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

Mercy

I tested this idea about 12 months ago. My only appliance on gas is the boiler so it was easy to take meaningful readings. I also installed thermometers around the house.

I like it warm but am out most of the day. My home is a large stone terrace ~ 115yrs old. High ceilings and all that.

I found that I was using much less gas by keeping the thermostat at 16'C at all times. This is as opposed to leaving it off for the 10 hrs a day I am absent and overnight (set to come on 1/2 hr before getting up)

I think that there are a couple of reasons for this.

When I came in and the house was cold, I felt much colder. Although it would take about 1hr to get back to 20'C, I was still feeling cold so set it for 24 to feel comfortable and turning down later once warm.

Now when I come in from the cold to a house at 16'C I feel immediately warm and often find that warming to 20'c is a bit unnecessary for at least a while as I do my 'house jobs' so the thermostat is not set to change but I turn it up to 18'C after about an hour.

In both cases I wore / wear a fleece and warm footwear.

My monthly payments for gas are lower now than last winter, despite the rises in gas prices. Even better - I do not feel cold so have more brain space for more important things.

You really do have to check it out for yourself to determine which side of the argument you fall on. For me it's a no brainer.

HappyMJ

Mercy wrote: »

I tested this idea about 12 months ago. My only appliance on gas is the boiler so it was easy to take meaningful readings. I also installed thermometers around the house.

I like it warm but am out most of the day. My home is a large stone terrace ~ 115yrs old. High ceilings and all that.

I found that I was using much less gas by keeping the thermostat at 16'C at all times. This is as opposed to leaving it off for the 10 hrs a day I am absent and overnight.

I think that there are a couple of reasons for this.

When I came in and the house was cold, I felt much colder. Although it would take about 1hr to get back to 20'C, I was still feeling cold so set it for 24 to feel comfortable and turning down later once warm.

Now when I come in from the cold to a house at 16'C I feel immediately warm and often find that warming to 20'c is a bit unnecessary for at least a while as I do my 'house jobs' so the thermostat is not set to change but I turn it up to 18'C after about an hour.

In both cases I wore / wear a fleece and warm footwear.

My monthly payments for gas are lower now than last winter, despite the rises in gas prices. Even better - I do not feel cold so have more brain space for more important things.

You really do have to check it out for yourself to determine which side of the argument you fall on. For me it's a no brainer.

Time it to come on an hour before you come home. It'll be 20 degrees and you'll feel warm and save a small amount of gas.

grahamc2003

Mercy wrote: »

I tested this idea about 12 months ago. My only appliance on gas is the boiler so it was easy to take meaningful readings. I also installed thermometers around the house.

I like it warm but am out most of the day. My home is a large stone terrace ~ 115yrs old. High ceilings and all that.

I found that I was using much less gas by keeping the thermostat at 16'C at all times. This is as opposed to leaving it off for the 10 hrs a day I am absent and overnight.

I think that there are a couple of reasons for this.

When I came in and the house was cold, I felt much colder. Although it would take about 1hr to get back to 20'C, I was still feeling cold so set it for 24 to feel comfortable and turning down later once warm.

Now when I come in from the cold to a house at 16'C I feel immediately warm and often find that warming to 20'c is a bit unnecessary for at least a while as I do my 'house jobs' so the thermostat is not set to change but I turn it up to 18'C after about an hour.

In both cases I wore / wear a fleece and warm footwear.

My monthly payments for gas are lower now than last winter, despite the rises in gas prices. Even better - I do not feel cold so have more brain space for more important things.

You really do have to check it out for yourself to determine which side of the argument you fall on. For me it's a no brainer.

But all you've proved is that when you turn the temperature up to 24 instead of 16, it costs you more gas. That doesn't surprise anyone does it?

I'm afraid your test doesn't disprove the very simply physics involved, which means it's cheaper to turn heating off when you're not there rather than leaving it on at the set temperature all the time.

It's best to consider heat loss rather than the actual heating - heat loss is a function (and nowhere near a linear function) of temperature difference - by turning the heater off while you're out, the house temperature (and therefore the heat loss) drops compared to keeping at a higher temperature all the time. The heating required is that which replaces the heat lost.

