Home working heating one room suggestions

I'm sitting in my unheated office/garage and currently have an infrared heater pointing at me. Find it a great way of heating me and not the whole room/building

I have a small portable IR heater for when I’m in the garage. Directly heats what it’s pointed at (I.e. you!) rather than trying to heat the whole room.

Little fan heater pointed at me if it's really cold but usually no heating and a thick fleece. Good slippers too. I don't mind it cold though.

I use hive trvs to only heat my room when I'm home alone. Works well

Air con installed. Heating and cooling and highly efficient

Slightly different strategy but I've been using a dehumidifier ( we have 2 x Meaco DD8L ) in the room i use for homeworking  which both kicks out a bit of heat and obviously also dries the air. Also given i have a drying rack in there, its doing that job too. Small enough room that the temperature is comfortable enough plus the air is drier so feels less heavy than other rooms

Thermal boiler suit for the win. 👍

Very small oiled filled radiator and keep the door shut works for me although there is a quite interesting program on BBC sounds that suggest using gas central heating is still cheapest as it's about a third the cost of electricity per kWh.

We currently use a tiny oil filled rad, I did briefly consider an infrared heater but got the impression they are only cheaper for short term use i.e an hour in the garage, not ten hours working all day.

Reason being that an oil filled rad will switch on and off with the stat (with only a click to give itself away) whereas an IR panel, fan heaters and to a lesser extent, upright convection heaters switch off obviously with a visual or audible cue that it's time to feel cold (and turn the stat up or put the main heating on).

I used the oil rad overnight in my campervan recently and although I could hear it clicking on and off, I didn't know whether it was switching on or off and no obvious change in temperature. Again better than the blown air heating as sudden changes in temp are not good for comfort.

Efficiency wise you're probably losing more energy to the rest of the house than you would if you just kept it the same temperature.

Bought a electric heater last winter and the smart meter told me it was costing more than heating the whole house.

MIL has a Dreo space heater that she uses in the living room in the evening. I think it runs at something like 900-1500W. Warms up really quickly and we’ve now looking at getting one vs committing more to either Hive or Tado.

I put Tado in last winter and my spreadsheet says we are consuming about 30% less gas - mainly heating one room rather than the whole house.

We have an old stone badly insulated draughty house so heating the whole thing was just costing money. Improving insulation throughout would be very hard - we have considered just doing the work room, or getting a really well insulated garden office 'pod'.

An electric heated throw?

Depends how hardcore you want to be but personal heat (electric blanket, heated slippers, etc) will be very much cheaper than heating the room. Also, a hat and fingerless gloves if you don’t mind feeling like you’re camping in your house.

Wear a couple more layers too of course. I have thick trousers and a big fleece hoody on for about 8 months of the year here anyway regardless of fuel prices.

Efficiency wise you’re probably losing more energy to the rest of the house than you would if you just kept it the same temperature.

This isn’t true - it’s the difference between the heat losses from one room to the rest of the house/that rooms outside walls vs the heat losses of the entire house to the outside walls. Assuming you keep the door closed on the room you’re heating that is !

I’ve been using an oil filled rad in my office room during the day, but am having a smart meter fitted next week so will have some fun and games experimenting with options such as using the gas CH and turning all other rads off vs the elec heater etc. I expect the gas option to use more energy but has is a lot cheaper per kw.hr than electricity.

Buy a bigger screen.

Seriously, in my study I have no heater. Even the radiator is turned off. Shut the door and between the laptop, me and a 34” screen there is more than enough heat. Normally have to open the door in the afternoons or strip off a layer.

Study is a small box room in a modern well insulated house and your situation may be different.

Been working from permanently for the last 3 years and intermittently for the last 10.

Can you insulate the room better too?

This isn’t true – it’s the difference between the heat losses from one room to the rest of the house/that rooms outside walls vs the heat losses of the entire house to the outside walls. Assuming you keep the door closed on the room you’re heating that is !

The maths on Heatgeek seemed quite persuasive. Given the average house has next to no insulation between rooms it seemed plausible to me.

I sit on a seated throw. It's amazing and costs pennies.

The maths on Heatgeek seemed quite persuasive. Given the average house has next to no insulation between rooms it seemed plausible to me.

Simple engineering logic doesn’t agree. The single room has the house insulation PLUS whatever insulation exists between it and the the rest of the house. It doesn’t need any maths, just a basic understanding of thermodynamics and heat transfer.

