Stones

Fair enough

I'm really struggling to come to a decision on which way to go. Cost wise, it doesn't look like there will be much in it (based on bonded installation taking longer than a floating installation), so it's really a case of what are the other advantages / disadvantages of both methods? We've covered heat transfer, and accepting there may be some minor difference but nothing significant, the only other two things I can think of are a springy feel if we float the floor as opposed to a solid feel if bonded, and secondly, that cooling the slab (if we found we had to) might be a little more problematic if we went with a floating floor - condensation issue between board and slab?

We currently have two industrial dehumidifiers running in our house. They went on about a week or so before the decorator was due and for the first day or two were pulling out 10 - 15 litres a day each. Vastly reduced now ( 3 or 4 litres ).

I wouldn't describe THTC as cheap by any means - we have it in the house we are currently renting: Heating control 9.34p / kWh, Standard energy 18.5p / kWh, Standing charge 14.09p per day Lowest standard rate available via online switch - 11.962p / kWh, Standing Charge 18p per day You have to be using quite a high % on the reduced rate to make any savings compared to a standard tariff.

Bit of a sweeping statement ? You qualified / explained the 'training' part which is fair enough, but are you seriously saying, that of the entire cadre of planning officers in this country, none of them have any design skills? And what do you actually mean by design skills? Being trained in something doesn't necessarily make you good at it or an expert. Equally some people have natural flare and ability, and I'm quite sure that it applies to design skills as much as any other walk of life. Are you saying only architects (or those with architectural training of some sort) are capable of producing a 'good' design?

I likewise thought about an inline heater, but came to the same conclusion. I couldn't see the point in introducing an additional layer of plant when I can deliver what I want from a single ASHP / Cylinder package. We all want to save money and minimise our energy consumption, but I think there are some things where comfort and convenience are more important, and having plenty of hot water on tap, is one of those things. If it costs a little more / I use more energy / I use more water then so be it.

Sounds like the best plan to me, but if you did need to down the route of new cills, I had mine (2mm / 265mm alu folded cills) fabricated and prefer coated to match the windows by a firm in Glasgow for £12 per linear metre.

The Nibe we had in our last house had that ability. As you say, I think it's pretty standard function. The difficulty we found with storing DHW at a lower temperature than traditional systems, is that you run out when using the shower because of the differential required for the thermostatic valve to work. We had IIRC 210 litre capacity but this was only just enough for two showers. However, whilst there may not have been enough DHW for showers, there would still always be plenty of water left over 38C but under 48C available for sinks / basins. To get round this, we have opted to go with a 300 litre cylinder. We don't intend heating DHW to more than 50C using our ASHP. I'm more than confident that the heat pump will be able to cope with this, albeit at a slighty reduced COP. Having number crunched, I don't think there is much (if anything) cost wise if we were to go the other route and simply preheat with a heat pump and top up with immersion / inline heater as a matter of routine. We will have a fortnightly legionella cycle via immersion top up.

Is your Maple bonded down or floating?

Hmmm, would you say random lengths are best avoided? I know a floated floor would have some 'spring' in it as opposed to a bonded floor.

That's what we have done. I didn't like the idea of the access requirements when they came in (primarily I think because of the truly horrific looking efforts being constructed in the early days), however, having lived with level access in a number of houses now, I have grown used to the practicality of them Great when the kids were young, and casting my mind back seeing my parents struggling to get a wheelchair bound relative out of the house down just one step,convinced me that it really is a small price to pay. If you really want the visual appearance of a grand stepped entrance, put the level access at an alternative door.

Still not made up my mind on this. What little I've been able to glean online hasn't really helped. I'm guessing that bonding down a floor is going to take longer than floating a floor. Anyone like to hazard a guess on exactly how much longer per m2?

I've had a look for some data about how much of a difference there is in respect of heat transfer but can't find anything meaningful. Looking at various timber flooring suppliers, the bonded option seems to be favoured, whilst the UFH suppliers I've looked at seem to recommend a floated floor in preference to bonded.

