Underfloor Heating and Carpets.

[peekay]

Guidance seems to suggest that specifically designed low tog rating underlay and carpets should be used to allow for efficient heat transmission, but is it really necessary in my situation?

 

Bit of background.... We have a wet UFH system throughout the whole house. Ground floor loops are laid on 150mmish insulation above the slab and set within a 100mm screed. First floor set within those cement board sheets with pre-routed loops then under 5-10mm of latex screed/self levelling compound. 

 

The house is very well insulated. Pretty much airtight with an MVHR system. 

 

We have an ASHP and the flow temperature to the UFH loops is about 35degrees. The whole house is heated to a constant 21 degrees 24/7. Each room is its own zone controlled by a thermostat and manifold.

 

We want carpets in the 4no upstairs bedrooms, a ground floor bedroom and ground floor sitting room.

 

Surely even if using cheaper standard thickness carpets and underlay the heat energy being transmitted to the room is the same, as there is nowhere else for it to go to. It still makes it's way though the carpet materials and in to the rooms, but may just take a bit longer for the room side surface to react and heat up/cool down, which I think as we keep everything at a constant temperature shouldn't really matter.

 

I would welcome any thoughts.

 

Thanks

[JohnMo]

We have standard carpet (wife insisted) and UFH underlay and it kills UFH performance pretty much. It's a bit like wearing a good overcoat on a cold day, you stay warm the cold doesn't get in. We run full weather compensation however.

 

But as you have thermostats run at a set flow temp, you may have to wack the flow temp up x degrees and it should work fine. You would need to fine a happy spot via trial and error.

 

Dig a bit deeper in your pockets and get proper carpet, dump your thermostats, run weather compensation and your energy savings will pay the extra needed for proper the carpets.

[Temp]

They recommend you keep the total TOG value to around 2.0 I think. You might get away with a bit more but how much is hard to say. There are special low TOG underlays that allow more to be allocated to the carpet.

 

Note that some carpets are available in two versions foam or Hessian backed. The small print in some contracts allows the shop to choose which they supply. Hessian has lower TOG but a harder feel.

 

 Go visit some carpet shops and ask about TOG values. If you get blank looks ask for another staff member or go elsewhere. Try out samples to see if the carpet and underlay with a low TOG are ok underfoot. Then you can decide if you need thicker.

[peekay]

25 minutes ago, Temp said:

They recommend you keep the total TOG value to around 2.0 I think. You might get away with a bit more but how much is hard to say. There are special low TOG underlays that allow more to be allocated to the carpet.

 

Note that some carpets are available in two versions foam or Hessian backed. The small print in some contracts allows the shop to choose which they supply. Hessian has lower TOG but a harder feel.

 

 Go visit some carpet shops and ask about TOG values. If you get blank looks ask for another staff member or go elsewhere. Try out samples to see if the carpet and underlay with a low TOG are ok underfoot. Then you can decide if you need thicker.

Thanks

 

We've looked in various carpet shops at the low Tog rated underlays and carpets. Have seen the 'keep beneath 2.0 tog total combined for carpets and underlay' repeated in many places.

 

 

I understand the need to use an underlay and carpet that will not be damaged by the heat from the UFH (degrading any adhesives or foam etc).

 

But my more general question of why does Tog rating matter in a sealed, insulated and consistently heated house with underfloor heating still stands.

 

I can understand the 'keep below 2.0' logic for a more traditional older style house heated generally by radiators at 60 degrees against the wall for 3 hours in the morning and afternoon, and only a small part of the heating system by UFH.

 

Lower tog carpets and underlays are generally thinner, less soft, more expensive and have a smaller range.

 

Is there any benefit in using a low tog system in my situation?

[garrymartin]

My notes say it's recommended to be not more than 2.5 TOG. Also in my notes, @JohnMo put it best from a physics perspective - "Insulated below at a higher thermal resistance to whatever is above the floor to ensure heat moves upwards not downwards".

 

So whilst the ground-floor bedroom and sitting room might be OK sitting on 150mm insulation, you may find that your chosen carpet provides enough insulation on the first floor that the heat radiates downwards instead of upwards.

[JohnMo]

We have 200mm of PIR insulation below our bedrooms and carpet, UFH will keep the rooms circa 18, we open the doors if we want them the same temperature as the rest of the house.

 

You may flow up to 35, but surface temp is only a couple of degrees warmer than the room, most the heating season. A nice layer of insulation (carpet and underlay) just stops that temperature reaching the surface. Net effect is rubbish heat output. It doesn't matter how long you wait.