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Hi Sorry, I have only just seen this. Still not finished. I am just getting to the stage of piping up my ASHP. Even without the heat on the foamed glass / limecrete does seem to have completely dried out the ground floor.

about 48 screws on a 8 x 4 sheet.

I have just installed some spreader plates for a wet UFH system. Due to the existing floor being uneven and noisy, I have build a framework of 3x2 CLS at 400mm centres. The attached datasheet gives heat output with two floor coverings - wooden floor or 10mm ply and carpet. Have I misunderstood this - the manufacturer is recommending 10mm ply as the deck on top of the spreader plates. I can understand that its best to keep it as thin as possible, but 10mm seems very thin. We have tried a sheet and put a lot of screws into it, but if you are between the centres, it does depress slightly. The small amount of deflection would probably not be noticeable, but I am concerned that this repeated movement might eventually cause the pipes to wear or fatigue. After the mammoth undertaking of fitting this system, I'd like it to last very long time and not be pulling up boards due to leaks in a few years time. So - am I worrying over nothing? Have I misunderstood the manufacturers spec? Has anyone used 10mm ply in this application before. If not, what should I use. I guess if I stick with ply I can keep it thinner than chipboard (22mm) as its stronger. 15mm, 18mm? Many thanks for any advice.

Whatever I was doing, I'd have laid the ground floor underfloor heating, as I needed a new floor, so its literally a couple of hundred quid extra to put some pipe in the floor. I have GF UFH in my solid walled Victorian kitchen and its great, so there is no way I wouldn't have incorporated this on the ground floor, regardless of the boiler type. However, I am kind of wed to the ASHP solution for other reasons - I've been given a Grant 6Kw invertor heat pump at cost price. We made a bit of a fag packet assumption that it would be a good size. Since my last post I have firmed up the calculations and I think our back of the fag packet calculation is vindicated. I have made a calculation for each room. Working out the thermal resistance / conductivity of the walls was a bit of guesswork, but I found a few academic studies where they measured this directly on loose rubble walls, so I have used this data. Most walls are insulated and there is a lot of insulation in the loft and beneath the slab. This means I have a loss of 3-4Kw depending on which U values you believe. I have likely been a bit optimistic, as there will be cold bridges and I have a chimney where the construction is a bit of an unknown. So I reckon I could add another 20 or 25% "contingency" on top of the calculated value. Although there is a lot of uncertainty, I think that the pump I've been given is an appropriate size. Or to put it another way; I don't really see how I can be any more accurate in my forecast, when I have such uncertainty on the construction methods! Where this has become a bit of an eye opener is the output needed per M2. In the upstairs rooms I am looking at 30-35 ish, which from what I can tell will require a flow temp of about 45C. This is higher than I thought I would need, and I assume will reduce the efficiency of my heat pump. I have tried to work out radiator sizes, but if assuming a flow temp of 45C, the delta T is only 15C, so there is a 0.7ish reduction factor, meaning that I would need big radiators. So whichever way I look at it (rads or UFH pipe), I will need a flow temp a bit higher than I initially envisaged. Sorry for the waffle. Does this sound reasonable? Will I be highly inefficient running at this flow temp? Forgot to mention, there will also be a 5kw log burner. My heat loss was based on a -3 outside and 20C inside. However, I think in all likelihood if it got that cold the log burner would be on. Just realised the above table says kw, but its just watts.

Its a shame the forum doesn't seem to allow photos, as you'd have seen the photos of the slab. There is about 400mm of a product called "foamed Glass" insulation under the limecrete slab. If you google "limecrete floor" you will get all the information on this. I believe that this will be suitable. We had already come to the conclusion that the spreader plates needed to be nailed up very tight. We were wondering about also putting some PU glue on them, to make sure they never try and come loose, but obviously this will be another mini layer of insulation. Any thoughts on this? It almost sounds as if you are saying that the spreader plate solution would never work very well, its always going to have to conduct heat through the floorboards, as they cant be nailed to thin air. I realised the upstairs UFH wont transfer the heat as well as the downstairs pipes encapsulated in the slab, but I figured that upstairs would also be getting some of the "heat rises" effect from the downstairs (which I expect to be a very stable warm temperature), with the bedrooms likely just needing a boost morning and evening. I'm finding this really interesting. I've heard lots of stories of people that have replaced a gas boiler with an ASHP through their existing rads, and it hasn't worked due to the rads being too small. I thought I was being smart in going all UFH to have the lowest flow temps, but you seem to be telling me I actually need rads?! I feel I should also reiterate, I have no mains gas (otherwise there would already be a nice efficient combi), so I am effectively competing with storage heaters. I only have a very small yard, so an oil tank or LPG would be quite difficult as well.

