I am considering replacing my Viessmann Vitodens 200-W gas system boiler with a Vitocal 200-A Monobloc ASHP. The indoor unit of the ASHP is almost identical in size to the gas boiler. Much of the electronic and plumbing connections should be able to be reused. Great!

Problem: The boiler is in the kitchen at the front of the house and the outdoor unit of the ASHP would need to go in the back garden. How to connect them with Uponor Ecoflex Thermo Twin HP, a large diameter insulated pipe for hydraulic, electrical and electronic connections?

The house was built in 1995 and has a concrete beam & block ground floor. My ideal solution would be to run the pipe under the house and up through a core-drilled hole in the kitchen floor. There is a kitchen unit close to the boiler and if it surfaced under that it would be almost invisible except for possibly some boxing at the back of a cupboard.

The excellent technical support at Uponor suggest that it is technically feasible but cannot identify a contractor that could do the work. They are only aware of contractors that undertake commercial/industrial projects.

The core drilling is feasible (although I don't know the Building Regulations aspects). I know that builders have put basements and wine cellars under existing houses. Others have sprayed thermal insulation under suspended floors. If a drain under my house broke I imaging there would be somebody that could fix it.

I really want to avoid the disruption of moving out furniture, ripping up carpets and floorboards and running large bore, insulated pipes up the outside and through the fabric of the house. If I can't avoid that aggravation I might just scrap the whole project!

With heat pumps set to become a common replacement for gas boilers, insulated pipe connections under the ground floors of houses without basements doesn't seem such an outrageous solution.

Has anyone achieved something similar?

What diameter hole do you want to achieve?
Do you know what the spec of the block is? I think they may well be a 3 or 7 newton strength i.e. a standard building block.
I would not think it was difficult to core drill such a block with a core drill in an SDS drill (not on hammer action), going through a beam would be a no no you would not do it with that set up anyway.
I have drilled through a cavity block wall i.e. 2 blocks with a 150 mm core drill without problem in order to get MVHR ducting to the outside.
The concrete drill contractors you mention are specialist who drill through concrete walls and floors often with rebar in and use specialised machines and jigs to hold the drill and guide it automatically, you no not need that if you have a standard beam and block floor.
How much space have you under the floor? DJH makes a valid point about the bend radius I guess the more room under the floor the easier it will be.

Why does it need to be insulated?

I would take out a whole block, easier, cheaper and quicker than drilling. Then fill back in with sheet insulation or foam strong screed on top

Are there any sleeper walls? It is ok to take out half a block underground between or parallel to beams but fill round pipe to rat-proof it

For folks who haven't seen this stuff - it's about 6" diameter so like sewer pipe, but heavier, needs lots of supports. It can just about be bent (comes in a huge coil) but is more normal to use elbows. Will be awkward to feed a long length under the house round obstructions and install supports and bends. Costs about £100 per metre so a longish run easily adds £k to the job.

Normally each run has a single hot water pipe through the middle, surrounded by a couple of inches of insulation. However the product mentioned in the OP has two pipes (F &R) and two electric conduits, through the same bundle, so doesn't have space left for much insulation. If using this, you would probably want to wrap a few inches (at least) of insulation around the outside. Beware that heat will leak across from the F to the R pipe, IE shortcut without going into the house.

This primary pipework is the hottest point of the CH system running effectively through the outdoors, so any lack of insulation will be costly!

I don't know about block floors. What dia hole can you core through each block before it falls apart? Needs big enough hole to feed the 6" stiff pipe through with wiggle room.

Alternative might be to split the bundle under the floor and run individual CH pipes and electrical conduits up through the floor, each through their own 2" hole, if these can be made without the block cracking between them.

