What water and overnight set-back temperatures do you use?

[dty]

How many kWh in 25 cubic metres ?

I'm averaging about 300kWh a day at the moment.

[dty]

Thanks for the input everyone.

I'm in a large 1950s house. We have recently had a fair bit of work done on insulation (including CWI) but the house still seems to lose heat quite quickly (old aluminium framed windows with 10mm double glazed units won't be helping, I'm sure). I've been using 15C overnight, but I'm having long warm-up temperatures in the morning, maxing out our 30kW boiler for over an hour.

My heating engineer (who is EXCELLENT, if you're reading this! ) suggested moving the DHW heat-up earlier, which I did, and I can see the morning spike not stressing the boiler quite so much now (although the noise of the boiler coming on at 5:30 is another matter...)

His next suggestion was to keep the house warmer overnight, and suggested 18C. Again, that has obviously had a beneficial impact on the gas usage first thing in the morning, but at the cost of overnight gas usage!

So I'm just trying to get a sense of whether 18C overnight, and ranging from there up to 21C during the day depending on occupancy and time of day is decadent, normal, or somewhere in between.

[rotor]

My "whilst we are awake" temperature is 21, and I still get cold sitting on the couch watching a movie.

[killa47]

For what it's worth - I also consider 21C a fair day-time setting and 22.5C a real treat for t'missus.

[DBMandrake]

Keep in mind with all these temperature comparisons that unless you're all using wall mounted stats like DTS92 your "ideal" comfortable temperature can't be directly compared with anyone else's.

This is because there can be a large temperature difference of 1-5 degrees between what an HR92 measures (beside the radiator) and what the temperature really is out in the room near the occupants depending on radiator type and location and room characteristics including furnishings.

For example in my living room where I now use a DTS92 but previously only used an HR92, even with a -1 calibrate on the HR92 I found in the winter I was turning it up as high as 23, (compared to 21 in warmer weather) while the real temperature in the room measured away from the radiator was more like 20-21 degrees. Since I've been using the DTS92 comfortable evening temperature for the living room seems to be about 20.5 to 21, even in the coldest weather!

(One reason I added the DTS92 was so that I could choose one set point that was comfortable no matter the outside weather conditions - and it does exactly that)

Likewise our dining room is particularly bad in this regard (not sure why) and even though I have calibrate set to -2 on the HR92, when it thinks the room is 20 degrees a table top thermometer says about 16-17 degrees! (It would only be 14-15 degrees without the -2 calibrate)

So don't take too much notice of specific temperatures if you only use the HR92's built in sensor, since room conditions can cause the measurement to be way out from what the room really is - just use what feels comfortable to you.

[SensibleHeatUK]

Thermal comfort is going to be as much about the radiant heat/cool sources in a room as much as dry bulb air temperature (which is what the thermistor in the Honeywell sensors measure), so even if you feel comfortable in a particular room at 21 degrees you might not feel comfortable in a different room with exactly the same air temperature. So for comfort it's more about finding the values that work for you in a particular room rather than becoming fixated on why 21 degrees may or may not actually feel comfortable.

[G4RHL]

So don't take too much notice of specific temperatures if you only use the HR92's built in sensor, since room conditions can cause the measurement to be way out from what the room really is - just use what feels comfortable to you.

The answer therefore is a wall stat in each zone but perhaps to limit the cash outlay, only in those zones that are frequenty used. In my case that could be as many as 7! However, I could possibly limit it to 4 and as I already have one wall stat, only 3 to buy! It is just as easy to turn the HR92 up in rooms that are not frequently used or places like studies. Food for thought.

[DBMandrake]

I'm averaging about 300kWh a day at the moment.

Thanks for the input everyone.

I'm in a large 1950s house. We have recently had a fair bit of work done on insulation (including CWI) but the house still seems to lose heat quite quickly (old aluminium framed windows with 10mm double glazed units won't be helping, I'm sure).

Ouch. In January we averaged 133kWh/day for gas and I thought that was pretty high - and this is after using Evohome scheduling to keep unused rooms down as much as possible. If I kept all rooms toasty warm I could probably hit 200kWh/day easily. (I have a few individual weekend days peaking this high)

Old 1930's fully detached bungalow here with a not very well insulated loft conversion and numerous small draughts around windows and doors that add up. (They are slowly being squashed, but it really needs a new front door and new kitchen and bathroom window, neither of which are properly sealed or double glazed) Also an old non-condensing boiler.

