@mattyfez the thread has moved on a bit but that amount of old, scraggy-looking fibreglass is about what we had when we moved in over 15 years ago.

I added some newer stuff over the top. if I remember correctly 200mm thick.

I suppose it made a difference. Awkward getting the insulation under the cables but otherwise OK.

My cost of electricity fell below 5p per kWh between 02:30 and 05:30 so the underfloor in the kitchen and the oil rad in the bedroom came on between those times this morning.

It definitely makes a difference and combined with the stove I don’t need to burn any oil quite yet other than for hot water.

Unless your boiler/system is massively inefficient, combined with a house that didn’t lose much heat then it holds true. For Joe Blogs in a normal house with normal gas (or electric, or oil, or LPG, or wood fired) heating it’s correct.

Sums?

My cost of electricity fell below 5p per kWh between 02:30 and 05:30 so the underfloor in the kitchen and the oil rad in the bedroom came on between those times this morning.

It definitely makes a difference and combined with the stove I don’t need to burn any oil quite yet other than for hot water.

Did the same this morning, we’ve an oil filled radiator set up to take advantage of the plunge pricing.

  Did the same this morning, we’ve an oil filled radiator set up to take advantage of the plunge pricing

I think there’s more on the way with this wind!

I’ve got more WiFi plugs arriving so I’ll put one on the heater in my office and maybe another somewhere else as well!

I turned mine back on a couple of days ago after I got home from work and it was still 15c in the house, it’s been nice waking up to a 20c house these past couple of mornings. In hindsight though I should have dusted the rads first, bit of a pong for the first hour of them coming on

Unless your boiler/system is massively inefficient, combined with a house that didn’t lose much heat then it holds true. For Joe Blogs in a normal house with normal gas (or electric, or oil, or LPG, or wood fired) heating it’s correct.

Sums?

U value x Wall area x Delta T

you cant adjust your wall area so the only two ways to reduce heat loss are to reduce U value or Decrease Delta T 

so assuming your U value doesnt change over night – the higher you keep delta T the more heat your losing. 

I think there’s more on the way with this wind!

I’ve got more WiFi plugs arriving so I’ll put one on the heater in my office and maybe another somewhere else as well!

Fingers crossed for a particularly breezy winter 😀

Yes I know the physics thanks but that’s not the whole story as I said.  How does having to run your heating* flat out for 2 hours in the morning change its efficiency?  How much warmer does the air have to be when the floor and furniture is cold in order for people to feel comfortable?

* by this I mean your specific heating in your house

the thread has moved on a bit but that amount of old, scraggy-looking fibreglass is about what we had when we moved in over 15 years ago.

Sorry to derail a bit again, but I’ve been looking at loft insulation to layer on top of the existing stuff, I’m lookin at probably 30m2, probably more like 25m2 actually accounting for leaving a gap around the edges

https://www.diy.com/departments/diall-insulation-roll-l-6m-w-0-37m-t-100mm/3663602481812_BQ.prd

This looks interesting as its non itchy, but £10 per m2 is crazy compared to what I presume is the nasty itchy stuff at £2.25 per m2

Is there such a thing as reasonably priced insulation that doesn’t require wearing a hazmat suit? lol!

Honestly at that price I’d wear the suit.  You can buy disposable ones, get some gloves, glasses and a mask – it’s cheap as chips and you won’t be up there long.

Yes I know the physics thanks but that’s not the whole story as I said. How does having to run your heating* flat out for 2 hours in the morning change its efficiency? How much warmer does the air have to be when the floor and furniture is cold in order for people to feel comfortable?

There is no magic woo, it’s just the first law of thermodynamics.

If you lose less energy, you don’t have to put as much in.

If it takes you 2hours of heating to warm it up in the morning, then the boiler would have to run more than 2 hours overnight to maintain it.

The only fly in that over simplistic ointment is boiler efficiency under different loads. But even if the boiler is more efficient at low loads (probable), it’s in the order of ~10% different.

In order for it to me more efficient to heat the house 24h/day from a conventional gas/oil boiler or normal electric rads, you would need a system that:
1) lost very little energy at all (thus you get no benefit from the reduced dT, which is a bit like saying you found £20 note that you dropped earlier, it’s not actually a benefit).
2) a heating system whos efficiency dropped massively as the load increased.

1 is rarely true, 2 isn’t true of most gas boilers (a condensing boiler is about 15% more efficient at 5% than it is flat out, and as you yourself pointed out, most boilers don’t go below about 30-50%.

* by this I mean your specific heating in your house

I’m not going to leave my heating on all night burning money to win an internet argument.

