JohnMo

I used their duct (90mm) and various terminals and connecting plenums (90 to 125mm) no issues. Also used the foam 150 and 125mm ducts, again no issues. Ubbink also connects with various other brands if you want to mix other companies components.

Poor sheep and cows. But than live in the same field as solar, a double use of the field.

Not sure you really save anything by not heating rooms, the unheated rooms just suck in the heat from other rooms, so net energy input really doesn't change. Would really try to move to a single zone per manifold, the loops in that manifold get balanced to get room temps you want. Having room sensors in each room allows you run all loops or none just by switching pump. So example, room 1 is targeting 20 and rooms 2,3 and 4 targets 20.5. if any room drops below there target all loops come online and later all go off. But better still balance the whole lot to run WC. If suitably balanced all should be ok. Issue I found was if you are shutting down loops you can run into the situation where only one zone is calling for heat and the boiler goes into meltdown, short cycling and all the gain just get burnt with excess gas consumption. Share your current boiler and mixer model/make?

Easiest analogy is car car anti freeze. You can mix manufacturer but not the chemical makeup up. Car antifreeze is easy, as it's colour coded, blue, orange etc. the colour determines the chemical makeup up. If you try to intermix chemical makeup you are asking for trouble.

And optimisers where they are likely to get periods of shade over part of the array. Or the shade bits on their own MTTP.

If you have a mismatch in floor output the simple first step is to reduce output from downstairs and/or increase upstairs. If downstairs gets too hot decrease output, by knocking off 0.5L/min off each room loop that gets too hot. Get downstairs to have a stable temperature before messing with upstairs. You may need to revisit this a few times over a few days. Then increase output from upstairs, go to manifold increase each loop flow by 0.5L/min. Leave for 24 to 48hrs between adjustments to see what happens. You need to ensure any thermostats are set to not influence anything while you set things up.

Forgot to mention your current mixing valves are unlikely to work or work well with WC. They may require to run at circa 50 degs to have any authority of manifold temperature. A boiler suitable for X or W plan or 4 pipe will have suitable control for switching between the two duties (CH and DHW). Look at Viessmann, Atag, Intergas boilers. Size about 20 to 24kW. If you are doing a new cylinder, buy a heat pump cylinder (3m² coil) so you get decent condensing and or rapid reheat when doing DHW.

For me, I would reduce to the number of zones down to a minimum. Your issue is you will have a slow system response and you room temps could fluctuate quite a lot of you are bouncing of a thermostat. Next choice of mixers, IVAR or electronic (ESBE etc) only. Or do you even need a mixer anywhere? Can your system boiler provide enough flow for all loops on its own? If not, heat only boiler and keep manifold mixer and pump. Then a single thermostat per manifold. Run an almost flat WC curve of about 35 to 40 degs. Low loss header - no Flow needed will drive system or heat only I suspect. I would start by looking at the longer loop and all pipes to and from that loop and look at pressure drop. Once you have that, it will set pressure drop for system, then add all the flows you need together all loops). Now you have a pump duty point. You can now make a sensible choice of system or heat only. Thermostats, implement in each room - but don't give all active control, use for analysis for system balancing. Don't install manifold actuators. Use a manifold wiring centre to just switch pump on or off if you keep the mixers. No mixers and balanced system still leave off you add later if you have a problem room that overheats.

I would just do it in 3x2 or 4x2 wood, was forced to use some metal studs behind our stove, much prefer the wooden stud walls - nice sturdy.

I was looking at our almost North facing roof over the summer and was really surprised by how much sun it actually got. North facing is seasonal producer, fine in summer, pants in winter - but all PV is pretty pants in winter anyway. Best way is model it on https://pvgis.com/en We have have loads of shading in general (loads of trees). The way I thought about is panels are cheap (£140 per kWp) so we have quite a few, yield isn't the best, but the number panels helps. Can you do a solar fence or similar or ground array?

If they don't know or cannot tell off the top of the head, gets new plasterers, as they don't know what they are doing. Plenty of metal tapes for doing such things.

Not really it's designed for cold climates which isn't the same thing. It has a Condensing rotary heat exchanger which us better at heat recovery in cold climates - or so they say. A very quick look at the install manual and it clearly states, DOMEKT units are designed for installation in household or technical rooms with an air temperature of 0 °C to +40 °C, relative humidity from 20% to 80% (non-condensing). It is recommended to install the air handling unit in a separate room or in an insulated attic So not sure it's suitable for your location - most units aren't really well suited for a cold or very hot loft space. Hence the issues you currently have. I would remove insulation from under MVHR and then build a box from 100mm+ PIR or insulated stud walls and box the whole unit in. Make a wall removable or add a door for maintenance. Then the unit is in loft, but within a heated envelope. Then just keep the unit you have. Other option is every time it's cold you have issues.

With the proposed falls are you simply inviting trouble. Any blockages from autumn leaves etc could lead to water accumulation at the house interface. Possibly water in the house. You would never slope a patio towards the house, so why would you do that with a roof? I would be sloping away from the house, simple and safe.

