Leaving the heating on for longer....

Totality

KimYeovil wrote: »

" 'Energy efficient' kettle "? My a!se!

We've got one of those Tefal 'One Cup' thingies which I'd consider energy efficient.

1carminestocky

Don't worry abut KY, he/she gets a bit grumpy a this time of the day, lol. Haven't got one but it's common sense that anything that restricts you to heating just what you need CAN be classed as energy efficient. For instance, when my SIL pops round to our house and pops the kettle on she invariably fills it to the max...to make 2 cups of tea! I've now banned her from touching the kettle as no matter how many times I've explianed it to her she was still filling it to the max.

jimbo_the_jetset

I've been having my own 'internal' debate on this. Wondering whether to have the heating come on for an hour early evening and an hour or so later. Or just on all the way though.

I think it is very house specific an must depend on how quickly your rads and house heat up and how quickly heat dissipates around the house. e.g. if the rads and house heat up quickly and the house holds heat then different times might be better. If they take a while to get going and the heat dissipates quickly then its gotta do that all over again at the next on setting then having it on to top up every now and then may be better.......

1carminestocky

Nathan_Gilbert wrote: »

Well spotted super sluth, yes I admit it it's my website but there is some great stuff on there and we are trying to make a difference both financially and environmentally, and I do practice what I preach, we have a Tefal Kettle and an Effergy Smart meter and movement sensing lights in the hall and landing. We have saved loads of money by being aware of our usage almost to the point of obsession and born out of that obsession was etree which I am very proud of. And on the phone scam thing O2 have promised that I won't see any charges for that international call. Have a good weekend xx

I'm sure you are very proud of it, Nathan, but it's against the T&C's of the Forum to advertise your own site, so please desist.

Cardew

mech wrote: »

The 6% figure is indeed suspect. Notice they use the magic words "up to". I wonder how they arrived at 6%. I suspect it's some kind of naive calculation along the lines of 6% being about a 12th of 80% of your heating bill (assuming 20% for hot water). Also assuming you start with the heating on 24 hours a day (2 hours also being a 12th of a day). This will not be even close to reality unless you live in an empty wooden chalet with a suspended wooden floor. Ie: Ultra-low thermal mass - no masonry anywhere to store heat between switch-offs and no solid floors. Even the heat stored in the water in radiators would affect the results significantly I would expect. The vast majority of UK housing is brick or stone and this acts like a giant storage heater.

I'm not even sure halving the amount of time my heating would reduce my consumption by more than 6% unless it started to mean my heating was on for less time than it takes to get the house up to temperature in the first place. I've also tried having the heating on 24 hours a day for long periods. That's 16 hours longer than I normally have it on for. Even with a margin for error I couldn't find an increase in usage of more than 15%. Typically 13%. Or looking at it the other way around, the savings from 24 hours down to 8 was just 11%.

Having the heating on only once per day instead of both in the morning and evening would give far greater savings if you can cope with that. This would dramatically increase the time in which the house can cool instead of charging it back up with heat halfway through.


However, the rule that states a 10% saving per degree lower on the thermostat is a good rule of thumb. It even seems to apply irrespective of the timer settings. Of course, in real terms, the saving between 21 and 22 degrees C on the thermostat is greater than the saving between 20 and 21 degrees, because it saves 10% of a larger number.

Mech,
Interesting post.

There seems little data available on the web estimating the saving made from having heating on xx hours a day against 24/7.

Clearly there are many variables, the standard of insulation in the property doubtless being the major consideration.

I have seen some figures suggesting that a well lagged Hot water tank will 'lose' around 3kWh in 24 hours. i.e. To keep a tank at the same temperature, when no water is drawn off, will take 3 kWh a day.

Given there is some loss of heat when the HW is on a timer(we rarely use all the HW in the tank) the real figure is probably around 2 kWh a day.

Not a huge loss, and of course that heat isn't really lost as it warms the house.

On the question of central heating on 24/7 or 8 hours, subjectively, I would have thought your figure of 13% was on the low side for most houses; but, as said above, I have seen no data to back that gut feeling.

Theo_Cupier

Posting this in another thread but it seems relevant here...

We have a large 4 bed semi. 14 radiators in total, from an efficient gas boiler. We have a room thermostat in the hallway, usually set to about 20C and every radiator in the house has a TRV - apart from the hallway radiator to control the room thermostat.

Loft insulation exceeds the current guidelines, modern double glazing throughout. Some of the original parts of the house are single skin (9" of brick with no cavity). The bits in the recently extended parts are cavity wall and insulated with rockwool. I'd say the cavity parts probably account for 60% of the external walls.

We are a family of 5 - 2 adults + 3 young kids. There is someone at home pretty much all the time - my wife and I work from home.

Anyway, enough background...

Our heating is usually set to come on early in the morning, stay on all day and go off around 10pm. The heating stays on and is controlled by the room themostat (and the TRVs in individual rooms).

