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

HappyMJ

Mark_Beech wrote: »

Those who are saying that this defies the laws of physics are simply not thinking this through.
The logic is that leaving the heating on 24/7 but controlled by a thermostat and turned down low overnight or when away from home CAN be as cheap as turning the heating on and off with a timer twice a day BECAUSE it takes an ENORMOUS amount of energy to reheat the fabric of a house that has been allowed to completely cool down. This will be less of an issue where the house is extremely well insulated and will be even more likely if its an old house with solid walls.
The other thing that people fail to recognise is the comfort factor. If heating only twice per day the fabric of the house will never get fully warm ..... you are essentially just reheating the air inside the house .... and it will never feel quite as cosy as when you heat 24/7.
It WILL almost certainly cost a little more to keep the heating on 24/7 - but not as much as many folk think. If you heat from say 7.00am - 9.00am then from 5.00pm - 11.00pm this will cost WAY more than a third as much as leaving the heating on 24/7.
Life's too short to be cold - and I know what I'm gonna continue to do!
It's a bit like the "where should I site the radiators" argument. The most EFFICIENT place to site them is on internal walls - but the way to be the most comfortable is to site them under a window. Guess where mine are!

Under the windows...it helps free up space in the room for furniture placement.

Life's too short to be cold. We all agree so if you are home then set the heating on and if you are out then turn it off timing it to come back on an hour before you come home again and you will save money and have a warm house when you are in it. You won't feel the cold if you aren't home in the cold house as you are out.

laptop80

Mark_Beech wrote: »

Those who are saying that this defies the laws of physics are simply not thinking this through.
The logic is that leaving the heating on 24/7 but controlled by a thermostat and turned down low overnight or when away from home CAN be as cheap as turning the heating on and off with a timer twice a day BECAUSE it takes an ENORMOUS amount of energy to reheat the fabric of a house that has been allowed to completely cool down. This will be less of an issue where the house is extremely well insulated and will be even more likely if its an old house with solid walls.
The other thing that people fail to recognise is the comfort factor. If heating only twice per day the fabric of the house will never get fully warm ..... you are essentially just reheating the air inside the house .... and it will never feel quite as cosy as when you heat 24/7.
It WILL almost certainly cost a little more to keep the heating on 24/7 - but not as much as many folk think. If you heat from say 7.00am - 9.00am then from 5.00pm - 11.00pm this will cost WAY more than a third as much as leaving the heating on 24/7.
Life's too short to be cold - and I know what I'm gonna continue to do!
It's a bit like the "where should I site the radiators" argument. The most EFFICIENT place to site them is on internal walls - but the way to be the most comfortable is to site them under a window. Guess where mine are!

If you turn the heating down low overnight what do you think is happening to the temperature in the fabric of your house? If you believe that warming the house takes an enormous (or ENORMOUS if we're going in for randomly capitalising words) amount of heat compared to maintaining the temperature, why turn down the heat at night at all? Seems counterproductive.

Go with whatever your preference I suppose. My preference is only putting the heating on when it's needed and having a small gas bill (an average of 11kWh/day on the bill that's just come in).

chris40

A neighbour keeps his place very warm, but sitchws off at night and opens the windows. His bills are double ours!
We keep a minimum of 17 degrees and 22 when we are in the sitting room.

I should have liked a more scientific answer rather than the one pulled out of the cliche box.

minijem

You seem to overlook one important point. The room stat usually controls the whole CH system. If you have TRVs (thermostatic radiator valves) in the same room as the room stat and you turn the TRVs down the room may not reach the temperature required to trip the room stat or it may take longer if you have other radiators set higher. This means that the boiler/pump will run for longer and more energy will be dissipated in the rest of the house.

On the other hand if the TRVs are set too high the room stat may cut off the heating to the rest of the house.

TRVs give much better temperature control because they shut down progressively as the target temperature is approached. Room stats turn the heat on and of with quite a large amount of hysteresis (i.e. they switch off at one temperature and switch on again at another temperature typically two or threee degrees below). This is easily detectable.

mickeydoodah_2

We have convector heaters in each room, and I've always kept all doors closed when the heating's on, so that the warm air stays put, and doesn't move into the unccupied hallway/landing area.

My wife comes from an open-plan house, where the heating system is under-floor forced air. Doors are left open all the time. She therefore prefers to leave the doors open hre too. Her reasoning is that if the air is circulating, we have fewer problems with condensation and the build-up of mould. But to me, the house feels much colder than it used to.

So, how do I convince her that closing doors (a) keepos the house warmer and (b) has no effect on the amount of condensation and mould? Or am I wrong in this respect?

Also, our interior walls are now painted, all the wall-paper has been removed. Does this have an effect on the efficiency of whatever heating system? The walls certainly feel colder to the touch than they used to.

grahamc2003

Mark_Beech wrote: »

Those who are saying that this defies the laws of physics are simply not thinking this through.

Just where does the (misplaced) confidence come from to post something like that on a public forum for all to read?

I don't mind at all you holding whatever views you like, however scientifically ridiculous, but please don't adopt such a condescending attitude, especially when you are wrong! Saying those few of us on here with a grasp of basic physics (that's all you need to understand this topic) aren't 'thinking things through' is rather odd from someone without even the basic capability to think it through.

minijem

Compact fluorescent lamps typically have a quoted lifetime of 10,000 hours or 5,000 on/off cycles. This means that for optimum service they need to be on for an average of two hours at a time. Therefore, do not switch off CFLs if you will need them again in a few minutes. However CFLs are now quite cheap so if you are not going to need the light for some time the energy saved by switching them off will offset any reduction in lifetime.

Wintry

It is certainly true that leaving the heating on all the time will use more energy, because the average temperature difference between the inside and the outside will be higher.

However, real life is more complex than this. Heat is transmitted by conduction, convection and radiation, and people's perception of warmth and cold is very different. You can have rooms where the air temperature is 20 degrees, but they feel different:

Room A has been kept at 20 degrees for a long time, so everything in the room is warm, including the walls, furnishing, carpet etc.

Room B has been rapidly heated so that the air temperature is 20 degrees, but the walls, furnishing, carpet etc. feel cold.

An individual who feels the cold will perceive Room B as colder. Their feet are cold because the floor is cold. The sofa feels cold when they sit on it. So what do they do? Turn up the heating a couple of degrees until they FEEL warm! This means that the savings from turning off the heating when the house is unoccupied are not necessarily as great as might be expected, and why some people find that the extra cost of keeping the heating on all day is negligible, because they can achieve their desired level of comfort at a lower thermostat setting.

GabrielMichael

"......turning your thermostatic radiator valves down will mean your radiators will not get as hot....."
Total tosh. How hot the radiators get is ENTIRELY dependant on the boiler temperature. What the TRV's do is decide when the room has reached the desired temperature - only then do they reduce the temperature of the water in the radiator - and ultimately turn off the water flow altogether, if necessary. Thank God I did school physics. Some people seem brain dead when it comes to home economics.

lauramaria541

hi thanks all for your useful discussion. Anyway, agreeing with Herongull respectively.