Can I calculate savings for turning down/off individual radiators?

ChasingtheWelshdream

Hi all,

Most of our radiators have TRVs

I’ve been wondering, is there a way to calculate how much gas is saved by turning a TRV down or off? I realise there are variables, such as output, pipe run length etc, but is it possible to come up with a ball park figure?

I ask as most of our TRVs are set to 3, our thermostat usually 15 and most rooms still don’t reach above 14 degrees. 

Our December gas usage was still very high despite the house generally feeling cold and us miserable. I would love to know how much energy we are actually saving, and how much more we could save by reducing the TRVs down more in some rooms. Or if it is a case of diminishing returns. 

We certainly cannot afford too many of December’s bills, so I am scared to keep the heating on/up, but am also wondering how much money we are actually saving.

I am on an insulation mission and am aware of all our black spots, that is another story.

Mstty

Yes you can closely monitor every change you make on your system with outside temperatures and the measurement will be the energy you use during that test period.

Too many variables as you have stated so become your own scientific experiment and log the results.

ChasingtheWelshdream

Thank you, so I assume it is a case of checking meter readings before/after each change then.

There isn’t a guide to say that say a 3000btu rad will use xxx kw on setting 5, reducing to xxx on setting 1? I haven’t found one but thought it worth asking.

I desperately want a smart meter but after months of asking  still being told there are none available.

Alnat1

A TRV setting of 3 is generally a temperature of around 20C. If your main thermostat is set below this temperature then the TRVs at 3 will never function and turn off as the room will never reach 20C.

Have the thermostat in the room you use most and need to keep the warmest. Either no TRV in this room or TRV on highest setting. Adjust the TRVs in other rooms so they turn off at the temperatures you need. This can vary with make/model and radiator/room sizes but consider TRV settings to something like this, * = 7C, 1 = 10C, 2 = 15C, 3 = 20C, 4 = 25C etc. They don't need to be on full numbers, maybe a kitchen could be on 2.5 and a spare bedroom on 1.25.

Reed_Richards

ChasingtheWelshdream said:

There isn’t a guide to say that say a 3000btu rad will use xxx kw on setting 5, reducing to xxx on setting 1? I haven’t found one but thought it worth asking.

The numbers on a Thermostatic Radiator Valve are related to the room temperature.  To maintain any particular room temperature you have to balance the heat output from the radiator with the heat loss from the room.  The rate of heat loss will increase the colder the outside temperature becomes.  So the you will not find the guide you are seeking because that's just not the way Thermostatic Radiator Valves work.  They will cause the radiator to switch on and off according to their setting so as to try to maintain a constant room temperature.  But the amount of time the radiator needs to be on depends on how cold it is outside and how draughty the room is.

matelodave

radiators dissipate their heat according to the their area, material that they are made from and the temperature difference between the rad and the room temperature called Delta T.

You need to get the rad specification, measure the flow and return temp across the rad to get its average temp apply a correction factor to take into account any difference between the radiator spec'd output and the room temp to get a rough idea of the heat output of the radiator at that specific DeltaT. Bear in mind though, as the temperature in the room rises, the delta T will reduce so the output of the rad will reduce so its not going to be easy to determine the heat output.

TBH a smart meter wont give you any more info than you can read from your existing meter especially for gas which only uploads info in 30 minute chunks. What it can do though is give you historical data. You can do some useful monitoring by reading the meter regularly, say evening and morning but you also need to correlate the consumption with room temps, outside temps, boiler temps running time etc and to any changes that you make to the controls, so a spreadsheet helps.

You also need patience to only change one thing at a time, give it a day or two to settle down and record what happened.

ariarnia

when we had our bathroom done. the plumber said 12000 btu was about equivalent to 3.5kwh. but that doesn't mean it uses 3.5kwh of heat. i think it means 12000 btu of radiators at some standard flow temp/in a set room would give the same heat in a space as a 3.5kwh electric heater. 

but for your question your actually asking about the thermostat not the radiator so the btu of the rad isnt really important. and as people have said thats more a question of how much heat is the room losing so how quickly does the temp drop when the valve turns off. 

the rule of thumb is turning a thermostat down 1 degree is saving 10%. its a bit more complicated as your talking about the impact on the system (which has multiple rads and probably a central thermostat somewhere) of turning down one valve. but if you really got into modeling it you could probably work something out. it would be crazy complicated with the number of variables tho. not a basic one line calculator. 

ChasingtheWelshdream

Thank you. I am confused though.

I am sitting in a room with the largest radiator which is set to 3. It is cold so presumably TRV has activated and turned off. The room thermometer says 13.9 degrees. 

The boiler thermostat is elsewhere (upstairs hallway) and set to 15. It is still firing as that room is currently 14.8.

The thermostat can’t go anywhere else sadly. It is a new Hive system that has been problematic from the outset (on another thread) and won’t communicate with the boiler anywhere else.

It just feels like a losing battle and is getting scary. Our house is cold, we don’t take have daily showers (flannel wash instead), have a combi boiler so not heating a water tank, am frugal with the gas cooker and have still used 2534 kW in December.  At one point in the cold snap there was ice on the inside of one window, despite being double glazed. We work from home with blankets, hats and fingerless gloves to keep the heating off whilst the kids are at school.

I am genuinely scared for the future. 

