Optimal heating times for central heating system operation

[Nick Odell]

News about the ever-spiraling energy costs prompted me to wonder: is there any data available about optimal length-of-time,time of day operation of a central heating system purely to keep the house ticking over, and to avoiding damp patches and frozen pipes?

I'll probably be away for a while during this winter and I wondered whether I ought to leave the c/h timers set so that the heating comes on for a short burst in the coldest part of the night to arrest the temperature fall, the warmest part of the day to boost the warming effect of the sun or at some other time(s) entirely? There's no overall thermostat but all the room radiators have thermostatic valves and the energy storage of the thick stone walls mean external changes in temperature take quite a while to work through.

Nick

[Harry Bloomfield Esq]

The recommended way is to fit a frost stat, or perhaps more than one in parallel, in the locations where pipework is most likely to be coldest. Most modern boilers include their own protection, built into their software.

Mechanical frost stats are usually set to 5C, to allow for their sluggish mechanical action. More modern and accurate stats could perhaps be set to an even lower temperature.

[Robin]

You may find your insurance mandates a minimum temperature. Tricky to show compliance with that if you have no master thermostat so I wonder if you've considered fitting one? A wireless one for c. £50 can [usually] be added easily enough to the "call for heat" circuit and put somewhere central. You can of course still use the radiator stats to limit the temp in any individual rooms which tend to go higher.

[Martin Brown]

You will have to experiment. You should check your insurance too. They may specify a minimum temperature or number of days left unoccupied.

It helps if you have a frost stat thermostat somewhere that can command heating on overriding the timer if it gets too close the the bone.

Thick stone walls have a tendency to become damp in winter if there isn't quite enough heating or air movement. Heating the house at the approximately the coldest time of day is probably the way to go since that is when there is most risk of penetrating frost.

Insulate all exposed pipes very carefully too.

[Brian]

I installed a Hive system a few years ago.

One of the benefits is allows you to see a graphical display of the temperature, admittedly only where the thermostat is but still useful.

You can also control the system remotely. I use mainly when returning from trips. In the summer / warmer months, just to ensure we have hot water, but in cold weather to ensure the house is warm.

I used the graphical temperature display to ‘optimise’ the on/off times for the heating, based our day (time we get up, go to bed etc). I forget the exact details but, in simple terms, the temp is set higher first thing for comfort in the morning, lower during the day ( when we are active ), a bit higher in the early evening, then the heating goes off mid evening. The house stays comfortable until bedtime. Hive works with Alexa so, if we need to adjust things on a particular day, we just do it via voice.

You can set the temp to, say, 10 degrees, to prevent freezing. (10 is higher than a normal frost stat.)

Assuming your timer has a standard MK14 back plate, the Hive box should replace it and add a room stat plus you get an internet interface.

[Harry Bloomfield Esq]

I have had 8 Smart Plugs, scattered around the place, using different access points - all controlled via Alexa which at times Alexa has lost control of. Some of them fairly essential that they do what they were set by Alexa to do and within a few days, or there might be consequences. I failed to find any way for Alexa to advise me in a positive way, if it was unable to control a Smart Plug, so I ended up devising a workaround of pinging every devise every 30 minutes and if there are two failed responses in succession, it emails me to let me know. I can then simply go and power cycle the Smart Plug to get it back in working order.

It runs in the background, while ever my laptop is turned on, which is adequate. Before setting this up, the only way to know a Plug wasn't responding, was to open the Alexa app on my phone or laptop.

[ARW]

During the cold winter in 2010 a friend of mine was flooded out after the incoming supply burst.

It came up behind the kitchen cupboards next to the external wall and although the CH kept the internal rooms warm, the incoming pipe burst.

Having someone to occasionally run the cold water would have stopped this happening.

[Brian]

I’ve got a number of plugs etc controlled by Alexa. (Between 10 and 20, plugs, light switches, sensors,…)

Only one, a switch*, seems to have a ‘ habit’ of not responding. It isn’t critical, a bit annoying. I’ve set up a way to recover the situation when it happens. It seems to be a Wifi dead spot issue**, although the coverage seems reasonable in the place where the switch is. Another unit close by seems fine.

• one of those rectangular ones

** it seems to go off line. However, cycling the power fixes it.

The Hive interface seems very reliable. I don’t recall any issues with it or it ever not responding. That said, we don’t use the Hive voice command that often. We use the voice commands with the Smart plugs etc numerous times per day.