Buy a bigger screen.

If you look at the power consumption of various different sized screens, that doesn't really seem like it'll make any real difference.

Could just run a 3W table lamp for as much effect (assuming you're running an external screen in the first place).

I use hive trvs to only heat my room when I’m home alone. Works well

There are caveats with this - your system has to be set up in a way that allow you to just heat one room, and many aren't. Consult a plumber, or spend weeks reading stuff on the internet about it 😉

It doesn’t need any maths, just a basic understanding of thermodynamics and heat transfer.

Hmm but a slightly more than basic understanding of how central heating works might actually throw it the other way. It's more complex than I at first thought. For example the rad in my work room is pretty small, and it can only dump about 500W of heat. But the lowest boiler out put is 9kW. So it's going to run for a pretty short time to just fill the water in that rad. The Heat Geek video does go into a lot of detail about efficiency that I didn't pay enough attention to, but it is quite complex. It's about the efficiency of how the heat gets from the gas flame to the air in your room.

I need to watch the HeatGeek thing but just can't see it being true in a lot of cases except say in a well insulated house where energy losses from the other rooms are low.

In a house with no external wall insulation, heating just 1 room is like heating a tiny house versus a big one.

Heat transfer between rooms isn't "lost" heat.

But when the rest of the house is cold you need to use more energy to keep one room at a higher temperature than the rest. And who has a completely uninsulated house? If you actually watch the video the "basic thermodynamics" are shown to be anything but.

More energy for that one room than you'd have to if the other rooms were heated, but less energy overall than heating those rooms directly.

Back in my youth, before central heating, the solution was either a Super Ser gas bottle heater or a paraffin heater. Google suggests the paraffin heaters are now available with elctronics, thermostats and clean burn which makes them odourless. Might be worth a look.

So, there is a Hive installed in the house and we are using that to decide how cold it is before we stick the heating on...I'm now thinking about the Tado radiator controllers.

What would I need to get? I'm assuming (hoping) it is just the Tado radiator controllers and I then go round the house and replace the control valves things on each radiator and stick these Tado ones one. Is that it?

Once installed, I'm assuming they will need to connect to the house wifi and I should be able to see them on Google Home and do some controlling from that (or the Tado app directly) - do they need a central controller or do they just fit on radiator and each one is connected to the house wifi?

Also fitting them, video suggests you can just unscrew the heating valve on the radiator and screw the Tado one on - is it that simple or do you have to drain the system before removing the valves?

I'm all for home automation, but it really needs to be beneficial - in this case, heating the individual rooms whilst not spending as much money on the heating. Ideally it needs to be fit on radiators and it then connects to the house wifi and Google Home can access and control it.

Also fitting them, video suggests you can just unscrew the heating valve on the radiator and screw the Tado one on – is it that simple or do you have to drain the system before removing the valves?

If you've got TRVs, it's trivial. If not, you'll probably have to drain the system.

So, there is a Hive installed in the house and we are using that to decide how cold it is before we stick the heating on…I’m now thinking about the Tado radiator controllers.

The main boiler controller (so Hive in your case) and the radiator thermostats need to be the same brand / system - so you need to buy Hive TRVs, or replace your Hive controller with a new Tado one.

What would I need to get? I’m assuming (hoping) it is just the Tado radiator controllers and I then go round the house and replace the control valves things on each radiator and stick these Tado ones one. Is that it?

Yes. (Hive not Tado for you)

Also fitting them, video suggests you can just unscrew the heating valve on the radiator and screw the Tado one on – is it that simple or do you have to drain the system before removing the valves?

Yes it is that simple. You need to have existing TRVs on the radiators. The Hive thermostat replaces the top bit. No need to drain.

I'm planning on picking up a rechareable heated blanket or gilet soon, I think heating me instead of the space may be cheaper, plus side is I can also charge the battery pack when I venture to the office once a week!

It's sitting still that's the biggest problem, IMO. With the door shut the combined effect of me, my laptop, dock and monitor heat the room quite well; you really notice the difference when walking out on to the landing.

However, sitting for a while I start to feel cold. Combo of alternating sitting/standing to work (with appropriate desk) and just walking out of the room to get a coffee usually helps.

I have a small oil filled rad but even set low I find the room gets a bit too warm and stuffy. Don't think I've used it at all in the last 12 months.

i've got a 15x10 office/studio at the top of the garden. built it myself so fairly well insulated, use a small oil filled radiator when required.

south facing as with big-ish windows so on a sunny day it doesnt need much heat at all. first thing can be a bit fresh so just put the radiator on a homekit plug so I can turn it on while I'm having breakfast in the house.

echo what someone else said about the monitor. I've recently been issued a 34" curved LG thing and it kicks out a huge amount of heat.

Once installed, I’m assuming they will need to connect to the house wifi and I should be able to see them on Google Home and do some controlling from that (or the Tado app directly) – do they need a central controller or do they just fit on radiator and each one is connected to the house wifi?

The TRVs connect to the controller, not directly to your Wifi - so yes they need a central controller. (Or they do for my Wiser ones). You want that controller to be the one controlling your boiler so the TRVs can turn the boiler on and off. For my Wiser system every radiator has a Wiser TRV and I don't use the room thermostat. I work from home and have scenes (called 'Moments') to quickly turn off all the radiators apart from the room I work in.

I got a sit/stand desk recently, and the increase in body temperature when standing is a lot more than I thought. I can warm myself up quite thoroughly by switching to standing mode.

Also a Zwift session provides a fair few hours of free heating afterwards.

Choose the smallest room with the most internal walls to work in. My box room office with 2m2 external walls takes 15 minutes of fan heater to then be warm enough all day. My partners spare room office with more like 10+M2 external walls needs the fan heater on all day when it's really cold (the radiator is chronically undersized).

On heating 1 room Vs the house. The heat loss is proportional to the temperature differential either side of a wall. So the hotter the house is the more energy you will lose to outside. This will in most cases dwarf the energy lost to the ambient house (16degC?) from a heated room. In reality I think it will vary case by case and come down to the thermal efficiency of the room you work in.

echo what someone else said about the monitor. I’ve recently been issued a 34″ curved LG thing and it kicks out a huge amount of heat.

https://www.lg.com/uk/monitors/lg-34wp65c-b

42W typical - I mean, that's maybe 10W more than a smaller screen.

But when the rest of the house is cold you need to use more energy to keep one room at a higher temperature than the rest.

More energy than what? That one room will require more heat if the neighbouring room is cold, but from a thermodynamics point of view, that should still be less than heating the whole house.

Thanks @sl2000 - off to do some more checking now.

Hopefully the final daft question - TRV = Thermostatic Radiator Valve? If so, is that the one where you can control how warm the heater is by turning the dial on the valve? All the radiators have those so hopefully a straight forward job - my DIY skills are woeful mainly due to lack of patience, this does sound like it would be a job I could do though!

that heatgeek article about lowering return temperatures is all well and good, but its playing with the margins. the theoretical difference between a 50C return temp (pretty normal) and a 40C return temp (really pushing things) is 3% of theoretical efficiency. Running a single room instead of a whole house can reduce the losses by around 50% - even if you're heating the water slightly less efficiently (which is debatable), the overall savings are more than compensated for.

Hopefully the final daft question – TRV = Thermostatic Radiator Valve? If so, is that the one where you can control how warm the heater is by turning the dial on the valve?

it is a thermostatic radiator valve, and it is normally a large dial with numbers on it, rather than a small knob. google imaged to see the sort of thing - if you're directly turning something which turns the metal tap, its non-thermo and you'd need to change that (including draining down the system) before you can add a smart trv

I'll have a go at the heating 1 room vs house thing too.

The two variables are rate of heat loss; and the cost of providing one unit of heat.

The heat is lost from the house to the outside (and to next door if you're in a terrace). That's proportional to the temperature difference inside to outside, the size of the walls, and the insulation. If you heat one room rather than the whole house the temperature in some of the rooms is lower, so the heat loss to the outside in those rooms is lower. You're heating those rooms with heat lost from your warm room to those rooms through the internal walls - but you're not having to heat them so much.

The cost of providing the heat is maybe what the HeatGeek thing says could be different (I've not watched the video of course). This would require a scenario where the boiler consumes more gas to put out less heat - and I can't imagine what that would be.

I think a combination approach works for me.

My office/bedroom has decent windows and gets quite warm from the sun when it's out.
Many days its more than enough heat.

When its warm and dry open the windows.. let the warm and DRY air in.

My big old desk has insulation round the back... some spare bits of polystyrene insulation left over from doing the floor in the kids room and a small (£20 Aldi) oil filled rad underneath (not been used yet this year)... so the warm air only has one way out .. my legs are tucked under (in fleece lined trousers as I type) and I can pull a duvet around when it gets cold.

