UFH in passive house build

[Nickfromwales]

With the steel supported on chairs, many choose to zip tie the Ufh pipes to the steel as a ready made 'clip rail'. 

I'd favour having the pipes clipped to the steel, and thus fully encapsulated in concrete. 

[MarkH]

29 minutes ago, Nickfromwales said:

With the steel supported on chairs, many choose to zip tie the Ufh pipes to the steel as a ready made 'clip rail'. 

I'd favour having the pipes clipped to the steel, and thus fully encapsulated in concrete. 

 

I was told that wasn't allowed but the guy who said it had no idea why it wasn't allowed. Makes perfect sense to me though as wouldn't the steel more efficiently dissipate the heat?

[jack]

Allowed by whom?  That's a good question! Our (private) building control has seen our plans including the UFH being clipped to the steels.  He's happy.  Several other people have had MBC houses (which all use this arrangement) signed off by building control.  I believe @Bitpipe had an architect (or perhaps engineer) who wasn't comfortable with this approach, but this was in a basement with some very stringent structural requirements.

 

Don't suppose the steel would hurt heat movement, but bear in mind that with a very well insulated slab you don't tend to use high heat levels.  Our ASHP is programmed to provide 25 deg C water to the slab during winter.  I programmed in a mild weather compensation curve starting at 10 deg C exterior temp, with the ASHP supplying up to 28 deg C water at a -5 deg C exterior temperature.  Never felt cold all last winter.  You basically keep the slab largely at the same temperature all day and night, rather than blasting heat in morning and evening like with a screed.

[Bitpipe]

1 hour ago, jack said:

Allowed by whom?  That's a good question! Our (private) building control has seen our plans including the UFH being clipped to the steels.  He's happy.  Several other people have had MBC houses (which all use this arrangement) signed off by building control.  I believe @Bitpipe had an architect (or perhaps engineer) who wasn't comfortable with this approach, but this was in a basement with some very stringent structural requirements.

 

Don't suppose the steel would hurt heat movement, but bear in mind that with a very well insulated slab you don't tend to use high heat levels.  Our ASHP is programmed to provide 25 deg C water to the slab during winter.  I programmed in a mild weather compensation curve starting at 10 deg C exterior temp, with the ASHP supplying up to 28 deg C water at a -5 deg C exterior temperature.  Never felt cold all last winter.  You basically keep the slab largely at the same temperature all day and night, rather than blasting heat in morning and evening like with a screed.

 

Yes, our engineer designed an 'open box' basement so there was a lot going on at the wall / floor interface. As such she was reluctant to have UFH pipes in the structural slab aside from a smaller area in the centre. We decided to forgo UFH in the basement anyway as it's well insulated and will have plant and other equipment generating heat so I'm not worried about it being cold. Also, UFH would have heated up the whole basement box, not sure how that would have worked.

 

Lovely and cool at the moment, definitely the trades favourite place to work! We have decided to forgo tiles for Karndean as we were worried that it would be a bit cold underfoot.

[Nickfromwales]

Not tiling it should make a huge difference underfoot . Good choice. 

[joe90]

Despite my post earlier we are changing our UFH design, It has been pointed out that zipping UFH pipes to steel can cause leaks due to vibration in pipes caused by the pump, also the manifold and pipe ends are left in the open during the build so could get damaged/ frozen. My builders brother does UFH all the time and he now believes pipes clipped to the insulation with 70mm screed over after the roof is on is a better solution for new builds.

[jack]

23 minutes ago, joe90 said:

Despite my post earlier we are changing our UFH design, It has been pointed out that zipping UFH pipes to steel can cause leaks due to vibration in pipes caused by the pump, 

 

Interesting theory.  The Wilo pump we have in our UFH system is completely (and I mean utterly) silent, to the point where I can't hear when it's on.  I can only just perceive a slight vibration when I put my hand on the pump.  I find it difficult to believe that there'd be sufficient vibration to cause any problems with leakage.  Admittedly our pump doesn't run at a very high setting. 

 

27 minutes ago, joe90 said:

the manifold and pipe ends are left in the open during the build so could get damaged/ frozen

 

I didn't install the manifold until after the plant room had been plasterboarded.  Until then, the end of each pipe was covered with a thick bit of plastic and gaffer tape.  Since the studwork went up just after the slab was poured, the upcoming pipes were never out in the open for any length of time.  It would have been trivial to knock up an OSB or plywood box and screw it to the studwork if the pipes had been in a more exposed place.  

 

Also, because we didn't fill the loops before pouring the concrete (risky according to some!), they had no fluid in them until we commissioned the system.  There was accordingly no potential freezing issue.