I realise that the ground floor slab will take a long time to get warm and a long time to cool. The first floor will have less thermal mass and will heat and cool faster. Are you saying that the UFH flow temp would also have to be higher on the first floor? How high can you go? I thought that you were limited to a floor temp of about 27C as it can damage flooring if it goes higher?

There is no extension, so all the walls are old. I have done some preliminary calculations on the heat loss. The house has 300mm of insulation in the roof. It is double glazed. The downstairs is 2-3ft thick stone walls with a loose rubble infill. The basic U value tables for these walls suggest they are very bad, but I have found a masters paper where they have measured actual values for these type of walls and they have found them to be significantly better than expected - I'd guess because there is all sorts of voids, sticks, brussel sprout stalks, straw etc jammed in the infil. The upstairs is a solid 9" brick, but with an air gap and insulated plasterboard. I may overboard this further with some more insulation. As old houses go I believe it to be well insulated, but there is obviously a huge margin of error in calculating the heat loss on a building with unusual construction such as this. I has assumed that with the low temperature flow from the ASHP that UFH would be best. I gather that if I go for radiators they need to be massive and potentially have the flow temp of the ASHP turned up higher?

Hi. I have a very old cottage which I am retrofitting with wet UFH. It is in a village with no gas, so heating options were limited to oil, LPG or electric. The cottage had a damp bitchumen floor, which needed dealing with, so I have laid a new "breathable" limecrete slab, complete with UFH pipes embedded. I plan to heat this from an ASHP. My Plumber (my brother, so I am not getting a new one 😊) doesn't do a lot of UFH, so this will be somewhat of a learning curve for us both. We have got some questions: I was going to do a zone for each room. However, I have been doing some reading and I believe this is now a bad idea, as small zones will make the pump cycle more. I have a 5 zone manifold. If I stick with the 5 circuits (2 downstairs and 3 upstairs) could I wire the actuators for the two circuits downstairs in parallel, so that thermally they were just one "zone", but using two circuits on the blending manifold. Could I then balance the temp in the different circuits by adjusting the flow through each one, as you would with a radiator? likewise could I then link the actuator wiring for the 3 circuits for the upstairs, so that these all open/close together? The upstairs wont be in a slab. The floor in two of the three rooms has been replaced with new joists and chipboard. I have the ceiling down. I was going to fit UFH pipe from below using the "fit from below" spreader plates. The third room upstairs still has the original oak joists and wide floorboards. The bottom of these are visible from the living room, so I can't use the "fit from below" type system. For this room I was going to use an overfit type board. Is it ok to mix and match both fitting types in the same installation? The floor is already not level and the overfit board will actually work in my favor in terms of levelling up the different floor heights. For the bathroom, originally I was going to put wet UFH under it, but I am now concerned that there might be times that you want a bit of warmth on the tiled floor in spring/autumn, when the rest of the system might not be on. Do I just fit electric UFH in this small room. On the face of it this will be more expensive to run, but if I end up having the ASHP cycling just to run this small room, then maybe it would be for the best. I am sure this question must have been asked before, what is the usual solution? Manifold placement. I have fitted UFH in my downstairs extension. Manifold placement was simple, as it is only in one room. In the cottage install I have ran the pipes that are already in my slab to the cupboard under the stairs. Now that I've done this I have some reservations! If I place the manifold on the ground floor, I will end up with a messy spaghetti, with the circuits going upstairs looping back on themselves. I wonder if I should have placed the manifold on the first floor, so that all pipes are exiting downwards to the circuit. Again, I am sure this must be a common question. Thanks for your time. Here are a few photos that might be of interest: Foamed glass insulation under the slab: Original part of the house with oak joists. The overfit system will be above this: 2ft thick walls with a rubble/earth infill: First floor brickwork in handmade bricks, this was behind a cement render:

Thanks for that. I assume the capacity of the system would only take into account the pipework to and from the manifold, as at any time any of the circuits off the manifold might be shut off?

Hi, this might be a basic question, but I am trying to spec out an ASHP system. My Brother has picked up a couple of grant inverter units, 6kw and 11kw. I need to do the heat loss calculations, but one of these should be suitable. I am reading through the installation instructions. The system layout shows a volumiser tank. There is a confusing (to me) statement that says you need one if your system doesn't meet the requirements, it then effectively goes on to state that all systems will need a volumiser tank of some kind, but without stating what "the requirements" are. My understanding is that they want a minimum amount of water in the circuit to prevent cycling on and off, so I was expecting to see what this volume was. Can anyone explain this better? As well as the cost of an extra item of equipment, its also the space to squeeze it in to such a small cottage!

