Jeremy Harris

Yes, I did buy some optical fibre and meant to have a go at rigging up something to hold fibres over the LEDs so that I could route the light out to an external display panel. I just haven't got around to doing it yet...

The choice of screw type is pretty critical. Many screws have a much smaller effective diameter than the same size nail, so are going to be significantly weaker (which is why nails must be used to secure joist hangars, for example). Also, lots of modern screw types are made of fairly brittle material, so tend to break rather than bend. Screws are good at pulling two bits of material together, but generally less good at taking shear loads, and often fasteners used to hold together a timber frame are taking shear loads. Not an insurmountable issue, just means using bigger screws of the right type. There's no doubt that using screws would be slow and expensive when compared to nails, too. Finally, I think it's worth considering whether screws that have been holding a structure together for a couple of decades are actually going to ever come out easily. I suspect they may not, so may cause more of a problem when dismantling the structure than if it had been nailed together. Bolts might be the best solution, but would be costly and awkward to use.

Sadly the Sunamp gives no indication of its state of charge, so there's no way of knowing if it's at, say, 60% at all. It's a significant issue, in my view, as not knowing what the thing is doing is one of the single most frustrating aspects of having one. Mine lives with the cover of the controller off, so at least I can see the status LEDs on the control board (I'm not recommending that anyone do this, BTW). Flow rate is not a worry at all with just a single Sunamp, now that they have increased the pipe size to 22mm and increased the performance of the internal heat exchanger (relative to the original Sunamp PV). They are capable of delivering pretty good flow rates, at least as high as the largest combi boilers that are available, and on a par with an unvented hot water cylinder, so it may well make more sense to just fit a single, larger, unit.

Depends. The maximum power we can put into our hot water heat storage system is 2.8 kW, and that could be very easily met by the excess power available from the ASHP. The only reason we don't use the ASHP to charge the hot water system is the problem with getting it to deliver water at a high enough temperature to charge the Sunamp.

I think you need to bottom out what the real heating requirement is, and work from there. At the moment there's a massive discrepancy between what your architect is telling you, which suggests a mean heating requirement of around 300 to 400 W, and your UFH figures, which suggest a massively higher heating requirement. If both floors are heated (and this is worth thinking about, as with a passive house spec there is rarely a need for first floor heating) then 205m2 at 50 W/m2 is an absolute maximum heat input of 10.25 kW, and frankly that's the sort of heating requirement that a 40 year old house might need. Something closer to passive house spec is unlikely to need more than about 20 W/m2, so that would be a peak requirement of around 4.1 kW. Our heat pump is rated at ~7 kW and cost around £2k installed. It's massively too big for our needs, but was the cheapest unit we could find at the time.

Pretty sure you need to either put the NRV in the hot pipe, or both. Putting one in the cold pipe won't stop the problem if it's the cold pushing into the hot, which is what it sounds like.

This is another clue that the 16.5 kW figure is way too high. A £250 oil bill, according to the architects calculations, with an 80% efficient boiler, would be around 3,571 kWh for the year. Hot water will be a fair hunk of that, roughly 1,000 to 1,100 kWh per person per year, so that needs to be subtracted. For two people, that would mean that heating energy use would be around the same as ours, about 1,500 kWh/year. That doesn't stack up with a 16.5 kW heating demand, as our typical heating demand is about 300 to 400 W, and in extremely cold weather this can increase to about 1.6 kW for a short period. It sounds to me as if a decimal place may have been shifted to the right by accident.

16.5 kW seems extremely high to me. Our 130m² (~1400 ft²) house needs about 1.6 kW when it's -10°C outside, and most of the time it only needs around 300 to 400 W in winter. Assuming that your house needs a great deal of heating, then the maximum heat output from UFH is usually around 50 to 60 W per m², so you can work back from that as an absolute worst case. Our UFH rarely needs to deliver more than about 20 W/m², for example, and we have about 75m² of heated floor area.

No devices needed, the buffer just has a flow and return from the boiler and a flow and return to the UFH. The UFH draws heat from the buffer at a fairly steady rate, depending on the heating demand and the boiler tops the buffer up as needed.

Lots of us here have installed ASHPs for a great deal less than that. Some have installed them for less than the ~£2k we paid. There are lots of people trying to charge ludicrous prices. Try looking at some real prices for ASHPs, like this randomly selected hit from a quick search: https://www.wolseley.co.uk/product/mitsubishi-ecodan-85kw-ftc4--ashp-pack/ For a new build you'd get the VAT back, making this full installation kit for a 8.5 kW ASHP less than £3,200. At most it's a day's work to install; with no experience at all I installed our similar unit in half a day. That's an expensive unit, too, if you shop around you'll get them cheaper, I'm sure.

The buffer needs to be sized to try and give the boiler as long a burn time as possible, but will always be a compromise, because of the space that's likely to be available. If you know your average heating demand in winter, then you can work out the buffer tank size needed to run the heating for a given time. For example, a 70 litre buffer, running between a boiler on temperature of 35°C and a boiler off temperature of 65°C, will store around 2.46 kWh of heat energy between those two temperatures, so would be able to run the heating for a bit over an hour at 2 kW between boiler firing periods. The boiler would be able to recharge the tank pretty quickly - a 25 kW boiler could do this in roughly 6 minutes, but would probably take a fair bit longer as it would almost certainly modulate down a fair bit. At a guess you might find that the boiler ran for around 10 to 15 minutes every hour. If just trying to run the UFH loops directly the chances are that it would cut out after a minute or two, due to the limited heat demand from the floor. We have a 70 litre buffer, and that can usually run our UFH for around 4 hours or so, without being re-heated, and we only run the buffer at 40°C, as it's heated by an ASHP.

