Radian

I think that's what I was suggesting yesterday but I'm not exactly sure what you mean by 'set time'?

I think you may be right. I can't find anything of this description. But does it actually make sense? Why would it need to present any 'user controls' i.e. you just black-box it? Your house might only cool a tiny bit but it's still measurable and is representative of the actual situation rather than any assumptions. If you can identify the precise indoor temperature set-point for night set back such that it will reach your daytime target in the chosen period following your morning start time, would this not have the desired effect? I might be missing something here but this scheme works well enough for me. My only problem is significant early morning solar gain which, by the time it arrives (if at all), the heat has already been put into the floor and the temperature overshoots as a consequence. I'm trying to set up a ML program to use a solar forecast to modify my set point to solve this but it's proving quite tricky. Most off-the-shelf thermostats have lousy hysteresis and poor resolution but there are sensors with improved granularity. I implemented my control system with sensors having a resolution of 0.1°C and was immediately struck by how sensitive I was to the effects of setting a temperature to some fraction of a degree. They say "save money by turning your heating down by a degree" but this is way too coarse. The funny thing is I implemented an Alexa smart home skill to set the temperature and found its spoken response rounds any given fractions. So if I say "Alexa set the heating to 20.5" it says "OK, autoset to 20". But what comes in from the Lambda function is indeed 20.5 so thankfully my code can act on it.

OK, thanks, not seen those before. Like you, I've also got bituminous felt but the house was built with eaves vents between every truss. 0.5m2 when I totalled it all up, so no shortage of ventilation. If you live in a rural area one issue you might run in to is cluster flies which live in fields during the summer and your attic in the winter. ?

What ya growing man? ?

You would get better range with Zigbee lamps but might need to buy a hub - unless your Amazon Echo device already supports it. Echo 4th Gen Echo Plus Echo Show 10 (all models except 1st Gen) Echo Studio

Not sure what you mean by Felt lap vents? Curious to know though!

The light in a given area is measured in Lux. This unit better represents perceived brightness and can be provided as a single figure recommended for a particular task. One lux equals one lumen per square meter so an 11m2 room as above, with a 1000 lumen light source would provide around 90 lux. Something like 200 would be more typical for a general domestic setting but it depends on the type of room. Here is one table of recommended lux levels for different activities. 90 Lux might just be enough in an adult bedroom. Nudge Nudge. Oh, and one more thing... it also depends on the age of the occupants. Over 65's require double those figures.

That makes a certain amount of sense. The more stationary the encapsulated air, the better the R-value. I have a very draughty loft (not a euphemism) so I'm considering a top layer of breathable thermal quilt to do a similar job. This is also reflective so may reduce overheating in the rooms below during the summer.

Quite right. How about two in series?

Tell me more, google won't...

You could use a 3-pole contactor like this (rated for up to 220VDC) and series-parallel up a bunch of modules to suit.

You're certainly confusing me with apples and oranges, apples and apples and so on. No wonder we seem to be spinning our wheels ? ? But I've been agreeing with you all along! My "explanation" continues to be that the heating effects (dynamics thereof as @TerryE puts it - while even he seems to think I'm disagreeing when I'm not?!?) are different, and therefore that the products are intended for different uses and require different electrical installation methods as a consequence. I just don't get how what I've written here might confuse readers - the only reason I keep littering this thread with my responses to you is because I have a passion about achieving clarity on this very issue. Again, I entered this thread with the observation that anyone not requiring the full 3kW on offer from a single Willis (or indeed 6kW from two) and who were considering plumbing in two for redundancy (possibly only connecting one to the electrical supply) has the option of wiring two in series with the advantage of safely making it 'plug and play' with a 13A plug. This also opens it up to control with standard time-switches, smart sockets etc. and may be particularly attractive for temporary use before full commissioning. This would be the only safe way to power Willis heaters without installing a new 16A/32A radial in 2.5mm/4mm cable - which would otherwise require the services of a qualified electrician.

As you know, there's no mechanical Arc Suppression in the bimetallic thermostats designed for AC so they would have to be bypassed or set to maximum (and not relied upon) and replaced with a DC contactor controlled by an additional thermostat. I would have expected this to still come in under the cost of an inverter as well as delivering greater efficiency. 12V invertors are a total joke. 100 Amps or more to get anywhere close to a kilowatt is madness! If you found a 48V off-grid invertor, that might make sense.

That's the exact point I was making earlier: Even 2kW heaters (the maximum usually available from reputable suppliers) are pushing it. I could only find one "13A" smart socket that was built with robust enough components to handle 8 Amps comfortably. A FLIR camera comes in very handy for this kind of exercise.

