mikeysoft

OK I was replying to your "fully insulate", so it confused me when you then said don't bother at all. I did watch it, and had watched a while ago along with his other videos. So to help my understanding, why would heating our poorly insulated slab (100mm EPS under) directly, i.e. pipes on top of the slab, be much different to (apparently) heating it indirectly via pipes on top of 25mm PIR? The implication is you get the same system performance (same downward heat loss)? Remembering that said 25mm PIR is already purchased and down, with a layer of DPM underneath, then DPM on top, and Profix PLUS panels affixed to the top slip sheet (plus PIR upstands around the edge of each room).

Sorry, I don't understand.

@marshian How do I fully insulate with 8 to 9cm build-up to play with?

Your advice was not to do UFH. That doesn't really help me.

Because variables might change over the years? Use of room; floor covering; change of heat source (boiler to heat pump or some other technology); external insulation; change of owner (and their needs); etc. @Nickfromwales you do many installs - what spacings do you use and how much do you vary that room-to-room?

We aren't going to tile over. This is a screeded system so there are no over floor boards.

Yes, thanks for everyone's input and time 🤩 In all honesty, doing a room-by-room analysis seems pointless and contrary to what some of the comments have been saying: that a retrofit low-build-up system is doomed to failure in a house like ours. It really doesn't feel like there's much variation possible. I came into this knowing that a retro-fit system is a compromise. We are not a PH. We are not ASHP running 24/7. We are not after nor can achieve ultimate efficiency - we are after comfort. We can't remove our house and slab and rebuild with 300mm insulation under the slab and a 150mm insulated cavity. So I have to make the best of what we have, as do plenty of other retrofit homeowners. My basic philosophy was to put a reasonable amount of pipe in the floor (16mm on 100mm centres), as that is permanent, in order to have plenty of opportunity to put heat into the house (distribution, controls and zones aside), given that we have a low insulation house. I'm aware that we would have bigger downward losses into the slab (reminder: our 100mm raft has 100mm EPS underneath from 20 years ago), and that will increase the running cost. How we configure and run the system can be varied over time with trial and error, perhaps needing some 'equipment' changes and or reconfiguration. I'm also aware that some carpets and underlay can insulate too much, but as you all know, there are low tog options for the rooms where we want that, even though these are not a magic bullet, and we may need design changes or other mitigations in the carpeted rooms. I'm looking forward to piping up soon, and having the Cemfloor Therm go down, so we can then start the UFH on the first floor and second floor! 😉

Thanks, but we don't want radiators. Are you are saying all UFH retrofits are invalid, if you can't put down 100 to 150mm of PIR? Anyone on here with UFH and carpets? If so, what floor temp are you running? What floor temp are you running @JohnMo? Running cost is not the only factor. We don't want a single zone - we want different temps in different areas of the house. Why do we have to have the whole house the same temp?

I absolutely want your input on retrofit systems, similar to my situation, that you have designed and installed - so yes, please, tell me what I should design? Your constraint is that I have an 90mm build-up to play with from the top of the concrete slab to the external door thresholds, said slab (raft) is 100mm thick with 100mm EPS insulation under, and an LPG heat source. And we like our reception rooms carpeted and at 21 to 22 degrees in the cold months.

Thanks @SimonD- good suggestion. The pipework is already in place like that; I'll look into the rest.

It's two years old @Nickfromwales. That was my understanding - the Greenstar range for gas or LPG are mostly the same bar the differences you outline. And yes it can modulate.

I have already done a LoopCAD design. Explain why? You seem to want to make negative comments rather than constructive suggestions to help people - surely the point of this forum: knowledge sharing and idea discussion? So you are saying most retrofit houses with pretty standard concrete slab floors are not suitable - give me some data/evidence to back-up your claim. I disagree - there are lots of examples online of people retro-fitting effectively in this way.

I was actually considering if we organise the circuits so that the 'carpeted' floors run on one manifold with the blending temperature set higher, than on the other manifold with non-carpeted rooms so that can be run at a lower temperature. Both manifolds are central in the house and co-located, so very possible. And 17mm pipe + 1.25" manifold in carpeted rooms? (17mm 5-layer pipe is hideously expensive compared to 16mm equivalent.)

What's a S or Y plan? We can run the boiler (Worcester Bosch Greenstar 8000 Life LPG 30kW) at the lowest temperature that allows condensing and gives a reasonable temp for the hot water tank (with a Legionella cycle in the tank).

@JohnMo Retrofit to a 20-year old 'individually built' property. Brick and block cavity wall but only with a 70mm cavity (fibreglass insulation), sat on a 100mm concrete raft foundation with 100mm EPS sat under the concrete, running with an LPG boiler. So not great for heat loss as mdern houses go. Want closer pipe spacings to give more flexibility for how we configure and run the system, and we like a warmer house AND we like carpets in reception rooms, as opposed to non-carpets in other big rooms.