But here’s an illustration, assume it’s 8C outside and heating is set to 18C to make dT = 10C.

Heat flux (im eliminating area for simplicity) is assumed to be 0.5kWh/degC*hour

Over 10 hours that’s 10C x 0.5 x 10 hours = 50kWh energy.

Let that drop to 15C inside and the heat lost is only 7 x 0.5 x 8, plus 10 x 0.5 x 2 = 28 + 2.5 = 38kWh

You can complicate that simplification with a specific heat capacity and mass of the building to give a temperature profile as a curve etc, but the end result would be similar.

I think there’s more on the way with this wind!

Tonight from 23.30 – 05.00 looking like near to 0p/kw. Pity I’ve not switched my energy supplier yet 🙁

I’m not going to leave my heating on all night burning money to win an internet argument.

I’m not asking you to. However, in my experience in my house, leaving it “on” all night but setting it back a degree or so means it never actually fires unless it’s a properly cold night, but it does mean that in the morning it can bring the house up to temp quite quickly.  If you’ve been following – in my house, the minimum output of the boiler is above the radiator output so we kind of need to get the rooms heated up before the short cycling happens which requires a certain temperature and it also needs the house to not be that cold to begin with.

On our coldest nights, with the heating off entirely, we drop about 5C overnight.  To put this back when people get up in the morning we had to get the heating to run for an hour – but floors and seats are all still cold.  Just as it got up to temp everyone left and the heating went off again. So it really was a huge waste of energy to have it on in the morning at all. But then if we didn’t turn it on we’d have a freezing house.The fact the temperature is even most of the time and the walls and furniture etc are all maintained at temp is the reason we can set the thermostat to 17.5C and be perfectly comfortable.  If the fabric of the house is cooled to 14C and then heating comes back on set to 17.5 it feels freezing.

But here’s an illustration

Yes, that says that a warmer house loses more heat – we know this.  What you’re not taking into account is how your boiler is working.  A short cycling boiler loses a lot of efficiency.  When you’re outputting your 9kW of heat, where’s it going?  If the air gets warm, the heating goes off but the mass of the house could still be cold.

All I’m saying is that there’s a lot you’re ignoring. This is why we have ‘smart’ heating controllers that test everything out to learn the optimum parameters for your house and setup based on weather, and how often the user calls for more heat etc – because you can’t predict it simply.

Sounds like you could do with bigger radiators rather than just burning lots of fuel (but efficient) for the sake of it.

Pity I’ve not switched my energy supplier yet

Ufh, bedroom heater, Tumblr drier are on and the oven is cleaning itself.

Meter said we were using 10kWh when I last looked!

All this flow temp talk, which I admit I’ve only really skin read, does it apply to (modern) oil boilers too? If it does I’ll read it in more detail.

Not as much, because they don’t have the condensing part.

Sounds like you could do with bigger radiators rather than just burning lots of fuel (but efficient) for the sake of it.

Ah, I’m not burning fuel for the sake of it. I’m aiming to find the cheapest way to be the most comfortable, which in my case means a relatively high ‘set back’ temperature of 16C. I mean you appreciate I’m not leaving the heating burning away at 21C all night right?

But yes I do need bigger radiators. I installed three last month, will probably do the rest next month.

mines a condenser – ive had it for 12 years i would not consider it modern

at the same time theres only 1 or 2 on the market that can modulate so its a law of diminishing returns but you can reduce short cycling to large degree.

but bigger radiators are king. most of my rads are at least double the size the rooms need for this reason – our kitchen diner has 3 large double  – and its not a huge room but due to surface area available it removes plenty heat from the system and ensure that my return temp is correct + my house heats quickly for low oil use and limited short cycling.

Yes I agree there. We had tiny rads all round. There were three without TRVs in the hallway and two landings which were 40 or 60cm single panel. We replaced the bottom one with a 140cm single and now a 160cm double.  Will replace the rest of the singles with slightly wider doubles, as space permits.
Even then the ballast rads (without TRVs in the hallways) won’t be anywhere near enough to dump the heat, so the TRVs and the main thermostat need to be balanced so they all heat up together. Kinda helps that the rad in the hallway with the thermost is now the last one in the loop so the other get heat quicker. When their TRVs turn off it puts more heat in the hallway so the main stat turns off after the rooms get warm.