Our house is large and old with 12 radiators, most of them undersized for the rooms, which I am gradually upgrading. The only warm room is when we have the woodburner lit.

ariarnia

ChasingtheWelshdream said:

Thank you. I am confused though.

sorry. i probably didn't explain what i meant very well. probably because i dont really understand what i'm saying like an expert would

basically if you put a 2kwh electric heater in a room with an outside temp of 15 degrees and set the thermostat to 20 degrees. it might burn at full power for a couple of hours (using 4kwh). then it would turn off. maybe an hour later it would click back on and use 500kwh to maintain the temp. and it would cycle on and off as needed until you turned it off. so you might use a smart monitor to measure its output and find in the full day it used 8kwh. 

the next day if the outside temp is 2 degrees but everything else is the same it might run for 5 hours before reaching temp and clicking off. then cycle on and off. so the same radiator set to the same temp for the same time might that day use 14kwh. 

so having the thermostat lower will save you money because the room will reach temp faster. but its not really the thermostat temp that determines how much energy is used so it can't be a basic reference table online. its the heat loss that matters. 

and because you can't get a smart plug in monitor for a gas radiator. then the only way you can easily measure how much energy is used and see what difference the lower thermostat temp means for your gas use is by changing the settings and taking regular meter readings (including making a note of the average outside temp i guess). its one of those things that you need to try over time to see what you can live with and what difference it makes. 

I am sitting in a room with the largest radiator which is set to 3. It is cold so presumably TRV has activated and turned off. The room thermometer says 13.9 degrees. 

The boiler thermostat is elsewhere (upstairs hallway) and set to 15. It is still firing as that room is currently 14.8.

The thermostat can’t go anywhere else sadly. It is a new Hive system that has been problematic from the outset (on another thread) and won’t communicate with the boiler anywhere else.

It just feels like a losing battle and is getting scary. Our house is cold, we don’t take have daily showers (flannel wash instead), have a combi boiler so not heating a water tank, am frugal with the gas cooker and have still used 2534 kW in December.  At one point in the cold snap there was ice on the inside of one window, despite being double glazed. We work from home with blankets, hats and fingerless gloves to keep the heating off whilst the kids are at school.

I am genuinely scared for the future. 

its a really scary time. the reason ive been spending so much time on here in the last few months is that learning things from the clever people on here and the threads people make helps me feel a bit more in control and gives me good ideas for how to make positive changes in our home  

i think reading this then one thing you might want to look at is if the boilers are balanced right. check everything has been bled, and test all the valves are working right. make sure the system you do have is working as well as it can for you. 

then id suggest looking at insulation and if theres anything you can do diy style to keep more of the heat your using in the house. lots of places have sales on now so its a good time to look for things like thermal curtains. we have sets on all of the windows and also curtain rails over several internal doors where theres drafts that mean the heat doesn't stay in the rooms we want heating. 

you can also look at heat loss between floors. the proper solution is insulation under the floor boards but a good half step is maybe some thick rugs (make sure they have non slip backing if you have wood anywhere and dont put one at the top of the stairs just in case).

one thing thats made a big difference for us is OH bought a huge tub (like 25m) of upvc door seals. our seals were probably 10 years old and all flat and brittle. so when doors and windows were closed and locked they werent compressing and giving a good seal anymore. it was a bit of a fiddly job but probably half an hour per door and no more drafts. the hall is now much warmer without any more heating. 

and the last suggestion sounds weird. but bare outside walls also lose heat (and if your neighbours dont have the heating on any shared walls). so large canvas paintings or even wall hangings if you dont mind them can add a layer of insulation on the walls while you consider things like cavity wall or external/internal wall insulation. 

just some ideas for small things ou might not have thought of now that might help this month so you can think about what makes a proper difference to prep for next year. hope that's even just a little helpful  

Cirrus1

ChasingtheWelshdream said:

Thank you. I am confused though.

I am sitting in a room with the largest radiator which is set to 3. It is cold so presumably TRV has activated and turned off. The room thermometer says 13.9 degrees. 

The boiler thermostat is elsewhere (upstairs hallway) and set to 15. It is still firing as that room is currently 14.8.

Is the problem that the room you are sitting in is 13.9 and not your max of 15?
If this is the case, why don’t you open up the valve fully, I.e. set the trv to the max it will go to? The room will never get to 25+ degrees because your room thermostat will turn off the heating at 15.
If your thermostat has reached its set temperature and you still need more heat in a room, you can boost via the app, the thermostat or the receiver. If all your rads have trvs, then the ones you don’t want boosted can be turned down and you just heat the room/s you want. After the boost period, the control returns to 15 degrees. Just a thought.

ChasingtheWelshdream

Thank you. 

Ariania, I am gradually adding wall insulation bit by bit and will be doing the suspended wooden floor soon. I can only do as budget/time allows but do have a grand plan.

The boiler and system are generally good and in working order and I maintain it as best I can (cleaning magna filter, bleeding etc when needed). I am gradually either replacing or adding radiators on a room-by-room basis. We do have high ceilings so generally larger rooms I guess take more energy)

Cirrus1, I am confused why the TRV turns off the radiator at such a low temperature but that in itself isn’t an issue if it is saving money. I had wanted to know how much it would save if I turned it off completely but I can see that is only going to be possible with a lot of patience and testing.

Unfortunately we can’t use the Hive app, the connection was too unreliable and constantly dropping out so we have had to put it in standalone mode. Hive have basically admitted it won’t work with our house setup. That is detailed on another thread but a huge disappointment.