This matches other peoples experience.   (wasn't I didn't trust poeple, was just my idea of lockdown enterainment ? )

 

Even if you run it as a single zone, you'll stil need a number of loops so it may still make sense to plan loops around rooms, even if your control system doesn't operate then independantly.  The other things to consider is that, even if you want to use it as a single zone (which makes sense), each loop will have a different length potentially and some rooms may have more sun.  Given this, my understanding is that you'll need to use one of these two approaches to avoid some rooms getting hotter than others:

1) Have thermostatic control per room/loop

2) Use self-balancing actuactors

 

(we are doing the latter)

 

Edited April 22, 2021 by Dan F

[Thorfun]

1 hour ago, Dan F said:

 

If in doubt about spacing, download a LoopCAD free trial which lets you design UFH and simulate it using your floor makeup and heat loss figures.  I did this, and 200mm was absolutely fine and only needed very low temperature.  This matches other peoples experience.   (wasn't I didn't trust poeple, was just my idea of lockdown enterainment ? )

 

Even if you run it as a single zone, you'll stil need a number of loops so it may still make sense to plan loops around rooms, even if your control system doesn't operate then independantly.  The other things to consider is that, even if you want to use it as a single zone (which makes sense), each loop will have a different length potentially and some rooms may have more sun.  Given this, my understanding is that you'll need to use one of these two approaches to avoid some rooms getting hotter than others:

1) Have thermostatic control per room/loop

2) Use self-balancing actuactors

 

(we are doing the latter)

 

cheers @Dan F. I have got LoopCAD already and put the basement in there but I haven't bothered with the heat calculations side of it all yet. I've just used it to get an idea of it all. I'll see if I can get to grips with the heat loss figures at some point.

 

Are your self-balancing actuators hooked in to your Loxone system? I was thinking of having underfloor slab probes but with only one zone I wouldn't know where to put them or if multiple would be required! I guess that comes much later though and we can always change the loops to multiple zones at a later date if required. the important bit is to get the loops in right first. everything else above the slab can be changed later.

[Dan F]

1 hour ago, Thorfun said:

I haven't bothered with the heat calculations side of it all yet. I've just used it to get an idea of it all. I'll see if I can get to grips with the heat loss figures at some point.

You don't have to use it to do heat loss calculations.  There is a way you can just plug in numbers from PHPP or SAP or something else.

 

1 hour ago, Thorfun said:

Are your self-balancing actuators hooked in to your Loxone system?

Not yet, but they will be.  A single 24v output from Loxone will drive all 9 actuators.  The balancing aspect of these actuators is self-contained.

 

1 hour ago, Thorfun said:

I was thinking of having underfloor slab probes but with only one zone I wouldn't know where to put them or if multiple would be required!

I've put a probe per room.  I haven't decided exactly how to control heating yet, but I'll use a combination of slab temperatues and room temperatures along with other variables potentially including outside temperature, occupancy, tarrif etc.

 

On other thing that temperature probe is useful for is ensuring, when cooling, that you don't cool the slab beyond the dew point (which can be calculated using humidy).

Edited April 22, 2021 by Dan F

[Thorfun]

I will be pulling the trigger on the materials for the basement UFH tomorrow. here's what I got from Wunda:

 

 

all seems pretty reasonable to me. any comments that would stop me from ordering this? I've deliberately left actuators off the order for now as I'm not sure how they'll fit in to my home automation yet and figured I could just add them at a later date once all of those decisions have been made. so it's literally pipe, pump and manifold. which should be all I need for prior to slab pour, right?

[Dan F]

@Thorfun Worked out how to integrate with the wunda "floor probe".  Might you be best to use the 1-wire sensors for loxone integration?  Also, is one really enough?  Even if you don't think you need one per room, still worth using a couple of either end of house and in case one fails for some reason.   I won't put them in concrete anyway, but rather use 2m max lengths of spare UFH pipe to create conduits for you to add them later.

 

You don't actually need pump or manifold for concrete poor, we didn't have either.  But having manfold will help, and will also make it easier to test everything prior to pour.  Make sure you've work out your UFH layout before putting order in, just in case you need another port.

 

BTW. I hope thats £1.30 for a bag of cable ties and not each!

Edited April 25, 2021 by Dan F

[Thorfun]

5 minutes ago, Dan F said:

Might you be best to use the 1-wire sensors for loxone integration?  Also, is one really enough?  Even if you don't thin

you need one per room, still worth using a couple of either end of house and in case one fails for some reason.

yeah, I'm thinking more than one probe. the original quote had one per zone but as I reduced it to a single zone they just reduced it to one probe. I think for the cost of them putting a few in will be best. I'll check out the 1-wire sensors for Loxone, thanks.