I've been using 15C overnight, but I'm having long warm-up temperatures in the morning, maxing out our 30kW boiler for over an hour.

I wouldn't have thought that "maxing out" the boiler for an hour to warm a house up from overnight was a particular problem ? In all the houses I've lived in recently warm up time during really cold weather has always been at least 2 hours - the default optimal start limit for Evohome is 3 hours...

It varies a lot from room to room and depends a lot on outside temperature but I typically see optimal start come on anywhere between 1 1/2 hours to 2 1/2 hours before scheduled times in cold weather to get the rooms up to temperature from being set back to 5 degrees overnight or while the house is vacant during the day.

BTW if your boiler can reach its set flow temperature from a cold system start in about 15-20 minutes then it is not being maxed out - if it was truly being maxed out it would not be able to reach the set flow temperature until some radiators started shutting down. Our boiler is 23kW however when I add up the 9 radiators they only work out to about 17kW if they were all on at once, and sure enough it has no trouble reaching the flow temperature in under 20 minutes from a totally cold start.

If the hot water is reheating at the same time that seems to take about another 6kW - in that case the temperature rise is very slow and the boiler does not cycle off for a long time, that shows that it is nearly maxed out, but again this is not really a problem and only occurs when hot water is heating and all radiators are wide open. I could wire the zone valves for hot water priority to avoid this but I prefer to have radiators still able to work during hot water reheat.

My heating engineer (who is EXCELLENT, if you're reading this! ) suggested moving the DHW heat-up earlier, which I did, and I can see the morning spike not stressing the boiler quite so much now (although the noise of the boiler coming on at 5:30 is another matter...)

Or you could put it later instead of earlier, so that most rooms are up to temperature by the time DHW comes on, which is what I did. For example on week days I have rooms scheduled to be warm by 5:30 using optimal start, and hot water switches on at 5am - by this time most rooms are most of the way towards being warmed up so radiators are starting to close. What do you mean by "stressing the boiler" ?

His next suggestion was to keep the house warmer overnight, and suggested 18C. Again, that has obviously had a beneficial impact on the gas usage first thing in the morning, but at the cost of overnight gas usage!

And will cause you significantly greater total gas usage! High night time set back temperatures is a big mistake when it comes to saving gas, there was another thread debating this recently and I like Paul's analogy - would you leave a pot simmering all night on the stove so you could boil your eggs quicker in the morning ?

Why not just let the zones drop right down over night and let optimal start do its thing ? That's what I do.

So I'm just trying to get a sense of whether 18C overnight, and ranging from there up to 21C during the day depending on occupancy and time of day is decadent, normal, or somewhere in between.

If you already use 300kWh in gas a day I wouldn't be using 18 degree overnight setback around the house that is for sure. I found even set backs of 14 degrees in the winter were costing me a lot of gas so I now stick strictly to bedroom (with 10 month old) 17 degrees and the rest of the house 5 degrees (basically off with frost protect) and have optimal start set to a maximum of 3 hours to give it full latitude to do what it needs to to get the house warm in time in the morning.

Keep in mind that most conventional timer / single thermostat systems will turn your heating OFF at night, no questions asked. So going from that to Evohome with high setbacks at night will actually increase gas usage not reduce it. Something I learnt the hard way over our first winter with Evohome...

If our bedroom wasn't so badly insulated and we didn't have a 10 month old trying to sleep there I would keep the bedroom off at night as well, but with him trying to sleep it's not an option. So it's the only radiator in the house that goes at night, and it only comes on if it actually needs to to maintain 17 degrees - so in warmer weather it automatically doesn't come on during the night since the room temperature doesn't drop below the set point. Or it might only drop below that as late as 3-4am.

[chrisgare]

Here are some graphs of my daily gas usage over the last 8 years. I installed Evohome 4 years ago and I hope they show how difficult it is to compare one year to another. MY usage down this year because I built an extension that removed two outside north-facing walls. More comments on the graphs soon.

a1.jpg a2.jpg a3.jpg a4.jpg a5.jpg

[dty]

I hope they show how difficult it is to compare one year to another

You need to start digging into degree days in an attempt to normalise for outside temperature variation.