Overlay UFH on existing uninsulated concrete slab with new gas boiler, worth it?

[BenB]

Hi all,

I have just moved into a four bed 1960s detached house and the heating is at the end of its life. I am planning to replace everything with a system boiler and an unvented hot water cylinder.

For the ground floor, I am torn between radiators and wet UFH. The floor is an existing concrete slab and I assume it has no insulation. I do not want to dig it up.

The finished floor will be a mix of LVT, engineered wood and tiles. I am looking at low profile overlay UFH systems with a thin insulation layer, for example Nuheat LowPro or Omni, that claim they can be fitted directly over the slab, I have a ceiling height of 2.43m.

Has anyone fitted insulated overlay UFH over an uninsulated slab with a gas boiler, and was it actually efficient in practice, or did you end up wishing you had gone with radiators instead?

Many Thanks, Ben

[JohnMo]

UFH either do lots of insulation or none, thin is the worst of all worlds.

 

But - If you do none, you really need the heating on 24/7 otherwise the floor heat just moves into the ground and dispersed, each time you start stop you waste huge amounts of energy.

 

Simple, do low temp radiators. Get a decent boiler that will do priory domestic hot water (PDHW), this will allow boiler to run high temperature for DHW and low temperature for heating to get optimum efficiency.

 

If you are getting a new cylinder, get one with heat pump heating coil, this will reduce heating time of cylinder and again also get efficiency from boiler.

 

Or get a heat pump connected to max 35 deg flow temp system.

[BenB]

Oh thanks, if I did insulate what spec would I likely need to put down?

[JohnMo]

7 minutes ago, BenB said:

Oh thanks, if I did insulate what spec would I likely need to put down?

Very minimum would be 100mm of PIR, then screed. But ideally 150mm+

[SimonD]

2 hours ago, BenB said:

Hi all,

I have just moved into a four bed 1960s detached house and the heating is at the end of its life. I am planning to replace everything with a system boiler and an unvented hot water cylinder.

For the ground floor, I am torn between radiators and wet UFH. The floor is an existing concrete slab and I assume it has no insulation. I do not want to dig it up.

The finished floor will be a mix of LVT, engineered wood and tiles. I am looking at low profile overlay UFH systems with a thin insulation layer, for example Nuheat LowPro or Omni, that claim they can be fitted directly over the slab, I have a ceiling height of 2.43m.

Has anyone fitted insulated overlay UFH over an uninsulated slab with a gas boiler, and was it actually efficient in practice, or did you end up wishing you had gone with radiators instead?

Many Thanks, Ben

 

There are some articles out there that talk about this. If using over-lay, then it must be one that uses an insulated backing such as pir. In effect, this creates a decoupling with the slab and as it increases thermal resistance to the slab, it pushes it upwards instead. However, you need this to be properly calculated by someone who knows what they're doing because floor down losses also depend on the shape of the floor and external sides.. It's probably going to be better than over-lay on a suspended floor, but neither are that ideal into uninsulated floor. 

 

The other thing you need to consider is that you'll be raising the finished floor height and this will have an impact across your entire house and will also impact your stairs, which may need modification to still comply with building regs. 

[saveasteading]

@BenB all the above is right and sensible.

 

If you have gas,  stick with gas.

 

Ufh on an uninsulated floor is throwing heat away. Modern rads will be much better than what you are taking out.