Electronic Thermostat - Can it be justified?

[Peter Hemmings]

Hi,

I have just had trouble justifying the buying of the above to my neighbour and wondered if, with new boilers they can still be justified. Background: I have a Baxi Barcelona fully pumped with two zone valves (DHW and Htg) with a CM67 in the hall and TRV's on most radiators but not in the hall. I leave the Heating controller on 24 hours with the DHW on once a day. I am very happy with the convenience of the thermostat and its operation in keeping the hall and downstairs at constant temperatures.

My next door neighbour has had a large extension built with 3 extra rooms and has ditched his old oil boiler and is fitting a new Valiant Combi non-condensing boiler. I told him of the benefits and he said that he was told by the Corgi installer that, as the has TRV's fitted (maybe to all radiators) and the boiler sensed temperature and was self regulating (sorry forgot the correct terminology) it would be of no benefit to him except the convenience of temporary overriding settings when on holiday etc!!

Unfortunately my argument that it was more efficient in maintaining temperature went on "deaf ears" as he insisted that TRV's would do the same on each radiator! Unfortunately I could not think of a reasoned case for my system and I am now not sure that there is one.

So, (at long last) can someone let me know if they are still worthwhile in these days of self-regulating high efficiency boilers or are the now redundant?

Thanks

[Dave Gibson]

I have TRV's on all my rads and must confess that the only thing I use my electronic timer/thermostat for is for the timer function (except at the beginning and end of the heating season). Normally I set the temperature to

26 deg and let the TRV's sort all the room temps out. Even though this way round the circulation pump is on throughout my chosen heating periods I still find it gives a higher overall efficiency. I will add that the 'stat is in the hall, normally our coldest room. At the beginning/end of the heating season (like around now, April/May time and Sept/Oct) I turn the hall rads off and reset the target temp to a around 22 deg. That way if we get a warm day the circulation pump stays off.

So in answer to your question, yes they still can be justified (IMHO).

Dave

[Christian McArdle]

It would only comply with the letter of approved document Part L1 if there is a boiler interlock that turns off the boiler totally when there is no call for heat. This normally requires either a room thermostat or a flow switch to detect that all the TRVs have closed.

Christian.

[N. Thornton]

electronic stats give much better heat regulation than TRVs, and thus save needless energy use. They also allow different temps for different times, again saving on energy. They typically pay back their cost in a couple of years I worked out.

Regards, NT

[IMM]

The CM67, and others, has an optimiser. You punch in your occupancy time and it delays the boilers firing until it needs too, keeping it off until the last minute if need be. They also have inbuilt boiler anti-cycling. Some boiler have this inside, but a belt and braces would do no harm.

[Pete Cross]

So once the room with the thermostat is up to temp, the rest of the house 'loses' it's heating until the thermostat closes again ?

[IMM]

That is why you put it in the coldest room in the house that requires a cooler temperature. The hall.

[IMM]

In your case it acts as a high limit and an optimiser, if it has one. having the pump continuously on is better than switching it off and on. If a the last closed TRV opens heat is readily available and no warm up period fro the boier. Make for a more even temperature.

If only TRVs are used on all rads then an auto by-pass valve needs to be fitted.

[Christian McArdle]

Yes. Either put it in the coldest room so the rest of the house is already up to temperature before it closes off, or put it in the room you are likely to be using (i.e. lounge) so you don't care that the rest may not be as accurately controlled.

Much better still, use subzoning and have different programmable thermostats for each zone. I have zones for upstairs (bedrooms), downstairs (receptions), kitchen and (soon) conservatory. This way each can have a different temperature profile over time to reflect usage patterns and each follow more accurately the desired temperature. The thermostats are placed in the most used (or only) room in each zone.

Christian.

[Dave Gibson]

Its a solid fuel boiler with indirect cylinder + heat dump on gravity circuit, so heating circuit does not require bypass.

Dave

[IMM]

My comments were directed more to the OP who has a Barcelona.

[Peter Hemmings]

Just a quick thanks to all who replied and FWIW my observations on subzoning.

Also in respect to savings (on my system) I can confirm it saved its cost in just over 2 years.