There are a few key points raised above:

- height of floor void versus bend radius. Bend radius might be 8xdiameter. Could use single pipe rather than dual.
- height of floor void and access to it for installer
- what is the floor build-up (blocks, sometimes there's a screed over the blocks to level the floor, then insulation, then floor slab/screed???).
- if you run underground externally, you'll likely want to pass the pipes over the foundation level from outside, through the blockwork underbuild. What depth is the top of the foundation? The solum may be above ground level, so would need to penetrate that unless the pipes rise above ground level externally.
- allowable length of pipe run, and can the run be shortened. Shorter run might mean lesser diameter, and so lesser bend radius (if that's an issue)
- confirm the pipe sizes, are they single or dualed, therefore what's the outer duct diameter. Could be 90mm if single, but could be 175/200 if dualed.

I would try to answer the above points, before considering the bit through the floor, as that's the relatively easy bit. If you take out a big enough area, then the pipes can rise at an angle through the floor, incorporating some of the bend radius above floor (should that be an issue).

Maybe a quick site plan sketch might help our understanding, and poss lead to ideas to help reduce the issues?

Should have mentioned that the location is Cambridge and according to Check the long term flood risks for an area in England (https://www.gov.uk/check-long-term-flood-risk) my house is "Very low risk" and "Unlikely" for all categories.

Maybe core drilling is the wrong approach for beam & block? The block dimensions seem to be 440mm (L) x 215mm (W) x 100mm (H). Chances of drilling an accurate and strong 200mm hole would not be good!

Perhaps the solution is to use a ready-made 200mm hole? Uponor's "Ecoflex Solutions Technical Information" lists a "Fibre cement pipe PWP" (Order Code: 1007370; liner pipe diameter DN 200; for jacket pipe diameter 140mm; length 400mm). Don't know how it would be set into the floor. One for a structural engineer?

An illustration labelled "Slip Brick Detail" in https://www.milbank.co.uk/app/uploads/2022/08/T150-2.pdf shows a pipe passing vertically through the join between two blocks.

Posted By: GreenPaddyI'd expect there to be insulation in the floor buildup, as 25mm 12 years ago would never have passed build regs.

The house was built in 1995. The architect was involved in the low energy renovation 12 years ago. The building standards were lower when it was built. The insulation was originally expanded polystyrene. Replaced with extruded polystyrene (XPS) because of load requirements of the washing machine and 350l thermal store (and water damage under a vinyl floor - minor drip from washing machine connection; plumber saved time by running microbore pipe diagonally across vapour barrier under chipboard creating small lake; fungal heaven; insurance job!). Microbore on ground floor for radiators was replace by 15mm copper during low energy renovation.

All good suggestions for further investigation. However, I am reluctant to have anything seriously invasive undertaken until I am happy that there is an approved way of passing the Ecoflex through the floor and providing support for it.

Typical insulated pipe building entries are horizontal. Viessmann's fixing suggestion is "The pipe is fixed directly in the brickwork with expanding mortar or concrete (no other accessories required)". Uponor have wall seals with metal faces that compress a rubber ring. Neither seem likely to work well vertically through blocks of low mechanical strength.

Thanks for the comments.

John,
For someone competent to crawl under the house installing heating pipes/supports/elbows/joints, they will have some (firm) ideas how much height they will need to work in, and what would be a sensible product to work with.
Why not get some candidates round to look?

From your description it's not obvious that you think there is a workable space under the floor (likely need a couple of feet height).

If not, rather than get bogged down with choosing piping products, take a step back. The installer will have faced this before. Kick some ideas around with them about where the indoor unit should go, or indeed whether you need a HP with an indoor unit at all. (The indoor units are just a box with plumbing bits in like zone valves, expansion tanks, pumps etc, which you might already have with your thermal store). Installing all the insulated multicore pipes linked above is going to cost a couple of £k which may be avoidable, or spent a better way?

Also let the HP installer buy the bits as then they can go within the zero-VAT scheme.

Posted By: john.connettMaybe even a ferret and a long piece of string?

Maybe not a ferret, but depending on what the ground surface is like underneath, then maybe a very long stick (several lengths of bamboo taped together?) to push a string through. Or possibly a remote controlled toy car?

