Retrofit UFH

[nwnw]

I've just arranged for quotes for installing an ASHP to replace our ageing oil-fired boiler.
I highly suspect they are going to come back and say that our radiators in the living space are too small and would need replaced.
For that reason, and for general comfort/insulation, I am considering retrofitting UFH for the living space.

The floor is currently wood on concrete, redone in 2006 and I assume uninsulated.  I would do an 'exploratory hole' to check this before proceeding!  The room is 5m x 4m.

My first thoughts are to lift the wood flooring, dig out the concrete to required depth (up to edges but not affecting founds), flatten with hardcore, lay insulation (100mm or 150mm PIR/PUR?) + DPM, lay UFH pipework and encapsulate in a 60-75mm concrete slab, re-lay wood floor.
I'm not sure that I would be able to have insulated upstands at the edges so I guess I would keep the UFH pipework inbound a bit more (500mm?) to reduce the thermal bridging.

Anything I'm missing or need to be aware of before speaking with installers/builders?
E.g. is it a good idea to be mixing UFH with radiators (in all other rooms)?

[JohnMo]

Obvious question, that's a lot of work, why not just install bigger rads (double or triple panels) or even a fan coil.

 

Your system will run at the temp of the highest flow temp rad, so zero gain in CoP.

[SteamyTea]

If you don't mind a bit of noise, how about plinth heaters.

Edited April 18 by SteamyTea

[Iceverge]

Or to confuse things further how about an air to air heat pump. 

 

Or to really confuse things keep the oil boiler and plough all the money into extra insulation, air sealing and mechanical ventilation. Preferably with heat recovery. 

 

It might end up making more environmental and financial sense.

 

 

[nwnw]

23 hours ago, JohnMo said:

Obvious question, that's a lot of work, why not just install bigger rads (double or triple panels) or even a fan coil.

 

Your system will run at the temp of the highest flow temp rad, so zero gain in CoP.

Ah, I was wondering that and have already asked the installer this question.  My assumption was that the flow temperature could somehow be reduced for an UFH loop.  I guess it just reduces the flow instead?

[nwnw]

15 hours ago, Iceverge said:

Or to confuse things further how about an air to air heat pump. 

 

Or to really confuse things keep the oil boiler and plough all the money into extra insulation, air sealing and mechanical ventilation. Preferably with heat recovery. 

 

It might end up making more environmental and financial sense.

 

 

I had quotes for exactly this a year or two ago.  Since then my oil-fired boiler has had numerous issues (to the point of needing replacement asap) and I've also realised that I can get a £9000 grant for a full ASHP (sadly no grant for air to air)!

The thinking behind the UFH was that it's also a chance to stick in 100-150mm insulation.  The heat demand survey shows a huge loss through the floor.

[nwnw]

20 hours ago, SteamyTea said:

If you don't mind a bit of noise, how about plinth heaters.

Direct electric?  I prefer the idea of a 4+ COP over the next 25 years.  🙂

[SteamyTea]

1 hour ago, nwnw said:

Direct electric

No, they are just fan assisted radiators that are small.

 

You can just plumb them in to the existing system.

 

https://www.plumbworld.co.uk/smiths-space-saver-ss55-hydronic-plinth-heater-with-brushed-steel-grille-1304-1261300

 

Edited April 19 by SteamyTea

[Super_Paulie]

For what it's worth I've got 2 plinth heaters, Smiths SS5. The heat they throw out is great, or at least the feeling of warmth is. I've got them as a backup incase the underfloor struggles in winter but they also can be set to just move air which is nice and cooling.

[SteamyTea]

29 minutes ago, Super_Paulie said:

For what it's worth I've got 2 plinth heaters, Smiths SS5

Is the noise intrusive, they show a low level 27 dB I seem to remember.

[Super_Paulie]

Just now, SteamyTea said:

Is the noise intrusive, they show a low level 27 dB I seem to remember.

On setting 1 you have to be right next to them to know they are even on. I previously had a SS7, which I got based purely on the wattage they move but it was too noisy for me, I've got tinnitus so really sensitive to noises and I just couldn't get away with it. Basically brand new in the box, tested for 5 minutes and that was enough for me. Even that is not particularly loud but it would drive me insane if I could hear it, the SS5 are borderline silent.

[Adsibob]

6 hours ago, nwnw said:

The thinking behind the UFH was that it's also a chance to stick in 100-150mm insulation. 

I would be surprised if you could take that much depth out of your existing concrete floor, without negatively impacting the structure in some way. Surely the concrete is doing something structurally.

 Do you have a cross sectional drawing of your construction or at least a year of construction and style/type of house? 

[SteamyTea]

7 minutes ago, Super_Paulie said:

tinnitus

Me to, since I was a lad.

You may want to read this.

 

 

[nwnw]

18 hours ago, SteamyTea said:

No, they are just fan assisted radiators that are small.

 

You can just plumb them in to the existing system.

 

https://www.plumbworld.co.uk/smiths-space-saver-ss55-hydronic-plinth-heater-with-brushed-steel-grille-1304-1261300

 

 

Ah, ok sorry.  Had a look at the SS5 and at 45degC ASHP temps it only puts out 0.6kW at the 'normal' setting (or 1.1kW at 70degC).  The existing double convector in my living area is rated at 2kW.  So I guess I would need at least 2.

