I have no knowledge of the system at all but the term ‘efficiency’ is similar to ‘sustainable’.
All other things being equal, i.e. the insulation levels and air leakages, adding or reducing thermal mass only effects the time that a room will get up to temperature and then cool down again, it will not effect the overall energy used. The overall energy use will be more affected by how you use it, i.e. the times you have it switched on/off for a desired comfort level.
Think of the tiles as a thermal damper, they will always lag behind the thermal input, less mass for a given SHC the faster they react.

Air-tightness and Insulation is the key if you are good at limbo dancing you can get so low that formal heating is no longer needed.

no and neither do I get cold or have a heating system --- I did put in some ufh pipes but they are not connected up

Here it is: Product is Lithotherm UFH tiles, made predominantly of crushed waste brick. As I say, I haven't used it in anger, just fnished laying the first system, but they claim relatively high thermal mass with exceptionally quick heat-up, and 30 deg C typical flow temp, so it's worth looking at. As is the wood-fibre insulation board we used underneath the tiles. Devil to put clips in though!

Position of the pipe is higher than usual, with the greater mass of the tile underneath the pipe, itself an unusual feature when most systems have the pipe dead against the top of the insulation layer. I'm looking forward to seeing the results...

Website is www.backtoearth.co.uk

Mm, I understand the theory ST, and I know this is an aside to the thread, but it may be worth spending a few minutes on this as it enters the edges of the comfort v economy debate. Thick screed slabs, unless they be in 24/7 public areas, are wasteful. Keeping UFH on constantly is wasteful. UFH was not designed as an economy measure, but a comfort one. The industry long argued that there was fuel saving due to lower flow temps, a little specious when the boilers back then were 82 deg C flow anyway, just to be mixed down. And having to stay on much longer due to the nature of thick slabs' heat requirements.

In a domestic environment, I consider thick slabs are wasteful, period. To argue otherwise is, to me, like saying that an ocean liner will use as little fuel as a speedboat, when constant, sometimes rapid, adjustments to course, often 360 degrees, are required. Not to mention halts for economy. Any extra distance that liner travels has been paid for in fuel somewhere along the line.

Let's displace another UFH fallacy - that it is cheaper to keep it on low than switch it off. (the Jet on take-off analogy, much better when its cruising) With a thick screed, that may be true, a problem of our own making, the tail wagging the dog - but economical it is not. We are questioning the very need to fly nowadays, not just the most economical way to do so. I am similarly questioning the need to keep UFH on as long as it is. CW's point of non-usage and waste feeds into this I believe.

My point: There is so much more room for error/overshoot with a thick screed, and given that multiple temperature changes are common in the UK, overshoot often does occur. Like the liner trying to stop or turn quickly, there is wasted energy here. We have fitted various generations of clever controls and it doesn't alter that fact, in my experience. I respect your right to think differently, but after 27 + years fitting diverse products in the UFH heating field, I have reached conclusions that lead me to believe that this company may be on the right track with their pipe-near-surface strategy, for quick response and thereby, economy, with lower flow temps and less thermal mass in the floor.

Ben
I agree with you that lower mass systems respond faster and therefore fit into out climate regime and lifestyles better. This is probably why we have used radiators filled with very hot water that are constantly cycling on and off, they respond fast to our changing environment.
But the question was it is it more efficient. This is really the wrong question. Should it have been "does it cost less to run than a higher mass system with out lifestyles and climate. Pedantic maybe, but this is why confusion exists.
Take the analogy of the ship versus boats, if they have to carry an identical load, which would be the best method to move that load in an identical situation?
I personally do not like the 'thermal flywheel' model to describe heating thermal mass. If is more like an clock but instead of hours and minutes has independent energy inputs and outputs, but, and this is the crucial part, it starts and stops at the same temperature not at the same time. So the minute hand is the energy input and whizzes around quite fast while the hour hand or the energy output, lags behind. When the minute hand stops the hour hand keeps moving until it has covered the same number of units (think of what one unit on a clock is, it is either 5 minutes or 1 hour depending on which had we look at).

Posted By: tonyFor intermittent heating ufh is not the better way to heat

I'd agree that UFH is a poor choice if we are talking about a poorly insulated house, with poor air leakage, an always available high temperature heat source (gas, oil, electricity) & no flow temperature control.

If we are talking about a well insulated airtight house with intermittently available heat sources (solar thermal, log burning boiler stove, Economy 7 ASHP/GSHP) then UFH could be a useful option. However, it is not a "bolt-on" solution. It needs to be designed with the house as a whole & thermal mass & flow temperatures need to be used to avoid over-heating. Simple on/off control strategies may not be appropriate & weather compensating flow temperature control may be required to avoid overshoot.

It's worth noting that a well designed underfloor heating system with appropriate floor coverings will require a relatively low flow temperature & a floor temperature only a few degrees above the required room temperature. If solar or other passive gains cause the room temperature to rise above the floor temperature then the heat output from the floor will stop instantly until the room temperature drops again, at which point the UFH automatically takes over.

But my main point is: I don't think you can look at UFH in isolation. Assuming you are using whole house heat recovery ventilation, the whole house needs to be kept at roughly the same temperature. If it's well insulated & airtight then it will only require a few kWh per day to keep the whole house at that temperature. So the question becomes: what is the most efficient way to deliver those few kWh into the house & at what time of day/night is it cheapest/most efficient to do it.