I’d like a bigger rad in the kitchen/diner but it would be in the way so I was considering kickboard radiators.

mines a condenser – ive had it for 12 years I would not consider it modern

Ours is a Greenstar Danesmoor External, fitted a couple of years ago, I dunno if it’s a condensor or not, guess I could find out.

but bigger radiators are king. most of my rads are at least double the size the rooms need for this reason – our kitchen diner has 3 large double – and its not a huge room but due to surface area available it removes plenty heat from the system and ensure that my return temp is correct + my house heats quickly for low oil use and limited short cycling.

Ah, this is interesting. In one of our rooms there’s two rads, both TRV’d, and I’ve turned one of them off as the room heats fine without it, thinking this would save fuel – would I be better leaving it on?

In one of our rooms there’s two rads, both TRV’d, and I’ve turned one of them off as the room heats fine without it, thinking this would save fuel – would I be better leaving it on?

If they are both on a TRV then turning one off makes no difference – with the same flow temp, you’d heat the room faster but the TRVs would turn off earlier.

However, with bigger (or more) the return flow is cooler which helps condensing. It also means you can run lower output (aka flow) temps which, if you have a modulating boiler, will result in more efficient running; and also result in lower flow temps which helps if you have a condensing boiler.

So in short yes, more/bigger rads is better.

So in short yes, more/bigger rads is better.

But only if you have a condensing boiler?

Hmm well – it would also work if you can turn the flame down on your boiler.  A larger heat exchanger extracts more heat, which is fairly intuitive, but if you make the flame smaller then the heat exchanger becomes effectively larger.  A modulating gas boiler does this for you to a greater or lesser extent.  Now the oil boiler IHN mentioned does apparently have a temperature control; not sure if it makes the flame smaller or just shuts itself off when hits the temp. Probably the latter.

If you don’t have a boiler that can reduce its flame, then more rads would allow the return temp to be lower; but this would make the flow temp lower as well since the flame is only adding X amount of heat to the water.  That would mean that the boiler would be less likely to short cycle before the house warms up.  More rads means more heat is extracted from the water, for the same temp – therefore if the boiler can only put in X and the rads can extract X it won’t short cycle whilst the house is heating up.

So yes, more rads is still better. How much better? Well, it depends.

No. In all cases a bigger emitter allows a smaller ∆t and greater efficiency.

Its why heat pumps like underfloor heating the best.

That would mean that the boiler would be less likely to short cycle before the house warms up

In all cases a bigger emitter allows a smaller ∆t and greater efficiency.

And why are these a good thing? (Genuine question, not arguing it cos I have no idea). If the answer is “read the rest of the thread you lazy get”, then fair enough:-)

Ours is a Greenstar Danesmoor External, fitted a couple of years ago, I dunno if it’s a condensor or not, guess I could find out.

IIRC All domestic boilers have to be condensing now, so your one will be.

And why are these a good thing?

Your radiators get water in at a certain temp, say 60C, and it exits at a lower temp cos it’s cooled down – and transferred heat to the air in your house.  Ideally the water exiting would be about 40C, then that means the return temp to your boiler is 40C.  Then it goes through the flames and heats back up to 60C and so on.

If your rads are too small, then the water doesn’t have time to cool down by 20C on its way through, which means that it might come back to the boiler at say 45C.  But it still picks up another 20C on the way through the flame at 1000C whatever, so then it’s 65C on the way out. And next time it’s 70C and so on. If your boiler is set to shut off at 70C it will then shut off but the water is still being pumped around. So the flow temp drops quickly down to say 50C at which point the boiler goes ‘oh that’s too cold’ and turns back on again. and so on.

The rapid turning on and off of the boiler is inefficient and can wear it out prematurely.  The solution to this could be to restrict the flow of water (or turn the pump down) so that it moves more slowly through the radiator and does cool down. But then, because you are putting not much water through, the amount of heat being emitted is a fair bit lower.

Big rads mean your water can flow through it quickly enough, and still cool down.  More heat is extracted from the water which means more heat into the room.  So it’ll heat up quicker, and the boiler water will stay at the right temp.

Looked at another way – radiators have a rated heat output.  A small single panel is about I dunno, 500W, a big double panel 2,100W, at a particular temperature.  If your rads are too small, the sum total of their output could be less than the boiler’s minimum output, so the flow water gets too hot and the boiler shuts off before your house is warm and the situation above happens.

The rads output more heat if they are hotter (of course) so with smaller rads you can run the system hotter. You might not prevent it short cycling in theory, but your house may get warm enough before it starts. But when running high temps you won’t be condensing.

Short cycling – where the boiler turns off and on every minute or less, is very inefficient.  Not exactly sure why, maybe a bit of gas is wasted as it lights up, dunno.

Ta. And boggo (big) rads aren’t that expensive either, right?

