I want my underfloor heating system to be very responsive so I don't want to lay it in a screed but instead use something like Wavin Thermoboard layed between battens on top of a chipboard floor. The final floor will then be floated on top of the battens.

Products such as Thermoboard are essentially a 50mm (or less) insulation board with grooves routed into them for the UFH pipes. The posh ones are foil faced with the foil extending into the grooves so that the foil acts as a heat diffuser. The cheaper ones use aluminium spreader plates inserted into the grooves.

They do exactly what I want but they cost a flipping fortune. For example, the list price of the Wavin Thermoboard product is about £45 per square metre. Ouch!

Given that there doesn't seem to be that much to them, how difficult do you think that it would be to make your own? My plan would be to take something like 50mm Celotex GA3000 (approx £5 per sq m), use a router to put some pipe shaped grooves in it and then lay the pipes in the grooves, pushing some thick foil (e.g. Bacofoil extra thick) into the grooves as the pipe goes in.

The surface of the polystyrene will be in direct contact with the wooden floor above as it will be layed between battens exactly the same height. As a result. I wouldn't even bother to glue the foil down as I think that I would get the best contact that way.

What do you think?

Have a word with a metal basher and ask how much it would cost to form a groove into a sheet of ali or even steel.

Just out of interest, as you are building a well insulated house why are you not wanting to incorporate thermal mass. Quick response time is useful in areas with large temperature swings/very low thermal mass/variations in solar gain. Could play havoc with the COP (think you said you had a heat pump).

@steamytea - Yes it will be a well insulated house but it will face south and, in our current house (next door to the plot), we start cooking as soon as the sun comes out. We currently have storage heaters and it's a nightmare. We end up with the windows wide open while the storage heaters pump out heat that we don't want. I don't want the floors in the new house to act like our current storage heaters.

The metal plates don't seem to be the expensive bit. It's the boards that seem to be a ridiculous price. One option is to rout my own boards and buy in the spreader plates. I am keen on the foil idea, though, as one of the selling points for the foil faced boards is that you don't get the ticking noises as the plates expand and contract.

aa44
We manufacturing heating and cooling boards (plasterboard,fermacell....), not too difficult if you know the right way to do it. If you have a CNC router is easy if not you have to make some sort of template I think (can take long).Depending on the floor size : you can make it cheaper or not.If you have lot of free time you should do it even if is no more than 100m2(the set-up time is almost same for 20m2 or 300m2)

Posted By: chuckeymelt the right sort of groove

Not recommended with PU foams and a definite no no with PVC.

A former made from a rod a few inches long, welded to something that can be bashed with a mallet may work, will end up with arms like a blacksmiths mind

A suitably bent piece of piano wire in an "instant heat" soldering iron can cut foam but its need a guide. I've used one of these to cut slots in model aircraft wings.

How important do you think it is to have the channel U-shaped at the bottom?

A simpler way to do it might be to take two 15mm boards and cut one of them into strips, say 200mm wide. You could glue these to the top of the other board leaving a 15mm gap for the pipe. Again, you could lay foil into the groove as you put the pipe in. One snag that I can see with this would be whether the pipe would stay in position as it was being laid.

@cwatters - I think that the OSMA UFH profile and Thermoboard are the same thing. They have rebranded all the UFH stuff as Thermoboard.

Is the plastic layer attached to the board over the foil? Could the same effect be achieved by laying a thin plastic sheet over the whole thing after the pipe was laid into it?

I think the U shape is important because the pipe should have a contact with a heat spreading layer(as big surface as big is possible) , more contact more efficient system.

Posted By: aa44we start cooking as soon as the sun comes out. We currently have storage heaters and it's a nightmare. We end up with the windows wide open while the storage heaters pump out heat that we don't want. I don't want the floors in the new house to act like our current storage heaters.

I don't think this is right. Your storage heaters are at their v hottest first thing in the morning - a massive/UFH wd be at its coolest (within its narrow temp-range band). When solar gain suddenly begins, on top of cooking, a massive floor wd stand the best chance of soaking that all up whilst keeping its cool (no htg system input to the UFH meanwhile, of course). A lightweight/UFH would rise rapidly in temp from solar gain plus cooking, and start radiating and convecting into the room. Your thinking, of using lightweight/UFH in the old way, of constantly adjusting output from max to zero and points between, in order to control rm temp minute by minute, wd only work in this case you're describing, if the lightweight/UFH cd also act as a cooler - i.e. circulating stone-cold or refrigerated water when cooling's needed. But that's not feasible, and you're not suggesting that.

Nett emission is roughly proportional to (*not* proportional to 4th power of) the temp difference between emitting surface and room.

For a couple of hours after your lightweight/UFH floor has finished absorbing significant morning solar + cooking heat (with the htg system not supplying heat to it), its body and surface temp will start quite high, and decline, as it emits all that absorbed heat fast into the room in a short burst - all of it dumped into the room (causing overheating) by lunchtime, with nothing left for afternoon/evening.

Whereas after a heavyweight/UFH floor has finished absorbing significant morning solar + cooking heat (with the htg system not supplying heat to it), its body and surface temp will be only slightly raised, so will emit all that absorbed heat only slowly into the room, in a long steady trickle that will only finish next morning, helping to keep the house warm in afternoon/evening and keeping the chill off overnight even if the htg's switched off.

The point of a heavyweight/UFH is that it maintains a fairly constant temp come what may, solar gain, whatever, and the room temp is pretty well locked that, come what may.

Solar heat coming in thro glass of course makes you feel hot if your body is getting it directly - but solar heat coming in thro glass doesn't raise perceived room temp (either radiant temp or air temp) until and unless the solar heat first warms up the surfaces it falls on, which in turn begin to warm up the air.

So if incoming solar heat does not have the effect of warming up the surfaces it falls on, then it won't raise perceived room temp.

Two ways to achieve non-warming of incident surfaces -
1) cool them, so the incoming solar heat is removed as it arrives (either to useful storage elsewhere, or to be 'wasted' by refrigeration)
2) incident surfaces are so massive that incoming solar heat takes a long time to warm them up - the body and surface of a massive receiving surface of course absorbs all (or most) of the energy that's falling on it, just as a lightweight receiving surface does - but the resultant temp change is small and slow in the massive case, large and quick in the lightweight case.

With lightweight/UFH, you will be much more likely to get solar overheating than with heavyweight/UFH.

@jules - The Polyplumb boards look a possibility but I think that you might need to rout another groove in every 150mm. As supplied the pipe grooves are set at 300mm centres which, according to the Polyplumb literature produces about 70 w/m2 at a flow temp of 60C. I want to use a heat pump so I want the flow temp to be as low as possible. One of Polyplumb's other systems, called Overlay, looks attractive but is still pricey at about £20 per sq m. The Overlay system uses 12 mm pipe at 150mm centres and supposedly produces 100 w/m2 at flow temps of 45-50 C.

I'm hoping that we are going to need very little heating. The walls will be about U 0.15 and it should be very airtight with a decent (90%) MHRV system taking care of the ventilation (apart from when I have to open the windows!).

Your comments do make me wonder whether we ought to try to achieve passive house, though. I am looking at a cost of over £10k to put in a heating system that I'm hoping not to use very much! It would be a huge leap of faith not to put any heating in up here, though.

aa44, that'll please tony! When top-up heating gets that small and occasional, you can just plug in a fan heater with a clear enough conscience.