Energy myth-busting: Is it cheaper to have heating on all day?

Smiley_Dan

Depends whether you have addressed ventilation or not...

lstar337

Richie-from-the-Boro wrote: »

The question in isolation has no end [answer] value. For example a generalist answer would be if your SAP [Band A] rating was 90-100 points it may well be cheaper to maintain a living temperature of 22°C. Put crudely if your SAP [Band F or E] was 20-50 points it would be a complete waste of time to leave your heating on 24/7 because you would always be loosing more heat than you could put in to the dwelling even at 24/7.

I think it is still better to not have it on 24/7. I live in a [Band A] property now and it only needs about 30 minutes of heat at about 7am and occasionally a 15 minute top up at 7pm to maintain a temperature of 23°C+ for the whole time we are awake.

I don't want to leave it on all day as the boiler may fire needlessly, wasting gas.

John_Pierpoint

Good point about cycling a gas boiler - a lot of people do this in the summer if they have a hot water tank that could be losing a couple of kW hours of heatproduced by a boiler that never getes as far as condensing. So running at 75% efficiencey if you are lucky.

John_Pierpoint

Smiley_Dan wrote: »

Depends whether you have addressed ventilation or not...

"Build tight and ventilate right".

Smiley_Dan

John_Pierpoint wrote: »

"Build tight and ventilate right".

That's my point. Maybe I misread your post, but I thought you were implying A rated dwellings had condensation because they are airtight, whereas of course if you've installed a controlled ventilation system that shouldn't be a problem.

Apologies if I misread.

malc_b

As my post explaining the maths is lost the past of this thread I'll summarise for new members as the question of why do we need this this thread needs answering.

In a simple physics model, yes, it takes less energy to heat a house only when you are there. But that is too simple. Depending on the house, the fabric of the house (wall, floor) can store a lot heat. That's how E7 heating works after all. You heat up a pile of bricks overnight and these bricks then give out heat all day. So when you heat you house when you get up in the morning you're heating the fabric too. The heat in the fabric leaks out while you're at work.

In other words if you look at it from other way, what and when is the house loosing heat you'll find it is still loosing heat 24hrs/day. You have to replace that heat. In fact intermittently heating a house might reduce the daily heat to 80-95% of the 24hr figure (if you search back in this thread you'll see I've proved that with maths).

OK, so intermittent heat saves a bit, case closed, right? Well no, unless we are taken electric heating with 100% efficiency. Oil, gas, coal even can be more efficient at lower power, like if you are heating 24/7. This is especially true for condensing where there is about 10% difference between high output, non-condensing, and low output condensing modes.

And for those who are wondering what the maths are here is a little thought experiment. Imagine a one room house, 0C outside, 20C inside. The loses are 1kW so it has a 1kW fire. Total loss over 24hrs is 24kWh. Now imagine the owner goes to bed, the fire is turned off. At that instant the inside temperature is still 20C so the loss is still 1kW. As the temperature falls the loss drops. Say 8hrs later it is 10C inside, loss is now 500W (and 10C is very cold house!). So 750W on average overnight. Total daily loss in this case is 16hr x 1kW + 8hr x 750W = 22kWhr. The saving is 8.3%. But also during the 16hrs the heating is on we need to put in 22kW so the fire must run at 1375W. If you use a more reasonable 15C after being off overnight then the figures are 4.2%, 23kW, 1478W.

This will happen in any home other than a tent. In any house when you turn the heating off the temperature stays higher than outside due the stored heat. Turning heat off saves losses but puts up the heating power needed when it is on. Hence it is quite probable that running in low power condensing mode 24/7 will use less fuel than 16/24 (in mid winter). The aim should be to run in condensing mode as much as possible (i.e. low radiator water temperature which mean low radiator output, at 60C diff (80C-20C) rad = 100%, at 40C diff (60C-20C) rad = 60%). So as the weather gets cold increase the heating hours rather than run not in condensing mode.

I would appreciate maths based arguments as to where that is wrong. Arguing that physics says it is wrong when I'm using physics to prove it is a waste of your time and mine. I'm not saying you lose less heat, I'm saying heating efficiency can exceed the extra heat lost so less fuel is used.

r2015

Say 8hrs later it is 10C inside

So when you get up to go to the toilet 7 hours and 59 minutes after the heating goes off you are freezing.

That is why in the middle of the winter my heating is on 24 hours a day, though I turn the thermostat down to maintain 18 deg c during the night when I go to my bed.

malc_b

r2015 wrote: »

So when you get up to go to the toilet 7 hours and 59 minutes after the heating goes off you are freezing.

That is why in the middle of the winter my heating is on 24 hours a day, though I turn the thermostat down to maintain 18 deg c during the night when I go to my bed.

The 10C is just an example to show the principle (and make the maths easy). I'd have said that 15C is more likely from my experience but it depends on how good the home insulation is. And remember this is when outside temp is 0C, that's mid winter in UK.

the_devil_made_me_do_it

Just thought I'd ask a few questions:


Last year I moved into a small 2 bedroom bungalow. I rent it off a social landlord. Unfortunately they ain't the best when it comes to modernising their properties. It was bit in the early 90's, but still has the original patio door which has a metal frame and a hard wood front door with a small non double glazed window.


It does have upvc windows throughout which have a controllable vent. The patio door as a vent of sorts, but it may aswell be closed for the good it does.


Every room has a radiator, with control valves (going from 0 to 5) and a thermostat in the hall way.


Now my main concern really is would it be better condensation wise to leave the heating on all day? During the summer there was no condensation at all. However, since it's getting colder, there is condensation on the patio door and on my bedroom window. This doesn't bode well as I suffer with asthma.


I'm also not clued up with thermostat controls either on the radiators or in the hall. The only room which I don't use heating in is the kitchen. The radiator is too close to my fridge so have had to turn that off completely. Although I'm hoping that when they re-fit the kitchen, they will some how move the radiator away from the fridge area.


The property does have decent loft insulation, although I'm not too sure about cavity wall. I have asked the landlord to fit a ventilation system in the property, but they are just trying to ignore my request. I can't afford to fit one myself, but would have to get permission anyway.


If someone can give me a hand sorting my heating out, it would be much appreciated


Oh and I hope I've made this a comprehensible picture of my circumstances.

Cyberman60

I've found it cheaper to have the heating off all day. I must be missing something !!

BTW.. I do get condensation on really cold mornings, but wipe it off the windows with a towel in the morning, or even open the windows if it's a nice morning. No big deal IMO.

Also, I sleep with window open which means no condensation in my bedroom.