Most efficient pipe insulation

[acresswell]

I've just been looking at pre-formed pipe insulation, because we'll have one-shot at getting our pipework really well-insulated before the ceilings go up!

There seem to be 3 basic types out there:
A) Polyethylene (the grey stuff you see in DIY stores)
B) Mineral wool with a foil surface  (e.g. Rockwool)
C) Phenolic with a foil surface (e.g Kingspan Kooltherm)

Has anyone done the thinking/calculations on payback times for putting in higher spec pipe insulation?

The main areas of pipework to be insulated will be:
a) DHW pipework as it spreads through the house.
b) short run from boiler (log gasification) to thermal store
c) the short run from thermal store to UFH manifold.
d) solar thermal to/from the thermal store

For the time being, I'm ignoring b,c and d...
   ...b and c are short runs with potentially high losses and I'm therefore willing to pay quite a lot more per metre for insulation.
   ...d needs high temperature insulation and is covered well on the solar thermal section of this forum
   ...so that just leaves me with the DHW to consider

The design has deliberately grouped the bathrooms together with the washing machine and WC below, but I still reckon that I'll need about 30-35m of insulation. Hoping to be able to use 15mm pipework throughout to reduce the time lag between turning on tap and hot water appearing. The first 2m of pipework will be common to all, so I might use higher spec insulation for that distance. There's one long-ish run (about 8m) to the kitchen tap & dishwasher.

Here are my options:
A) Polyethylene (the grey stuff you see in DIY stores)
about 0.039 W/m.K at 40 degrees C
13mm thickness for £0.53/m      X = 1.05
19mm thickness for £1.39/m      X = 1.88
25mm thickness for £2.20/m      X = 2.26

B) Mineral wool with a foil surface  (e.g. Rockwool)
about 0.037 W/m.K at 40 degrees C
20mm thickness for £4.60/m      X = 6.22
25mm thickness for £5.22/m      X = 5.64

C) Phenolic with a foil surface (e.g Kingspan Kooltherm)
about 0.021 W/m.K
15mm thickness for 2.94/m      X = 9.33
25mm thickness for 4.65/m      X = 8.86

Prices exclude VAT and are based on just buying a metre or two. I'm sure I could reduce them by shopping around.

The X value is my attempt to quantify the price per resistance to heat loss.  It's price divided by thickness and then multiplied by the W/m.K.  It's in some horrible non-SI unit.

Based on the X-value, C) would seem to be very expensive. There's no real difference in the W/m.K between A) and B) so I might as well go for the cheaper Polyethylene insulation.  I suppose B) and C) are really designed for big industrial plants rather than my dishwasher.  I suspect I'll end up using some of the rockwool stuff round the boiler pipework (unless the phenolic stuff is ok at high temperature).

How does water byelaw 49 influence this choice?  (various sites refer to this byelaw, without actually telling me what it says ... and a quick google didn't tell me)

I appreciate that quality of installation (avoiding gaps, taping joins, etc) will be just as important as the materials. The last time I plumbed a house, I bought a length of 28mm insulation, and then cut short sections to go round each of the isolating valves.

Is the Polyethylene stuff OK next to expanding foam or does it 'melt'?

What do you think of the spiral bubble wrap stuff (e.g. http://www.screwfix.com/p/spiral-wrap-50mm-x-7-5m/62194 ) Might it be a useful top-up to the polyethylene or would I be wasting my time and money?

Any thoughts?  Have I missed anything or made any mistakes?

Thank you

[clockmanFR]

As a matter of interest what kind of pipes are you insulating, copper, speedfit type polybutylene/pe-x barrier ?

I allways fit 22mm dia speedfit type, (with plenty of support brackets), whenever i can, this ensures a good flow to all appliances. (adhere to Speedfit recommendations when connecting to hot tanks, use copper for a set distance)
There is nothing worse than having a piddling shower and waiting hours for the bath to fill and then find its gone cold.

I find 22mm standard clip over type polyethylene and taped joint is pretty effective.

 

[stannn]

I have always had my doubts about plastic water pipe but, some time ago, someone here commented on mice chewing through it. I will stay with copper. They also chew the insulation.
Stan

[Justme]

As each time you use a tap / service is likely to be quite a time from the next / last use you will still loose virtually all of the heat in the standing water any way no matter how good the insulation is. So unless you use a constant flow system (and I would not) I think you will get better results by using 10mm pipe so the hot water gets to the tap sooner & when turned off less volume of water is in the pipe to loose the heat. If you have a bath you might want to 15mm that one bit on an independent leg.

If you want / need frost protection why not just fit standard wall insulation in the bits that contain the pipes? But just put it between the pipe & the cold side leaving the warm side insulation free.