Actually, a follow on question. Say I put enormous radiators throughout the house, what would happen if the water returning to the boiler was at, say 20deg?

And, they’d need to be carefully balanced, right? Because otherwise the heat might have been taken out of the water before it got to the radiators at the end of the chain?

Actually, a follow on question. Say I put enormous radiators throughout the house, what would happen if the water returning to the boiler was at, say 20deg?

If the water returning is quite cool, it’s unlikely the water exiting the heat exchanger is massively hotter unless the flow is really restricted, it’s all the same water circulating reasonably quickly. The boiler just dumps some heat in it and passes it on, it can’t hold it until the output temp has reached a set level.

And boggo (big) rads aren’t that expensive either, right?

No, not at all. Replacing our 60cm singles with 60cm doubles (type 21) costs £55 each I think. The 160cm one was maybe £120 IIRC. It would have cost £500 to basically double the rad area in our whole 3 bed house.

it’s all the same water circulating reasonably quickly.

You can control how fast it circulates. My 12kW boiler can raise the temp 20C at best – in fact, there is meant to be a limit on this, you need a minimum flow and there is consequently a maximum recommended temperature increase. It can be less if the flow is faster.

Condenser boilers use the heat still in the exhaust gas to add heat to the return water from your central heating ring main . Via a heat exchanger. This is where a lower water return temperature is most beneficial. As the TD is greater more wasted energy in the gas exhaust can be utilised.

The drawbacks are the boiler still needs to get the output temperature to around 65c to heat your rads , and then the air next to the rads. So modulating , condenser boilers which can go down to 3 or 4kw can heat an entire house if big enough rads are correctly balanced via the locksheild so flow and energy transfer takes place effectively. By adding another heat exchanger the rise in temperature can be reduced making the boiler cheaper to run .

Short cycling is the boiler firing for less than a minute , then off again, then on again a minute or two later etc  This is bad for the longevity of the internals. The h.e gets alot more expansion and subsequent contraction movement potential causes cracking , valves and solenoids cycle more frequently, electrodes and transformer does more work.

What you want is a boiler which fires up on full chat for maybe ten minutes then starts to reduce the flame by turning down the gas.like boiling a pan of water , alot of energy to get to boiling , then a tiny amount to keep it there.  Allowing the primary and secondary he to get to operating temp and staying there. With just the gas solenoids and pump and exhaust fan running constantly. Then after a few hours the system shuts down and goes through a cooling cycle with the fan and pump to gradually remove the heat .

Older system get hot spots caused by rust build up in the primary from the rads and insufficient  inhibitors and calcium carbonate in the secondary from hard water.

The drawbacks are the boiler still needs to get the output temperature to around 65c to heat your rads , and then the air next to the rads.

No, you can run the temps lower than that. Mines set to 50C currently. It may need to be higher when it’s colder, that’s what weather compensation is for; it also depends on your house which is what the learning algorithms in Nest are for.

You can’t really heat your hot water when the flow temp is that low though. I use cheap overnight electricity for that.

Yes , 

As you have previously posted, a 50c output temperature takes 2hours in the morning to get  all your house warmed through, including the soft furnishings. That’s with outside air temperature still relatively mild .

Drop the outside air temperature by 5c, and in the real world people want heat way quicker than 2 hours , more like 20 mins as they are up and about then leave for work. So most people run the CH system from 0600 – 0800 , then off.

With the 50c , low flow , throttling back scenario you run, your house gets comfy as everyone leaves for school and work.  So you either turn on the heat earlier or run a higher boiler output temperature.  I know you are optimised for your own particular circumstances but for the people still going to work all day it’s a higher work load for less time for the boiler. It might cost more to run but alot of people don’t care, they just want to be warm as they grew up in painfully cold , damp houses and don’t want to put their kids through the same, or see being warm as a right , or a status symbol. Even if they can’t afford it. 

As you have previously posted, a 50c output temperature takes 2hours in the morning to get all your house warmed through, including the soft furnishings. 

Don’t think so, I am running 50C because I have an overnight set back temp only 1.5C lower than the daytime. If I let it get cold overnight then yes 50C would not be enough. But I believe the house is more comfortable this way and it’s cheaper, for us. The high set back temp is part of the low and slow strategy.

I like being warm too btw. Point is that 18C in a house that’s already warmed through at 18C is a lot more comfortable than 18C when the whole house was 14C an hour ago.

Down to 12.5C in the lounge now, heating time is approaching soon 🙁

You must be cold?

You must be cold?

Nah, I’ve got a woolly jumper and a hot water bottle