 

Still, if you feel it's a risk, there's nothing to be lost (other than costs) by going the separate screed route.

[TerryE]

MBC have done 100s of installations this way.  I am not aware of any problems.  If you get a decent pump, it will be properly balanced and have a power consumption of 10s of watts.  The pipe is in an entirely set matrix, so any differential effects per steel crossing are going to be in the µW. It will actually be worst across a hetrogenous interface from a stiffness PoV e.g. concrete and PUR or EPS.   It sounds to me as if your builder is coming up with pseudo-science to support an approach which is easier for him and which is going to involve the transfer of a lot more money from you to him. 

 

Our pipe ends above the slab were open to the weather for about 2 weeks.  As Jack says, we simply taped over the ends of our UFH circuits and left them dry.

[joe90]

Dear Terry, my builders brother has been doing UFH for many years and a lot of his work has been with pipes clipped to steel and he has had to go back on a few where the pipes have rubbed on the steel, we also discussed the merits of pressurising whilst concreting or not. It his his opinion that pressurising can cause the pipe to swell and when the pressure is released, and during normal usage the pipe will be marginally smaller than the hole in the concrete and pumps can cause slight pulsing which could lead to ruptures in the future. This theory fits with my " purely theoretical" thoughts. He also expressed concern with walking on the pipes during the pour process and the possibility of the steel and pipes rising during the pour which cannot be seen. He tells me that most UFH installed lately in his area ( in new builds) is now done on top of insulation under a screed.

 

 " It sounds to me as if your builder is coming up with pseudo-science to support an approach which is easier for him and which is going to involve the transfer of a lot more money from you to him."

 

You could not be more wrong, the installation of the UFH is purely my job at my cost, although he will be laying a screed in addition to his fixed price he is not charging me for it. He offered his brothers advise like any good builder would as he has a very good reputation locally and wants me to be as informed as possible. It's not " pseudo-science" it's real life experience from someone that does this work all the time.

[PeterW]

Ok - the only way to damage a pipe in this way is to cause the damage during installation - PEX is good to 10 bar, UFH is 1-2 at most and to get PEX to expand more than 0.5mm needs around 4 bar. Pumps are circulation pumps not pressure pumps so there is no way for a pulse to be created unless there is a fast actuating manifold valve and even then, that would be a sub second pulse only when it closes. 

 

Whilst I respect he's been doing it a while, I would hazard a guess that the recalls are due to pipe damage on install that manifests as a leak later. 

 

If you pressurise PEX to 3 bar during a pour, it will need a significant force to deform it hence why they always suggest to pressurise as you're effectively walking on a very rigid tube. Without water in it, you stand the risk of deforming something that is inherently unstable due to its shape i.e. a thin tube. 

 

I don't know of a single supplier that would warrant their product if it hadn't been pressurised at pour - who's providing the pipe ..?

[Guest Alphonsox]

We used the "clip to insulation" route - I doubt that zipping to mesh is any quicker/cheaper. You can buy or hire a clip insertion tool, we used a rubber hammer and a small child. I'm not sure I buy the other arguments for its use. You can happily walk on pex-al-pex pipe with no ill effects, once the screed is down nothing is going to move. We poured with the pipes at mains pressure (3 bar), I would have thought that thermal expansion of the pipes would fill any theoretical gap.

[joe90]

PeterW, Wunda. I agree that damage is most likely during installation/pour. It's been said on here( somewhere)  that pressurisation during the pour should be 6 bar, 3 sounds more reasonable as that is like normal working pressure . Our build is being done over the winter and even if the water pressure was released it will be difficult to get all the water out to stop freezing whilst the house is being built. It also appeals to me to lay the pipes from/to a fixed manifold then screed over later. In theory I,d prefer to walk on pipes laid on EPS rather than point loading on steel mesh wobbling on chairs. As the pipes are in a thinner screed heat up times will be shorter.

 

Confuscious he say, "there is no right or wrong, just opinion"

Edited November 9, 2016 by joe90
Typo

[Stones]

Our UFH pipes are clipped onto the insulation, covered with 100mm concrete slab.  The main reason for us doing it this way was it saved the cost of having to lay a 70mm screed.  I didn't see the point of paying to dig out the foundations a bit deeper, then pay more to fill it back in again.

Edited November 9, 2016 by Stones
Typo

[TerryE]

5 hours ago, joe90 said:

My builders brother has been doing UFH for many years and a lot of his work has been with pipes clipped to steel and he has had to go back on a few where the pipes have rubbed on the steel, we also discussed the merits of pressurising whilst concreting or not. It his his opinion that pressurising can cause the pipe to swell and when the pressure is released, and during normal usage the pipe will be marginally smaller than the hole in the concrete and pumps can cause slight pulsing which could lead to ruptures in the future. This theory fits with my " purely theoretical" thoughts. He also expressed concern with walking on the pipes during the pour process and the possibility of the steel and pipes rising during the pour which cannot be seen. He tells me that most UFH installed lately in his area ( in new builds) is now done on top of insulation under a screed.

