First Floor UFH - Role of Subfloor Insulation

[Adsibob]

Are you sure you don’t have air in the pipes?

[SanMan]

1 hour ago, Adsibob said:

Are you sure you don’t have air in the pipes?

How can you tell? Cold spots? It is much harder to feel for cold spots on a floor (compared to a radiator). And how do I bleed? Open the bleed valves on the manifold? Thank you. 

[Olf]

On 12/12/2022 at 07:04, SanMan said:

Also, 18 is the point it gets to and then the floor protection probe switches the heating off until the boards have cooled enough. It switches back once the temperature has dropped to nearer 17.5 - so in practice the room is rarely at 18 for all that long, but just under. 

My question is really: is my concern of heat loss into the ceiling void below valid? Or is it not worth upgrading the insulation and directing the heat upward as the room below is heated?

OK, that is a whole different problem then!

Adding insulation under the boards = it limits heat flow downwards = more heat stays in floor structure to flow upwards = reaching surface temperature quicker (=using less energy to achieve sufrace temeprature in that room, though kitchen will use more to maintaing temperature there). The same with changing flow temperature, fixing potential air blockages etc - they won't increase floor temperature, as it is capped by the protection.

Once you start with floor temperature of 27'C (regardless how achieved) and the room gets only to 18'C, that means energy emission from the floor at 27'C balances all the losses through walls and ceiling, with 18'C being equilibrium achieved.

From here I'm afraid there are only bad and worse choices:

- increase emission by increasing floor temperature (adjusting cut off threshold) - risky

- find and fix paths of heat escaping through the walls and ceiling - tricky and potentially costly. You did mention celotex in the loft, but how well laid? UPVC window, but how well fitted? What is the wall structure, if filled cavity then how well? Thermal camera would be your friend here.

- if none of above then sit and wait for warmer weather, as then with the same floor output the losses will reduce and so equilibrium temperature increase. Addidtional heat source in the room necessary for cold periods like now.

 

 

 

 

 

[Adsibob]

1 hour ago, Olf said:

OK, that is a whole different problem then!

Adding insulation under the boards = it limits heat flow downwards = more heat stays in floor structure to flow upwards = reaching surface temperature quicker (=using less energy to achieve sufrace temeprature in that room, though kitchen will use more to maintaing temperature there). The same with changing flow temperature, fixing potential air blockages etc - they won't increase floor temperature, as it is capped by the protection.

Once you start with floor temperature of 27'C (regardless how achieved) and the room gets only to 18'C, that means energy emission from the floor at 27'C balances all the losses through walls and ceiling, with 18'C being equilibrium achieved.

From here I'm afraid there are only bad and worse choices:

- increase emission by increasing floor temperature (adjusting cut off threshold) - risky

- find and fix paths of heat escaping through the walls and ceiling - tricky and potentially costly. You did mention celotex in the loft, but how well laid? UPVC window, but how well fitted? What is the wall structure, if filled cavity then how well? Thermal camera would be your friend here.

- if none of above then sit and wait for warmer weather, as then with the same floor output the losses will reduce and so equilibrium temperature increase. Addidtional heat source in the room necessary for cold periods like now.

 

 

 

 

 

This is a good point. My own view is that manufacturers err on the side of caution and so a manufacturer's recommendation that the floor be limited to 27C is just an ideal case scenario. 29.5C or even 31C should be fine. I would start by making sure there are no draughts in that room and seeing if there are any other ways to boost the insulation of the walls, ceilings etc.

Then, if still no improvement, try increasing the limit to 29C and seeing if that makes a difference. If not, increase to 30C. Keep increasing until about 32C. After 32C I think the risk of floor failure become more realistic.

[SanMan]

19 hours ago, Adsibob said:

This is a good point. My own view is that manufacturers err on the side of caution and so a manufacturer's recommendation that the floor be limited to 27C is just an ideal case scenario. 29.5C or even 31C should be fine. I would start by making sure there are no draughts in that room and seeing if there are any other ways to boost the insulation of the walls, ceilings etc.

Then, if still no improvement, try increasing the limit to 29C and seeing if that makes a difference. If not, increase to 30C. Keep increasing until about 32C. After 32C I think the risk of floor failure become more realistic.

Thank you. We have a very expensive prime engineered oak floor, so I am very reluctant to raise the temp above the manufacturer’s recommendation - in fact, when the probe triggers a switch off at 27, the residual heat often takes a while to reduce and the probe reads as high as 28 - so increasing the cut off would really take it nearer 29 or beyond - not a risk I am willing to take. 

 

The system performed fine all last winter. I think there must be sludge in the loops or air. I noticed last night that the pressure gauge is slightly down on target and the “shot glasses” on the flow meters have black stuff in them, making them hard to read. No idea how to clear that without my plumber who is not getting back to me.

 

Thank you for your help. 

[Adsibob]

21 minutes ago, SanMan said:

We have a very expensive prime engineered oak floor

So do we. Laid as herringbone in two rooms and planks in three rooms and a hallway. Manufacturer and supplier insisted we couldn't exceed 27C. We have, by at least 6C and no disasters yet. But I agree with you that if you are seeing stuff in your flow meters, you need to get that fixed first.