Schedule - On low all the time or off and then on when needed?

nickharper

With the recent cold weather in the UK I have found it's taking a lot longer to heat up.

I am at work in the daytime and when home at around 5PM with the heating off it's around 9 degrees. To then heat up to about 17-18 it takes a couple of hours.

Is it cheaper to have it set to stay at around 13 while I am at work and then go up to 17-18 so there's less of a climb?

DM932187

Proverbial can of worms, @nickharper.

An indoor temperature down to 9C from 18C in a working day indicates a significant heat loss from your property, or at least where the stat is.

Generally speaking, it will always be cheaper to heat a property only when and to the temperature you need it.

However, as you've discovered, you need to schedule around the thermal properties of the building and your heating system.

For example, we have a largish Edwardian house with some SG. Roof insulation has been upgraded, drafts minimised but otherwise, this is the old coal-fired draughty shed thrown up circa 1900. The boiler is a Viessmann 100 with basic weather comp. Single zone, manual TRVs throughout. Two tado stats as wall reference points (hallway and lounge) due to differing thermal characteristics in those two locations.

As the boiler runs relatively cool (running around 55C flow during the current cold weather), to achieve peak efficiency, we cannot use an aggressive setback when scheduling. During the day, the stats are set to 18C hall and 18.5C lounge, and in the evening, that increases to 18.5C and 19.5C. At night (from 11pm), the setback temperature is 17C, and right now, that means the heating kicks back in at about 2:30am and works its way back up to 18C for 6:30am.

I have had this system in place for over 10 years, and each year have contemplated your very question. I've found that if I leave the heating on a set temp 24/7 that is more expensive. However, if I use aggressive set back the house is either uncomfortable (as it takes an age to recover) or I have to increase the boiler flow temp (thereby reducing efficiency).

So the answer is, there is a sweet spot and you'll need to experiment.

Start with your boiler flow temperature. If you have a fixed flow temperature (no weather comp or load comp), then set it around 55C at the moment and see if your house can hold the set temperature. If yes, lower it a bit and repeat, If no, raise it.

Then try a much less aggressive set back temperature. Start with 4C max and see how that goes. Due to your apparent heat loss, my guess is that might be too much. What seems to be happening in your case is the thermal mass of the house is cooling far too much and you're spending quite a while reheating the walls, floors, furniture, etc. before the room stats to feel warm again. Adjust the setback accordingly.

Will it be cheaper? I can't say. It might not, but I tend to look at it this way. I can run my heating super cheaply and fail to heat my house, so every penny I spend is wasted. The house is still cold and the wife and kids give me a hard time. So instead, I've found the sweet spot and have to accept there's a consequent hit.

nickharper

Thanks very much, that's really helpful.

Yes, no doubt the heat is being lost and I have some insulation arriving for around the windows as I think a chunk of it is being lost there but without a doubt some of the walls actually feel cold to touch on the plaster.

I just don't want damp and then the couple of hours of being cold when I get in for it to then go off again and have to do it all again the next day.

At the moment it seems to sit at around 9-10 degrees with the heating completely off.

DM932187

What's your current indoor humidity looking like? At this time of year, even in the UK you should be able to keep it below 50%. Any higher, and you're probably allowing too wide temperature swings, thereby increasing the RH (and/or not allowing sufficient ventilation)

I wouldn't switch your heating off at all. Just set it back. Max 4C unless you're away for a day or so, in which case 12C minimum setting and turn it back up before you get home.

Slow and low on the boiler if you can, to maximise condensing efficiencies. Will run longer but will be more comfortable and reduce cold spots and humidity

nickharper

The Humidity thing is a weird one also. Currently Tado says 60% although I have a dehumidifier not far from it that comes on at 50% and usually says about 45%.

It is also the cost, currently finding it impossible to get off PAYG (which was there when I moved in) due to British Gas being a nightmare to change the meters.

Thanks, I will have a look now at setting it to 12C and try and automate making it turn up for when I get in.