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

lstar337

malc_b wrote: »

Cardew I can't tell house much gas your house will use in various situations. The aim of the maths I've put together is give a better understanding. Going back to the car analogy, I'm trying to show how to get the best mpg out of a car to new driver, some rules to follow and why that is the case, i.e. highest gear but not struggling, 50mph not 70mph, correct tyre pressures, empty boot, brake use to minimum so predictive driving with large gap to car in front so you don't need to brake hard when he does.

But you'll agree that turning the engine off when not needed will save you more money, hence why we have start-stop engines on modern efficient cars.

malc_b wrote: »

The rule should be keep the boiler in condensing mode as much as possible. Running as short as possible

Pretty sure that's exactly what we have said all along.

malc_b wrote: »

and cranking up the flow temperature which you would have to to get the shortest run time is NOT the way to stay in condensing mode as rule.

I don't believe anybody in this thread has ever said anything about cranking up the output temp to keep the run time as short as possible.

The advice has always been to use timers to make sure the boiler is not running when the house is empty, and is off or on low during the night when heat demand is low.

orrery

lstar337 wrote: »

I don't believe anybody in this thread has ever said anything about cranking up the output temp to keep the run time as short as possible.

Oh, indeed that may well be sensible. I understand that it doesn't sound intuitive, but it all hinges on how the boiler behaves.

To assume that the boiler can be set to 50C flow and that it will all be fine is (for most people) an error. To make that assumption requires that the boiler can handle that under all circumstances. It is likely to be fine in the start-up phase in a morning where the flow temperature builds up to 50C. Once the house is up to temperature, little heat will be required and many boilers will be unable to maintain 50C as the return temperature rises, and boiler is likely to react with modulating, possible over temperature and then shut down, then possibly continuing with short cycling. It would be rare indeed if gas boilers could simply maintain 50C flow in all seasons and under extremes of house temperatures.

Instead of that, it may be better to set 68C as a flow temperature and avoid that difficulty (the boiler can now continue on full power from 50C up to 68C and still deliver a return under 50C). The more rapid heating will get you into the proportional zone quicker and proportional control will then use shorter bursts which are all likely to be on full power, which delivers much better heating and still maintains condensing mode.

I've just completed the same exercise on my daughters house - the boiler was doing a lot of short-cycling. We've installed Nest to control it, replaced a tardy tank stat and upped the boiler temperature. So, more rapid response of both c/h and h/w and minimal short cycling (there is still some as h/w approaches target, if the c/h isn't on at the same time).

It isn't a theoretical issue, it all down to how the boiler behaves.

Raxiel

For what it's worth, my boiler manages its own flow temperature between 10°c and 90°c (allegedly at least, Ives never seen it below 20°c or above 70°c) via load compensation on the boiler and weather compensation on the matching smart thermostat.

Unless it gets really cold, the radiators never get scolding hot and the return should always be cool enough for condensing to occur.

I don't stand around outside watching it, but there always seems to be visible vapour whenever it's operating.

It probably uses a bit more electricity to run the pump (pretty much non-stop on a cold day) but not enough to make a noticeable impact on the meter.

Weather compensation is a real pain to set up though.

Cardew

Raxiel wrote: »

Weather compensation is a real pain to set up though.

What setting up is required on your system?

I have weather compensation see -: http://viessmanndirect.co.uk/files/8e57dbc7-8a10-4065-bcc6-a27700ee752a/weather_comp.pdf

Fitted about a year at the same time as new Viessmann boiler with an unvented(pressurised) HW system; and have no instructions for setting up - albeit the Viesmann plumber who installed it presumably set it when commissioning the system.

It works exactly as described in the above link with the water temperature very low in mild weather. In fact the only downside of weather compensation can be the low water temperature in mild weather.

I recently, at short notice, needed, to use a large lounge that we don't routinely heat; it was at 16C. With the water temperature at about 45C it took an age to warm up the room and bring it to an acceptable temperature.

To test the system worked, I hung a bag of ice near the outside sensor and the water temperature rose markedly.

Raxiel

Cardew wrote: »

What setting up is required on your system?

I have weather compensation see -: http://viessmanndirect.co.uk/files/8e57dbc7-8a10-4065-bcc6-a27700ee752a/weather_comp.pdf

Fitted about a year at the same time as new Viessmann boiler with an unvented(pressurised) HW system; and have no instructions for setting up - albeit the Viesmann plumber who installed it presumably set it when commissioning the system.

