Programmable thermostat

[DerbyBorn]

I love my programmable stat. It doesn't need to be fiddled with once it is set. Should I feel the need for a bit extra heat it is only a matter of pressing the "up" button. The programme will revert at the next timed event. No danger of a forgetful person leaving it set on full heat. Also no risk of getting too cold in the night as could be the case using a programmer. I would go down the route of fitting one and setting it carefully in discussion with the lady - agree times and temps - then go back after a few days to see if any setting need to be tweaked. Many people with bi-metal types end up using them as an on/off switch and rarely let the ting work properly.

[tony sayer]

In article , Fredxx scribeth thus

Course arrange to go there as and when to change the batteries wontcha;!...

[Peter Parry]

Honeywell CM907

As with most programmable thermostats setting it up is a shade tedious but it has several significant advantages in use compared with the bent metal devices. Firstly the hysterisis is low so it maintains room temperature well. It also alters the heating on and off times depending upon room temperature so doing a good job of matching the required heat profile so it will rarely need to be played with.

Secondly, once set properly if it does need to be altered it is very easy to manually raise or lower the temperature for that time period and afterwards it will revert to the program settings. With manual thermostats the user has to remember to lower them. Some people seem to think thermostats control the rate of heating and turn them higher "so the room heats up quickly". This leads to the average temperature in the house creeping upwards and fuel bills doing likewise.

[The Other Mike]

Honeywell CM901 (wired) Honeywell CM921 (wireless)

[Tim Streater]

I assume that these things control the rads directly, i.e. they turn the TRV on/off as they think the need arises? I also assume that if each one thinks it needs hot water it is signalling the central controller to keep the boiler turned on?

If now each decides its up to temp and stops signalling the controller, what happens then? Does the controller turn the boiler off?

[Dave Liquorice]

Er, no not in the context of this thread so far that is. I think you can get things that do do what you suggest.

This thread is about a normal programmable thermostat. Generally they are just a replacement for the traditional bimetal mechanical thermostat.

What they offer is a temperature profile through the day. For example at night it will have a set point of say 15C, then in the morning it could have 19C for a couple of hours then drop back to 15C when everyone is at work through the day, back up to 18 when the kids come home and 21C for slobing out infront of the telly after dinner.

They also have a much lower temp range when switching in either direction (off to on or on to off). Ours keeps the room to the set point within about 0.5C (1C range), a mechnical stat would be doing well to keep the room within 2C (4C range) of its set point.

[Tim Streater]

So is each of these just working by turning the boiler on/off then? If they're not controlling the TRVs, and a thermostat wants to say "That's enough heat in this room thanks", what if another wants the boiler on? Or are they separate heating circuits each with its own shutoff valve and separate pipework?

[DerbyBorn]

For an elderly person this is important - if it is set and left alone then surely this is a good thing. One doesn't want an elderly person turning the thermostat down too low. Mine is set to 17C through the night - however, it rarely switches on. If it does - then I am pleased as the house soon gets up to temp at getting up time.

[chris French]

In message , Tim Streater writes

There would normally be just one, it's just a replacement for a single temp room stat. Though they can be used to control zone valves etc. if you want, but that isn't waht is being talked about here

[YAPH]

...

The Honeywell CM9xx series is the most old-lady-friendly I've used. I don't think there's any progstat which is particularly non-techie- friendly to set up but the Honeywells are pretty easy to use, even if all you do is poke the up or down buttons to adjust the temperature for a while.

Their 1-day models are the CM901 (wired) and 921 (wireless). There are also 7-day types: Cm907 and 927 respectively.

[Dave Liquorice]

"These" being a traditional mechanical stat and a programable stat? Then yes they control the boiler.

That room doesn't get the heat it wants. With a properly installed, sized and balanced system that apparent problem isn't really one, as the house in general will cool and warm "as one". So when the room with the stat has cooled enough for it to want heat the other rooms will also only just have got to that temperature.

Problems will arise if the room with the stat has other significant heat sources so it doesn't cool as fast as the rest of the house. The room with the stat shouldn't have TRVs on the rads either or if they are fitted they should be would right up, otherwise the two unconnected control systems are likely to "fight" if the TRVs are set lower than the stat as the latter will never reach it's set point so will never switch the boiler off.

[Tim Watts]

Some of the really fancy ones have a few extra buttons for one shot specials like "stay on for another hour".

Considering the cost is a small matter of code and a couple of extra buttons it would be nice if the cheaper ones put some thought into it.

In fact, thinking about it, I can only think of the following manual overrides that might be commonly useful:

1) Manually up/down the thermostat for the current switching period

2) Holiday for a day - multiple presses gives N-days (on display obviously)

3) Stay on for X-extra hours (multiple presses again).

That's 4 buttons. I suspect a fair few do 1) anyway.

I did wonder what it would be like to have the whole lot networked and stick a touchscreen in the hall with a StarTrek L-CARS interface - then I realised that no-one could possibly make an L-CARS interface actually do anything useful - it looks good at a distance, that all...

[YAPH]

The Honeywell CM9x7 series do that. They're the best of the bunch I've looked at but getting long in the tooth now (they come set to a date in 2005 when you power them up!).

One feature they really really should have but don't, which would cost £0 to implement (being in software) is to run as a 5+2 or even a 1-day unit. (Their dedicated 1-day units, the CM9x1s, have fewer buttons).

A more accurate clock would be nice, too: it's surprising how much they drift, and you tend to expect electronic stuff like this to be accurate so find yourself looking at the display and assuming it's the right time.

But really nowadays, with multiple zone control increasingly being mandated in new build and retrofits, is the ability to link them together: two or more units in tandem (so if you set holiday mode on the master it propagates to the slaves) and to a central control unit (PC or smartphone) so you can set up the programs more easily.

It would be non-trivial to implement: even the wireless units, which already have a transmit link to a remote relay unit, would have to have receive capabilities. I have no idea if they're working on anything. Maybe some new entrant to the market will do it. But it would need to combine the ease-of-use of Honeywell's interface with the extra functionality.

[Alan]

In message , Ret. wrote

I have one that also requires me to dig out the manual when I want to change it. Not only is setting the device non-intuitive but the manual is poorly written.

[John Rumm]

I quite like the Centaurstat one the SF do. Once setup has a nice clear display of the current temperature and the demand temperature. Plus buttons that let you nudge the temp up or down. The batteries last for many years between changes.

[John Rumm]

Something of relevance with harder to heat properties, is that some of the prog stats are also "optimising". These learn the heating characteristics of the building and account for them. Hence if you have an overnight tempoerature of 15 deg, and say want it to be 19 deg at

7am, the stat will learn when it needs to fire the heating so that the temperature actually is 19 deg at 7am rather than just the demand being 19 at 7 am. (this might mean it needs to fire the heating at 5:30am for example if the place has a slow warm up)

[Fredxx]

Many thanks, precisely the sort of answer I was hoping. The CM907 and

901 seem identical, apart from being a 7 or 1 day program. I shall look at the instruction manual to see how intuitive it is.

[Fredxx]

Many thanks, there does seem a small consensus that this is the easiest to get to grips with. I don't need a wireless one as the siting of the existing one is convenient, and won't need any tidying up!

[The Other Mike]

The Honeywell ones allow a minimum (and maximum?) set point so you can stop them winding the set point to levels that can cause health problems.

[Fredxx]

I was thinking more of the display, buttons and ease of use. Currently things aren't a problem, but was thinking of the future.

I have no idea how intelligent other stats are with regards on off heating times. I would guess they can easily monitor the rate of change in temperature to limit overshoot which invariably happens in old fashioned bi-metal ones.