marshian

The radiator with the highest mean temp would be the one that emitted the most heat (that might not be the highest difference)

He didn't say his floors squeaked He asked the question "would option 1 lead to squeaky floors?"

Just to show potentially how much a leaky cistern could hurt here's my water usage when I had a a cistern that was overfilling and letting water flow into the bowl due to a failing fill valve It was in a the downstairs toilet which is rarely used and was the only explanation for the increase in water usage The £ killer is not the billing for the water used it's the £ sewerage charge based on ~80% of the water used

@Nick Laslett have you got any pictures with the in roof install finished? I will at some stage need to strip my south facing roof to replace the felt (Old bitumen style felt from the 80's) I have a small stock of spare roof tiles from when I did the extension (I could still get the original tiles then) but the in roof solar PV looks like I could get away without trying to find seconds to match the existing tiles.

comes with wifi connectivity out of the box so all the parameters (boiler run time, cycles (starts) all avaliable - if the house heat loss is 8kWh at -2 I’d go for one of the OP’s selections because at 10 deg C OAT they would be a good match but if the OP’s heat loss at -2 was 4kWh I’d go for the viessmann - low and slow like a heat pump is a much better way to heat a house

Sheesh....................... I posted it because it's useful to have an expectation of what your return temps are likely to be based on a lowered flow temp. 30 Deg Boiler Flow Temp 20 Deg Room Temp You aren't going to get a DT of 20 and a boiler return temp of 10 Deg I think you need to consider the audience that the blogs are aimed at - mainly the general public / DIY enthusiasts It's a "rule of thumb" - a "guide" call it whatever you like it's not "Gravity" They do training sessions for Heat Engineers that are way more detailed

Unfortunately the three boilers shown compromise space heating min output by increasingly high min modulation I'd pick the smallest one on that basis Actually I wouldn't I'd go for a Viessmann 200-W and have a CH min modulation of 1.9 kWh regardless of how big the HW side was https://viessmanndirect.co.uk/Catalogue/Residential-Boilers/Viessmann-Combi-Boilers/Vitodens-200-W-Combi-Boilers/Vitodens-200-W-35kW-Combi-Boiler-Z020316 HW 17l/Min @ 60 Deg C for the 35kWh Combi CH Modulation range 1:17

Fix the leaking cistern - if the noise stops happy days that water leak could cost you a significant amount…….

Table generated by "Rule of thumb" Heat Geek article said As the controller causes the return temperature to drop and get ever closer to the room temperature, it becomes increasingly more difficult to shed the heat. This is because the 'heat transfer coefficient' of the radiators drops. For example, if you have a room of 20°c you'll never be able to get a DT of 20 if your flow temperature is for example 30°c. A more realistic target is a DT that's around 30% of the flow temperature. For example; If we have a flow temperature of 70°c, (70 x 0.3) gives a DT of 21°c. If your flow temperature is 50°c this would give a DT of 15°c (50 X 0.3) and so on. This is not exact, it's just to get the flow rate in the right ballpark. There are more complex calculations for this if you need but really not worth it.

To get your head around all aspects of boiler sizing, efficiency optimisation etc etc have a watch of this

Found it https://www.heatgeek.com/do-we-really-need-dt20/ Basically as you lower the flow temps the delta between flow and return will drop I'm currently running ~30 deg Boiler flow with a 7 Deg drop at the return of the boiler Flow Temp Return Temp Diff 80 56.0 24.0 75 52.5 22.5 70 49.0 21.0 65 45.5 19.5 60 42.0 18.0 55 38.5 16.5 50 35.0 15.0 45 31.5 13.5 40 28.0 12.0 35 24.5 10.5 30 21.0 9.0

Sorry I must have missed it but why would you specifically want opentherm over std weather compensation using an external temp sensor?

Alternatively increase your rad sizes (in alignment with room heating requirements) and then lower the flow temp at the boiler. The lower the boiler flow temp the less expansion in the pipes and as a result the clicking reduces. In our house used to be terribly noisy every time the boiler fired up on 70 deg flow temps. Over the years (with improvements to rad sizes and house insulation) I've managed to reduce flow temp to 45 to 55 deg C (manual weather compensation and scheduled heating periods) With a boiler change as well as a move to WC flow temps and heating 24/7 it's now at ~30 deg I only get click clacks from the pipe work just after I have finished a HW cycle (because the boiler heats the HW tank at 80 deg Flow Temp and a small slug of 80 deg HW gets dumped into the CH circuit when the boiler reverts to CH at ~30 Deg C and this does create a little pipe work noise for a couple of mins

Ahh google informs me that is the std for graded timber used in the trusses. I'm pretty sure the Trusses would have been fabricated by local roofing company but they've been amalgamated into another company.

Took pictures so I don’t forget BS 4978 - is what they are marked up as

1. yes lower the return temp (below 54 deg C) the better the condensing and efficiency improvements @JohnMo has experience with atag - I don’t 2. Circuit size and volume of water in the rads normally drives the need for a volumiser @JohnMo is your man for discussion around that 3. No you will always have a difference between flow and return unless your room and rad temps are equal 4. You really want to make A, B or C work don’t you???? I’ve no further comments on any of those schemes

On the plus side @Ann D Mann credit is due for the choice of user name - did make me chuckle a liitle

much better reply than mine - said it all so well bravo @SteamyTea

so as “waste not want not” people surely you can see that adding 1. A boat load of extra cost 2. A shed load of complexity and probably 3. A bucket of safety risk (kettling a HE behind a stove leading to steam which considerably ramps up the pressure in a circuit and that would be “sub oprimal” Would not be a “waste not want not” solution Treat the stove as a stove and let another heat source do what it should be good at all in my opinion of course you will do what you want at the end of the day but remember one thing - you came on here asking for advice If you came on here asking for your options to be validated you should have said so at the start - no-one would have responded

@Nickfromwales any chance you can fix the replies within quotes by @Ann D Mann - makes it hard to read….. @Ann D Mann reply outside/below the quoted box please or your replies get buried in the quotes and they need to be expanded to read

from my perspective 1. Zone valves do wear out (or rather the heads fail eventually) 2. zone valves (if not exercised) can stick so in the late spring, summer and early Autumn where in a conventional S plan zone valve arrangement the CH zone valve would see no activity at all because the HW zone valve would be the only one opening and closing once a day. with NO and NC valves they both get “worked” every-time HW is requested (so you could say in that period I am doubling my zone valve electricity consumption but as it’s only for a short period I’m comfortable with the cost benefit analysis. I will also switch the boiler from weather compensated operation to dumb boiler mode as the viessmann HWD box - throws everything at the HW circuit in order to minimise HW re-heat time (20-30 mins) and this does have a cost. I can revert to a 55 deg flow temp for HW - give the boiler an easy life and get condensing efficiency gain for the 60 mins the HW will take (as opposed to the first 3 mins of the PDHW set up) it’s about 1kWh of energy saving a day

yes and no On my system the two zone valves are wired together NO (Normally Open) zone valve for CH - no activation required and has no influence on CH circuit - call for CH or no call for CH it remains open * NC (Normally Closed) zone valve for HW - it’s at rest closed - call for HW come and it opens - and the feedback signal energises the NO CH valve to close that valve. HW complete the NC valve for HW closes back to it’s unpowered rest position - the signal/voltage to the NO valve for CH is lost and it reverts to rest position (ie open) Result is (in my house) 23.5 hours out of 24 hours the zone valve consume no power at all

I don’t understand why anyone is using S or Y plan if they have a boiler capable of running PDHW - it’s just nuts. I’d also just echo the comments of @JohnMo and @Nickfromwales - what you are proposing is a metric ton load of complexity and cost for very little gain - use the stove as a stove and enjoy the ambience and hope you neighbours don’t mind the atmosphere. You are designing the perfect racehorse but you’ll end up with an elephant or a camel both of which aren’t competitive at horse racing events. Yes I know camel racing is a thing but that’s not really the point.

Just for the records

Thanks all that made the effort to get out on this cold winters evening and @Alan Ambrose for the prior "site visit" Sorry (Not sorry) for my structuring exercise 😉 As I said I "planned" the discussion points in the car on the way to the meet. Something to "build" the evening providing some "Dimension" and "Detail" that could help conversation flow and it's often said confession is always good for the soul What's said at a Build Hub EA meet up stays within the group