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

wantanswers

Hi Cardew.

I've been looking for information on the EST Website re Opentherm Technology which looks interesting and potentially appears to have the benefit of improving efficiency.

I've looked at Vokera heating for life Linea one high efficiency Combi Boiler and part of their literature says they are "Awaiting confirmation of Energy Saving Trust Recommended certification mark."

DO the EST have any information/opinion about Opentherm Controllers or technology?

Do you know if Vokera have attained the certification mark?

Is there a section re EST website that I can view Opentherm?

Cheers.

Cardew

macman wrote: »

Turning the 'stat up does not 'get the house warmer quicker'. All it does is continue to heat the house to the higher temp, thus using much more gas!
All a 'stat does is turn the boiler on or off a selected temp. It doesn't alter the output from the boiler, or heat the house up quicker on a higher setting.
A very basic (and expensive) misunderstanding here.

He actually said 'the gas central heating boiler set at a high temperature'

i.e. the boiler water temperature and not the room thermostat.

That boiler control will determine the speed at which the house heats.

Cardew

wantanswers wrote: »

Hi Cardew.

I've been looking for information on the EST Website re Opentherm Technology which looks interesting and potentially appears to have the benefit of improving efficiency.

I've looked at Vokera heating for life Linea one high efficiency Combi Boiler and part of their literature says they are "Awaiting confirmation of Energy Saving Trust Recommended certification mark."

DO the EST have any information/opinion about Opentherm Controllers or technology?

Do you know if Vokera have attained the certification mark?

Is there a section re EST website that I can view Opentherm?

Cheers.

Just phone or email them, their job is to advise and they are very helpful.

147718

malc_b wrote: »

By this I assume you mean the water temperature dial on the boiler and not the hall thermostat?

On any modern system the water max temperature dial on the boiler should be set to max and left there. The only exception would be something like a coal fired system where the boiler is always lit and the thermostat controls the tick-over rate too. Then you'd turn the dial down in spring/summer/autumn to lower the tick-over.

The lower you have the dial set the more likely it will operate and cause the boiler to short cycle. That is the hall thermostat is demanding heat, the water is up to temperature but the house isn't yet warmed so the pump is still running. The boiler stat cuts the burn then 2 minutes later it burns again, briefly, then the boiler stat cuts out again, etc.. That mode of operation is best avoided as it is inefficient.

This applies to modern oil boilers and similar gas boilers. There are modulating gas boilers which might be different. I'm not familiar with those and maybe the dial modulates the burn rather than cutting in and out. It is the cutting in/out you want to avoid.

But the best way to save money would be to fit a predictive controller in place of a simple thermostat. With these you set what temperature you want and when. It works out when to turn on the heat to achieve this, the boiler time clock is set to 24hrs on. So say you want 20C at 7am and it is a warm night. It will ramp up the heating at say 6am. If it is a very cold night it would start at 5am. It also works on set cycle which is more important for oil where each start loses a drop of oil. So oil cycle would be 15 minutes. It works out you need say 50% power and so does a 7.5min burn every 15min. For gas it would use a 5min cycle so do a 2.5min every 5min if it needed 50% power.

Hello and thank you for your comment
I do mean the boiler setting and not the hall thermostat
my boiler is about 15 years old and is not a condensating bolier
At present it is set low and it would seem I need to up the settings?

Cardew

147718 wrote: »

Hello and thank you for your comment
I do mean the boiler setting and not the hall thermostat
my boiler is about 15 years old and is not a condensating bolier
At present it is set low and it would seem I need to up the settings?

With a non-condensing boiler there is apparently little difference in efficiency whatever the temperature of the water.

I have my 24 year old boiler set at maximum 82C and the manufacturer said that was marginally more efficient.

Some people don't like their radiators that hot if they have toddlers. Also a surprising number of people don't have a method of regulating their Domestic Hot Water(DHW) temperature e.g. a tank stat, so you would not want DHW at 82C.

With condensing boilers the principle is to get the return water temperature as low as possible so it gets in condensing mode.

oldskoo1

On my boiler which is non modulating and non condesning I think the stat just controls when the boiler shuts down. On low it shuts down sooner whilst the pump draws water and heat away. The temp drops and it comes back on again

I don't think the stat control has any influence on gas volume to the burner afaik - on my boiler

I still don't know if 4 is better than 6 max, I just have mine on 4 and pump on max 3 and the boiler hardly ever cycles now. Cycling I think is inefficient, I think you can stop cycling by running it on max so it stays on longer. Pump speed still has to be high enough to pull water out quickly enough.

macman

Cardew wrote: »

He actually said 'the gas central heating boiler set at a high temperature'

i.e. the boiler water temperature and not the room thermostat.

