Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Underfloor heating and energy losses

  1. Aug 7, 2016 #1
    If I have underfloor heating, whether the materials which is a better insulator on the floor (eg.a wood in relation to the ceramic tiles) affect on higher energy losses? Or the entire system will be more inert? It is assumed that the whole house is well insulated?

    I'm also interested in the same thing if the furniture is located in a place where it passes under floor heating pipes. Would it create a greater fuel consumption?

    Tnx for answers!
  2. jcsd
  3. Aug 7, 2016 #2
    I have never heard of such heating before. So is your house going to be somewhat like a vessel kept on a stove??
  4. Aug 7, 2016 #3


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    We have UFH in our house. Some rooms have wood flooring on top, others have carpet and some have stone/tile.

    Yes there is a small effect.

    Consider the heat balance... To maintain a constant temperature in the room the UFH has to deliver as much power to the room as escapes through the walls and windows. If it supplies more power the room heats up. If it supplies less the room would cool down.

    The amount of power flowing from the UFH into the room depends on the thermal properties of the floor covering and the temperature difference between the UFH and the room. If you put an insulator like carpet on top of the UFH you might have to increase the flow temperature to "push" the same amount of power into the room.

    If you increase the flow temperature this increases the losses flowing downwards into the ground. It can also have other effects, for example if you are using a heat pump then the COP (coefficient of performance) of the heat pump can depend on the flow temperature. The hotter the required flow temperature the lower the COP. If you are using an oil or gas boiler/furnace then increasing the flow temperature can also increase the return temperature. In extreme cases this can stop the boiler/furnace operating in condensing mode.

    None of this should be a problem in a well insulated modern house. However not all modern houses are well insulated. The building regulations in the UK are quite poor in my opinion. If a house was "well insulated" would it need a heating system at all?

    If you must have carpet in some rooms try and keep the total TOG value as low as possible (under 2.5?). It is possible to get special low TOG underlay (TOG about 0.6 or 0.7). Not all carpet salesmen understand the effect that carpet can have on UFH. Some told us that "all of their carpet was suitable for UFH". What they meant was that the UFH wouldn't damage the carpet. Some manufacturers make the same carpet with either hessian or rubber backing. The hessian version will probably have a lower TOG value than the rubber. However the carpet shop may have Terms and Conditions (T&C's) that allow them to supply either version!

    If you plan on having wood floor I recommend "Engineered wood" over UFH. This is typically 21mm thick (7mm of oak on 14mm plywood). Looks great and doesn't warp or cup like solid wood. You can use/risk wider boards if they are engineered than if they are solid. You can also get engineered wood in 14mm thickness but that might not be strong enough.

    It's hard to beat stone or tiled floors with UFH in a bathroom. Nice and warm in the winter and cool in the summer.
  5. Aug 7, 2016 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Its' not a problem for most houses but it could be an issue for badly insulated houses with small rooms. Put a lot of furniture and some rugs and you can have a problem getting enough heat into the room. Can be an issue for small bathrooms. How much active floor area is there if you don't put UFH pipes under the bath, shower and WC.
  6. Aug 8, 2016 #5


    User Avatar
    Science Advisor

    The majority of heat lost downward into the earth from UFH is lost along the edge of the floor slab where the distance to the exterior soil surface is a minimum. To reduce this fringing loss and better maintain floor temperatures near exterior walls you can put a 1 metre wide strip of 6 mm thick expanded polystyrene, (EPS), below the slab and footings. You do not need to insulate most of the floor area, only the strip along external walls. It is not something that can be retrofitted, you must think ahead.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted