marshian

Link to Urban Plumbers Heat Loss Calculation Video on YT Watch it - you have most of the dimensions you need and for building fabric there are plenty of resources on the net for W/m2 I started to build my own spreadsheet years ago which was actually fairly accurate on the rooms I did but then I found I could pay £12 for a single use of Heat Engineer software and plug all the info in there and get a very accurate result (Provided you understood the inputs) however they now charge £100 for single use so I can't recommend them anymore. In a nutshell it's just Math but be very careful with ACH (Air Changes per hour) many on line tools massively over egg this element and as a result heating systems are over sized.

Oh and I do think those calcs are a little on the strong size Based on Heat Geek Guidelines Quick and Dirty from your earlier calcs Says for Renovated property with CWI and over 75mm of LI - best case 40 W/m2 worst case 65 W/m2 So Your worst case would be 11.5 kW best case 7.5 kW (not including HW Demand) I have an early 80's 4 Bed detached house which is a stupid T shape so lots of rooms with 2 or more external walls and my overall W/m2 is 35 Improvements post construction are CWI, 300 mm of LI, SUDG Windows and Doors, 52 m2 of 75mm PIR under the suspended ground floor - not much more I can do to it now.

Heat loss calcs A great video by Urban Plumbers covering how to do a basic heat loss calc - worth watching There are other tools on the net like Heat Punk who offer online modelling of heat losses @Jeremy Harris Tool on here is often highly praised but I've never used it All fine until the end - based on the above you need a 16kW boiler max

No problem at all - glad the internet could help PS bloody crazy for GW to have a parameter default set at 75 on a condensing boiler

Twice in a day........... 3rd party controls don't add efficiency they kill it - manufacturers advertise it as "Smart" but what it really does isn't Size the boiler to one that modulates down to your house heat loss at whatever the worst OAT in winter for your area is. If you can size it to modulate lower than worst case even better but unless it's a huge leaky gaff you'll have to settle for worst case heat loss because in any half decent house with std improvements of CWI, current regs Loft insulation and double glazed windows and doors you are going to struggle to find a boiler that can go lower than worst case. Size the rads to the meet individual room heat loss at sensible low flow temps Run Weather compensated with DHWP and balance the circuit and you won't need TRV's as anything other than limiters for solar gain

I never understand why people go for third party controls when a boiler manufacturer offers controls designed to work with the boiler?? (I'm speaking as someone with Drayton controls and a Viessmann boiler but they have no link to the boiler - fundamentally it's just a nice interface for scheduling and the "smart" TRV's make excellent temp limiters in rooms where I can't get the flow rate low enough or rooms with solar gain) Viessmann just go with WC flow temps and DHWP Get a cylinder with a heat pump sized coil and size your rads for a low flow temp (mid 20's to mid 30's) and fit them with pressure independent TRV bodies with flow rates set to the room heat demand and enjoy a quiet efficient boiler which will maintain a sensible temp 24/7 with no intervention from you. PS it really does read like an AI bot question

The min outputs are very much aligned to flow temps you are running My Viessmann 100-W 16 kW Heat only (Open Vented) is rated at 2.9 at 80/60 but that increases to 3.2 at 50/30 I'm running it at max 32/25 at -2.5 OAT - it's range rated to absolute min for CH and my data gathering tells me that clearly it's running at 4.0 output under those temps which is perfect for me because house heat loss is a smidge under 4.0kW So in a nutshell the modulation ratio is actually 4.0 but it doesn't really matter to me as it's sized to meet the heat loss of the house with a max of 16 kW which I need to heat HW tank in a reasonable time frame. Ignore the yellow highlighting I used the image elsewhere (Highlighting the importance of knowing what your boiler needs to function properly)

What's the gap on the other side? (opposite)

I wouldn't worry about it - expansion and contraction is normally in the width rather than length - because my flooring finishes at a UPVC french door I have almost zero gap at that end (2mm and I filled that with silicone to stop it being a dirt magnet) Work in progress picture from when I did it

Last floating oak floor I did was front hall, toilet, main hallway and dining room as one continuous floor - I removed all the skirting boards and I had cork strips between floor and walls as expansion packers When I had finished the floor I replaced all the skirting and that hid the cork strips For the Lounge which I did a few years later I didn't do it as a floating floor and used hidden nails into the subfloor on every row - I left an expansion gap of 10mm round the edge which was covered by the skirting once replaced Both floors have now been down several years and no difference between them in terms of movement

Exactly - it was a real surprise to me how effective "cold to touch" rads are as space heaters in shoulder seasons I was tweaking the balance of my rad circuit this morning (since I increased my pump speed the burn times have lengthened and rooms have started to overheat) OAT was 10 Deg C - target boiler temp was 27 Deg C but I increased the WC curve to extend the burn time so I could get round and measure all the rads Flow Return Diff Room Target Boiler 32.4 25.3 7.1 Kitchen 29.8 26.0 3.8 21.0 20.5 Dining 30.8 27.2 3.6 19.5 20.0 Lounge 31.0 26.2 4.8 19.5 19.0 Hallway 29.6 24.2 5.4 19.5 19.0 Utility 25.8 22.2 3.6 18.0 18.5 Toilet 27.6 23.6 4.0 19.5 19.0 Front Hall 24.4 18.4 6.0 17.0 17.0 Bed 1 28.8 24.2 4.6 20.0 20.0 Bed 2 25.2 21.0 4.2 20.0 19.5 Bed 3 27.8 23.4 4.4 20.0 19.5 Study 28.6 22.8 5.8 19.0 18.0 Bath 29.2 21.6 7.6 20.5 21.0 Ensuite 29.0 22.0 7.0 20.5 21.0

Just a random thought from me - those valves are full bore ones and not the restrictive types?