 

6 minutes ago, Dan F said:

Make sure you've work out your UFH layout before putting order in, just in case you need another port.

already put the layout through LoopCAD so I know myself and Wunda are on similar wavelengths. Plus they will do a design for me so I can see once that's done if further changes might be required.

 

7 minutes ago, Dan F said:

BTW. I hope thats £1.30 for a bag of cable ties and not each!

?. so do I!

[Thorfun]

35 minutes ago, Dan F said:

use the 1-wire sensors for loxone integration

hey, @Dan F, quick question on these temperature probes. do they need to be installed within the slab? can they be installed under the tiles/finished flooring and on top of the slab? that would mean I wouldn't have to make a quick snap decision on them to get them in before the slab pour.

[Thorfun]

19 minutes ago, Thorfun said:

hey, @Dan F, quick question on these temperature probes. do they need to be installed within the slab? can they be installed under the tiles/finished flooring and on top of the slab? that would mean I wouldn't have to make a quick snap decision on them to get them in before the slab pour.

I guess I could also use an angle grinder to cut a narrow and shallow groove in to the slab to accommodate the probe after the pour as well? 

[jack]

21 minutes ago, Thorfun said:

I guess I could also use an angle grinder to cut a narrow and shallow groove in to the slab to accommodate the probe after the pour as well? 

 

I've got one sitting on top of the slab under my kitchen island, held in place by an offcut of insulation and half a brick on top! Could've drilled a hole for it, but it needed doing fast. Maybe you'll get better functionality if you bury the sensor deeper?

[Thorfun]

7 minutes ago, jack said:

Maybe you'll get better functionality if you bury the sensor deeper?

and that is the important question that I don't know the answer to! but, I wonder if you really need to know the temperature of the slab deeper than near the top anyway as the heat will end up rising to the top of the slab anyway. and if you're measuring for running an ASHP in cooling mode and are worried about condensation at the pipes then the pipes are near the top of the slab as well.

 

would those 50mm difference between putting the probe at UFH pipe level in the slab or on top of the slab under the finished flooring really make much of a difference in the grand scheme of things?

[Bitpipe]

On 22/04/2021 at 13:12, Thorfun said:

thank you @jack. puts my mind at ease.

 

I also asked for them to just make it all one zone after reading on here. I think with a slab this thick the response times will be so slow there's no point of having individual zones and we'll just keep the whole basement at a constant temperature, assuming we even need to turn it on for most of the year that is!

 

Our 120m2 basement has no heating at all.

 

Slab is 300mm thick and sits on 300mm EPS 200. Walls are 200mm thick with 200mm EPS.

 

The gas boiler, UVC and MVHR are in the plant room, a couple of fridges are in the hall and the kids have TVs, consoles and some musical kit in their dens.

 

Always a comfortable 20^oc down there, year round.

 

If £800 buys you peace of mind for future proofing then fine - if it were me, I'd only commit to the in-floor pipe for now, bring it up to the manifold location and leave the rest of the kit until your general first fix.

 

What you really need is a pipe de-coiler as UFH pipe is impossible to lay without one. Look to borrow or hire one.

 

Are you having heating in the floor above also?

Edited April 25, 2021 by Bitpipe

[Thorfun]

6 minutes ago, Bitpipe said:

 

Our 120m2 basement has no heating at all.

 

Slab is 300mm thick and sits on 300mm EPS 200. Walls are 200mm thick with 200mm EPS.

 

The gas boiler, UVC and MVHR are in the plant room, a couple of fridges are in the hall and the kids have TVs, consoles and some musical kit in their dens.

 

Always a comfortable 20^oc down there, year round.

 

If £800 buys you peace of mind for future proofing then fine - if it were me, I'd only commit to the in-floor pipe for now, bring it up to the manifold location and leave the rest of the kit until your general first fix.

 

What you really need is a pipe de-coiler as UFH pipe is impossible to lay without one. Look to borrow or hire one.

 

Are you having heating in the floor above also?

I’m happy to pay £800 for peace of mind. If we never use then great! But at least the pipes are there if we do. 
 

thanks for the de-coiler tip. Will look in to it. 
 

definitely having UFH on the ground floor but still undecided about the first floor. If it turns out the pipe and manifold are only around £800 then I might just lay it anyway. But that’s definitely a decision I can make a lot further down the line. 

[SteamyTea]

1wire sensors are so cheap, put in loads, just space them midway between pipes and extra ones near walls.