 

 " It sounds to me as if your builder is coming up with pseudo-science to support an approach which is easier for him and which is going to involve the transfer of a lot more money from you to him."

 

You could not be more wrong, the installation of the UFH is purely my job at my cost, although he will be laying a screed in addition to his fixed price he is not charging me for it. He offered his brothers advise like any good builder would as he has a very good reputation locally and wants me to be as informed as possible. It's not " pseudo-science" it's real life experience from someone that does this work all the time.

 

Joe, as Jack said we don't pressure test the UFH loops when the concrete is wet.  In my case it will have cured for about a year before I pressure test.  Any test will simply be a case of go / no-go to use any given loop, since by then it won't be practical to attempt to dig out to expose the pipe and effect a repair.  Given then the concrete totally cures with the pipe unpressurised, there isn't any material scope of pipe swelling to create expansion voids in concrete.  I still don't understand the mechanism by which the pipe could shrink back and end up marginally smaller than enclosing run in the concrete. 

 

If there is some mechanism that I haven't considered then surely the same mechanism would apply for pipe embedded in render.   However both the plastic formers and underlying insulation have a considerably higher plasticity (orders of magnitude higher) so the only possible scenario that I can think of and in which pipe flexing could occur as you describe is one where the Pex pipe is in direct contact with the plastic former or insulation and here the concrete will effectively be inelastic and the Pex can deform by compressing the former and insulation underneath.

 

As to the steel rising during the pour, it is over 3 times the density of concrete so this isn't going to happen, is it?   The MBC ties down the Pex pipe the day before the pour, so there isn't any scope for extended rubbing.

 

If I understand the trust of your argument correctly, it is that there are possible weaknesses with Scenario A, therefore I will not use Scenario B which is nothing to do with Scenario A.  Sorry, but I can't share this conclusion.  I am not saying my approach is risk-free, just that it was simple and cheap, and in my view has less risks than the alternative that you propose to substitute.  I am not challenging your decision for your slab.  That's your call, but this advice is addressed to @Novice, so we should give both arguments for him or her to assess.  

[Nickfromwales]

9 hours ago, joe90 said:

Despite my post earlier we are changing our UFH design, It has been pointed out that zipping UFH pipes to steel can cause leaks due to vibration in pipes caused by the pump, also the manifold and pipe ends are left in the open during the build so could get damaged/ frozen. My builders brother does UFH all the time and he now believes pipes clipped to the insulation with 70mm screed over after the roof is on is a better solution for new builds.

Does he mean a slab, covered in insulation and then the pipes and screed ? 

I understand that you sound happy with your change in direction, but I can assure you that there would be absolutely no degradation caused by the pump running. The pipes and concrete set as one, and therefore there cannot be ANY movement. Movement is required to caused abrasion, so that type of fault / leak simply wouldn't occur IMHO. I believe he has given you a bum steer there, and I've also fitted this stuff for years, AND been responsible for screeding it.

The only difference between me and your chap is I have zero stories to tell about leaking / damaged / burst Ufh pipes, howsoever caused . I know which one I'd listen to. . 

[Construction Channel]

9 hours ago, joe90 said:

zipping UFH pipes to steel can cause leaks due to vibration in pipes caused by the pump,

 

i also had this thought when i first heard of the idea, also with the heating and cooling, 

after hours of thinking through what could possibly happen it occurred to me that even if the pipes did move enough in the concrete that they wore against the steel it would only ever take off the surface as the concrete would then be holding the rest of the pipe away from the steel.

 

 

[Nickfromwales]

11 minutes ago, Construction Channel said:

 

i also had this thought when i first heard of the idea, also with the heating and cooling, 

after hours of thinking through what could possibly happen it occurred to me that even if the pipes did move enough in the concrete that they wore against the steel it would only ever take off the surface as the concrete would then be holding the rest of the pipe away from the steel.

 

 

+1

[dogman]

16 hours ago, joe90 said:

He also expressed concern with walking on the pipes during the pour process and the possibility of the steel and pipes rising during the pour which cannot be seen.

The last house i built i used a flow screed on top of clipped pipes. It was pressured to working pressure during the installation.

Both methods require the floor to be walked on during installation.

One thing to look out for

If you are putting any pipes in ducts the ducts will rise in the flow screed as there is a lot more air in the pipe and you only have 70mm of liquid to stop this