I suspect the first thing to do is make any kind of hole at all, either in the floor or through a wall, and push an endoscope camera with a light in to see what's there. The camera needs to have distant focus, as well as short range.

Posted By: djhMaybe not a ferret, but depending on what the ground surface is like underneath, then maybe a very long stick (several lengths of bamboo taped together?) to push a string through. Or possibly a remote controlled toy car?

I have had similar thoughts. Running a string then a draw rope should be relatively easy (assuming no obstructions).

However, insulated pipes are usually rolled into position to avoid damaging the outside casing. Would it be acceptable to pull/push a pipe into position? Are there ways to protect it using a slippery channel or mat? Would a pulley wheel be needed to provide a straight pull?

Posted By: djhI suspect the first thing to do is make any kind of hole at all, either in the floor or through a wall, and push an endoscope camera with a light in to see what's there. The camera needs to have distant focus, as well as short range.

Having been involved in looking for tube leaks in a 1923 Babcock & Wilcox water tube boiler using a camera on a stick I know how tricky it can be to interpret the images! Maybe it would be easier looking under a house?

I think there are questions to answer before making holes. I need to know if there are permitted ways to pass pipes or other services through an existing beam and block floor that comply with Building Regulations.

There are still questions that probably need answers from a beam and block expert and someone with experience working with these pipes.

Thanks for the comments. It feels like I am moving towards a solution.

Posted By: Peter_in_Hungary

Posted By: john.connettI need to know if there are permitted ways to pass pipes or other services through an existing beam and block floor that comply with Building Regulations.

There should be no problem coming up through a block because the blocks are only infill between the beams and removing a number of them won't affect the integrity of the floor.

Given that the elements are not structural I don't see that building regs would be involved or have an interest.

A lot of the blocks here are hollow with 2 holes (the blocks have a central divide) that are 18cm wide and 12cm deep. these holes line up as the blocks are laid on the beams so it would be possible to pass a pipe down the centre of a row of blocks once access to the ends is made - if you have that type of block.

Totally agree except think the UK blocks used are solid variety. Just consider the blocks as being floor boards over joists. A hole in the floor board is not considered structural but in the joist yes

Posted By: cjardIn parallel to this, you should investigate relocating the indoor unit instead of becoming blinkered into having to reuse the boiler location. Mostly that's a nonsense with ASHP because they store their DHW in a tank and it is the tank that should be located close to where water is used, not the indoor unit. The shorter your pipe run from tank to tap/bath/etc, the less standing cold water you have to draw off to get hot.

Existing tank, 350l with solar thermal, is in a ground floor under-stairs cupboard. Doubt if the indoor unit would fit in there as well. Even if it did, it would require a contortionist to plumb and maintain it. Similar problems with the pipe run. Either boxing through the lounge over the beam and block floor or up the outside wall, through the first floor and back down. Don't think I am becoming blinkered but other options seem less appealing.

Posted By: WillInAberdeenThe 'indoor unit' for that ASHP is a box containing: a circ pump, a diverter valve, an immersion heater, a safety valve. It would be surprising if you don't already have all those things for the TS?

Device	Location	Notes
Circulation pump	Gas boiler
Flow/return plumbing to TS	Gas boiler
Diverter valve	N/A	System boiler. Mains pressure DHW via TS.
Immersion heater	TS
Safety valve	Gas boiler	Drain plumbing in place
System controller	Gas boiler	Including mains power connection
Bus terminals	Gas boiler	For heating circuit with mixer module, solar thermal module
Outdoor temp sensor terminals	Gas boiler

The gas boiler is conveniently close to the Consumer Unit for additional power connections for the ASHP outdoor unit (and 3-stage instantaneous water heat, if required).

I'm not sure I understand your simpler or less disruptive solution.

(Apologies for the strange table formatting).

Posted By: john.connettadditional power connections

Perhaps additional cabling is easier to run than insulated pipes?
(I write this having just put a decent conduit under the new bathroom floor in readiness for a cable from CU to boiler room, to facilitate Heat Pump power supply in future)