Absolutely yes add inhibitor - without it (in the absence of properly conditioned water which on a sealed system is the alternative) you can quickly get corrosion in the system - bad for rads, pump and boiler

When I posted comments I hadn't picked up the heat source was ASHP As I understand it the SCOP or COP improves the lower the flow temp is and it's at it's worst when doing HW at elevated temps Running it thro HW tank coil first then rads is going to be poorer COP more of the time surely??

Water takes the shortest path? what happens to the flow temp in the rads when the tank is fully heated? the Tank needs 60 deg C to get it to a sensible 50 temp DHWP is the process to follow to separate HW demand from CH so you can run two boiler temps

All of this post is related to CH only - not HW OK since I've had this boiler installed it's always had a little niggle where even range rated down to min (19 out of 100 so should be 3.2 kW but is actually realistically 4.0 kW due to low flow temps I'm running) it occasionally ramps up to 20% to 30% just before shutting down or even sometimes in the middle of a burn cycle resulting in an early shut down for over temp.... It's definitely worse on warmer days. If I'm in the kitchen and the boiler is on a burn cycle I can hear the tone change as it ramps up. Viessmann replaced both Main Board and WC Temp Sensor in March this year to eliminate those as a reason for the behaviour even though I wasn't convinced by this action. It improved it enough that I didn't notice it happening so much but it definitely still happened. I've tried to understand what is driving this issue but not been able to (so I've actually put it down to a "characteristic" and recently I increased the range rating to 30 out of 100 (roughly 6 kW) - logic being the boiler is ignoring it anyway so might as well give a bit more head room back Strangely and I hadn't heard it do it since - then on Sat it did it again and then again on the next cycle. I went and checked the circulation pump - I'm running it at 0.5m3/hr on CH and 0.6m3/hr on HW and the pump was 0.4m3/hr flashing with 0.5m3/hr a little lower than normal but all 4 of the rads where TRV's can and do intervene were closed. (Difference in flow rate is accounted by the lack of resistance thro the coil as opposed to 13 rads with flow controls/restrictors fitted to all of them) I bumped the pump speed from 1 to 2 and it was rock solid on 0.6m3/hr It didn't do it for the next two cycles I put the pump back down to 1 and it did it on the next cycle. I went back to the manual - I'd made the assumption that the boiler flow rate requirement would be at peak output and running a 16kW boiler range rated to 6 kW I could comfortably run at 0.4 to 0.5 m3/Hr I dislike system noise so really want to run the pump on the slowest speed but it looks like the boiler likes a little more flow. Early days but I really hope that's resolved the niggle - I might range rate it back to minimum and see if the issue comes back

this was why my suggestion of two tank set up - one for kids bathroom and one for the others - could schedule the reheats to be just before requirements and size the tanks accordingly - as a result you don’t end up with one massive tank that takes a while to reheat or requires a serious kW input to do it faster and the boiler can be sized more appropriately for house heating needs (plus each tank if chosen wisely with a heat pump compatible coil wouldn’t need the boiler to ramp up to very high flow temps) OP’s house still in planning stage so finding space for the two smaller tanks can be incorporated into the design

@Nickfromwales was far better qualified to answer - sorry for the delay in responding was at a funeral (Brother in Law) all day yesterday.

Hey Zeus that's a bloody annoying feature if you fit WB on a regular basis...............

Like he said - plus the added issue of if you are hot swapping something and it's goes wrong (for whatever reason) you are in a whole heap of pain and stuck with your fingers in holes trying to explain to the significant other what the bloody hell they need to do to drain the system down so you can take your fingers off the bloody pipes - which is what I meant by point 4. First time.............

Correct.................... It might be not what you meant but I don't disagree 😉 Counter view - when the BUS grant ends the inflated costs of heat pump conversion will also end - manufacturers will reduce their prices we won't have MCS stupid rules impacting sizing and if the grant harvesters move onto something else we will be left with companies/heat engineers that do a much better job

I've done the same before but I think there are a couple of points to think about 1. The condition of the olive 2. Possible need to PTFE tape or remove and replace the olive 3. Miss match on old nut to new fitting 4. First time.................. I'd drain down

You might require several top ups as you bleed air out of the system - that's just a consequence of introducing air into pipe work - it will find it's way to rads and as a result you will need to bleed them several times

Oh that for sure

Except that it doesn't go off like a cartridge of silicone - had my tube for nearly 10 years and it's still usable - which considering a normal cartridge of silicone is knackered after 6 mths makes me feel the product is a different formulation