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

Ultrasonic

richardc1983 said:

Ultrasonic said:

richardc1983 said:

Ultrasonic said:

richardc1983 said:

Ultrasonic said:

richardc1983 said:

Good test to do, as this is what opentherm control does basically starts off higher then as room temp approaches the set point it backs off on the flow temp. You’ll also have less cycling of the boiler. When the boiler cycles you have unburnt gas in the gas chamber the fan purges it up the flue, this isn’t factored into efficiency ratings but it’s worth considering. 

I suspect I'll have far more cycling of the boiler actually as I'd normally have the heating switched off for chunks of time whilst I'm at home whereas with the very low flow temperature I'm intending to leave it on all day. 

True in that respect, you in it in shorter periods to begin with, but still no harm in experimenting is there as may be better if you are at home to leave it on low. 

What boiler do you have, you may be worth finding out it’s minimum turn down. 

I checked the manual before doing this but I have a Vaillant EcoTec Pro 28.

Found it. It’s not the best in turns of minimum output of 5.4kw in Non Condensing mode and even worse when in Condensing mode of 6.9kw minimum output. It has a turn down ration of 1:5. So you could even say that at 6.9kw when in condensing mode it’s not able to modulate further. When it’s in non condensing mode it can go down to 5.4kw but then that’s less efficient due to not condensing. You set the output range via the flow temp on the boiler OR via an opentherm or weather compensated controller but I know Vaillant doesn’t have opentherm they have their own version of it which ties you into their controller. 

I'm afraid I've read what you've written but I don't actually understand what any of that means in practical terms. What are you saying I should or shouldn't try?

I was naively just going by the statement that the max. flow setting range was 30 - 80 °C. Before seeing your post I had been nosing at a bit more of the installation manual and was wondering if the anti-cycling time set may be an issue, or indeed a clue to not try to push this too far.

There is nothing you shouldn’t try you just need to experiment and see what works best :

What did the points you mentioned mean though? Presumably they were giving some relevant info?

Northern_Wanderer

Ultrasonic said:

As you suggest, the logical thing to do to counter the slower warm-up time is to have the heating come on earlier but I'm totally with you on not wanting to be woken up early by the heating as a result.

What I'm giving a go today out of curiosity it to have dropped the heating temperature to 40°C after having initially warmed my lounge up quicker with it set to 55°C. I'll see how this goes in terms of maintaining a comfortable temperature during the day as I'll be home for at least most of it. When you were referring to 'fannying about with the thermostat' were you referring to changing the heating hot water temperature like this, or an in-room thermostat? If the latter I'm not quite sure what you had in mind.

I set my thermostat to 19.5C and then have the separate programmer set for "All Day" so my heating comes on at 7am and goes off at 10pm. I'm happy to lower the temp to 18C if I go out. But I don't want to "Fanny about" keeping my heating on all night at a lower room temp becasuse I'd have to manually set it to 17C or so before going to bed (if I remember) and then in the morning it's not going to warm up to my required temp until well after I manually up the thermostat to 19.5C.

Northern_Wanderer

richardc1983 said:

I think Northern_Wanderer you would find at lower flow temps those noises of the heating system contracting and expanding due to higher flow temps may not wake you up as much with a lower flow temp and using a night set back. It sounds like you have an older type thermostat where you can only set 1 temp at a time possibly. However some people have the boiler in the next room or loft above them and can here the boiler pump and fan etc power up. 

You are right it will take longer to recover to your comfort temp if the flow temp is lowered and the temp of the house drops too much at night, this is why it’s recommended to use night set backs but appreciate this isn’t for everyone. 

My boiler is in the loft, so that's why it wakes me up when it switches on. It's a three year old room thermostat but as you say, I only have only temp it can be set at.

Northern_Wanderer

@Ultrasonic because my boiler is in the loft I can't constantly alter the flow temp sadly. I also now realise that I don't gain from the heat coming off the boiler. But hey ho, I'm very happy I don't have storage heaters. I could however think about altering the flow temp a bit in spring. It's just that I'm in the northern part of the country and it can get very cold here at night even if the days are warm.

QrizB

Ultrasonic said:

What did the points you mentioned mean though? Presumably they were giving some relevant info?

The "best" way to run a boiler is for it to match (modulate) its output to the heat demand from the property. It seems as though the minimum output from your boiler is 5.4kW (non-condensing) or 6.9kW (condensing).

There will be times when the heat demand from your property is less than that. At those times your boiler will not be able to modulate to a low enough power and so it will have to cycle instead, switching on and off. This is a less efficient way of operating.

Ultrasonic

Northern_Wanderer said:

@Ultrasonic because my boiler is in the loft I can't constantly alter the flow temp sadly. I also now realise that I don't gain from the heat coming off the boiler. But hey ho, I'm very happy I don't have storage heaters. I could however think about altering the flow temp a bit in spring. It's just that I'm in the northern part of the country and it can get very cold here at night even if the days are warm.

