Dreadnaught

Modifying what I said in my first post, I have just read a host of @TerryE's splendid posts about his own build and I am now persuaded by the merits of a Willis Heater heating the slab and the ingenious use of the slab as a heat store. Thus my my latest best guess for internal services or my build is to drop the ASHP and add a Willis heater and stick with UFH, E7, SunAmp (especially the new model with two temperatures, one of which is suited to UFH) with E7 and PV. And maybe plan for the possibility of a heat pump later if cooling turns out to be needed or if the economics of a HP is justified by realised space-heating requirements, which I suspect will be unlikely as I plan to build only a small-ish two-bedroom house. And even if cooling is needed, as @JSHarris said in a post, a cheap commoditised air-to-air HP may well be a wiser purchase particularly as the floor slab is probably not the best location for the delivery of cooling, given the nature of convection and the risk of condensation (which is probably small if well controlled and cooling is only by a few ºC). I admire the simplicity of this approach. It is just what I am seeking. And could require very little maintenance. As @TerryE well said, the only traditionally mechanical part will be the water pump(s).

Fair point @richi and well said. (should probably have skipped the bit in brackets). Thanks @JSHarris I have not read that. I will do so with interest, appreciated. I agree that Cochrane surveys are the gold standard. Jeremy, more generally I am impressed by your breadth of knowledge and that of many on this forum. I am learning a lot by following threads on a great range of diverse subjects (even the splendid sparring with @Fredd).

This PDF from Southern Water in my view summarises fairly the difference between (i) salt-based softeners, (ii) phosphate-based ones, and (iii) "physical-softeners". https://www.southernwater.co.uk/Media/Default/PDFs/2835b_WaterSofteners_A4Notes_Nov12.pdf (By the way, I hold a different view on the sodium-health issue, a more conventional one in line with that of scientific-advisory councils around the World. As far as I can see, the evidence is strong that a high-sodium diet leads to higher blood pressure, which in-turn leads to increased cardiovascular disease, all on a population-wide basis (@JSHarris result not withstanding). Cardiovascular disease is a major cause of death. (Degree in physiology and PhD in biochemistry). Interesting thread. I plan to add a salt-based water softener to my build, when I get to it (and a non-softened tap for in the kitchen for cooking/drinking). Having done so past research on water softeners some time ago, I am tempted to use an older design of softener, a single-tank type, and one that has a tried-and-tested mechanical mechanism for timing and managing the resin ionisation step (no power supply needed). My research suggested to me that the modern two-tank systems are a marketing gimmick. Anyone can tolerate a few minutes of hard water once in a while if one attempts to draw water while the tank is regenerating. The added complication of two tank system provide only that marginal benefit for rather more complication. Having said this, it seems from what I have read that most salt-based water softeners are low maintenance (other than feeding them salt), no matter the type, so its probably marginal.

Thanks all. Advice much appreciated.

A very interesting insight. Good to know. I have not started my build yet but I am a convert to the simplicity and speed of SIPs. I will be looking out for this issue. Am reading your blog and finding that to be very informative too.

Hi, Tom here. New to the site. I am a passive-house enthusiast, already planning designs for a new build but I have not even found a plot yet, so I am probably letting my enthusiasm get ahead of me. I aim to build a small home in the South East of England, probably around Hertfordshire or Buckinghamshire. I have no experience in building but have been reading intensively for a few months now and have learnt a lot from this site and many other blogs, including Jeremy Harris' and podcasts, including Ben Adam Smith's House Planning Help podcasts and by visiting houses on the Passive House open days. I am fully convinced that Passive House is the best way. And have been persuaded that SIPs above a floating concrete slab might be a good construction approach. For DHW and heating, my latest best guess for internal services is an ASHP, UFH, SunAmp with E7 and PV. Best regards, Tom