OK so reading the old threads on BH re insulated pipes, there seem to be two camps:

1. Roll your own. Copper or plastic pipe (maybe 22 copper, 28mm plastic/pex). Insulate with grey PE sponge (or even Armaflex) / air tight foam / eps/xps sheet etc. Even EPS beads if you can keep them watertight. Plus a bit of UV protection. Heat loss a bit unknown but I guess can be calculated. Cheaper (mostly except for thick Armaflex) but maybe a bit prone to problems unless done v. carefully.

2. Buy an expensive multipipe pipe product designed especially for the purpose. Maybe Calpex or Rehau (preferred according to one Build hubber) or Uponor / Isoflow / Hiline / Primary Pro. Either multiple single insulated, dual or fancy multi-pipe including power & data. Interestingly, some of these suppliers don't seem to supply U-Values, which is a bit disconcerting. This option seems to run from pricey to eye-wateringly expensive, but maybe less error-prone.

   Why do I ask? Because I need to specify seals right now (which means I need the number, diameter and smooth/corrugated nature of the pipe). This for the as-yet unspecified pipe running to a fairly undetermined place 😆. Probably for a Panasonic Aquarea J in 5 or 7kW. Location could be about 7m away or much further (20+m) - it all depends on how much my noise-sensitive wife reacts to the noise from a friend's HP next weekend.

   What's the up-to-date hive-mind's thinking on this subject?

Our fat (insulated) pipe is circa 25m from heat pump to manifold.

In the end it was all part of the price for the whole install, however when we looked at the cost it was somewhere (depending on brand/source) between 1.7 and 2.3k which in the scheme of things for a "known" outcome.......

Wasn't convinced the pre made stuff had a great U value and was stupid expensive, so rolled my own. We are about 5m underground and quite a bit over ground via an insulated shed. We used 28mm hep2o and transitioned to copper (28mm) though the wall. Started with 6kW heat pmp down sized to 4kW

We had the 1m run of ours, before it dropped underground, wrapped in a single layer of armflex by original plumber. I then added a few more layers of it, then wrapped it on duct tape. It's reasonably neat, but gives me the satisfaction it's over kill!!

1 hour ago, JohnMo said:

are about 5m underground

We're about 5m internally (to side of screed under kitch units) ans 20m underground min of 700mm cover (sometimes more)

It depends completely on where it is running. Distance and location.

Eg. At extremes

It might be a long way and through a cold loft.

Or a short distance straight to the manifolds.

Here are my experiences.

1. Steading... straight through the wall to the room inside. Armaflex or similar for 600mm

2. Current project... straight through the wall to an insulated plant room, with armaflex or eq. Then in insulated pipes within the eps floor insulation to the manifolds.

3. Office block we built 20 years ago.. 10m from heat pumps to the building, underground in a trench. The very expensive insulated dual pipe (isoflow?) , in earth, then leftover kingspan wall panels over the trench and then buried.