Talk to me about thermostats!

[snowballer]

This is the age old debate but I'm still dithering.

We have an oil boiler, not a combi. We have a thermostat in the hall. The boiler can be set to ON/OFF/TIMED. The timer can be set for three periods in the day. Historically we have had the heating set to come on for 2 hours in the morning, and 3 or 4 in the evening.

My question is - is it better/more efficient to have it set on "ON" all the time, and use the thermostat to keep it at, say, 18 degrees? Or to have it only on in the times periods (also thermostat controlled)?

What do others do with a similar set up?

I suppose the question is also whether it's more efficient to heat the house from cold for short periods twice a day, or to keep it running at an ambient constant temperature? 🤔

I'm interested in this too. We have a gas boiler but have always done timed in the past. We're going for constant but a lower temp this year..

We switched to a programmable thermostat about 4 years ago and the heating is on FAR less than it was when it was on constant on the timer. It's great in spring and autumn too as it just takes care of itself, no switching it on only to find yourself too hot the next day when the weather is warmer again. We still have it off completely overnight and during working hours when we are all out though by setting the thermostat lower in those periods.

Mine is gas but I have it on a timer and then use the thermostat to control whether the heaters actually heat the place e.g. although my timer may have the boiler 'on' between 6 and 10am my thermostat is down at 15⁰C so unless the temperature drops below that my boiler will not heat the rooms.

Unless your house has fabulous insulation I can't see it being cheaper to have the boiler on all the time.

Boiler on permanently for us.

The house is set to 16 at the moment and is cheaper on a daily basis than having the temperature drop right down. The boiler is actually on less as it takes less time to warm the house back up. It's a combi though which might make a difference.

Our house is very well insulated and we have a combi. Hopefully that means constant will work better for us... Its set for about 19 degrees.

I think you're better off running for longer at a lower temperature. This is what they say on the Octopus Energy website, and I've read a news article saying similar (think it was the BBC):

At their default setting, these temperatures are usually too high. This doesn’t make your home warmer, but it can add massively to your bills and emissions. It’s like putting your foot flat to the floor when driving – it’s hugely wasteful but doesn’t really affect your journey time.

If you have a combi boiler, we recommend setting your flow temperature to 50c for heating and 55c for hot water – it’ll take a little longer to heat up, but the gas and CO2 savings make it more than worthwhile!

If you have a boiler and a hot water cylinder, we recommend setting the flow temperature on your boiler to a few degrees over 60c for heating and hot water, and setting your hot water cylinder to 60c also (you’ll usually find the control for your cylinder ⅓ of the way up the tank.)

Here's the link:
octopus.energy/blog/winter-workout-gas-saving-tips/

That isn't saying anything about room thermostats and is talking about hot water temperatures. It is not saying to keep your heating on all day

From the link you posted:

Turning your heating off when it’s not needed is a quick way to save
.
Making sure your boiler isn’t running 24 hours a day is a great way to cut down your bill. Most boilers or thermostats will let you set a schedule, so you can turn the heating off or set it lower while you’re tucked up in bed. The trick is to set your heat to come on 30 minutes before it’s needed, and shut off 30 minutes early as well – so the room can heat up and you make the most of residual heat.

Articles I've read seem to only compare a) timed with b) on low all day. There doesn't seem to be anything about "on" but with thermostat controlling whether it actually clicks on and off! If that makes any sense.

Or maybe b) above is actually what I'm talking about?

Gah I'm an intelligent and competent human but I can't get my head round this! If I was on gas I'd just test the cost against a smart meter, but oil usage is so difficult to monitor in any detail.

Essentially you pay for the heat lost so heat on all day costs more, I think this is a Martin Lewis conclusion.

My understanding is that energy/heat loss isn't linear. I think it is a square rule, but I may be incorrect.
Basically the bigger the difference in temperature between the hot thing (your house) and the ambient temperature (the outside) the faster the heat loss will be.

Therefore keeping your house at 20 all day when you are out will cost more energy than letting it drop and then heat up again.

We have oil and a thermostat and we just installed hive digital TRVs on all our radiators bar one. So now the boiler is always "on" but only drawing heat when asked. I can also heat one room in the day (my office) and the rest of the house isn't heated so not wasting that energy. It's only been in place a few weeks though so I'll let you know about usage!

Yes, what @TeenDivided said. Just put it on when you need it. Ours is on for an hour when we get up. Then an hour in the evening. Obviously if it's super cold we have it on for a bit during the day too, but it's never on overnight here