Retrofitting - UFH - Wundatherm Rapid Response vs Screed kit

[agamemnon]

Hello,

 

We are considering to get rid of our radiators and wanted to retrofit UFH, we want to go ahead with Wunda's products and I wanted to double check what the difference is with using the board based Wundatherm rapid response, against the Screed based kits? As the screed based kits are cheaper, can they be used for a retrofit? Any advantage vs disadvantage of one system over the other apart from the costs?

[JohnMo]

Whatever system you go with ensure your insulation below the UFH is good.  Otherwise you will be pumping plenty of heat into the ground, which be costly.

 

If your floor isn't well insulated, UFH is not a good solution.

 

Basically the rapid response is cut boards with a reflective foil and your floor covering is attached directly to the board.  The pipes are therefore close to the surface, so heat to room is quite quick.

 

Screed system is buried in a screed layer, the thicker the screed, the slower and more stable the heat is.

[agamemnon]

Thanks

 

So with a room height of 2.4m what kind of insulation would I be looking at. Reading this forum values of 100mm are being mentioned which means 10cm, but I am not sure if that is in a new build house or a retrofit. 

The flooring is concrete, bitumen DPM and then marley tiles as floor level. 

 

It would be good if there is either a tagged threat, which would be a tutorial of what to look for, especially as different values including delta and so on are thrown around. I am not familiar and would like to know what they mean.

 

I am able to measure the volume of a room, and the BTU, but not sure how that translates to UFH.

 

[JohnMo]

UFH doesn't care if it's a new build or old house.  So the basics are

 

Pipes in the floor circulate water from a manifold, which will include a mixer valve and pump.  The mixer valve determines the flow temperature through the pipes.  The pump circulates the water around the UFH system.

 

The higher the room heat loss, the higher the flow temperature has to be to get and keep the room at the required temperature.  This is where a good or poorly insulated floor comes in to play.

 

Couple of things to remember, the ground below your house is always at or around 8 degree C.  Heat likes to travel towards cold, the colder it is, the quicker it tries to get there.  The water flow temperature can vary between around 25deg for a well insulated house and above 40deg for a not so well insulated house.

 

A well insulated floor will ensure most of the heat travels upwards in to the room. As the insulation will slow down the downwards travel.  A poorly insulated floor, will do the opposite, most the heat will flow down towards the 8 deg ground, rather than the 20 deg room.

 

The delta T, delta just means the difference between two values.  So the delta T in UFH is the difference between the water going in to the UFH pipes and the temperature of it coming out.  

 

The energy your UFH gives to the room is managed by setting a mean flow temperature, which is the mid temperature between the flow and return temperature going into the UFH pipes.

 

So as an example, your mixer is set at 40 degrees, the return temperature is 34 degrees.  So your delta T is 6, your mean flow temperature is 37 degrees.

[agamemnon]

Thank you. So, how do I decide about the thickness for the insulation below the UFH? 
 

Prior to our decision of wanting the UFH, we bought 5mm XPS, and 10mm laminate, the wunda system which is 16mm, a insulation thickness 10mm? And then dpm plastic sheet?

[JohnMo]

How old is your house? It may already have some floor installation?

 

5mm XPS isn't very much insulation.  Ideally you would want 10 to 40 times that, but that would not be practical.

 

I would go online and look up a floor u value calculators and play with that.

 

That will tell you the floor u value, which is the amount heat you loose downwards in watts per m2 per degree.

 

So if you have a 30 degree mean flow temp, the ground is 8, you have a delta T of 22.  If your U value was 1.0 your downwards heat loss from your UFH water flow will be.

 

22x1=22W per m2, so over a 8hrs a 30m2 area would loose.

 

22x8x30= 5280Wh or 5.2kWh

 

The same area with radiators and a room temp of 20degrees would loose

 

20-8=12 delta T room to floor.

12x1=12

12x8x30=2880Wh or 2.9kWh

 

As a real example my floor u value is 0.09. my flow temp is 27.

Delta T is 19.

19x0.09x8x30=410Wh or 0.4kWh.

 

 

[agamemnon]

3 hours ago, JohnMo said:

How old is your house? It may already have some floor installation?

 

5mm XPS isn't very much insulation.  Ideally you would want 10 to 40 times that, but that would not be practical.

 

I would go online and look up a floor u value calculators and play with that.

 

That will tell you the floor u value, which is the amount heat you loose downwards in watts per m2 per degree.

 

So if you have a 30 degree mean flow temp, the ground is 8, you have a delta T of 22.  If your U value was 1.0 your downwards heat loss from your UFH water flow will be.

 

22x1=22W per m2, so over a 8hrs a 30m2 area would loose.

 

22x8x30= 5280Wh or 5.2kWh

 

The same area with radiators and a room temp of 20degrees would loose

 

20-8=12 delta T room to floor.

12x1=12

12x8x30=2880Wh or 2.9kWh

 

As a real example my floor u value is 0.09. my flow temp is 27.

Delta T is 19.

19x0.09x8x30=410Wh or 0.4kWh.

 

 

 

The built is 1960s semi bungalow. From my understanding and looking at the old floor plans, it's concrete, screed, bitumen and then marley tiles. Doesn't look like any floor insulation.

 

I will certainly use the U-calculator. thanks for that.