[biff]

the big positives for the plastic pipe,
           it dont throw off the heat in transit like the copper does, 
         the hot water stays warmer in the pipes for much longer.
         it is much quicker and easier to plan and if you want to travel long distance to an outside shed,its not a problem.
        it gives a much greater degree of protection to frost.i have seen plastic pipes frozen solid but apart from pulling back on grab ring it thawed right back into action,even the grab ring accepted the pipe with a little push and no leaks.if this had been copper the damage would have been horrible.
   support is essential for good performance in c/h,if the pipes are not supported then little hollows form when the pipe becomes live(with heat) and the pump has more work to do.
 the molecules in the copper allow the beads of water to race across the surface when new,however ,even after 10yrs the copper still allows the water to pass more freely,so like it as not the pump has that little bit more work to do with the plastic.
   one can invest in barrier pipe,the type which has a layer of plastic,then alloy,then plastic.i used to do underfloor heating with this pipe,you could shape it and it would hold it shape when hot.it did not come alive with the heat and slightly less support brackets were needed..
 the pipe i used had italian fittings which had double O rings.the fitting were really nice to look at and the pipe itself looked decent facework in anyone garage.,,copper still has it uses but plastic is here to stay.just as long as you use the fittings properly and any old fittings ,be sure to check that the grab rings are facing the right way..to be honest,the origional german barrier pipe with the italian fittings,in white pulled me out of more jams than enough.
    one other thing,when pricing a job,i could work out exactly how many fittings i needed and cable the pipework neatly and decreetly with only a fraction of the hassle of the copper.the copper stopped 1 mtr from the boiler.
                                                                                        biff

[wookey]

You missed out a 4th type of insulation: Nitrile rubber (e.g. 'armaflex'). It's much more robust, resilient and flexible, and easier to glue than the polythene stuff with a slightly better heat resistance: 0.033 W/mK. Armacell produce a foil-wrapped version of this too. It is of course significantly more expensive. The ability to glue all the joints sells it for me as that stops a lot of heat-loss, and the flexibility is great too. I assume the phenolic stuff is rigid?

[acresswell]

Thanks for the responses.

I'm planning on using plastic pipe, largely to reduce the number of joints (but also possibly becasue I've got most of a roll of speedfit  left over!).  I love doing "proper" soldered copper pipework, but I'm not as fast at it.... so I will save it for the solar system.

I think Justme's point about losing all the heat anyway is an excellent one.  I think I'll just stick to the 25mm grey stuff and spend the pennies I save elsewhere.

I've never used pipe smaller than 10mm diameter, but I'm tempted to at least run the feed to the kitchen (and the last few metres to each handbasin) in it. I've therefore just been looking at insulation for 10mm pipe, but if I want 19mm thickness the only people who seem to do it are Armaflex... and nobody seems to do 25mm wall thickness.  Since the surface area to volume ratio is going to be greater on a small pipe, I'd have expected thicker insulation, not thinner! Any thoughts?

Does anyone know of a "pipe friction calculator" that will let me check I'll still get a decent flow rate to the kitchen tap & dishwasher using 10mm pipe? Or anyone got any experience of it? (It's an 8m length)

Thanks for all the help

[brackwell]

acresswell,

What you say about the insulation is correct but remember it is the trapped air that provides the insulation not the material itself. Put the 15mm insulation on the 10mm then you have a air gap just like double glazing even better. Ideally need to seal the ends to stop convection currents.  In reality this is academic on a sink as this is a short time event.  It is true that below about 5/6 mm pipe insulation does nothing as the surface area is increasing faster than the insulation levels!

You will have no probs with 10mm (continuous) on mains pressure. It is joints,elbows and particularly taps which reduce pressure and flow and this is the real advantage of continuous plumbing in my opinion.  However another reason for not having joints with plastic pipe is that when doing a joint you should use a pipe insert which obviously reduces the bore.  It is best to use steel inserts rather than plastic as these have a larger bore.

The biggest source of pressure loss will be the tap. A modern fad is for these block mixer taps but if it is also taking the direct mains to the house and therefore has to be kept separate  they then put one outlet pipe down the centre of the other.  This is not really a problem with mains pressure and is there regardless of what pipe size you use.

[clockmanFR]

Regards 10mm pipe.

I have used it on only one occasion with a 2m run, and i will not do that again. This was to a hand basin, yes, it piddled. (toilet feed are slow but okay)

My hot and cold are both direct feed and can reach 5 bar, so soft solder is not used here, if its copper then its 0.5mm wall and silver solder/brazing, but good old speed fit is European normed with its 10mm and 22m and goes up to serious bar pressure.

[A.L.]

hello,

Does anyone know of a "pipe friction calculator" that will let me check I'll still get a decent flow rate to the kitchen tap & dishwasher using 10mm pipe?

do not know of one but the tables at the bottom of this page might help www.heatpumps.co.uk/DHW.htm

[brackwell]

clockman,

I have to think you must have another issue not related to the pipe size.

Assuming one requires 10L/s  (although i could and do live with something less than this )
     "        5m pipe run
     "        3 bar mains pressure

then the difference between 10mm pipe and 15mm pipe is.

Pressure drop 10mm 0.278 bar  / 15mm 0.05 bar    ie not a lot

I suggest you are loosing a lot of pressure before you get to the 10mm bit of pipe and/or you are loosing it in the tap.  Some taps i think have pressure reduction inserts in the end perhaps you have one to remove.

Ken

[clockmanFR]

Yep that's the problem, 10mm speedfit internally becomes 8mm, add insert, then internally you have 6mm dia for the water to flow through then a couple of 90 degree bends, stainless steel flex hose to the tap, hey presto a 'piddle'.

I once had a brand new tap shear at the body thread, (had 2m run 10mm speedfit) and the water only gushed out upwards of about 9 inches straight into the handbasin sink.

[johngabriyal]

Thanks for this info!!