 

 

[Thorfun]

8 minutes ago, SteamyTea said:

1wire sensors are so cheap, put in loads, just space them midway between pipes and extra ones near walls.

 

 

in the slab or on top of the slab? I ask as it they're in the slab then most seem to come with 3m cable at most so I'll have to support them some how to keep them out of the way for the slab pour which could be a pain

[SteamyTea]

1 minute ago, Thorfun said:

in the slab or on top of the slab

Ideally in it, but near the top.

You can extend a 1Wire cable to about 10m.

If you can find a way to fit them in a channel on the top (push in a bit of half round moulding when the floor is cast), that could be an easy way to set it up afterwards.

Just make a large X 15% of the wall length from each corner.

[Dan F]

UFH pipe is perfect for the Loxone 1-wire sensors (and probably other similar ones too).  Given they are a snug fit it's easy to push sensor lead down into them, even up to 2.5m when you do wiring later.  Just cut bits of UFH pipe to length of sensor lead -300mm or so and close one end with some pliers and then weave them between steel mesh and UFH pipe to a decent location.  Remember to mark pipe with room name and tape open end just in case.

 

[Bitpipe]

16 hours ago, Thorfun said:

I’m happy to pay £800 for peace of mind. If we never use then great! But at least the pipes are there if we do. 
 

thanks for the de-coiler tip. Will look in to it. 
 

definitely having UFH on the ground floor but still undecided about the first floor. If it turns out the pipe and manifold are only around £800 then I might just lay it anyway. But that’s definitely a decision I can make a lot further down the line. 

 

My suggestion is to pay the £400 for pipe now and only spend on the manifold, pump later when you decide to commission it in first fix.

 

Very easy to over spend at this stage of the build, you may want that £400 later on

[Thorfun]

12 hours ago, Dan F said:

UFH pipe is perfect for the Loxone 1-wire sensors (and probably other similar ones too).  Given they are a snug fit it's easy to push sensor lead down into them, even up to 2.5m when you do wiring later.  Just cut bits of UFH pipe to length of sensor lead -300mm or so and close one end with some pliers and then weave them between steel mesh and UFH pipe to a decent location.  Remember to mark pipe with room name and tape open end just in case.

 

that's a great idea using the pipe as a conduit for the probe. cheers!

 

those Loxone probes seem to be double the price of the Wunda ones which are probably double the price of generic ones. any obvious reason to go for the Loxone ones over the non-Loxone ones?

[Thorfun]

54 minutes ago, Bitpipe said:

 

My suggestion is to pay the £400 for pipe now and only spend on the manifold, pump later when you decide to commission it in first fix.

 

Very easy to over spend at this stage of the build, you may want that £400 later on

this is very true. but if I want to test the pipework before the pour I need a manifold, right? 

 

although from the reading on here the pre-pour testing of pert-al-pert pipe doesn't really seem necessary.

[Dan F]

7 minutes ago, Thorfun said:

those Loxone probes seem to be double the price of the Wunda ones which are probably double the price of generic ones. any obvious reason to go for the Loxone ones over the non-Loxone ones?

 

Have you worked out how to integrate with the Wunda ones?   Are they 1-wire, or proprietary and only work with Wunda thermostat?  Would they fit down UFH pipe?

 

Generic ones could work very well, just slight additional risk with quality I guess, also look at length of cable and how easy they will be to work with.    I orginally bought all Loxone ones because, like you, I thought I might need to actually put them in the slab itself and so didn't want to take any risks with quality.   If you can put them in later, then you work out what to use later, with the obvious caveat that they'll need to fit down UFH pipe.

 

[Thorfun]

3 minutes ago, Dan F said:

Have you worked out how to integrate with the Wunda ones?   Are they 1-wire, or proprietary and only work with Wunda thermostat?  Would they fit down UFH pipe?

not worked it out nor know the answer to the other questions!

can't find much information about them on the Wunda website either (https://www.wundatrade.co.uk/shop/home/quick-shop/wundatherm-quick-shop/controls-quickshop/floor-probe/#)

[Nickfromwales]

Also, iirc, Wunda don’t do the uber low temp pump and blending set atm. Therefore, if you buy now, I doubt if that kit will cope with the intended application. 
Totally agree; pipes now, cap them off with self-amalgamating tape, not cap ends, and leave for now. 
 

23 minutes ago, Thorfun said:

but if I want to test the pipework before the pour I need a manifold, right? 

No. Just a few 16mm elbows to daisy chain the loops one to the next, put cold mains on the first pipe, and a pressure gauge on the last one.