 

My subsequent question is, I am thinking of going for the Wunda Rapid Response, which are 20mm thick, am I required to add  another layer of insulation below the boards? If I am adding another layer of insulation below the UFH boards, should I only consider the Insulation's U value of combine the Insulation and UFH boards?

I am certain, that I will use the board system instead of the plastic sheets and screed one.

 

My final question is, as there will be a 8-10cm difference in the height, should I have my doors bottom cut, or have the lintels above the doors moved higher up?

 

 

 

[Olf]

 

On 30/08/2022 at 21:52, agamemnon said:

We are considering to get rid of our radiators and wanted to retrofit UFH

 

What is driving this idea to start with? By now you see that your floor structure is not suitable for UFH, frankly contrary to the claim on their website 'So in comparison to a system using just radiators, it’s superior in insulation and will heat more sufficiently with better energy efficiency'. Don't get me wrong, I'm using the very same boards, but upstairs only and even that with in between joists insulation. For me it was to gain extra surface and room layout flexibility restricted by the radiators, so what get you hooked on UFH?

[agamemnon]

5 hours ago, Olf said:

 

 

What is driving this idea to start with? By now you see that your floor structure is not suitable for UFH, frankly contrary to the claim on their website 'So in comparison to a system using just radiators, it’s superior in insulation and will heat more sufficiently with better energy efficiency'. Don't get me wrong, I'm using the very same boards, but upstairs only and even that with in between joists insulation. For me it was to gain extra surface and room layout flexibility restricted by the radiators, so what get you hooked on UFH?

 

There were a couple of factors. Firstly as we going to have laminate flooring without any carpets we want a warmer floor, secondly it is more energy efficient, thirdly our pipes aren't in the floor but are mounted to the wall and coming down from the ceiling, so no more pipes. 

 

I disagree that it is not suitable, but it is personal preference. I may have to raise door lintels mainly, as calculating the u-value, the minimum thickness i require is 40mm. So overall size will be 85mm height changes in elevation, I am not fussed about ceiling height reduction as smaller volume to heat up, but mainly about the door heights.

[JohnMo]

11 hours ago, agamemnon said:

 

Secondly it is more energy efficient, thirdly our pipes aren't in the floor but are mounted to the wall and coming down from the ceiling, so no more pipes. 

Sorry but dream on, your downwards heat loss makes, UFH less than efficient.  Slightly oversized rads to run at a lower temperature would be more efficient, as the downwards heat loss is lower. Your boiler would operate in the same region as it would with UFH so it's efficiency would be the same.

 

Bury the pipes in the wall they are gone.

 

As you say it your choice, your money.  But seems a lot of work for higher energy bills for ever more.

[Olf]

11 hours ago, agamemnon said:

secondly it is more energy efficient

 

That is not true. UFH suppliers marketing juggles with numbers to their liking end end up with such statements (as I quoted in previous post) 

 

11 hours ago, agamemnon said:

thirdly our pipes aren't in the floor but are mounted to the wall and coming down from the ceiling, so no more pipes

You still need to run pipes from the heat source to UFH, add manifold and pump and there may be more pipes exposed than currently

 

11 hours ago, agamemnon said:

but it is personal preference

Not quite, Building Regs Part L claim otherwise.

Also with large losses downwards your system may end up so inefficient that you'll never reach a comfortable temperature indoors. At the same time using a lot more energy, with current £££ price tag. Is that preference?

 

11 hours ago, agamemnon said:

calculating the u-value, the minimum thickness i require is 40mm

Something is off with the calculations

 

11 hours ago, agamemnon said:

I am not fussed about ceiling height reduction as smaller volume to heat up, but mainly about the door heights

Depending on walls construction, that will be less or more, but still disruptive work  - on top of the mess and restrictions in using the space when laying UFH.

 

Imho using decent insulation under the laminate and going electrical mat under traffic areas for comfort/boost is the way to go in this case. If you're committed to butchering the walls to lift the doors, chasing to hide the existing pipes is a breeze in comparison.

[agamemnon]

9 hours ago, JohnMo said:

Sorry but dream on, your downwards heat loss makes, UFH less than efficient.  Slightly oversized rads to run at a lower temperature would be more efficient, as the downwards heat loss is lower. Your boiler would operate in the same region as it would with UFH so it's efficiency would be the same.

 

Bury the pipes in the wall they are gone.

 

As you say it your choice, your money.  But seems a lot of work for higher energy bills for ever more.

 

9 hours ago, Olf said:

 

That is not true. UFH suppliers marketing juggles with numbers to their liking end end up with such statements (as I quoted in previous post) 

 

You still need to run pipes from the heat source to UFH, add manifold and pump and there may be more pipes exposed than currently

 

Not quite, Building Regs Part L claim otherwise.

Also with large losses downwards your system may end up so inefficient that you'll never reach a comfortable temperature indoors. At the same time using a lot more energy, with current £££ price tag. Is that preference?

 

Something is off with the calculations

 

Depending on walls construction, that will be less or more, but still disruptive work  - on top of the mess and restrictions in using the space when laying UFH.

 

Imho using decent insulation under the laminate and going electrical mat under traffic areas for comfort/boost is the way to go in this case. If you're committed to butchering the walls to lift the doors, chasing to hide the existing pipes is a breeze in comparison.

 

Fair enough. Apart from running the u value calculations I did the calculations of running rads against uhf. Seems rads with better floor insulation is more economical. Thanks for the scrutiny.