Foldyard

I found this bit of info which probably answers my question as regards whether a thicker wooden floor should cause a large increase in fuel bills: "The flow temperature depends on the required output and the chosen flooring. Normally, the flow temperature is 30 to 45 °C, and it should not exceed 50 °C. The flow temperature has a limited impact on the heat energy consumption. If the temperature is raised from 30 to 45 °C, heat energy consumption only increases by 6%, as energy consumption is determined by the difference between the flow and return temperature. It is only marginally more expensive to heat a thick plank floor than a thin engineered wood floor, but it takes a higher flow temperature to ensure the required surface temperature."

Yes but it only slows down the heat transfer. If the heating stays on constantly, then over time the extra layer of wood will heat up to the same temperature as the underlying layer, more or less, given that the two layers have the same conductivity and heat capacity. Or am I wrong? With your insulation example it takes longer for the heat to get through the extra layers so heat is being lost at a slower rate than the heat being added to the interior of the house.

I appreciate everyone's comments. I understand how various factors influence the efficiency of the system, but for the moment I am focussed on floor covering thickness. I am also thinking about it in abstract terms, which may not accord with experience. JohnMo said: "3. For a given heat flow into the floor (product of flow rate and dT). The more restrictive the surface finish is, the more difficult the heat transfer mechanism. So instead of transferring the heat from the pipe, to the floor, to the room (heat flow is restricted by floor covering), the return flow temperature stays slightly warmer, decreasing dT quicker than normal and shutting down the heat compressor sooner. Less heat is actually transferred to room." I get the bit aout "the more restrictive the surface finish it etc..." ie if the thermal resistance of the material is greater it may require more energy (and a higher temperature of the water in the pipes) to get the surface temperature to the 2 or 3 degrees above room temperature than a material with a lower thermal resistance. What I am struggling with is where you have a material of a given thermal resistance and them make it thicker. The material has the same thermal resistance and so heat is going to flow though it the same, whatever the thickness. You have an extra amount of material to heat up initially so it will take longer, but once it reaches an equilibrium temperature, I would have thought that the temperature of the water in the pipes would be more or less the same. I am probably wrong but I would like to understand why.

Well the carpet covering is not the same material as the tile or wood floor underneath. If it has a greater thermal resistance than the tile or wood then it might require a higher running temperature in the UFH to achieve the necessary surface temperature at the carpet/air interface, in which case there will be greater energy usage. Alternatively it may not be possible, as a practical matter, to achieve an appropriate temperature if the thermal resistance of the carpet is sufficiently high.

I don't think insulation under the screed is an issue. All materials on top of the screed will insulate to some degree, but that's not the point. If it is the same material only thicker it just means that it will take longer to heat up from a cold start. Once the temperature at the surface reaches the appropriate temperature, the energy usage should be the same whatever the thickness.

I have a wet underfloor heating system embedded in a screed. On top of the screed I have a plywood base and oak floorboards. The oak floorboards were kiln dried to 6% moisture to avoid movement. My heating is provided via a ground source heat pump. My heating bills have been much higher than those predicted when the gshp was installed. The installer says that this is probably due to the thickness of the wooden floor covering, rather than any problem with the gshp system. My take on it is that the thickness of the wooden flooring shouldn't have any (or more than minimal) effect on energy usage. It just means that the floor takes longer to heat up when first turned on. The amount of heat energy used is going to be about the same. SInce I have the heating on all the time (in winter) I don't see how the thickness of the wooden floor should make any difference. Anyone?

....but I agree it might be best to hide it

He doesnt need to. He is simply justifying the bill for his building services to me.

Thanks for the responses. I agree that if I were to hire scaffolding on its own, the hire of the scaffolding would not qualify see: 3.4.2 Goods on hire Goods hired on their own are always standard-rated. Examples include the hire of: · plant and machinery (although plant hired with an operator can be zero-rated where all the conditions in paragraph 3.1.2 are met) · scaffolding, formwork or false work (although the service of erecting or dismantling can be zero-rated where all the conditions in paragraph 3.1.2 are met) · security fencing · mobile offices But (i) I am not actually hiring any scaffolding and certainly not on its own; it belongs to my main contractor he is not supplying it to me. (ii) Even if my main contractor was hiring the scaffolding and using it to provide his buiilding service to me, it would be a cost component of the contractors supply and not something specifically supplied on to me.

I have completed a barn conversion and I am about to submit a vat reclaim 431C. My question relates to the information given in the invoices about the work done. My main contractor (MC) billed me weekly for labour and monthly for other costs ie materials, subcontractors etc. I was operating on a daily rate basis, so the MC would list on the invoice the number of workers of a particular skill eg bricklayers, ground workers, joiners etc, together with the daily rate for each worker and the number of days worked in the week. This is totted up to give me a figure for labour costs for the week. More often than not, there is not much if any detail on the particular jobs they were working on. Obviously bricklayers lay bricks but the invoice does not say that that the bricklayer was working on a particular part of the building. Is this going to cause a problem with reclaiming vat. It goes without saying that all the work is being done on the construction of my barn conversion, but does HMRC get anal about it and expect this to be spelled out in every invoice. As another example, the MC had its own scaffolding but would charge me a cost for using it on my build. Does it matter that the invoice does not say that it is being used in the construction of my barn? I would appreciate any guidance on this. Thanks