I assume the heat from them is better distributed, given that it is blown rather than convected?...what are people's experience of this?  Or do they create a 'wind-chill' effect?

[nwnw]

13 hours ago, Adsibob said:

I would be surprised if you could take that much depth out of your existing concrete floor, without negatively impacting the structure in some way. Surely the concrete is doing something structurally.

 Do you have a cross sectional drawing of your construction or at least a year of construction and style/type of house? 

I think the floor was relayed in 2006 when the house was reconfigured.  The stone walls have been standing for 120 years before that so I think will be fine as long as I don't undercut the founds.  Although I guess given the age it was probably built straight on the ground.

 

[Super_Paulie]

1 hour ago, nwnw said:

Ah, ok sorry.  Had a look at the SS5 and at 45degC ASHP temps it only puts out 0.6kW at the 'normal' setting (or 1.1kW at 70degC).  The existing double convector in my living area is rated at 2kW.  So I guess I would need at least 2.

I assume the heat from them is better distributed, given that it is blown rather than convected?...what are people's experience of this?  Or do they create a 'wind-chill' effect?

 

Absolutely warm as toast. I'd imagine any pet you have would just permanently position themselves in front of it whenever it's on.

[Adsibob]

2 hours ago, Super_Paulie said:

I'd imagine any pet you have would just permanently position themselves in front of it whenever it's on.

Depends if the pet is reptilian or mammalian.

[Adsibob]

3 hours ago, nwnw said:

The stone walls have been standing for 120 years before that so I think will be fine

Sorry, I may have confused the issue with my question; how long the wall has been up is not relevant in that sense; ie longer is not necessarily better. The reason I was asking is if, for example, it was a Victorian terrace, or a 1930s semi, we could take an educated guess at its likely construction.

[nwnw]

5 hours ago, Adsibob said:

Sorry, I may have confused the issue with my question; how long the wall has been up is not relevant in that sense; ie longer is not necessarily better. The reason I was asking is if, for example, it was a Victorian terrace, or a 1930s semi, we could take an educated guess at its likely construction.

For reference it's a stone walled, detached house.  Built about 1880 I think.  Walls are about 50-55cm thick, I assume rubble filled.

My point was that the walls were there long before a cement floor was laid, so it should be in no way structural.  

If I was digging out then I would intend to taper in (45 deg?) at the edges and ensure that I am in no way compromising the wall foundations.

[nwnw]

The realisation that I probably can't lower the flow temperature as I still have rads in other rooms has got me thinking again about UFH.

I would still love to put some insulation in though - and this may help bring the room demand down such that I don't need a massive radiator (or multiple plinth heaters!).

 

Is there good insulation that can go directly under wood flooring?  There is a slight step down to the living area so I could install to 30mm without a massive impact.

[SteamyTea]

1 minute ago, nwnw said:

Is there good insulation that can go directly under wood flooring

Well Phenolic Foam is about as good as you can get, you may need to fit some battens to support the floor boards, but they will only be a relative small percentage of the floor area, so maybe some sort of high density plastic.

[nwnw]

44 minutes ago, SteamyTea said:

Well Phenolic Foam is about as good as you can get, you may need to fit some battens to support the floor boards, but they will only be a relative small percentage of the floor area, so maybe some sort of high density plastic.

I was assuming that you need special insulation for the compressive strength, but I guess the battens get around that.

Thinking further about this though...the battens will likely create thermal bridging points in the insulation so am I possibly better off with XPS or PIR that has greater rigidity and doesn't require battens?  Also easier to install and cheaper.

I see Kingspan Thermafloor comes in 30mm.

[SteamyTea]

You may be worth going for radiators as the thermal losses though only 30mm of insulation and then into the floor will be quite high.  You will need to run your flow temperature higher as well, which is never a good thing with wooden floors.

[nwnw]

19 minutes ago, SteamyTea said:

You may be worth going for radiators as the thermal losses though only 30mm of insulation and then into the floor will be quite high.  You will need to run your flow temperature higher as well, which is never a good thing with wooden floors.

I may be adding confusion.  If I was going for UFH then I would be digging out and installing thicker insulation. 

The 30mm was just to be laid on top of existing slab.  I'll need to recalculate the room demand based on the extra insulation to see if the rads need upgrading.

[Adsibob]

If you are going to go down the UFH route, you can put down 150mm of PIR and then 30mm to 75mm of XFLO FF boards, which can be routed with your own design for loops, or can come prerouted with standard pipe routes. On top of that you can lay engineered wooden floor. Will be rock solid, no battens required:

https://www.cellecta.co.uk/product/xflo-ff/

But keep in mind that if you are going to cut the concrete out at a 45 degree angle, then at the perimeter of the room you won’t have much insulation. That isn’t the end of the world, particularly if you have furniture up against most walls in any case, but not ideal.

 

how tall are the ceilings? Maybe dig the PIR into the concrete, but float the XFLO FF boards on top of the concrete to at least get some insulation at the perimeter.

Edited April 20 by Adsibob