Best pipe for UFH

YoungAndBroke

Hi, I am at the start of a new build and I am investigating our heating system. We are installing UFH upstairs and down. There seems to be a lot of focus on whether we use a heat pump (air or geo) or oil to drive but I have been struck recently by the difference in piping that are proposed by different providers. This will be harder to replace than a heat pump so I want to make sure I get it right.

I have been quoted for the following four with pex-al-pex being the most common.

PEX-AL-PEX
PERT
PEX
PERT-AL-PERT

From what I can tell, the "-al-" version is cheaper with the aluminium being added to create the oxygen barrier and I think it makes the pipe not bend as much?? Once shaped, it should stay in place. From what I can tell, most installers are using this to enable them give a more competitive quote.

It seems to me that using straight PERT or PEX could be better as the whole pipe is an oxygen barrier then, rather than the thin aluminium layer. And PEX handles high temperatures better but PERT should be fine for the low temperatures needed for UFH. Trying to get guarantees from suppliers at the moment, a longer guarantee could point to a better product.

Am I missing anything here?

Calahonda52

Can't comment on the pipework options, until I put on the screen specs I thought I was in a Big brother thread

However, oil and UFH is not the best idea: now loadsa folk will pile in here and say otherwise but you can't defy the science.

Whats the rest of the house spec like:
U values on walls, roofs, floors, windows doors etc and the Air tightness target.

I have attached some pages form a 2015 Leaving Cert Text book which may help
The TGDL 2011 U value one is what you need to meet the regs, your target should be way ahead of that.
What does the energy demand profile calc look like?

What do the Life Cycle calcs on payback for the air vs geo look like?

YoungAndBroke

I am deliberating trying to avoid another heat pump vs oil discussion here and would like to focus just on the best pipeworks for UFH, advantages/disadvantages of each. There are enough heat pump threads on here already but I can't find anything on UFH pipework. This is the stuff you are burying in your house so it is essentially part of the fabric of the house and not easily replaced. I want to put the best stuff I can in here

Spec on the house might be important alright. It is 3,400 sq foot, aiming to achieve the following u-values

Windows = 0.82
Walls = 0.15
Roof = 0.13
Floor = 0.13

And a target airtightness of <1.0ACH. The house is being constructed as block on the flat, externally insulated with 200mm EPS with quinnlites at junctions with the floor and attic insulation so I would hope to eliminate as many cold bridges as possible. After that, we have lots of solar gain with large windows to the south and west of the house. We are going to install UFH upstairs and down.

TPM

Calahonda52 wrote: »

However, oil and UFH is not the best idea: now loadsa folk will pile in here and say otherwise but you can't defy the science.

I will start it off then
well just a quick comment if you are thinking about oil make sure you use a suitable thermal store.
there are plenty of systems with oil boilers straight to UFH but it is by no means ideal or efficient

TPM

re the pipe itself im really only familiar with the alu-pex which tends to be used because it is pretty strong and easy to use.

although you shouldn't have to consider pipe getting damaged during installation, being covered by the floor and/or other construction it is something you do need to take into account because regardless of who is to blame of pays for it you dont want to have to dig back up floors chasing damaged pipes.

some brands of alu-pex carry a fairly long guarantee

and as for one type of pipe versus another you need to take manufacturer into account
as Calahonda52 said its all down to the spec of each pipe brand

ferryman35

What you are looking for is a pipe that offers flexibility and strength - and usually as you gain on one parameter you loose on the other. You need flexibility for workability, the ability to make radiused loops or have your circuit follow around corners.

So in that regard PEX wins. The multilayer pipe will function once installed, but the installation is harder - you should 'widen out' the pipe spacing before you make the loop so that you get a smooth curve rather than a pointed arch on each loop....wishful thinking of course. Good PEX pipe can make an 'in-line' loop without a bother.

Above all avoid kinks and joints in the screed.

One manufacturer I am familiar with quotes a 50 yr life for their PEX iirc. If you have plastic piping & stainless manifolds there is very little to degrade in the system - a small bit of good inhibitor would keep the pump / buffer bodies in prime condition.

Some installers clip the pipe directly to the insulation but i don't like this approach - I think the pipe heat transfer is better if the screed encapsulates the pipe.

Once installed there should be nothing in the process that could damage the pipe but obviously care should be exericsed.

Your supplier should give you a pipe optimisation schedule as part of you design. Each pipe circuit is designed to be a maximum length of 80-100m - so a big room might involve 2 / circuits for example.

So if your job needed for the sake of argument say 830m - well you can make that up with a 1x500m, 1x 250m, 1 x 100m coils - but you couldn't get 5 x 90m circuits and 1 x 100m circuit from the 500m roll so you need to know which roll to use for which circuit if you can follow that!