That boiler control will determine the speed at which the house heats.

True, but many would interpret that as meaning an increase in the room 'stat setting-I know I did. Poster has now clarified (thank you), so all is clear.

147718

Cardew wrote: »

With a non-condensing boiler there is apparently little difference in efficiency whatever the temperature of the water.

I have my 24 year old boiler set at maximum 82C and the manufacturer said that was marginally more efficient.

Some people don't like their radiators that hot if they have toddlers. Also a surprising number of people don't have a method of regulating their Domestic Hot Water(DHW) temperature e.g. a tank stat, so you would not want DHW at 82C.

With condensing boilers the principle is to get the return water temperature as low as possible so it gets in condensing mode.

The DHW is set at 60 C (fixed) and I have comprised with the boiler setting at mark 3 on a max scale of 6
I will monitor carefully and based on what I have been reading on this thread will adjust accordingly Thank you for all your contributions Very educational

malc_b

Cardew wrote: »

Have there been any non-modulating gas boilers in production in the last 30 years?

You tell me, or better still look on sebuk. Scrolling down the list I found an on/off boiler first made in 1992 and still in production (I'd searched current boilers only).

the water max temperature dial on the boiler should be set to max and left there. The only exception would be something like a coal fired system where the boiler is always lit and the thermostat controls the tick-over rate too. Then you'd turn the dial down in spring/summer/autumn to lower the tick-over.

Cardew wrote: »

Really?

Given all modern gas/oil boilers are condensing, I think you might have some disagreement with that statement

I've an oil boiler and it is NOT condensing and I deliberated fitted a non condensing (some years back) at the time. If that sounds an odd choice I should add the flue points across the fence (1m away) into next door so I thought it best not to run the risk of dumping smelly wet flue gas into their garden.

Also, all oil boilers are on/off so the front water dial doesn't modulate as I assume it may do on a modulating gas boiler. It just causes short cycling. So with an on/off control limiting the water temperature you may stay in condensing mode boosting efficiency but then you short cycle reducing efficiency. Which wins?

The correct way to stay in condensing mode is to run the boiler steadily so the thermostat just calls for a brief burn each time which just makes the radiators hand hot, not mad hot. In other words the water dial has no effect then. It's just the fact that the house only needs a small input of heat to restore the temperature. This sounds very like 24/7 running doesn't it? Which I think may be why people report seeing fuel savings on 24/7.

malc_b

grahamc2003 wrote: »

2nd para - Saying 'there could be a saving' is a mssive understatement. Remeber the situation is 8 hours off - that is one hell of a time to counteract by boiler inefficiencies introduced.

This is exactly the natural thinking but TOTALLY wrong. 16 on, 8 off feels like a saving of 1/3 but look back at the calculations I've done, they gave a saving of 8%. This is because the house stays warm overnight so the losses stay high. The better insulated the house the less the saving because the higher the overnight temperature. Counter-intuitive isn't it.

And it gets worse. The total heat needed by the house for a day is thus 92% not 100%, but we now only have 16hrs to put that heat in so the boiler output is 92x24/16 = 138%. Are the radiators 138% of the required size? Do we have to run in non condensing to reach 138%?

That's why I say that it isn't as clear cut as claimed and I'm not surprised to see people report savings running 24/7. Yes they would be well advised to work out why 24/7 is cheaper as it is really a badly designed system.

grahamc2003 wrote: »

It's also a mistake to simply assume the boiler will be less efficient when turned on after being off for 8 hours. That depends on many factors, and I bet there'd be more which are more efficient in that regime than those which are less. Simple assuming a poorer efficiency negates any savings is wrong.

I haven't assumed that. What I have said is that boilers are less efficient at max loading, especially condensing as they stop being condensing. That's a fact. So it is thus possible to see that running steadily 24/7 rather than max loading in the morning may see an increase in boiler efficiency that more than counters the increased house heat loss. This would explain the reports of savings on 24/7.

grahamc2003 wrote: »

Just to add a further point - heat loss is a function of temperature, net heat loss (i.e. heat loss less heat gain) is a function of a temperature difference.

I'm not sure what your point is. House heat loss is usually just calculated on the temperature difference inside to outside and the U values for the walls, windows , etc.. If I've ever implied absolute temperature I meant temperature difference.

It's probably worth point out all the calculations are based on mid winter running with a large inside to outside difference. In sprint/autumn the heat required is less so the boiler and rads would be then more than 138% of the required level because the requirement is lower.