SimonD

Very true -it's like the ones who call to book in a service because the boiler isn't working right. They say they're surprise as it was only done recently while the paperwork says 7 years ago!

It's quite funny you say this. In three years I have only been asked once for an unvented service and that turned out to be because the bubble needed to be recharged on a MegaFlow, queue twiddling my thumbs for 45 minutes listening to bubbles in the cylinder and a customer repeatedly asking me if I was okay. When I service a boiler and they have an unvented cylinder I always tell the customer that it needs an annual service and they shrug because they don't even want to pay for the boiler to be serviced. They don't even ask me how much the unvented service would cost.

Oh, I see! There was me being a bit dopey. A thread sealing compound will do it - I always use Loctite 55 myself - your PTFE liquid should do the job.

Can you share a photo?

None, you should just have a nice little rubber (epdm) washer in there on the flat face.

As @joth says, there are other factors to consider in how the system will work with solar gain with plenty of ways to mitigate the problem without zoning that shuts down flow to a specific area. The zoning proposal is more likely to increase your costs, not the other way round. Okay, so you will have received a design from the installer. So what are the individual room loss the installer calculated? And how do these each match up with the UFH design? And what flow temperature is being proposed. What has the installer calculated the existing UFH output to be at design temperatures? Additionally, when doing a heat loss calculation without blower test results, a lot of assumptions have to be made, including with ACH and MVHR. Also, because heat loss calculations are fundamentally based on SAP too, there are further adustments that can be made for thermal bridging, which can have a big impact on the overall heat loos calculation. In addition to this, and something that is often overlooked is that loss through the floor and therefore the floor's U-value, varies depending on the floor dimensions and the specific arrangement of the room and external walls - a lot of designers don't know this and put a single figure in because it isn't specifically covered in the design training, not even in Heat Geek training. Here's a specific example regarding my house: MCS Umbrella does a heat loss calcuation using my given U-values and floor plans - heat loss about 7.5kW My heat loss calculation - 4.83kW This is the difference between a 9kW heat pump and a 6.5kW heat pump by the chosen manufacturer. Now, the other night, at -6 to retain a steady state of about 21.5C indoors my heat pump had to produce 3.8kW for 2 hours and for the rest of the time knocked itself back to 3.1kW. So even my heat loss calcuation taking into consideration thermal bridging and careful calculation of ventilation rates is slightly high, but I dread to think what things would be like if I'd put in a 9kW unit. Now, your installer may have covered all this, but I'm not so sure given the first design using buffers etc. My other question has to be why no one, including your architect, has suggested waiting until you've completed your blower tests before doing the heat pump design?

A lot of them are nowadays - even ones set up by merchants charge a hefty 1000-1500 for the privilege. Some will also send someone to site to complete the commissioning costing another 400-500

Here we go again. In some ways he's correct. In others he isn't. MIS 3005-D provides a basic procedure that must be followed. The Standard for heat load calculations and the correct method is defined by BS EN1283-1 2017 which is also covered in the CIBSE Domestic Heating Design Guide. Lots of designers and installers falsely believe it's prescriptive, but it isn't, especially where building details are known. The outputs aren't defined by the procedure/standard/methods, but fundamentally by the inputs. Again, this is kind of correct. The changes were implemented in June this year according to the standard BS EN1283-1 2017. This provides two methods of ventilation calculations. one based on actual door blower tests and the other based on a simplified method, which isn't too many miles off the old one. It's also based upon the designer's perspective on the building. The standard also includes infiltration losses based on the building height and exposure. What was his basis for telling you this? Is this installer MCS certified or using an MCS umbrella? What heating qualifications does the installer hold above the basics? I'd really be wanting to use someone who has at the very least done extra training by some recognised provider in hydronics. So in terms of calculated heat loss what are the figures being used for reference for all their design?

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With a flow return 35/30 something like DT50 output of 1985. Have a look and play with the attached spreadsheet. What I've generally found with radiators is that as soon as you get into the 35 and below flow temp and DT5 the sizes start to get quite ridiculous, especially with warmer rooms - e.g. with this one the conversion factor is 0.115 bathroom rad size estimate.ods

Neither! It's a good room-by-room heat loss calculation that must come first which you then use to size the heat source, followed by the emitter design. Then you look at flow rate, velocity and pressure loss through your pipework.

Nice floor then! 😁 What are you planning mean water temp wise v air temp as at 26 you'll need to have a very small DT?

Why as low as 24? Most of my commissioning of wooden floors over ufh say max 27C floor temperature and on gas systems this has sometimes required floor temp sensors.

I'm all on radiators. Hindsight since getting the heat pump tells me UFH would have been a good idea and I could have run much lower flow temp. But isn't that self-build and learning for you? The rads aren't too intrusive thankfully. Quite pleased though as my calculated theoretical flow temp at -3 was 37C.

-6 last night with pump running at 32C flow temp most of the night with a peak of 34C after a defrost cycle. Indoor temp just above 21.5. I actually had 4 defrost cycles between 10pm and 9am.