In message , Christian McArdle writes

A word of caution here, it really is "horses for courses". I had a well insulated double glazed 70's semi and plumbed downstairs and upstairs zones on separate thermostats/timers. The system worked OK but as I left most doors open, the upstairs bedroom heated up during the day and only in the extremes of winter would it call for heat!! So (in my particular case) the extra expense/time fitting was not justified. I agree with the subzoning principle for your layout. but I think cost benefits of plumbing four zones might well be marginal particularly if you had to pay for all the work!

Thanks

[Christian McArdle]

Ideal then. The subzoning would mean that there is no call for heat and the upstairs radiators don't get hot, saving you money.

For me, it was just the cost of the thermostats and zone valves. Around 60 pounds per additional zone. There was no appreciable need for extra pipework, certainly nothing in comparison to the extra length needed to relocate the boiler to the loft.

The conservatory should always be on a separate zone, if at all possible. This would save a fortune if you use the room infrequently (i.e. as a dining room). I wanted a separate zone for the kitchen as has very different construction to the reception rooms (much more external wall and window) and runs a fan convector, which wouldn't share a zone particularly well with radiators.

Christian.

[Peter Hemmings]

Christian,

In message , Christian McArdle writes

Yep, agreed but my point was that originally the upstairs rads had TRV's which also did not call for heat. OK, I accept electronic thermostats are more efficient but the overall cost (in my case) would probably take have taken considerably more than

2 years to recoup.

Yep I completely agree with the above but my case was somewhat different.

Thanks for the information All the Best

[martin.shaw11]

"electronic thermostats are more efficient but the overall cost (in my case) would probably take have taken considerably more than

2 years to recoup."

A study was carried out using similar houses and families to find out what the energy saving was for an electronic thermostat. There turned out to be none. This was because the ordinary thermostat had such a large hysteresis that it was used purely as an on off switch and was off for significantly long times, particularly at night. Obviously the electronic version is superior (I know I recently upgraded to one) but don't expect any running cost savings necessarily.

[Christian McArdle]

That sounds like a comparison between an electronic (non-programmable) type which is set to target temperature all the time to a manual type used as a switch. How would it compare to a programmable one, which is also off for long periods (i.e. overnight)?

Christian.

[Martin Angove]

Define "off" though. Most programmables don't actually go off overnight, just down to some lower-than-normal temperature. This winter, for example, I fitted such a device in my parents' house. We happen to be lodging there at the moment with two small children and there is also a slightly wimpy lodger who can't stand the cold yet sleeps with his window wide open (a crack I can understand).

In the "old days" before the programmable, the heating used to get switched off overnight at the main switch (no timer) and so if the house temperature dropped, it dropped and you cuddled deeper into your duvet. When I was a child here in the 70s there were no radiators upstairs and the single glazing would sometimes have beautiful fern-like patterns of frozen condensation on them on a winter morning. Plenty of "me too" replies to that one I suspect.

This winter, since the programmable, I have been woken several times by the sound of the heating coming on at (say) 3 a.m. (the pump is the other side of a plasterboard wall from the head end of my bed) in order to keep the thermostat happy: it is set to an "off" temperature of 14C. Below this certain people start complaining :-)

To return to the question though, I suspect that there is a *lot* of complicated background to deal with before you can compare mechanical with electronic, programmable or otherwise. For example, although the "off" period of a mechanical may be longer, so too may the "on" period - occupants only turning the thing down when it is too hot, and probably opening a window as well!

To veer wildly off-topic, my mother-in-law has a thermostat which I am pretty sure doesn't work. She regulates the house temperature (no TRVs anywhere) by twiddling the flow temp. knob on the front of the boiler :-)

Hwyl!

M.

[Christian McArdle]

That's hardly the fault of the thermostat. Set it to 5C and tell them to stop whinging!

Apart from the manually operated aspect, this is probably an efficient method of modulation, as conventional boilers have greater thermodynamic efficiency at low temperatures. However, you must be careful if there is any sign of condensing operation if the knob is set too low. She should ensure that no visible steam or water comes from the flue.

Christian.

[martin.shaw11]

Good point. I think the comparison is still interesting though. There was still a problem, because the poor response of the mechanical thermostat meant that the system was switched off by the consumer until they got cold and then they switched it back on only when they could be bothered ie when it got really cold. On the other hand the 'electronic' consumer tended to have their house on the warm side because they comfortably could. I can't remember where I saw the article (it was on a website) but the article was pretty convincing.

[Paul]

The Baxi Barcelona actually has a built in flow switch which automatically shuts the boiler off if all the TRVs close.