That basically just leaves my hands... which last year I just used to warm up periodically under the duvet...

This year we put the heating on for 2 days and it dried the house a lot... it's not been needed since but I think it will end up being switched on a couple of days a month just to keep the house drier.

Simple engineering logic doesn’t agree. The single room has the house insulation PLUS whatever insulation exists between it and the the rest of the house. It doesn’t need any maths, just a basic understanding of thermodynamics and heat transfer.

+1, I'm not convinced either. It might be true in small houses with good insulation on external walls (like a flat or a terrace), but would flip the other way at some point, and I'd suspect it's not that big a house.

the theoretical difference between a 50C return temp (pretty normal) and a 40C return temp (really pushing things) is 3% of theoretical efficiency.

I dispute that 50C is normal. It's been quite a challenge to get mine down to that level, because my boiler is rubbish at turning itself down. The difference between a badly set up system and a well set up one could easily be 8% in my house even if you aren't short cycling which will bring it down even more.

8% of a £300 monthly bill (for some, not me fortunately) is still a significant amount of money.

I plan to do an experiment in the coming days if I can find two days of similar weather. I'll try heating the house as it is, then I'll go and turn all the TRVs down manually and compare the next day.

thats the diagram that talks about lowering return temp. Not sure how it applies to a tanked (non-combi) system where the feed temp will be at least 70C anyway (to get the tank hot enough to avoid legionellas). I guess the flipside is that by not maxxing out the boiler (into non-condensing mode) when running the hot tap, you water heating is a lot more efficient.

Not sure how it applies to a tanked (non-combi) system where the feed temp will be at least 70C anyway (to get the tank hot enough to avoid legionellas).

There's a Heat Geek video about this too. 60C is enough to kill Legionella instantly, but 50C is enough to kill it in 2hrs, so it's plenty. It also says that tanked systems are far harder to optimise because you still need the flow temp high for the hot water even when heating it to 50C as the coil in the tank can only dump so much heat. The only way round it is to have a boiler that knows when it's heating hot water rather than rads and turns itself up.

I'm going to avoid this by using a timer on the immersion heater to heat the HW cheaply overnight, but I can only do that because I have an EV tariff. If/when the car goes back I might have to investigate hacking the boiler to allow the flow temps to be turned up and down digitally so I can automate it.

he difference between a badly set up system and a well set up one could easily be 8% in my house

how did you get to 8%? you would have to drop your return temp from 116C (Which we can all agree is unlikely) to 40C return temp.

Assuming you're not sending boiling water out, the hottest you can push out is maybe 90C, which (for a 20C drop) gives a 70C return temp - around 87% efficiency. if you can get that down to 40C (unlikely with the same rads) you would see a 5% saving. Yes, that could be significant, but not nearly as significant as the savings in only heating one room in your house. Fortunately, you can both reduce the flow temp and only heat one room

With my system turned up I got output temps of 75C and return temps of 65C which corresponds to about 85% efficiency, and with it turned down I get maybe 45C return temps for most of the cycle giving me 92% or so, so maybe 7% difference in efficiency.

I can't get a 20C drop across the boiler. If I turn the flow down to allow more heat to be lost from the water in the rads, then the output temp goes up because it's also going more slowly through the burner so it gets hotter, and this ends up raising the return flow temps as well. I did get close to a 20C drop by restricting the rads to lower the flow even more, but that was tested during the day. It might actually go over 20C when it comes on first thing in the morning and the boiler manual tells you not to have a drop greater than 20C - but it doesn't explain why, so I don't know if it damages things or not.

My boiler is widely regarded as one of the worst ever made though, and I don't have an intelligent flow/pressure sensing pump either which means it's just about the worst possible condensing setup out there.

molgrips boiler woes. again...

I think your 65C temp would be more efficent than that, but there's an easy way to test. Measure the water coming out of your condensate drain. For each litre that comes out, you've saved around 7p in gas (compared to running with zero condensing).

But when the rest of the house is cold you need to use more energy to keep one room at a higher temperature than the rest. And who has a completely uninsulated house? If you actually watch the video the “basic thermodynamics” are shown to be anything but.

By heating one small room you're losing energy to the rest of the house, and then to the outside. By heating the whole house, you're losing all the energy to heat the small room + the rest of the house.