[Harry Bloomfield Esq]

All of mine are reasonably well covered by wifi, some extremely well, but I have known them simply stop responding. All are addressed almost daily. I'm not clear whether the regular pinging helps maintain contact, but since I started pinging I have not suffered a single failure.

[Theo]

If you don't have a thermostat, how does the boiler know when to come on? Or does it just burn all the time the timer tells it to be on, or you don't use the timer and just run manually for an hour or two at a time?

Burning when all the TRVs have cut off the radiators is very inefficient, since all it'll do is circulate hot water around the pipes constantly but not actually emit very much heat since pipes aren't radiators. That means the water coming back to the boiler is almost as hot as that which left it, but yet you're still running the boiler and the pumps for no reason. If it's a newish boiler it may modulate the output down, if it's an old one I imagine most of the heat goes out the flue.

So I'd strongly recommend fitting a central thermostat to turn the boiler on and off based on temperature. If you're doing that you'll need to do some wiring changes, and it may be worth fitting a 'smart' or internet-connected one so you have external control. Not all internet connected controls are smart - learning the temperatures etc etc - some are just a dumb programmer with a phone app to set the times. But even the dumb kind might allow you to see what's going on from afar.

Theo

[The Natural Philosopher]

Boilers have a circulation temperature thermostat so if te circvulating water gets too hot, the boiler (but not the pump) will shit down

No, the burner shuts down

When you start from the wrong assumptions, its hard to come to the right conclusions

I run one loop without an overall thermostat. The pump runs all the time, but the burner fires up only when needed

[Nick Odell]

The last two words above: technical jargon, eh?

I'm pretty sure that's how my system works though having read through this discussion I can see the advantage of thermostatic control of operations in my unattended scenario. I'm not so sure about using smart devices to do the controlling: partly because this is such a low-tech installation that having to do everything from scratch looks prohibitively expensive and partly because as a dyed-in-the-wool Luddite, I'm not confident the kit would always reboot and work correctly after the repeated power cuts that the government insists we are not going to get this winter. And 8000 miles is a darned long way to come to press a reset button.

Nick

[Nick Odell]

Having now R'd TFM I see that the combi - a Baxi 105HE - is supposed to have a low temperature sensor which will automatically fire up and pump water through the system at 30degC if the boiler temperature drops below 5degC. Since the combi is in the coldest room in the house anyway, I feel that would work brilliantly as a protection against frost, if it works. Is there any way of testing in advance that the protection circuit is working? Short of filling the boiler room full of ice cubes, that is.

[Harry Bloomfield Esq]

Trust it to work, it relies on the same temperature sensors it uses in it's normal operation. If the boiler works properly and obeys it's front panel boiler output temperature setting, no reason why it should not also detect <5C and switch on.

[Robin]

But for how long does it do so?

ISTM designed to stop the boiler from freezing. So it'd be reasonable for it to stop heating when the boiler gets warm (for some value of "warm"). The question is how warm will the rest of the place be by then? You might be lucky and find it's fine. OTOH you might find that the boiler - the place where all those flames and a heat exchanger etc are - gets warm a lot faster than other rooms. Do yuo feel lucky?

More positively, a possible experiment for a coolish night:

a. turn up radiator thermostats

b. measure temperature of boiler and of other rooms

c. run boiler until temperature of boiler rises by (say) 10C

d. measure temperature rise in other rooms

e. wave wet finger to try to estimate what the effects would be with 30C water, heat loss through cold walls and all the other bits I've not thought of :((

[Robin]

On less sober reflection, it would seem sensible for the boiler, after being triggered by <5C, to run until the return temperatures reaches a certain limit. That could put more heat into the property. But without knowing the limit I'm lost as to how you can predict how much and the overall effect.

[Nick Odell]

Thanks, Harry. I appreciate the advice.

Nick

[Nick Odell]

I suppose (without any evidence) that if once triggered it is going to run up to 30degC it is going to determine that figure from the temperature of the return flow. In which case a certain amount of warmth will have spread around the house in the meantime.

I can see I'm going to have lots of fun playing with thermometers this autumn.

I can still see the benefit of wiring in a room thermostat. The installation/user instructions mention the 'stat but don't specifically say how to wire it into the boiler. I presume for frost protection when the boiler is otherwise inactive it ought to be wired in parallel with the timer; for overruling the timer for normal domestic use it ought to be in series.

Nick