Dave_C_2

Hugo_Rignold wrote: »

...It is also the reason old farmhouses tended to have an aga or rayburn ticking over 24/7 to keep the place warm.

Nit - pick. Nothing to do with the fact that farmhouses may not be connected to the gas mains and AGAs can be run off solid fuel, including wood.

+1 for the laws of physics - turn it off and save money!

Dave

John_Pierpoint

A heat pump is a box that is turned on and it heats the house, fuelled by electricity. I think that passes "the duck test". Tens of thousands of homes are now heated by domestic heat pumps.

Cardew wrote: »

John,
With respect you have widened the discussion too far by bringing heat pumps into the thread.

Firstly a heat pump is not a heater.

It is an appliance to extract and transfer heat from the outside ground or air into the house.

The reason that it is not recommended to 'turn the temperature of a heat pump down when out of the house' is because they have a lowish heat output, which together with water at a relatively low temperature, means it needs to run long periods(or 24/7) to keep the house at an acceptable temperature.

Indeed one of the criticisms of heat pumps is that they have to use electricity to heat the house when there are no occupants, or the occupants are in bed.

That said heat pumps still obey the laws of physics, if you turn them off for a period you will use less electricity than keeping them on 24/7.

You won't because the heat pump has a mind of its own and will turn on full price day time electricity in addition to its pumping function, in a desperate attempt to keep the home (and the hot water) at the required temperature.

The appalling NIBE company is still promoting its Indian Rope Trick of a heating system as though it had had no problems [Like scoring a BBC "Rip off Britain" (8/3/13) feature not once but twice].
We both had things to say about this fiasco of public money being spent on housing authority tenants in new build property.
The more the tenants tried to save money by turning it off, the more it cost them.
We both commented at the time:
http://forums.moneysavingexpert.com/showthread.php?t=2959648&highlight=nibe

For those without the time to read the thread, the story goes like this: All housing estates and now local authority development plans have to be "sustainable", what ever that means the courts have yet to define.
This means making the house air tight. That means there will be condensation problems especially with tenants on "the social" - You know what they are: know nothing about heat and think opening the windows or doors for 5 minutes "lets all the heat out", while trying to dry the washing on a radiator. So we now need to put in a mechanical ventilation system. Let's add a heat pump to the extractor fan to reclaim the energy that is lost by the forced ventilation and use that to heat the home. The kit fits conveniently in the kitchen or under the stairs and now as landlords we don't need to pay for the annual Gas Safe certificate.

If you were a tenant on benefits in the middle of winter, when air source heat pumps cannot cope with the demand anyway, what would you do? You have freezing cold air coming in through the vents in the living room and it only gets warm when being sucked out of the bathroom. Heat or Eat? Well I would go out and collect some of the million tons of scrap wood that goes to Landfill each year and burn it. Even if I did end up smelling like a gypsy.

Sorry you are no longer allowed new homes with a chimney, as by definition it sucks heat out of airtight houses [well it does not automatically as it can be room sealed like a balanced flue gas boiler, but you know these social tenants they would sit there with the doors on the front of the log burner open "because the glass blocks the heat".]
So we now build houses with fake fibre glass chimneys because that is "sustainable".

The tenant would be better off with night storage heaters, black mould and no draughts, or so they think as they stuff up the vents.

John_Pierpoint

Any one want to talk about solar gain and zero carbon homes?
There is an opinion that the government has been stitched up, by listening to the 10 companies in the country who build 50% of all the new homes.

Mercy

grahamc2003 wrote: »

But all you've proved is that when you turn the temperature up to 24 instead of 16, it costs you more gas. That doesn't surprise anyone does it?

I'm afraid your test doesn't disprove the very simply physics involved, which means it's cheaper to turn heating off when you're not there rather than leaving it on at the set temperature all the time.