It's more efficient to just heat the one room.

I use a wi-fi oil filled rad in my (not very insulated) garden office and it does the trick. I have it come on at regular intervals to keep damp away from the computer etc. Albeit, Ive reduced those intervals recently

It’s more efficient to just heat the one room.

In terms of heat loss, yes. But your CH system will be running less efficiently if you do just heat one room, that's the point. Possibly significantly so. Whether or not that cancels out depends on a lot of factors.

Also if you turn off all the rads except one, you may damage your boiler unless there's a bypass circuit installed. If there is, you're just paying money to pump a few hundred litres of hot water around a loop whilst only a small part of that is actually being used to heat the room.

Whether or not that cancels out depends on a lot of factors.

Anyway the point is there are so many different factors in house design/insulation, boiler type/rad arrangement, room usage, etc it's ridiculous to say "this is always going to be the case" (even the HG don't say that on their site) especially given people here have actually been monitoring their gas consumption and reporting the opposite!!

Although I will turn our boiler flow down, as it's pretty high, I can see how that'll make a difference!

If there is, you’re just paying money to pump a few hundred litres of hot water around a loop whilst only a small part of that is actually being used to heat the room.

not disagreeing that some hot water is being pumped around. Its not hundreds of litres though - that would require nearly a kilometer of 15mm piping. However, that water is pumped around whether you're heating one room or the whole house, so unless you're heating none of the house, the point is rather moot.

Similar but unrelated......

Empty house in a cold area (and poor insulation) with all rads with Smart TVRs (Tado in this case) set to frost protection.......is it cheaper to let the system do it's thing with the rads calling for heat relatively frequently throughout the day as they bounce off the frost protection temp; or is it cheaper to put the heating on for the whole house for an (guessing here) hour in a nice boiler effient burst to raise the temp up enough that it might last until the next programmed warm up without anywhere calling for heat. I'm think the 1hr burn would win.

Re the WFH single room issue - regardless, keeping the human in the room warm seems to be the win here with the room heated as little as possible. So heavy jumpers, heated blanket, maybe even fingerless gloves and a hat. Those duvet slipper things.

Empty house in a cold area (and poor insulation) with all rads with Smart TVRs (Tado in this case) set to frost protection…….is it cheaper to let the system do it’s thing with the rads calling for heat relatively frequently throughout the day as they bounce off the frost protection temp; or is it cheaper to put the heating on for the whole house for an (guessing here) hour in a nice boiler effient burst to raise the temp up enough that it might last until the next programmed warm up without anywhere calling for heat.

Frequent-ish to a lower temp rather than once a day to a higher one is best - the lower the average temperature over 24 hours the less heat lost. But all radiators together is best to reduce cycling. I expect that setting all the Tado's to heat to 6 or 7 degrees for 15 minutes every 4 hours might do it. They would then all come on together and switch off once 7 degrees reached one-by-one. Depends how quickly the house cools as to how often and what temperature is best. You can tell from the Tado reports what the radiators have been doing.

Bg engineer told me to leave heating on all day on frost protect, 7 degrees I think, as house is left empty for a long time. Setting the timer, as he said, is academic as cold periods can happen at any time. Worked so far, boiler not had to do anything.

Bg engineer told me to leave heating on all day on frost protect, 7 degrees I think, as house is left empty for a long time. Setting the timer, as he said, is academic as cold periods can happen at any time. Worked so far, boiler not had to do anything.

That is effectively what a smart system set to frost protection is. But I question it's efficiency. Sure, it stops damage, but a system bouncing off the frost temp will, in a proper cold snap, having it coming on and off many times a day. With the smart system this is even worse as each room can call for heat independently magnifying the calls. My theory (and sl2000 above seems to agree -ta) is to preempt the frequent calls by raising the temp a bit above the frost protection level once, or a few times a day with a boiler efficient blast.

Obviously this is a mute point if it's not that cold outside...but for context where I live we did not see a positive Deg C temp day or night from Dec 24th 2020 to Feb 14th 2021 - so 7 weeks of sub zero 24hr a day. The loch half a mile away froze to 8 inches thick. At those kind of temps frost protection in an empty house (and energy efficiently sorting it) really comes into play.

An IR panel would be good for just heating 'you' at a desk - MrsF has one next to her and she feels the cold. Fairly low wattage and they are usually temperature controlled from a remote - so you leave that near you !