It's not my soil, its my neighbors. Its not like they have built a muck heap against my house, its just the general ground level on that side of the property. Both are 400+ years old and I assume the ground level has built up over the years. French drain is something I have thought about, but I think will need their agreement. I don't think I can just march into their back garden and start digging. To complicate matters, the house is currently for sale and under offer. So I doubt they want me digging up the garden and potentially disrupting their sale. I plan to speak to he new owners. I suspect ground level is also high against their wall as well.

Lots of points raised above - I'll try and cover them all. Damp - the house was empty for 2 years. The guttering at the front was leaking and there is a back wall which is below the ground level of my neighbors garden. Some of the damp is localised to these areas, however all skirting boards were rotting at the base, where moisture was getting around the edge of the bitchumen floor, even those in the middle of the house. Its a little difficult to isolate how much of the damp has come about due to it being unoccupied (heating off and no ventilation) and how much is intrinsically to do with the construction. I am hoping that by addressing the aspects which are in my control, the finished house wont have any damp. Guttering is fixed and I plan to install a heated and breathable floor. The outstanding item that isn't within my control is ground level on the back wall. The new floor would be insulated beneath with 100-200mm foamed glass. Do people fit heated slabs with no insulation, I haven't heard of that before? Currently the house is a bit of a building site (ceilings down, loft insulation peeled back) so I don't think I'll be able to run the heat loss experiment, as its not representative. I can do excel, so I'll have a go with that. Here is an example of one of my stone walls. I have been repointing today with an NHL 2 lime. I am loath to box in something as old as this with rockwool / kingspan, I appreciate this might mean a compromise on the heating bills 😊 Before [img]https://i.ibb.co/zSpRPS2/IMG-20220329-083633.jpg[/img] After [img]https://i.ibb.co/b5Km3kx/IMG-20220409-164851.jpg[/img] Looks like my links aren't working.

I am currently renovating a very old stone cottage, dating (I believe) to the early 1600's. The property is in a village with no gas, and until recently had storage heaters. The property is currently empty. It has a solid floor which has been "sealed" with bichumen, but is causing damp around the bottom of the walls. I am going to install a new limecrete slab, to try and counter any damp issues, so it makes sense to install UFH at the same time. I believe the more constant temperature from the UFH will benefit the old property . I also have the ground floor ceilings down, so could even fit wet UFH under the first floor. At the beginning of the project I was going to run this from a small oil boiler, but then the oil price went crazy! It is essentially a 2 up 2 down small cottage. the ground floor walls are 500mm thick stone, although this is unlikely to be solid. I believe it is an outer skin and inner skin and loose rubble / earth infil. The first floor is oak timber frame with brick infill panels. The first floor has been "dot and dabbed" with insulating plasterboard. The roof has 300mm+ of loft insulation. The windows are double glazed. There is one chimney, which I am going to fit a log burner. My gut feeling is that it is quite well insulated, although the EPC gave it an "F" stating that it needs wall insulation on the downstairs walls. I am loath to do this both for aesthetic and damp reasons. I want the external stonework on show (and also some internally). I realise that running an ASHP non optimally can be expensive and cold, but I think the UFH and the fact that I am benchmarking (cost wise) against storage heaters or oil heating, will skew the sums in favor of the ASHP. I think I am at the stage where I need to get a better calculation of the losses from the building to determine the size of the ASHP I would need. (I have been offered a 10KW unit from my brother at a good price).I've had a quick look at working out heat losses. I am a bit confused because I have varying construction in different areas - stone, brick with dot and dab. Do I just work out losses for each room and add them up? To be honest I am very confused. Is there an idiots guide? I would also like to try and get a grant, but I think this wont be possible while I haven't got my stonework insulated. I suspect I could probably get my cottage listed, but this would seem like an excessive step to take just to become eligible for a 5k grant 😁 I would appreciate any advice.

Hi, I have just found this forum while doing some research on an old cottage I have recently purchased. Specifically I am looking at installing an ASHP, as there is currently no heating (well, there were storage heaters, but they are now disconnected). I think I'll make a post in the ASHP forum, although the topic is quite complicated taking in sympathetic restoration of an old building, lack of insulation, damp etc... Lots of fun!