I've recorded our meter readings daily for the past few weeks and as the weather gets colder we typically use 3 cubic feet of gas (which is about 95KWh, if my calculations are correct).

Yesterday, we went out at about 9am, so I turned the heating off and set it to come back on again late in the afternoon so the house would be warm when we got home. The house hadn't actually got up to temperature by the time we left, although the heating had been on for 3 hours by that time.

When we got home the heating had been on for about 5 hours and the house was still not "at temperature" according to the hall thermostat.

I assumed that a whole day of inactivity would reduce our gas consumption for the day - since it wouldn't be ticking over all day. In fact our gas consumption for the day was actually slightly above normal - 4 cubic feet (126KWh).

My best guess is that on a "normal" day, the heating takes 4 hours to get the house up to temperature and is then on periodically when the hall thermostat detects that it has dropped below 20C to keep the temperature "topped up".

However, yesterday, the heating was on for 3 hours until I turned it off. This didn't heat the house through. The internal temperature dropped throughout the day and needed 6 hours of constant heating to get up to temperature, which is actually more than it would be on in a "normal" day.

Not sure whether the theory agrees with what I've observed, and I only have 1 day of observation to work on, but it seems to suggest that there is a tipping point where it's more efficient to keep a house warm versus letting it heat up, cool right down and then reheat again.

I'd be interested in other views on this.

Cardew

Theo_Cupier wrote: »

we typically use 3 cubic feet of gas (which is about 95KWh, if my calculations are correct).



Not sure whether the theory agrees with what I've observed, and I only have 1 day of observation to work on, but it seems to suggest that there is a tipping point where it's more efficient to keep a house warm versus letting it heat up, cool right down and then reheat again.

I'd be interested in other views on this.

Just a small point, it is 300 cubic feet of gas; a gas unit on an Imperial meter is 100 cubic feet - but the important point is that 95kWh is correct.

Your suggestion that it is "more efficient" to keep a house warm, depends how you define efficient.

More practical - possibly! However if you define efficient as 'cost efficient' then it quite simply would defy the laws of physics for it to be true.

Theo_Cupier

Cardew wrote: »

Your suggestion that it is "more efficient" to keep a house warm, depends how you define efficient.

More practical - possibly! However if you define efficient as 'cost efficient' then it quite simply would defy the laws of physics for it to be true.

We used no more gas to do this than we did by letting the house get cold and trying to reheat it.

That's my definition.

I tend to agree with the physics argument but I can only go by the evidence I have collected. If it helps someone to say "have you tried changing [this] or [that] with your heating to make it more efficient then I will have learned and be happy. For now, I go with what I see.

mech_2

Cardew wrote: »

Mech,
Interesting post.

There seems little data available on the web estimating the saving made from having heating on xx hours a day against 24/7.

Clearly there are many variables, the standard of insulation in the property doubtless being the major consideration.

I think the main considerations are the thermal mass of the building materials and adjoining neighbours who could be sucking your heat.

A detached converted barn with 2 foot thick stone walls (like my dad's house) probably buffers so much heat that a timer is almost pointless.

The house I'm in this weekend is a new-build terrace. The party walls are stud partitions (yeah, I know - noisy). If the neighbours have a similar heating regime you can't exchange much heat. If one house is on a timer and an adjoining household is heated constantly, the timed household gains. Therefore it's always going to be a better idea to heat these houses on a timer.

I'm not sure how much difference insulation makes. It should narrow the difference, all other things being equal.

I have seen some figures suggesting that a well lagged Hot water tank will 'lose' around 3kWh in 24 hours. i.e. To keep a tank at the same temperature, when no water is drawn off, will take 3 kWh a day.

Given there is some loss of heat when the HW is on a timer(we rarely use all the HW in the tank) the real figure is probably around 2 kWh a day.

Not a huge loss, and of course that heat isn't really lost as it warms the house.

I have a combi boiler now, so I haven't thought about HW tanks in the last few years.

On the question of central heating on 24/7 or 8 hours, subjectively, I would have thought your figure of 13% was on the low side for most houses; but, as said above, I have seen no data to back that gut feeling.

My house is a small 3-bed 1930s semi with a condensing boiler, suspended wooden floors downstairs and about 6 sq metres of south facing windows. The central heating pipes are microbore. About half the external was are cavity insulated and half not (they gave up halfway through - the cavity is too narrow), 100mm of loft insulation, double glazing, but wooden front and back door. There is a chimney, but it's closed off.

It was a fairly rigorous test - daily outside temperature and seasonal thermal gain were factored into the comparison. I can think of aspects of my house that could narrow the percentage difference and others that could widen it. I'm not sure which are most significant, nor what kind of construction is most prevalent in other houses.

This year I had planned to improve my insulation levels, but so far all I have got around to doing is draughtproofing the front and back doors and lagging the heating pipes in the crawlspace under the floors downstairs. Already this has reduced consumption measurably. Double glazing made sod-all difference. So people without double glazing: panic ye not about your heat loss. Double glazing is overrated and measures costing 100th of the price have more effect.