Thanks, think I'll buy a small oiled filled radiator and continue to wrap up in layers and blankets, sadly wooly hats no go for the number of online meetings I have, although I'm going to move the kettle upstairs through the day time, every little helps

Podcast referred to above costing small elec heaters v central heating was sliced bread, r4.

All this argument over technicalities of heating - when the answer is insulate the room you are in as best you can....

The main boiler controller (so Hive in your case) and the radiator thermostats need to be the same brand / system – so you need to buy Hive TRVs, or replace your Hive controller with a new Tado one.

Not necessarily; without a Tado boiler controller the TRVs can't turn the boiler on, but they can still turn off the radiator they control so it won't do anything when the central controller turns the system on. This can still be useful if you want to heat a central bit of the house always and specific rooms sometimes.

We ran some Tado TRVs with a Nest central controller for a while before we fully migrated to Tado. If you've already got a system that supports TRVs I don't know why you'd do this, admittedly...

Do you need to hear the room?
I bought some lined trousers and sometimes wear a battery heated gilet when it cools down. With the heat from the laptops end electrics it keeps me plenty warm enough to function

Just another thought, what about something like a Kotatsu? Sounds very STW niche friendly.

sliced bread, r4.

That's the one. On a slightly different topic and related to the pod cast I'm wondering about a ceiling mounted IR panel in the garage. Current heater us a fan heater which as the podcast notes gets very addictive and then you overheat only to be cold again when turned off. Anyone any real world experience of IT heating panels.

Tje obvious answer is a new PC with one of the Nvidia 4090 cards in. They can draw 600w, so aim the exhaust at yourself while you work and let the graphics card warm you. Or, when/if it catches fire, let the fire warm you.

continue to wrap up in layers and blankets, sadly wooly hats no go for the number of online meetings

Yes It wouldn't be good to fail a workplace suitability assessment via teams......

Interesting article on the beeb over the weekend about the effects on the brain trying to work in low temperatures....

Interesting article on the beeb over the weekend about the effects on the brain trying to work in low temperatures….

Do you mean this one? Linky

If so, then I read that article, and wasn’t sure if I missed something but it seemed to be looking at the health issues of living at 10degC without whilst wearing a thin, short sleeved unbuttoned shirt and shorts. I didn’t understand then and don’t now - surely that’s a study into the effects of wearing unsuitable clothing, not of temperature?

Manual TRVs here, I turn the ones in the other rooms off manually. One advantage of not having many rooms.

Measure the water coming out of your condensate drain. For each litre that comes out, you’ve saved around 7p in gas

Is that true? Doesn't the bulk of the condensate get exhausted with the flue gases, hence the plume you see from boilers?

Just listened to that BBC podcast.

For now, it looks like I will keep using my oil-fired CH with EvoHome TRV's. Whenever the heating is on, both our towel rails in the bathrooms are on too so at least towels etc dry too.

Those infrared panels looking an interesting proposition, but they didnt compare the cost of them.

The other option is maybe the diesel heater? I've seen a lot of installs in sheds, workshops and houses

Worth taking a look at the FB group

I installed one recently in my van. It's been awesome

Is that true? Doesn’t the bulk of the condensate get exhausted with the flue gases, hence the plume you see from boilers?

Isn't the plume from vapour that condenses in the flue or outside, so doesn't contribute to the heat output from the boiler?

I suppose theoretically condensing 1l of water releases 0.7kwh of energy, which at 10.3p/kwh is 7.2p...

I hadn't thought of it that way before. This makes me feel better about the times I've been splashed by our boiler's condensate pump that is meant to empty into a gutter but does it a bit too enthusiastically so it sort of goes everywhere...

We have solar panels but no battery storage (yet). My working from home in a single small room involves a small 500w oil filled electric radiator that I turn on during daylight. The panels, even in winter, can generally supply enough power to run the a 500w heater. Power from the grid obviously kicks in when the solar output drops below 500w.

The radiator is under my desk by my feet.

Also, hoodies and slippers.

Not sure how it applies to a tanked (non-combi) system where the feed temp will be at least 70C anyway (to get the tank hot enough to avoid legionellas).

This is why we just upgraded our system to Priority Domestic Hot Water. Twice a day we tell the hot water to come on, and this tells the boiler to output 70C water while a valve ensures that the water goes only to the cylinder. Takes about 20 minutes to get the cylinder up to temp, then the valve closes and the boiler goes back to 55C for the central heating (see chart below).