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

Smiley_Dan

orrery is correct, it's one of those times you're best off ignoring what actually happens and just concentrating on the concept because you're unlikely to time it correctly anyway.

givememoney

richardsoffice wrote: »

“Should I use a tumble dryer, or place washing on an airer with heating on? . . . A. An airer is better because tumble dryers use a lot of energy.” :think:

Martin, are you aware that drying cloths on an airer is one of the BIGEST causes of damp in people’s homes (especially flats) If you must dry clothes indoors in the winter use a tumble dryer which is rigged to vent outside either via a preinstalled vent, or a hose hung out of a window.

I am a property landlord and I see this time and time again, drying clothes in a modern well insulated and draft proofed property without a power fanned vent such as from a tumble dryer causes black mould within the property this mould gives off spores that affect the occupants health especially young children this can lead in extreme circumstanced to developing pneumonia.

!!! Please remove this dangerous and ill-founded advice from your latest Martin’s Money tips!

Regards Richardsoffice

I have been drying my clothes on an airer for years and years and we do not have any damp in our house. In the summer it goes on the line if the weather is good and if we come home from being away which we are, a lot, in the summertime and the weather is bad, it goes in the tumble drier but other than putting towels in it for 15 mins once a week to soften them, I don't use it.


We have double glazing and central heating and thick loft insulation. We are both pensioners now, so are in a lot during the week and don't want to be cold. If we know we are going to be out all day we turn the thermostat right down. We turn it down of a night so it just comes on if it is very cold.

Cardew

Smiley_Dan wrote: »

At the risk of raising my head above the parapet...

I think there are a few real-world things to consider which cloud the *interpretation* of the physics (they do not change the physics).

Overheating. A higher rated power source is more prone to expending extra energy as the heat curve the thermostat follows will be naturally more peaky. Improvements in technology try to avoid this, but this will always be a problem *to an extent* with higher grade heat versus lower grade.

Insulation. Discussions about Passivhaus are a bit academic in the sense there are so few of them; however, there are better insulated and airtight houses now (not as many as we should have, but still). This makes differences in cost increasingly negligible (I'm talking about highly insulated here, but not necessarily PH).

Heat generation technology. Some technologies work best at lower grades of heat, and are cheaper ways of generating heat. Heat pumps being an example, which have to be run for much longer than other heat sources.

Lifestyle. It matters whether the occupants are in all day, or work a 9-5. If they are in all day, that leaves more choice as to heating technology; this is one variable where low grade heat is more suited. If you have the heat on longer, it can also work better with houses with higher thermal mass. Whereas those coming home from work want instant heat; timber framed houses may be better there.

I am NOT disputing the laws of physics. They are clear. And in the general case, it is best to time your heating so it is only there when you need it. Furthermore, most of the posters who dispute the physics don't have highly insulated homes with heat pumps. However, the laws of physics are just one input to this; looking at the thread title, also important are economics. And there's also an implied notion of comfort; how much heating is enough?

As you say the laws of physics are quite clear. It ALWAYS takes more energy to maintain a set temperature, than bring that body(i.e. property in this discussion) back up to that set temperature. Hence timed heating will be cheaper than constant heating.


Each year this subject is raised several times and from some posts on MSE people could be forgiven for thinking there are exceptions to that law - and there aint!


Heat pumps are no exception. The only reason they have to be run longer, or even 24/7, is that the low water temperature(typically 30C to 40C) is incapable of bringing a property back up to temperature quickly; not so with a gas/oil boiler that can heat water to 80C if required.


It is also pertinent that heat pumps are not cheaper to run than gas.

maxmiler

PigletJohn wrote: »

You said on the Myths page "Turning your radiators up and down using thermostatic radiator valves on the side of them affects how quickly the room heats up. If you have them on high, your radiators will emit lots of heat quickly until the set temperature is met and vice versa."


This is not true. Turning up thermostats does NOT make the room heat up faster and does NOT increase the temperature of the radiators or their output. It only causes the room to continue heating up after it has reached your comfortable temperature, resulting in the room getting too hot.


If a stat is set to e.g. 20C, it will run the heating (or continue heating the radiator) at full power until the room hits 20C; then it will turn off, and will come back on if the temperature drops below 20C (radiator valves may be able to partially open if the temperature has only dropped by a tiny amount). If you set it to 30C, it will still take exactly the same time to reach 20C, but then it will continue wasting energy until either you manually turn it down, or the room reaches 30C.

It appears that you have not been reading this thread.

I'm not a heating expert, but I do know that TRV's are analog, not digital. So as the TRV approaches its set temperature it begins to close, thereby reducing the flow of hot water at say, 18 degrees if it is set to 20 (depending on TRV).
Whilst I agree that it is not good practice to set it higher than the temperature that you want, for a quicker warm-up a little overshoot might help (albeit at increased cost and the need to remember to set it back). But I reiterate it is not good practice.

maxmiler

Cardew wrote: »

As you say the laws of physics are quite clear. It ALWAYS takes more energy to maintain a set temperature, than bring that body(i.e. property in this discussion) back up to that set temperature. Hence timed heating will be cheaper than constant heating.


Each year this subject is raised several times and from some posts on MSE people could be forgiven for thinking there are exceptions to that law - and there aint!


Heat pumps are no exception. The only reason they have to be run longer, or even 24/7, is that the low water temperature(typically 30C to 40C) is incapable of bringing a property back up to temperature quickly; not so with a gas/oil boiler that can heat water to 80C if required.


It is also pertinent that heat pumps are not cheaper to run than gas.

But surely one of the points that has been made very well by Malc_b (bearing in mind his caveat) is that the boiler can be more efficient if run with a lower water temperature. So there can be a fuel saving in certain cases by having the water temperature lower but the actual heating on for longer.

oldbaldeagle

Even if you are on Economy 7 never ever leave washing machines or dishwashers running overnight; they can leak or, especially in the case of dishwashers, catch fire.
Also, if you plan to leave your home unoccupied for more than 48 hours, check your insurance; there is more than likely a requirement that the heating be left on continuously at a minimum of 10C during the months of October to March!

Cardew

maxmiler wrote: »

But surely one of the points that has been made very well by Malc_b (bearing in mind his caveat) is that the boiler can be more efficient if run with a lower water temperature. So there can be a fuel saving in certain cases by having the water temperature lower but the actual heating on for longer.

That is not in dispute, if you can keep the boiler in condensing mode the boiler will be more efficient.


However how does that affect the principle that maintaining a set temperature is more expensive than having it timed?


So have your boiler in condensing mode on timed, and it will be cheaper than the same boiler in condensing mode 24/7!


You can have electrical heating which is 100% efficient but the same principle applies; maintaining a set temperature etc etc

PigletJohn

but maxmiler, surely you do not think that "If you have them on high, your radiators will emit lots of heat quickly until the set temperature is met " is correct?


What you are describing is the reduction in input as the room nears its target temperature, to avoid an overshoot taking the temperature above target. When the radiators are already fully hot they will continue emitting heat for a time even if you turn the valve off.


Turning up the stat does not increase the output of the radiator.

orrery

PigletJohn wrote: »

Turning up the stat does not increase the output of the radiator.

As has already been explained, and we have discussed this at length previously, within the flow control range (say 4C), it does.

Outside of that range, 100% flow is 100% flow - you can't get 120%. However, if you are 1C below your target, then the flow rate may already have been moderated back to 75%.

Interestingly, the same may now be true of the main CH thermostat - mine drops into proportional control within 1.5C of the target.

50Twuncle

Do dehumidifiers warm up the air in a house or not ?
I think that less humid air FEELS warmer than damp air - but is this a myth or not ?