Thanks. Well spotted. The measurement procedure was changed in the latest CIBSE revision. It used to be full storey height, which was when I created the spreadsheet, now it's just internal measurements, ignoring height of floors. So you're fine. The old process also used to call for adding 1/2 thickness of all partition walls.

You should have a ground floor u-value in the designs somewhere? On ventilation loss, you're fine as you've put it in. Regarding ceilings, what is the build up you have? I assume there's 100mm insulation in there?

Here's a single sheet spreadsheet you can use that covers all the basic heat loss calcs. Should be fairly self-explanatory. I built it using open document format so it runs best in LibreOffice or similar, but excel will be fine even if it then throws up compatibility errors. For the whole room losses you need to calculate all walls, ceilings/roof and floor and then air change rates. If you have a solid ground floor, room temp - 7C for design temp difference should be fine although some regions say 10 is fine. For any part walls, which I assume you may not have, use your target room temp - 10C. For your air change rates, with MVHR, 0.5 is the max you want to go for. Internally, with a well insulated home with MVHR, you can assume no difference in temperture between rooms so those internal walls/ceilings/floors can be set to 0 losses, unless you want to have different temperatures, then you need to input U-Values and temperature differences between those rooms. Have a crack at it and let us know. Heat loss single sheet.ods

True, but you also have to look carefully at the Viessmann outputs as although their performance curves appear to be honest in the reduced output just above 0C, their 8kW is unlikely to perform in this situation so it would probably need to be a 10kW unit going by the rated output as opposed to max output. Someday we might see some consistency around output figures that are also properly localised. Interestingly, I was listening to HVAC education hub's interview with Graham Hendra re his new appointment as an R & D development manager for Haier. He acknowledged that they need different products for different geographical zones due to environmental conditions...so maybe watch this space?

Yes, you're almost there. 1. You must confirm your calculated room-by room heat loss - this is the foundation of everything. 2. You then take each room's floor area and divide the room's calculated heat loss by the area. This gives you a W/m2 value. 3. You would then normally use this W/m2 value to determine the pipe spacing and output for each room, getting the flow temperature as low as possible Unfortunately, the UFH has already been installed in your ground floor, but you can work around this using both mean water temperature and flow rates through the system. At present, assuming the 3.3kW heat loss is the correct value the UFH system you have had designed and partially installed would output this at a mean water temperature (flow temp+return temp/2) of around 27C - obviously this is just an averaged value as it just divides your heat loss by your total floor area of 158m2. This gives about 21W/m2 that the underfloor heating needs to produce. The advantage you have here is that the spacings are pretty close and this means you have the opportunity to run your heat pump at low flow temperatures.

I agree with @JohnMo. Yes, these are premium models with great reputations, but there are lots you could choose from that could bring you in under the BUS Grant. If the installation is as straight forward as you describe, I think even a Vaillant unit could give you some change out of the grant too.

As I'm using clay paints, which may behave differently to the scrubbable paints, I use the auro plaster primer https://www.auropaint.co.uk/product/plaster-primer-no-301/ It goes on a treat and works far better than mist coat. but as it works with emulsion, it might be fine.

It's much more than for a gas boiler. There's virtually nothing in a gas boiler, even a system boiler - gas valve, fan, heat exchanger, circulation pump and pcb with some wiring. Plus it's far less volume and weight. A heat pump, lets say with the output required for the OP at about 5kW for arguments sake will weigh nearly 3x the boiler and have about 3x the packaged volume. From a manufacturing perspective it's far more complex. But over its lifetime the heat pump will produce much, much less especailly as the grid continues to decarbonise. For example, this article: https://les.mitsubishielectric.co.uk/the-hub/carbon-embodied-operational-and-whole-life-cycle

Nowadays, I rarely just change the motorised head. Even in my short time operating my business, I had a few too many call backs after just changing the head, so I now just do the whole thing as you never know how old the valve is because it is so common for plumbers to just chuck in the motorised head. Looking at the pipework arrangement, you might be lucky and be able to create a no pressure pocket so as to limit the drain down - is the system pressurised or open vented? Totally bemused why someone would need to get in an electrician to wire it in. Even if in doubt and you don't want to go into the wiring centre, it's so easy to buy a 5 way connector, made especially for this purpose so you can cut and strip back the existing cable to the 2-port valve and connect it with the 5 way. Available at any decent plumbers merchant. E.g like this https://www.teslauk.com/product/7831/easyplug-3-or-5-way-wiring-connector

That limits the options to about one. Although the Ideal thermostats are actually black on the face, but unlikely to work for you. What ASHP do you have and do they not have integrated controls? There is a tendency for some European controls to default to on if there is a problem, either with connection or batteries. The Viessmann controls do the same as they say this removes the risk of freezing if there's a control failure. So first I'd suggest the controls supplied by your ASHP manufacturer. Another, although not in black are the EPH CP4 controls as they function without internet connection and you can buy them with or without a wifi hub. The EPH controls can integrate with weather compensation curves etc. but it entirely depends on what you've got. For UFH you've got Heatmiser which it seems pretty much every other UFH supplier uses/copies under white label.