Yes, whilst I think 55°C is just about OK for me right now, I suspect I would need to turn this up if there were sub-zero temperatures outside.

Ultrasonic

QrizB said:

Ultrasonic said:

What did the points you mentioned mean though? Presumably they were giving some relevant info?

The "best" way to run a boiler is for it to match (modulate) its output to the heat demand from the property. It seems as though the minimum output from your boiler is 5.4kW (non-condensing) or 6.9kW (condensing).

There will be times when the heat demand from your property is less than that. At those times your boiler will not be able to modulate to a low enough power and so it will have to cycle instead, switching on and off. This is a less efficient way of operating.

Naively I'd have thought that the way the boiler switches on and off would make the average power match the demand? As in, won't extra heating power just heat the water up a bit more but then need to not come on again for longer to balance this out?

Not saying you're wrong - just trying to get my head round this.

QrizB

Ultrasonic said:

QrizB said:

Ultrasonic said:

What did the points you mentioned mean though? Presumably they were giving some relevant info?

The "best" way to run a boiler is for it to match (modulate) its output to the heat demand from the property. It seems as though the minimum output from your boiler is 5.4kW (non-condensing) or 6.9kW (condensing).

There will be times when the heat demand from your property is less than that. At those times your boiler will not be able to modulate to a low enough power and so it will have to cycle instead, switching on and off. This is a less efficient way of operating.

Naively I'd have thought that the way the boiler switches on and off would make the average power match the demand? As in, won't extra heating power just heat the water up a bit more but then need to not come on again for longer to balance this out?

Not saying you're wrong - just trying to get my head round this.

When the boiler switches off, it runs a flue fan purge cycle that clears gases from the combustion cylinder. This loses heat from your boiler (and hence from your home) to the outdoors. Then when it switches back on, it runs the flue fan for a short period before firing up which loses more heat.

It isn't very much each time, but it all adds up and whittles away at the efficiency.

[Deleted User]

I know a number of friends and family who are absolutely convinced that setting the room stats low but leaving the heating on constant is cheaper than switching on/off as and when needed.

Their theory is a simple one :
Leaving the stats low and heating on constant, after a day or so the house will settle into a comfortable average ambient temperature, not too hot or too cold.
However, manually switching on/off over the same period of time, as and when needed wastes gas whilst trying to bring the house up to room stat temperature .

I would imagine that this theory will depend on a number of factors.

How large is the property.
How well insulated is the property.
How efficient is the heating system.
Are all the rooms used daily or can some rooms have their rads turned off.
Are you relying on a single room stat to control your whole heating or do you have rad stats fitted as well, which can be set lower.

There's lots to consider, and in my opinion the answer is not as straightforward as just leaving your heating system tick over day in day out.

For instance where is your ground floor room stat installed, many homes have them installed in the hallway which might be the coldest part of the house, therefore the stat is constantly switching on your boiler to heat up the whole of the house even though it's only the hallway that might be the coldest, so if you have no rad stats fitted in your rooms you will be burning gas for the fun of it trying to heat up the hallway which might not even have a rad there, so the stat will be asking the boiler for heat but it might take forever for the stat to benefit from the heat.

Correct room stat location is very important, for an efficient heating system to work correctly.

Another theory is that you should only have rad stats fitted on upstairs rads, as heat rises upwards and will help warm bedrooms naturally and therefore the rad stats will knock off the rads more frequently, helping to reduce extra gas usage..

Towel rads, very nice to look at but do absolutely nothing to warm up a bathroom, yes they get extremely hot to touch, but offer no ambient temperature whatsoever.
If you have towel rails in bathrooms with stats fitted it will be a waste of time.
Towel rails are only good for 2 things, warm/dry your towels and they look nice.

So, do we leave the heating on a low constant setting or switch it on/off as and when needed ?

It's a question that will divide many householders. 

QrizB

Deleted_User said:

Towel rads, very nice to look at but do absolutely nothing to warm up a bathroom, yes they get extremely hot to touch, but offer no ambient temperature whatsoever.
If you have towel rails in bathrooms with stats fitted it will be a waste of time.
Towel rails are only good for 2 things, warm/dry your towels and they look nice.

Towel rails have a rated heat output, just like a radiator does, and measured/calculated in exactly the same way.

Here is an 1818BTU, 533W radiator:
https://www.screwfix.com/p/kudox-premium-type-21-double-panel-plus-single-convector-radiator-600-x-400mm-white-1818btu/46858

And here is an 1889BTU, 554W towel rail:
https://www.screwfix.com/p/blyss-towel-radiator-1600-x-600mm-chrome-1889btu/2238v

The towel rail will heat your bathroom just as effectively* as the radiator will.

* Output may be reduced if you actually hang towels on it, of course!