Same here, no mice, or spiders, now that I've been spraying peppermint oil around the door thresholds once a month or so (does the spiders a favour, as they die once they get in anyway, as there's no bugs in the house for them to eat). At the last house we'd regularly get mice in the loft, and I'm certain the only way in was for them to climb the walls and get in through gaps around the soffit, or under the tiles. That seems to be how they are getting into my workshop, as the only evidence of them is in the loft space. I'd need a very hungry cat to get rid of them, as I must have trapped around a dozen so far. It's why I'm building a multiple capture live trap, so that I can just collect as many as possible in a deep bucket (too deep for them to be able to jump out). The trap is a walk-the-plank arrangement, with an infrared proximity sensor that releases the plank, so it tips down and drops the mouse in the bucket. A small geared motor then resets the plank to horizontal, ready for the next mouse. The hope is that, with a bit of peanut butter on the end, I should be able to get a bucket load of mice each night.

Might be one for @Nickfromwales Ours fits from behind the wall, and luckily I can access it from behind.

I'm battling with mice at the moment, but in my workshop. On my desk in front of me right now are all the 3D printed parts for my multiple mouse live trap, complete with LCD activation counter, so I can glance at a display and see how many mice there are in the bucket...

I would guess this might be the hot favourite for where the fault lies. I believe that shower mixers shouldn't be able to do this now, as they are supposed to have built-in NRVs on both inlets. Certainly the one that I fitted to this house had NRVs fitted as inserts as supplied. Not sure about other bathroom mixer taps, though.

It almost sounds as if cold is mixing with the hot, going the wrong way around the system. Years ago I had this happen with a faulty shower mixer, inside the thing the hot and cold feeds managed to get connected together when a seal failed. This did pretty much what you're describing, as when a hot tap was opened, cold water would flow backwards from the shower mixer.

Many years ago we had an oil boiler that was just a heavy annular steel tank, with a spinning disc burner sat in the bottom. I don't think anything could have ever blocked the heat exchanger in that. Took a few hours to get hot, though. Nice and simple, though, nothing much to go wrong.

You can get 50mm/2" galvanised pre-threaded, with couplings (also rated at 50 bar) in 6.4m lengths: https://www.pipestock.com/malleable-iron/threaded-steel-tube/galvanised-heavy-grade Not cheap though, at £280/length.

Maybe just use 50mm/2" galvanised for the lower section, then switch to MDPE when the pressure's down to a lower level, higher up the hill?

I can see where the 16 bar is coming from, ~14 bar for the head plus 2 bar working pressure. Whether a half way option might work depends on the pressure in the main. It'd need to be over 7 bar to get half way, perhaps a bit higher as the water supplier won't want any suction on their main, so will need to ensure a bit of headroom. Even HDPE is normally only rated to 12.5 bar, though, so suspect you're going to have to use galvanised iron pipe. This is usually rated at 50 bar, so more than enough, it's just a bit of a PITA to lay.

I've just merged these two threads into a single thread to avoid confusion.

Depends entirely on the heat demand from the UFH. Worst case for us, in really cold (-10°C) weather, would be a demand from the UFH of around 1.5 kW, so no boiler would really be able to modulate down that low. Our normal heating demand of maybe 400W or so would be way lower than any boiler could cope with. I believe that the lowest output that the Ecotec Plus range can modulate down to is around 3.5 kW (might be an idea to check with Vaillant if this is accurate - off the top of my head I think it was set by the d0 variable in the set up menu). That's probably too high for most UFH systems, I suspect, so a buffer tank would be needed to allow the boiler to run well without excessive short cycling (although the Ecotec Plus has an anti-short cycling time delay, so it would just shut down for a while under these conditions). In general, condensing boilers are a fair bit more efficient if they can run for a reasonable period of time. Although the spec gives a high efficiency figure of around 89%, this can only be achieved during a long burn. A series of short burns will bring this down to around 60% or so.

I'm pretty sure it's just different firmware, so the higher rated models just turn things up a bit more. These are fully modulating boilers, so they vary their heat output on demand anyway. The boiler we had at the old house was a Vaillant Ecotec Plus.

The running cost will be a lot higher with instant water heaters and electric showers. Worst case from an ASHP in wet and cold weather might be a COP of about 2.5 heating water, probably an average of around 3, so using stored heat from the ASHP would be roughly 1/3rd the running cost. Showers are our biggest hot water usage by far, around 6 kWh to 7 kWh per day, for the two of us. With ASHP heating the water at E7 rates that would cost about 16p to 19p/day. With non-E7 run electric showers the cost would be around 92p to £1.07/day, so a lot more expensive. We heat our hot water using mainly diverted PV, boosted during winter with an overnight E7 boost. Since January this year we've used about 610 kWh of off-peak electricity to provide hot water, so at a guess I'd say that we're unlikely to use more than about 900 kWh of paid for electricity to heat water for the whole year. That's at 8.148p/kWh, so the total cost for hot water for the year would be around £73.33. If we used electric showers, then the total cost for the year would be well over £300.

Are you sure about this? Oil price at the moment is about 5.6p/kWh Electricity running an ASHP would be a bit less if you don't have Economy 7, around 5p/kWh, and a lot less if you do have E7, less than 3p/kWh An ASHP costs pretty much the same to install as an oil boiler, probably less, as there's no oil storage tank needed. I paid £1700 for our ASHP, that is over-sized for our house, and it cost about another £300 for installation related stuff Our house is all-electric, and a bit smaller than yours, at 130m² (around 1400 ft²) and our total electricity usage (including charging my car) is £48/month, so about £576/year. Heating is only a small part of that total, maybe £150 at the most.