You need to do the pressure drop calculation really. Depends on flow rate, length and number of bends in the duct. But would suspect 160mm is fine and 250mm overkill. I just taped between membrane and duct (foam ducts)

Can you adjust your pump speed to a higher setting? This will increase flow available.

Is it really a down side? If you only allowed UFH return back to boiler the flow through the boiler would be very low and most likely just short cycle.

So they took the merry p!ss really. Scottish grant is something like £9500, so they charged £11500 for a heat pump and cylinder? Still completely unconvinced by MCS, glad I did the self installation.

That raises a question - do you not run WC all the time, are you trying to run WC and a schedule at the same time? Or running WC and thermostats? You need every loop on really, otherwise you get a miss balance of flows.

I don't want or need a buffer - it's a thought process, and as @Nickfromwales says captures the details in one place for others. This is not a volumiser thread either. I had already had 2 coffees and been out with the dog, before writing the original - decided it was too cold outside to do much else.

No need to obsessive about this - are rooms warm enough or hot cold? But generally the best way is based on room temperature not flow rate. An ideal flow rate and dT doesn't matter if you room never gets hot. Run pump at full speed, set flow rates, then reduce speed until you see flow rates start to drop.

As title, some systems need a buffer - not many, but some do. So as a way to look at and have a ready place to get info I thought I would start a topic. I used ChatGTP to see what design features I would need and sizing for best CoP. Many of the details are for my house to get some real feedback. You will see buffer suggested are pretty big, the control logic is a little more complex than you normally see. And may suggest why installing a cheap small buffer leads to flow temp distortion and poor CoP. Here is the output Great — here’s a practical, ready-to-use design + sizing guide tuned to your system (ASHP that’s currently short-cycling, 100 mm slab, 3.6 kW space heat at –9 °C, Octopus Cosy battery available). I’ll give clear rules, exact formulas you can use, a small numeric table (common ASHP sizes × target extra run-time) and a concrete recommendation you can install or ask your installer to follow. # Short summary recommendation (if you want one-line) Use a **tall, well-stratified 4-port buffer cylinder** with **good internal diffusers**, **~150–300 L** depending on ASHP size and whether you want to batch-charge from battery. Insulate 50 mm+, place 2+ sensors, fit anti-thermosiphon valves and a low-loss hydraulic layout. See details below. --- # Why a 4-port, tall slim buffer? * **Preserves stratification** (keeps top warm, bottom cool) → **low return temperatures** to the heat pump → higher CoP. * **Hydraulic separation** (4-port) avoids forcing the whole buffer to reheat unnecessarily when the heating circuit cycles. * **Internal diffusers** or perforated tubes reduce mixing and maintain layers. --- # Sizing fundamentals (exact, so you can calculate) Use the energy balance: **Q (J) = m (kg) × c (4186 J/kg·K) × ΔT (K)** For 1 kW running 1 minute → 60,000 J. From that you get: * **Volume per kW per minute** (water, ΔT = 10 K): **≈ 1.433 L** * (If you allow ΔT = 15 K → ≈ 0.956 L per kW per minute) * (If ΔT = 5 K → ≈ 2.867 L per kW per minute) So: **Volume (L) ≈ 1.433 × ASHP_kW × desired_minutes** (for ΔT =10 K). I prefer using ΔT = 10–15 K for realistic usable storage without overly high temperatures that harm CoP. --- # Concrete numbers (helpful quick reference) Volumes shown are litres of water required to supply the listed extra run-time (i.e., how much buffer you’d need *in addition to the live heat* to extend continuous run): DeltaT = **10 K** (typical usable layer) * 6 kW ASHP: 20 min → **172 L**, 30 min → **258 L** * 8 kW ASHP: 20 min → **229 L**, 30 min → **344 L** * 10 kW ASHP: 20 min → **287 L**, 30 min → **430 L** DeltaT = **15 K** (if you accept larger temperature swing) * 6 kW: 20 min → **115 L**, 30 min → **172 L** * 8 kW: 20 min → **153 L**, 30 min → **229 L** * 10 kW: 20 min → **191 L**, 30 min → **287 L** Interpretation: * If you only want **hydraulic decoupling / low-loss header** (not storage for long batch charging), **25–50 L** can be fine (with correct 4-port and diffusers). * If you want **meaningful cycling reduction** (extend runs from ~20 min → 30–40 min) expect **~150–350 L** depending on ASHP size and acceptable ΔT. * If you want **multi-hour thermal store** for tariff batching, you’re into **200 L +** territory and up. --- # Practical recommendation for your case You said the ASHP is oversized and currently runs ~20 minutes. You also have a 13.4 kWh Cosy battery you use for price-optimised charging. A pragmatic choice: * **If your ASHP is in the 6–8 kW range:** pick **~150–250 L** (aim for the 15 K numbers if you want a smaller tank). This will: * noticeably reduce short cycling, * keep return temps lower if piping is done right, * allow battery-assisted top-ups during Cosy windows. * **If your ASHP is 8–10 kW or you want 30+ min buffer:** pick **~300–430 L** (10 K basis). * **If you only want hydraulic decoupling (minimal size):** a **25–50 L** 4-port low-loss header will stabilise pumps and avoid low-flow faults but won’t give long run-time. Given your floor load is only 3.6 kW, you don’t need an enormous store to meet instantaneous load — the buffer’s role is mainly *smoothness and batch charging*. I’d suggest **~200 L (4-port tall slim)** as a balanced start for most oversizing situations — it gives sensible cycle reduction and allows useful battery charging without being huge. --- # Detailed features to specify / ask your installer for 1. **4-port hydraulic layout (opposite ports for heat pump vs heating circuit).** * Use a buffer with dedicated upper/lower ASHP ports and opposite upper/lower heating ports (true 4-port), or a low-loss header arranged the same way. 2. **Tall & slim geometry** (height >> diameter) to help stratification. * If constrained, add **internal perforated diffuser tubes** or baffles. 3. **Sensor pockets / ports** at several heights: * Top (priority heat), mid (control), bottom (return temperature). * Use these with your controller: ASHP enable at bottom-mid threshold, stop at top setpoint. 4. **Insulation:** factory polyurethane ≥50 mm, aim for heat loss <1 W/K. Avoid bare tanks. 5. **Internal flow directors / diffusers** to reduce direct flow between inlets and outlets. 6. **Anti-thermosiphon / non-return valves** on ports or integrated valves to stop night thermosiphoning. 7. **Low hydraulic pressure drop** (quoted <10 mbar @ 20 L/min is good) so pumps are efficient and ASHP doesn’t hit low-flow alarms. 8. **Ports for electric immersion** or plate HX if you want to use battery / immersion backup later (useful for Cosy charging). 9. **Multiple sensor inputs on controller** and logic: run ASHP when bottom < X and top < Y, maintain minimum runtime (e.g., 20–30 min) and inter-cycle hysteresis. Prefer to control by buffer top temp, not by boiler return temp. --- # Control & setpoint suggestions (to protect CoP) * **Target top temp for space heating:** keep moderate (e.g., 40–45 °C for high-temp radiators, 28–35 °C for underfloor). Avoid pushing buffer top >50 °C unless required. * **Return temperature:** design to keep return as low as possible (<30–35 °C for best CoP with low-temp emitters). * **Minimum ASHP run time setting:** set to compressor minimum (e.g., 5 min) but aim for **30 min target runs** where practical. * **Use bottom sensor as ASHP start/stop control** to avoid reheating the whole cylinder and preserve stratification. * **If using battery:** schedule batch charge so ASHP or immersion boosts top temp in Cosy windows; use buffer top sensor to prevent overheating. --- # Pump & flow guidance To size flows: **Flow (L/min) ≈ 2.87 × ASHP_kW ÷ (ΔT in K / 5)** when using ΔT = 5 K baseline. More simply: * Per kW at ΔT = 5 K → ≈ **2.87 L/min per kW**. Examples: * 6 kW @ ΔT 5 K → ≈ **17 L/min** * 8 kW @ ΔT 5 K → ≈ **23 L/min** * 10 kW @ ΔT 5 K → ≈ **29 L/min** Aim for a ΔT of 4–6 K on the heating side for best pump sizing and system efficiency. --- # Installation checklist (to hand to your installer) * 4-port tall buffer, internal diffusers or baffles * 2–3 sensor pockets (top/mid/bottom) * Anti-thermosiphon valves on legs * Low-loss header connections, minimise deadlegs * ≥50 mm foam insulation jacket * Port for immersion/coil if battery backup wanted * Pump sized for flows above (including variable speed pump preferred) * Control logic: buffer-bottom start, buffer-top stop, minimum run timer, hysteresis --- # Final practical pick & next steps * **If you want a single concrete spec now:** choose a **200 L tall 4-port buffer** if your ASHP is around **6–8 kW**. It’s a practical compromise: reduces cycle count, preserves CoP, and is small enough to fit plantrooms while giving battery-assisted batch charging usefulness. * If your ASHP is **8 kW+** or you want full 30–60 min batched runs, step up to **300–400 L**. Would you like me to: * calculate the exact buffer volume required for a known ASHP nominal power if you tell me its kW? * sketch a piping diagram (4-port) and provide a parts list (pump sizes, valves, sensors) you can hand to an installer? Pick one and I’ll produce the wiring/piping/control diagram and an exact parts list.

I use similar with zero issues.

Why, just get some pipe insulation on there - job done. See no advantage making stuff damp for the sake of it.

Answered your new thread on the same subject

We had a converted barn in the 90s done that way. And did similar to a house (1830) we did up in 2012. In the house the windows remained in the stone wall - with a small thermal bridge.