Need help on concrete floor underfloor heating

[SDUGoten]

When I started renovating my house, I then found out the floor under the original wooden board is concrete and there is not enough space to put any insulation down there.  I think I have to install overlay style underfloor heating board something like Polypipe Overlay plus on top of the existing wooden board.   The questions are...

 

1.  Would putting overlay underflooring heating board without insulation down below would be enough for heating the house?

 

2.  I wonder what is the sizing of the combi boiler should I use?  The existing house have relatively new Greenstar 34CDI combi boiler for a 1000 feet terrace house (3 rooms).   I wonder if that is good enough if I am planning to do underfloor heating for 3 rooms on 1st floor and living room + kitchen on ground floor?  (Each floor has its own manifold and boiler is in the kitchen on ground floor)  Or do I need a even bigger combi boiler?

 

Thanks. 

 

 

 

Edited May 1, 2022 by SDUGoten

[Conor]

No. Stick to rads. Would be a criminal waste of energy. Only other thing I can think of is to remove the existing floor structure, clean up the slab, put down a DPM, 100mm PIR, UFH and 50mm liquid screed (assuming you've got about 150mm depth to work with). That would just about do.

[SDUGoten]

4 hours ago, Conor said:

No. Stick to rads. Would be a criminal waste of energy. Only other thing I can think of is to remove the existing floor structure, clean up the slab, put down a DPM, 100mm PIR, UFH and 50mm liquid screed (assuming you've got about 150mm depth to work with). That would just about do.

 

My house have a fairly high ceiling (2.5M+)  i wonder if i can place a 100mm PIR on top of the concreate slab and water pipe you saw in the picture , and then put underfloor overlay board on top, and finally put LVT on top of it?  Would that be sufficient to keep the insulation like that?

 

 

Edited May 2, 2022 by SDUGoten

[Nickfromwales]

7 minutes ago, SDUGoten said:

 

My house have a fairly high ceiling (2.5M+)  i wonder if i can place a 100mm PIR on top of the concreate slab and water pipe you saw in the picture , and then put underfloor overlay board on top, and finally put LVT on top of it?  Would that be sufficient to keep the insulation like that?

You'd have to build up the existing floor with a blinding layer, to make it snooker table flat. This needs to be immaculate work, and robust enough to not settle retrospectively, as it'll be what levels the whole floor and stops it caving in. I've been to many where the sub-floor prep has been ignored / not given the attention it needed, and I've been asked to rip the lot out and start again..........mostly insurance claims at that point due to the costs and inconvenience.

Can you dig out a core to see what thickness the concrete / screed (?) layer is and to confirm what is that you have to work with? You may find it's just a sub 100mm layer which could be removed easily.  

[Nickfromwales]

The bottom line is, there is no short-cut here. 

[Iceverge]

11 minutes ago, SDUGoten said:

My house have a fairly high ceiling (2.5M+)  i wonder if i can place a 100mm PIR on top of the concreate slab and water pipe you saw in the picture , and then put underfloor overlay board on top, and finally put LVT on top of it?  Would that be sufficient to keep the insulation like that?

You would need to alter all the doors ( internal and external ), the stairs would have a dangerous half step at the bottom, all the countertops would be the wrong height.  Your windows may be too low for Bregs. Unfortunately it's normally not a practical solution. 

 

Like @Conor says UFH is enormously wasteful without a well insulated floor. A u value of 0.16 is mandatory to install it in a new build in Ireland. This is about 150mm PIR. 

The concrete below the floor is probably only 50mm thick and could be removed very quickly. Otherwise stick to rads. 

[JohnMo]

On the boiler questions, if it's heating the house now, it will heat with an alternative heating system, as the energy lost from the house will not change.

 

Unless of cause you do UFH without suitable insulation below the pipes, then loads of energy will be pumped into the ground under the house, as that would be the easiest path for the heat to travel.