Continuing this topic in its own thread, my reply to @SteamyTea is that yes, this sounds like it could have mileage. However, DC breaking is, as you are aware, more onerous than for AC...

I fully understand and respect your POV which appears to have been been formed through experience and sound technical advice. However, it cannot be denied that both 3kW electric kettles and 3kW Willis heaters look absolutely identical as an AC load. Yet, as you point out, one is routinely equipped with a 13A plug and the other " would absolutely never be on 13a plugs" - in your own words. To identify and explain the actual reason behind this difference is, I feel, valuable information - not scaremongering. It should certainly not scare your clients as you are doing things correctly. But this kind of 'gotcha' persists throughout the self-build environment and I've seen other members making mistakes along these lines so feel compelled to maintain its visibility wherever I see it arise.

If you can set out for bricks OK, I'd say dive right in then. I think you'll learn little without laying on proper muck (he says, using the vernacular; this stuff is the absolute magic that turns our building units into houses that we can live in rather than being a pile of building materials). You would have to really screw-up to produce something you couldn't get away with after rendering. This time of year 5 or 6 to 1 will take a couple of days before its difficult to clean off - should you look at your previous days efforts and decide to re-do an area. Be super-critical to begin with and eye it up from as many directions as you can. You really don't have to put up with anything you feel uncomfortable with.

I can't parse that at all. 2000 Joule/seconds? Some energy was involved for some time. Maybe it was 1/1000th of a Joule collected over three weeks or so.

You seem to be talking about the thermostats on the immersion heaters, so why are you concerned about their switching capacity? The current they break will be half of what they're normally dealing with when seeing the full 240V across their loads. But yes, this might be a cheap way to bring the load down to something a relatively small PV could supply. I'd be interested to know where you can get a 2kW invertor for £40. A while ago I bought a second hand ABB 3.6kWp for £50 and thought that was a steal! Picked it up to test some modules out of a PV supplier's liquidated stock but haven't got enough to get past the 120V minimum input voltage. Just taking up space at the back of the garage now. Oh, and capacitor/resistor (snubber) networks are sometimes used to prevent contact arcing - but only for inductive loads. The sudden interruption of current causes the collapsing magnetic field to set up a large voltage as it 'attempts' to keep the current flowing around the freshly opened circuit. A capacitor across the switch contact will present a low impedance path (zero impedance initially) so a low value resistor in series with that will limit the current, absorbing the power stored in the collapsing magnetic field and turning it into heat. Not needed for switching purely resistive loads although there's always parasitic inductance lurking around in the wiring so has to be evaluated on a case by case basis.

In which case, for mqtt, Tasmota's got you covered (you probably already knew that because you were going to roll your own in LUA).

Get Elon to drill for it on the moon. 100~150Hz. Damn that'll be annoying.

It seems that people can be misled by thinking that if a 3kW kettle is OK using a three-pin 13A plug then any 3kW load is similarly safe. The kettle, however, is only operating for seconds and any warming of the lead and plug goes unnoticed as the heat has insufficient time to build up. But even a lesser load like a 2kW convector will cause noticeable warming of its cable and plug and this is when drawing only around 8 Amps. This is why typical 3kW immersion heaters are connected back to their own 16A mcb in the consumer unit. I would be far more comfortable with 1500W running for twice the time - so long as it made up for losses and fit within any time-limited tariff.

Snap! We recently completed an extension to our existing garage/workshop to provide an additional workshop and music room adding another 90m2. Yet to decide on heating though. Currently going through winter with a couple of 2kW convectors to see what energy use is likely to be. So far it's pretty close to the estimates for fabric losses. We hedged our bets by laying an UFH heating loop in the downstairs floor. ASHP is logical for us but placement is an issue. A2A is a better fit for upstairs which could also use a little cooling in the summer (a roof mounted PV would make sense with this) but noise is an issue. If only the cost of electricity would reach parity with gas, then a cheap willis heater for the UFH would be just perfect!

Pretty sure it's a development of the Thermoacoustic Heat Engine

One additional thought - if installing a pair of heaters for redundancy, consider wiring the two 3kW elements in series. This will obviously reduce the power to 1.5kW but, if that's enough to meet your energy requirements then it will reduce the current draw to one suitable for standard 13A plug and time switch etc. It will also considerably prolong the life of the elements by reducing switch cycling, scaling, spot boiling etc. - some of the issues I've seen people have with these heaters.