Good point, last house we rented had a mix of tile and carpet over UFH, and there was a slight variation in how warm the rooms felt, although I do think that wind direction (and consequently wind induced heat loss) had a far greater impact on how rooms felt. The house will have a mix of tile (kitchen, utility, vestibule, bathrooms and a small downstairs space, the rest timber flooring (inc bedrooms). Bedrooms have been zones but the rest is to be controlled by the master stat. Bathrooms and utility being slight warmer not an issue for us, and the kitchen is open to the main room, so in reality probably not that great an issue. The plan is to operate the UFH such that the pump circulates regardless of whether heat is being called for to try and maintain an even a temperature as possible.

Thanks Dave, They have proposed an underlay specifically for UFH, and I've no doubt it will work, its really a question of how well it will work, and given the low flow temperatures we usually discuss for new well insulated builds, is it really going to make any difference if the heat transmission isn't quite as good when compared to a bonded down floor. Easier and cheaper to lay, and if it did ever need to come up a lot easier to remove.

In my local builders merchant today looking at flooring, and they had a rather nice engineered board at a good price. The difficulty is that this particular board has a 'clic' fitting system, making it unsuitable for bonding to our concrete slab. I have always been under the impression that the best solution with timber flooring over (wet) UFH was to bond it down with a flexible adhesive, however, floating a 'clic' floor in conjunction with the appropriate underlay does appear to be another (and seemingly quite popular) option. Instinct tells me heat transfer is going to be better if the wooden floor is fully bonded down to the concrete slab, but what in reality is the difference likely to be if we opted for a floating floor? Poorer heat transfer and slower response time, but as we are planning to run the slab 24/7 at low temp would this really be an issue? Thoughts?

One of my friends did exactly this, worked well and no issue with BC.

I'm using the Amvic system. The choice of this system is purely down to the fact it is the system used by my builder (and the other ICF contractor working up here). Whilst it doesn't have a 'passive slab', all the feedback about running costs that I obtained from people living in houses built with this system led me to the conclusion that it wasn't worth worrying about. My builder did go down to an awareness session for another system a few months ago, but has yet to make the switch, the main issue being that the premium charged for the time / labour saving differences (passive slab / additional insulation slotting into core) is significantly more than the actual financial savings to the builder / his clients.

The plan is to landscape around so only the lid is showing, but until we reach that point, I can't say for certain - digger driver currently off work walking wounded

It's a very good point that you make about storing DHW at lower temperatures requiring a larger cylinder. We had 230 litre DHW capacity in our last house, stored at 49C. Enough for 2 showers, but not much more, hence my decision to increase capacity up to 300 litres. Storage temperature was dictated purely in terms of the minimum temperature required to allow thermostat shower mixers to produce a hot enough shower.

Had the same nonsense at my last workplace. A large amount of old office furniture (25 years old) was replaced at the end of the financial year. The caretaker stacked all of the old furniture at the back for with a sign saying help yourself, which staff duly did, until someone from admin said this wasn't allowed and it could only be sold or disposed of to a licensed operator. I actually tried to buy a couple of desks but they couldn't even decide how to charge and wouldn't accept offers. In the end they paid to get them removed...utter madness.

Did you have to prime the concrete in any way first?

John, like you I went round in circles with my DHW and heating provision. In the end I decided to go with a Mitsubishi Ecodan ASHP and pre-plumbed cylinder. Several reasons for doing so. 1. Having done my heating calcs and knowing our DHW useage, I costed out a variety of different solutions. ASHP had the lowest running costs and over both a 10 and 15 year period had the best return on capital. 2. The ASHP system I have chosen can be programmed (easily) to provide cooling if required 3. A bolt on kit is available for the pre plumbed cylinder which would allow the installation of a secondary heating circuit if we find we need a wet duct heater / cooler for the MVHR ductwork or went for a fan coil heater. I'm planning to heat my DHW to 50C (legionella regime every week). With a 300 litre cylinder, this should give us more than enough for our requirements relative to our usage pattern, without the need to top up using immersion or an inline heater - I'm happy to accept the reduced COP for DHW. A 300 litre cylinder also gives me options should I choose to put in some Solar PV and a diversion device at a later date. We had planned a WBS, but I finally managed to persuade my good lady that it wasn't going to be needed, and in any case, there are not that many trees up here to burn!

This is what we did in our last house and will be doing in the one currently being built. Works really well.

Useful tip, thank you.