It's best to consider heat loss rather than the actual heating - heat loss is a function (and nowhere near a linear function) of temperature difference - by turning the heater off while you're out, the house temperature (and therefore the heat loss) drops compared to keeping at a higher temperature all the time. The heating required is that which replaces the heat lost.

Not sure if the question has changed as I've not read everything.

I was answering the question in the first post - is it cheaper to leave the heating on all day or words to that effect.

My answer is yes. I'm saving money.

I appreciate that more could be done but in answering the question I must say yes.

I do not try to change the laws of physics. I could probably use less gas. I gave a real life example from a real life. Not a controlled trial.

I must be using less gas than I was as my bills are lower.

I do not understand quite which bit you don't get?

Now for more interesting stuff. :rotfl:

HappyMJ

Mercy wrote: »

I do not understand quite which bit you don't get?

All of it really...turn boiler off...gas usage equals nothing therefore money saved. The higher the temperature of the house the more heat is lost and more gas is used to maintain the temperature. If you turn it off during the day then less heat is lost at 15 degrees than if the house remains at 18 degrees. It isn't much but there is a difference.

malc_b

People are again saying is obvious from the physic when it isn't. I explained this in previous post but before I get stamped on let me say:

FACT 1: Heating 24/24 a house loses more heat than 16/24 (or xx/24)
FACT 2: A house losing more heat is NOT the same as using more fuel

Consider a house at 20C with outside at 0C and say it is losing 1kW through the walls etc.. So you have a 1kW fire on and the house stays at 20C. Then you turn the fire off. What happens? Does the inside of the house fall immediately to 0C? Obviously not. So the house is still losing just under 1kW. If we say the heat is off for 8hrs and in that time the temperature drops to 10C inside the loss starts at 1kW and ends up at 500W, call it an average of 750W (it's not a straight line fall so assuming straight line gives ~10% error so close enough for an example). Hence for those 8hrs this house loses (8x750W) 6kWh of energy. This comes from the house structure and has to be replaced when you next heat the house. Hence:

FACT 3: When CH is switched off the house continues to lose heat from its structure for many hours/days. When the CH is switched on this energy debit has to be repaid.

That is the physic of the situation so what does that mean for the CH? Having the CH off longer means that the average house temperature is lower so the total loses are lower. But the shorter you run the heating the harder the CH has to run when it is on as you have to both balance the standing loss and replace the energy in the house structure. And running CH harder, especially condensing, usually means less efficient which is why longer CH can mean less fuel used which proves fact 2.

The post above has reported just this effect. When the house is heated 24/24 to 16C it is more comfortable at a lower temperature and uses less fuel. The house structure is warmer, no cold walls to create draughts and make you feel colder.

Also, going back to the 1kW house, if heated 24/24 that would use 24kWh/day. Heating 16/24 is a 22kWh loss (16 + 6) which the CH has to supply in 16hr. So the CH has to supply 1375 W over 16hrs rather than 1000W, at 37.5% increase. The loss saving is 8.3% which is the same order as the difference between condensing and non-condensing modes. Plus if the house stays warmer over the 8hrs, i.e. falls to 15C rather than 10C with is more realistic then the 8% falls to 4%.

BTW a radiator (1700W nominal at 80C water) which gives 1000W at 60C water would need to be at 71C to give 1375W.

malc_b

johnsiddle wrote: »

My grand daughter has just purchased a brand new house from Taylor Wimpy.
The combi boiler fitted uses a remote, all in programmer/room stat.
The programmer never switches the heating boiler off it actually sets the thermostat to 10C min or which ever higher temperature you specify.

how does this fit in with the advice to turn the boiler off when not needed.
Is this boiler so very in-efficient?????

:T:T:T

The boiler as a combi will stay on to provide "instant" hot water whenever a hot tap is turned on. A modern boiler shouldn't have a pilot light so won't be using any gas. If the hall thermostat is at 10C (or 5C) then the CH heating won't be on either unless the house is very cold and you would want the heating to come on then to prevent pipes freezing. If the house has been heated and the heating is turned off overnight then the temperature is unlikely to fall lower than say 15C. So these controls are not unusual and not inefficient.