After that its a question of good controls to get the best from your system - but like the oil debate that's another story!

murphaph

Watch your pipe spacing and loop lengths! I agree wholeheartedly that the most important thing to get right is the pipework which is all but impossible to improve later. The heat source is comparatively easy.

Try to get loop lengths in the 70 to 100 metre range. Avoid short loops which act as a shirt circuit to the manifold and make balancing difficult.

Space the pipes as if you are using a low flow temp system (narrower spacing). This way you can opt for oil or gas now and still be able to replace with a heat pump in 20 years should you choose too. If you space at 300 centres you can forget about a heat pump in the future!

YoungAndBroke

Thanks all, I think I am coming around to PEX myself. Seems to be the better guarantee and I can't get away from the fact that a composite makeup for a 2mm pipe wall seems a bit too much, a layer of pex, a layer of alu and then another layer of pex and I think something else. I can see why lads perceive the alu composite pipes as better but I hope I won't be relying on the aluminium to hold up once its buried in the floor. It's just there as the oxygen barrier. Pert seems to have an issue at higher temperatures and I know I will never be running water at 90 degrees through it but my paranoia can't get away from the chance it could happen

Yeah, centres are another thing to watch. Some lads are coming in cheaper with their quotes but they were spec'ing 200mm centres. Most are spec'ing 150mm centres with 100mm in the bathrooms. One recommended 100mm throughout and another 130mm. Size of pipe is another. The pex-alu-pex all seem to have an inside bore of 16mm. Some of the pert have 17mm or 18mm internal which has to be better. All contributing to the headache I am having trying to make my mind up

To be honest, I was expecting more responses on this. Do you think if I linked to the heat pump thread in the Renewables section, would I get more input there? Moderator, what do you think?

ferryman35

When you bend the aluminium barrier pipe, you compress the material on the inside of the bend and stretch it on the outside. As this is basically a multi layer pipe - the layers start to delaminate, and this effect is added to by the constant heating and cooling that obviously happens with a cooling system. Eventually might be a pretty long time, but eventually that pipe will fail.

PERT is basically PE pipe but one process short of PEX - the crosslinking step. This is what gives the PEX its extra strength. The benefits of PEX are well worth the extra cost of this one additional step.

Within PEX, the molecules are normally crosslinked longitudinally, although one manufacturer has a patented process for crosslinking circumferentally - which has the effect of making their pipe both stronger and more flexible at the same time.

froshtyv

There is any amount of underfloor heating pipe in the Irish market.

From my experience, the Irish mentality seems to be the cheaper the better. Whether this is the builder or the end user.
You can get a Chinese multi-layer pipe for half the cost of German equivalent.
So unfortunately the type or quality of pipe being used doesn't even come into the equation in 99% of cases.

If you are concerned about the pipe being used, a good quality pipe should have a certificate indicating its test standard.

Generally PEX is used with a panel fixing system (some call them "mats) The multilayer pipe tends to be used with a clip and rail system.

Pert-AL-Pert I would see as a cheaper pipe due to it not being crosslinked, and it isn't able to with stand higher temperatures compared to Pex-AL-Pex.

YoungAndBroke

I have talked to a couple of local plumbers in the last week and they would all only use a product from Wavin called Hep2O, made of something called polybutylene and is guaranteed for use in UFH for 100 years, seems like a good option

froshtyv

YoungAndBroke wrote: »

I have talked to a couple of local plumbers in the last week and they would all only use a product from Wavin called Hep2O, made of something called polybutylene and is guaranteed for use in UFH for 100 years, seems like a good option

Any manufacture can give a long guarantee on the pipe. If for example the pipe was to fail, the longest length they would have to cover would be circa 100m

A 100m length of pipe is of little value to replace.


A system warranty is a different warranty altogether.

This would entitle you to claim for any work that would have to be carried out to take up floors etc.

You might want to bear that in mind, they are two totally different guarantees.

YoungAndBroke

This is what I got off the local Wavin rep, 100 years for pipe, 25 years for manifold, 2 years for stats. Of course, the plumber needs to install it correctly but the couple of plumbers I have talked to about our job have a good relationship with the rep and there seems to be good feedback either way. That caveat is going to be the same for any pipe used

"Provided that our published advice has been adhered to regarding a product’s installation and use, the following apply:

• Flexius underfloor heating and cooling pipe is guaranteed for 100 years and is manufactured under the BSI Kitemark. Certification Scheme;

• Hep2O push-fit fittings (used in some systems to connect the pipework) are guaranteed for 50 years and those used within. Hep2O underfloor heating systems are manufactured under the BSI Kitemark Certification Scheme;

• Hep2O’s Composite Manifold is BBA certified for a 25 year service life; Certificate No. 10/4738; Its electrical components are subject to a 1 year warranty.

• The Hep2O underfloor heating controls range is covered by warranty for 2 years;

• All other Hep2O underfloor heating system items are covered by warranty for 1 year."