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

lstar337

bobstheboy wrote: »

I am taking issue with you claiming that you can keep a house at 21c all day long with the heating on for an hour at 6am and 30 mins at 6pm, in winter months. Just explain how your house can stay at 21c for ELEVEN hours without any heating !!!!! Impossible. Are you really expecting us to believe that there will be no heat loss for eleven hours ?

Did I say no heat loss?

OK, I can't be bothered to go back through my posts but if I did say it stays at 21c then that is not completely true. What I should have said is that it stays above 21c. IT's a small but important distinction.

Maybe you have no experience of a well insulated house, but it is really quite different to a poorly insulated building. I have lived in both. The heat loss is very slow, and that is the important part.

You say without any heating, but I never said that. The house is lived in so It is getting heat all the time. Firstly, I have a large window and large french doors which are south facing. The floor is concrete and acts like a huge thermal store. This unfortunately results in unbearably warm temperatures in summer and we have to use blackout curtains to reduce the heat collected during the day. Secondly there is a myriad of electrical items in my house that give of small amounts of heat, add them up and it is not insignificant. The tumble drier and washing machine, while not used every day, add a considerable amount of heat to the house. Cooking is another considerable contributing factor.

So the house is in fact losing heat all the time, it just isn't doing it fast enough to override the heat going in.

Incidentally, all the things I have mentioned above are perfect example of why anybodies 'real world' measurements are not considered as fact. There are way too many variables.

I hope this answers your question.

Cardew

I think many people underestimate the solar gain(greenhouse effect) on some houses.

My study has a large window and a large velux roof light at 45 degrees. Even in winter the temperature can rise during the day by 1C with no heating on all day and the PC on standby.

malc_b

lstar337 wrote: »

Sorry Malc, sorry Richard, you are wrong about this and Cardew is right.

I do wish people would read fully what I put here, which is a fully reasoned mathematically PROOF that is possible to use less gas. Please take the time to understand it rather than just come out with silly examples that just show you have not read it.

To draw an analogy it is like I've said to you that I plan to drive from Bristol to London at a steady 50mph to save fuel and you have said no you should drive as fast as possible as the shorter the journey the less fuel I will use. And taking my 50mph to extreme would I use less fuel if I travelled at 10mph?

We all know cars so we all know that putting your foot down to get home before the petrol runs out is stupid. What is so different about the idea that this also applies to condensing boilers, putting the thermostat pedal to the metal uses more gas.

The key bit of info that I think most people are missing is the thermal lag in a house and the fact this gives a very small difference between 16/8 and 24/0. In the example I give here it comes out to be 8% based on the overnight temperature falling to 10C. My house I reckon falls to 15C which would make the difference ~4% which less than the difference between condensing and non condensing mode. People tend to think that turn off the heating and the heat loss stops. That is only true if when you turn the heat off the inside temperature drops to the outside temperature (aka a tent).

I'm not claiming that heating 24/7 saves energy. IT DOES NOT SAVE ENERGY. What it can do is SAVE GAS which is all I'm interested in, the MONEY.

As I explain at the end of the proof the ideal way to run the boiler is to have in always in condensing mode and ON FOR AS LONG AS NEEDED. In spring and autumn you might get away with shorter running times and still be condensing mode all the time. The optimum way to run a condensing boiler is to force it to be always in condensing mode (i.e. low water temperature) and then increase the hours as the season gets colder. Most people do the opposite, fix the hours and turn the water temperature up (if they change the water temperature at all).

malc_b

Cardew wrote: »

I think many people underestimate the solar gain(greenhouse effect) on some houses.

My study has a large window and a large velux roof light at 45 degrees. Even in winter the temperature can rise during the day by 1C with no heating on all day and the PC on standby.

What isn't well explain is the ABC rating of new windows. IMO part of the typical dumbing down of everything. Best I've found is here where it explains there is some magic formula that gives the energy loss/gain of a typical window. A rating means 0 to 10 kwh/m2 energy gain per year for typical window (which I assume means the average of a vertical, N,S.E and W facing so a south facing window is 2 or 3 times this figure and a velux more solar gain again). A+ is 10-19, A++ is 20-29 BTW.

Cardew

malc_b wrote: »

I do wish people would read fully what I put here, which is a fully reasoned mathematically PROOF that is possible to use less gas. Please take the time to understand it rather than just come out with silly examples that just show you have not read it.

malc_b,

I have read it. I don't wish to get into an argument, but while I understand your reasoned argument - it ain't proof. You are using several unverified assumptions, not least that a boiler in a house that has cooled (after CH switched off) will be operating in non-condensing mode with a subsequent loss of efficiency of x%.

Why is it silly to use the heating off for 2 years, 1 year, 1week, 1 day 1 hour etc analogy?

P.S. The link in your post on solar gain of windows isn't working for me.

lstar337

malc_b wrote: »

I do wish people would read fully what I put here,

I don't need to read it malc, if you had disproved to basic laws of physics, you would be famous and not posting here.

I therefore assume you haven't.

lstar337

malc_b wrote: »

To draw an analogy it is like I've said to you that I plan to drive from Bristol to London at a steady 50mph to save fuel and you have said no you should drive as fast as possible as the shorter the journey the less fuel I will use. And taking my 50mph to extreme would I use less fuel if I travelled at 10mph?

What if the first 1 mile was all uphill and the remaining 117 miles you just turned off the engine and rolled?

lstar337

malc_b wrote: »

I'm not claiming that heating 24/7 saves energy. IT DOES NOT SAVE ENERGY. What it can do is SAVE GAS which is all I'm interested in, the MONEY.

What your saying is if we both went away for a 2 week holiday (we don't have to go together ), you with your heating on 24/7 and me with my heating off, You would use less gas than me?

I'm not convinced.

lstar337

malc_b wrote: »

As I explain at the end of the proof the ideal way to run the boiler is to have in always in condensing mode and ON FOR AS LONG AS NEEDED.

That is a completely different argument than you were making earlier. Now you agree with myself and Cardew.

My boiler is always condensing and run for as long as needed (1 and a half hours), and there is no advantage to running it 24/7.

The_Green_Hornet

There seems to be a lot of specious arguments and false analogies being used on both sides which doesn't do anyone any credit on here.

As I understand it the basis of the myth is that once you have heated your house to the desired temperature at the start of the day it costs less to keep it at that temperature by running the heating on/off throughout the day than it does to switch the heating off, let the house cool down and then turn the heating back on to get it back to temperature later on in the same day.

Surely there must be a peer reviewed scientific study somewhere that someone could post a link to?