David

Hi Crusoe,

We had been looking at this system (also being promoted by DPS Heatweb) for many of the reasons you suggest for our extension, but had some concerns about the strength and stability of this system with individual clay tiles laid directly on insulation and ceramic tiles as the finished floor. How did the completed installation feel to you? Do you feel the tiles may move / crack with insulation compressing over time? How do you think it would stand up to heavy loads on the finished floor eg a heavy kitchen table or aquarium?

Gary

Gary/Colin: Bear in mind we haven't lit the heatpump or WB for a test yet - I was hoping for some feedback from a user myself to shorten the learning curve on user temps. As far as stability goers, it feels remarkably stable for what is essentially a floating tile cradling the UFH pipes.

I'll feed back in after a few weeks of operation - hope you're not in too much of a hurry....

What, like the household cat sitting on certain spots on the floor where the pipes are, so I know its warm enough....problem is getting said feline to regurgitate the info it has subconsciously absorbed. Could put a sensor in a mock furball in din-dins perhaps?

Seriously - what would you suggest that will A. Identify the difference between this UFH and A N Other and
B. Relate that to fuel consumption, bearing in mind that this will be fed, eventually, by heat-pump, WB stove and oversized solar array? Flowmeters, or Grundfos' excellent heat-recording device don't fit the bill here, so I think it is a case of user feedback plus an experienced eye coming to some conclusions.

Edit: Note on stability: With polystyrene/poron or celotex, this system would, IMHO, be a non-starter, but the insulation/sub-base is a dense wood-fibre insulating board, which doesn't 'give' like foam or poly. No surprise that the tile co sell that too....

I firmly believe in thermal mass plus reasonable insulation plus reasonable air tightness PLUS an thermally efficient house (cuboid) design.
We used to heat 3750 sq ft with one 2250 litre fill of 28 sec oil(kero) plus a wood burning stove in the front room.
I now heat with a log burning central heating boiler.
If the temp in the Hall = central location is 18 deg at night it will usually only have dropped back to 17 deg in the morning, in exceptional weather conditions 16 deg.
there is thick slab underfloor heating downstairs which acts as a hugh storage heater, and was designed to do so.
The underfloor runs for about two or three hours continuious in a 24 Hr period ( generally in the late afternoon) then gets switched off. This does not result in any excessive heat, because the floor can absorb the heat so provided.
The underfloor may exceptionally get a wee 1/2 Hr "dig" on a colder morning.
The radiator circuit is also on for about a 1/2 Hr in the morning and at bedtime.
It is a "buggers muddle" of a system........but hey it works.
The wifes various house plants absolutly thrive on the stable temperature.
I am currently investigating my options for insulating the roofspace better, preferably between the rafters. Blinking expensive though.
Cheers

Crusoe,
Yes thanks for reply, newish to this forum and very much a greenhorn to heating but learning, currently looking at uf options for a new build, was thinking of thin screed ~40mm but have seen this clay tile on www and I am curious. My thoughts being that in new build, close to but not passive, big thermal mass in the UFH is not needed, more so if house has good thermal mass already. Therefore getting a quicker response and the build retaining the heat... as you have said already But can we also run this at a lower temp which from my limited knowledge is key. What thickness is the wood waste board and is it fixed/stuck before laying the tiles? It is a good sign that you still need the belt by the way, when the work pants stay up without it then you are in bother

Posted By: LdriverMy thoughts being that in new build, close to but not passive, big thermal mass in the UFH is not needed, more so if house has good thermal mass already. Therefore getting a quicker response and the build retaining the heat... as you have said already

To benefit from the thermal mass in the slab, you need to minimise the thermal resistance between the slab & the air in the room. These clay blocks will not help.

I think they will help in a poorly insulated less than airtight hosue because they allow more responsive intermittent heating. However, I would question why quick response is required in a house with near Passivhaus levels of performance. Fast response times imply a powerful heat source. This is not necessary in a house which will only lose 1-2 degrees per day when unheated. Better to trickle the heat in using a cheaper lower power heat source.

David

Posted By: SteamyTeaIs the not dependant on how the house is used. It may be empty for prolonged but known regular periods (out at work) and heating then is unnecessary, so fast response my save energy even with a less efficient system.

Yes & with a house insulated to current building regulations & heated with a gas fired boiler there is no argument. Better to turn-off the heating when you're not there.

However, a near Passivhaus standard house with high thermal mass which only loses 1-2 degrees per day will lose, say, 0.7 degrees while you are at work. So the reduction in heat loss due to internal temperature drop will be minimal.

All of the heat loss will be taken from the thermal mass of the building & will need to be put back into the thermal mass of the building when you turn the heating back on. So the net result is that you've saved very little energy.

If you're using a gas fired boiler this becomes a bit academic, because the energy price doesn't depend upon on time of day. However, if you want to maximise use of solar you may choose for example to rely on passive solar/thermal mass during the day & run a ground source heat pump overnight on an Economy 7 tarrif to "top-up" the thermal mass.

David

David,
I think the clay blocks are under the pipes with floorcovering and screed on top as crusoe said. Therefore the resistance is much less than a traditional ufh screed of pipes under 75-100mm concrete.