[Nickfromwales]

Will deffo need a sizeable buffer tank too, so when DHW is being drawn for extended periods of time ( drawing a bath / showering back to back in the mornings ) the UFH has a reserve to draw from. That would be a minimum of 150L, but bigger would be better say 200L. Remember that a combi cannot deliver heating whilst producing DHW  

[SDUGoten]

2 hours ago, Iceverge said:

You would need to alter all the doors ( internal and external ), the stairs would have a dangerous half step at the bottom, all the countertops would be the wrong height.  Your windows may be too low for Bregs. Unfortunately it's normally not a practical solution. 

 

Like @Conor says UFH is enormously wasteful without a well insulated floor. A u value of 0.16 is mandatory to install it in a new build in Ireland. This is about 150mm PIR. 

The concrete below the floor is probably only 50mm thick and could be removed very quickly. Otherwise stick to rads. 

 

What about 1st floor?  1st floor won't have space for insulation right?   So, there is no need for insulation for 1st floor if I am installing underfloor heating on 1st floor too?  Thanks.

[SDUGoten]

19 minutes ago, Nickfromwales said:

Will deffo need a sizeable buffer tank too, so when DHW is being drawn for extended periods of time ( drawing a bath / showering back to back in the mornings ) the UFH has a reserve to draw from. That would be a minimum of 150L, but bigger would be better say 200L. Remember that a combi cannot deliver heating whilst producing DHW  

 

Even with 2 port valve to splitting from the manifold , the combi can't delivery heating while producing DHW?   Do you meant that if I have underfloor heating turn on, I won't have hot water for shower?

Edited May 2, 2022 by SDUGoten

[SDUGoten]

6 hours ago, Conor said:

No. Stick to rads. Would be a criminal waste of energy. Only other thing I can think of is to remove the existing floor structure, clean up the slab, put down a DPM, 100mm PIR, UFH and 50mm liquid screed (assuming you've got about 150mm depth to work with). That would just about do.

 

Could I use something like this works?  Those foil insulation which is thiner

 

https://www.superquilt-insulation.co.uk/product/ybs-superquilt-for-roofs-walls/?attribute_size=1.2m+x+10m+Roll

[Nickfromwales]

23 minutes ago, SDUGoten said:

 

Even with 2 port valve to splitting from the manifold , the combi can't delivery heating while producing DHW?   Do you meant that if I have underfloor heating turn on, I won't have hot water for shower?

A combi cannot deliver heating and hot water at the same time. It has an internal diverter which chooses either one. DHW ( domestic hot water ) takes priority, so if you turn the heating on at 07:00 and get up, and 3 people take a 10 min shower each, the heating will be off, and the house remain cold, for that 30 plus minute period.

27 minutes ago, SDUGoten said:

 

What about 1st floor?  1st floor won't have space for insulation right?   So, there is no need for insulation for 1st floor if I am installing underfloor heating on 1st floor too?  Thanks.

As you'll already be inside the 'insulated envelope', you wont need the insulation on the 1st floor, quite the opposite. 

24 minutes ago, SDUGoten said:

 

Could I use something like this works?  Those foil insulation which is thiner

 

https://www.superquilt-insulation.co.uk/product/ybs-superquilt-for-roofs-walls/?attribute_size=1.2m+x+10m+Roll

A product with largely bogus claims. Every mass builder would be going for this if it was any good. Pile of crap i'm afraid. 

[Iceverge]

3 hours ago, SDUGoten said:

 

What about 1st floor?  1st floor won't have space for insulation right?   So, there is no need for insulation for 1st floor if I am installing underfloor heating on 1st floor too?  Thanks.

@Nickfromwales beat me to it. 

 

In general, UFH is unsuitable for houses without very good insulation and airtightness.  Unless you tackle these first the UFH heating will be very expensive to run as it'll need to be on long before and after you need it due to it's slow response times. If you concentrate on heating the house only when you need to via high temp radiators or air heaters or similar with quick response times it'll be much cheaper to run. 

 

 

 

 

[Nickfromwales]

Yup. A sizeable investment would be required for this instance, and would still likely be the best of compromises. It will work, just not as efficiently ( cost effectively ) as conventional radiators.