It works exactly as described in the above link with the water temperature very low in mild weather. In fact the only downside of weather compensation can be the low water temperature in mild weather.

I recently, at short notice, needed, to use a large lounge that we don't routinely heat; it was at 16C. With the water temperature at about 45C it took an age to warm up the room and bring it to an acceptable temperature.

To test the system worked, I hung a bag of ice near the outside sensor and the water temperature rose markedly.

For mine it's all done via the control app for the thermostat
https://i.imgur.com/LooS3Lx.png

It does just 'work' if you leave it at the defaults, the pain is tweaking it so it sits closer to target temperature.

There's not a lot of setting up, just the upper and lower bounds of the _/ˉ curve, and an offset (so, with an 'influence' of 3, if the inside temp is 2 degrees below target it raises the water 6 degrees above the curve). The pain is it can take a long time to see the effect of any changes and if they work.

I didn't get any instructions with it, but Worcester were able to provide some quite technical documents on request.

Edit:https://imgur.com/a/M09OQ

Our house isn't that big, so we just heat all of it. If I did need to heat a room quickly my options would be to temporarily disable WC or manually set it to something ridiculous like 30°c to give the system a fright, and then turn it down as soon as the rads got toasty.

[Deleted User]

My house has an E/F energy rating (it's a poorly insulated student home with drafty windows and doors) - am I right in thinking that by having the heating on all day when nobody is in, the heat is simply being lost/wasted and is costing us a small fortune? The argument in favour of keeping it on all day even if nobody is home (at around 20'C) is that it saves money because the boiler has to work hard to heat the house up from cold temperatures...

I keep coming home to an empty house that's been kept at 21'C for 4-5 hours because my housemates won't turn the heating off when they leave (I get up early and leave before them).

Can someone reassure me of my sanity, or offer some advise, please? :undecided

Cardew

justwilliam25 wrote: »

My house has an E/F energy rating (it's a poorly insulated student home with drafty windows and doors) - am I right in thinking that by having the heating on all day when nobody is in, the heat is simply being lost/wasted and is costing us a small fortune? The argument in favour of keeping it on all day even if nobody is home (at around 20'C) is that it saves money because the boiler has to work hard to heat the house up from cold temperatures...

I keep coming home to an empty house that's been kept at 21'C for 4-5 hours because my housemates won't turn the heating off when they leave (I get up early and leave before them).

Can someone reassure me of my sanity, or offer some advise, please? :undecided

Yes you are correct that 'am I right in thinking that by having the heating on all day when nobody is in, the heat is simply being lost/wasted and is costing us a small fortune?'

daveyjp

The boiler merely heats water to the temperature set by the user and then heats as required to maintain the heating water temperature.

It won’t ‘work harder’ if it is colder. Once the water is at the set temp thats it.

victor2

daveyjp wrote: »

The boiler merely heats water to the temperature set by the user and then heats as required to maintain the heating water temperature.

It won’t ‘work harder’ if it is colder. Once the water is at the set temp thats it.

Of course it will work 'harder'. The water is returning to the boiler at a cooler temperature from a cold house when compared to the house at an increased temperature. Therefore the boiler has to keep heating the water until a satisfactory return temperature is achieved.
Therein lies the main topic of discussion in this epic thread - is it cheaper to let the house cool down when vacant or keep it warm?...

reeac

Blackbeard_of_Perranporth wrote: »

This forgets that overnight your house can fall in temperature to around 5C and then slammed up to 20C which it never reaches, back to 10C during the day and then never reaches 20C in the evening. The condensate remains after the morning shower, doing more damage to the walls, tiles in the bathroom!


My thermostatic time-switch control the house temperature 24/7 and my furnace is hardly on. Current utilities are £75 a month, fixed until December 2018!

A neighbour who lives in a similar property only blasts her central heating to save money currently pays more than me!

Light frost last night so I got up at 0600 and checked temperature in the hall where the thermostat resides. It was 17C so had fallen only 3C between 2230 when the heating had switched off and 0600. Our place is a 1996 bungalow built to then building regs. but with some extra roof insulation so not exactly Passivhaus standards but still not much heat loss overnight.