There is a lot of advice about this online, all one stop solutions that work for everyone. However, the vast majority of this advice does not consider how these rules change depending on the property type you have and how the weather changes over the period of winter that we use our central heating. You may find online videos that have a title like “Don’t turn down/off TRVs to save money”, but by the end of the video, they are basically saying “but turn down TRVs to save money”. The fact is, for most people, any single answer solution is wrong. We need to understand how this advice applies to us and our home, if at all. To help, we will give you a bit of background info on how energy works, some simple steps that anyone can use and then some more detailed steps around specific property types and ages, which may apply to you. One common misconception is that “turning off a TRV means the boiler and radiators have to work harder”. What is meant by this, is that turning off a TRV means you have to turn up the boiler temperature. This is not true, at least not for most of the winter.
What is the best way to reduce heating costs? Lowering the boiler temperatures is the best way to do this, however, it isn’t an either or solution. A lot of people start to use home heating from October through to March. Getting our boiler temperature as low as possible is key, however, for the majority of the year we can also lower our TRV settings or put them in the frost protection mode.
What is frost Protection mode? Simply put, this is a TRVs version of “Off”. When in frost protection mode, depending on your model of TRV, this actually still heats the room to 5-7°C. So they are never actually off. As the name states, this feature is designed to protect your system from the colder temperatures that could cause the water inside to freeze.
How does Energy Work?
If you have read our
Energy Movement blog, you will understand that while we calculate room heating loss requirements based on a winter design temperature, generally speaking during most of the winter the outside temperature is higher than this. For example, if we are in the south of England, we work out our radiator size and room energy requirements based on a winter design temperature of -1°C and a room comfort temperature of say 20°C. So, if we say that our room requires 500 Watts of energy when it is -1°C outside and we want to heat the room to 20°C. What does our room energy requirement look like when it is warmer outside?
| External Temperature |
Internal Comfort Temperature |
Temperature Difference |
Room Energy Requirement (Watts) |
| 20 |
20 |
0 |
0 |
| 19 |
20 |
1 |
24 |
| 18 |
20 |
2 |
48 |
| 17 |
20 |
3 |
71 |
| 16 |
20 |
4 |
95 |
| 15 |
20 |
5 |
119 |
| 14 |
20 |
6 |
143 |
| 13 |
20 |
7 |
167 |
| 12 |
20 |
8 |
190 |
| 11 |
20 |
9 |
214 |
| 10 |
20 |
10 |
238 |
| 9 |
20 |
11 |
262 |
| 8 |
20 |
12 |
286 |
| 7 |
20 |
13 |
310 |
| 6 |
20 |
14 |
333 |
| 5 |
20 |
15 |
357 |
| 4 |
20 |
16 |
381 |
| 3 |
20 |
17 |
405 |
| 2 |
20 |
18 |
429 |
| 1 |
20 |
19 |
452 |
| 0 |
20 |
20 |
476 |
| -1 |
20 |
21 |
500 |
| -2 |
20 |
22 |
524 |
| -3 |
20 |
23 |
548 |
| -4 |
20 |
24 |
571 |
| -5 |
20 |
25 |
595 |
Well, we need less energy. This is why, for the majority of the year, our boiler temperatures are probably too high and our TRVs in unused rooms do not need to be on.
Simple Steps that work for all property types and locations
In these simple steps, we have considered how energy works and the various types of heating systems and property types out there. From the old single brick properties with bad energy performance to the new build properties with great energy performance. These are our rules of thumb to help lower our heating bills:
- Lower the boiler temperature as much as possible, there are caveats to this, so we have prepared separate advice around this in our Weather Modulation guide.
- Turn down TRVs in unused rooms as low as possible, or start with putting them ‘off’ (Frost protection mode) apart from in hallways and landings which should always be on.
- If your heating starts to struggle as the winter gets colder, the first port of call is to open up the TRVs instead of turning up the boiler temperature. You may only need to open the TRVs a small amount to achieve this as opposed to fully opening them, it would be a gradual process as the winter gets colder. You can gauge this by whether or not your room with the main boiler thermostat reaches the desired temperature.
- If the rooms in your home do not reach comfort temperatures after that, then turn up the boiler flow temperature.
- As the days become milder, then we reverse the process by turning down the boiler temperature (if we turned it up) and starting to shut off TRVs.
This is manual weather compensation and modulation in a nutshell. The most efficient way to run our central heating is all down to how cold it is outside. There are still some other considerations here though, like “Where is the room that is unused?”, as opening up a TRV can do very little to reduce energy bills.
How does internal heat energy work?
We can possibly have a variety of unused rooms, the locations of which may mean that turning up a TRV doesn’t actually help us. One of the larger issues with online advice and calculations is that they generally believe that because the home has an energy requirement for our winter design temperature, that turning off a room using the TRV simply means that all other radiators have to heat to a higher degree (i.e. higher boiler flow temperatures) to be able to heat the home to the required temperature. However, whether that is true all depends on the home layout. First, let’s try to understand why people say “turning off a TRV means the boiler and radiators have to work harder”. We will start by using the common diagram which is fairly unrealistic for most homes.
Why do people say “turning off a TRV means the boiler and radiators have to work harder”
Let's examine the model they use to determine this: We have 4 rooms, all requiring 500 Watts to heat the room to 20°C when it is -1°C outside. We have installed this
Typhoon vertical radiator in every room, which has a heat output of 576 Watts at Delta 45. This is a boiler flow temperature of around 75°C with a return of 55°C (see our
Energy Movement Blog for more information around this).
Room A is our reference room – This has the main boiler thermostat. We can never turn this radiator off as we require this room to work with our boiler. If we did turn it off, then our boiler would stay on all the time which is not good for our pocket. This room should always have a manual valve in place and not a TRV, as the TRV and boiler thermostat would conflict. The other rooms have TRVs, so while all radiators are on, everything is fine. But what happens if we set the TRV in room B to frost protection mode (this would be a room temperature of about 7°C)? Other advice usually states that you still need 2000 Watts total to maintain an average ambient (room comfort) temperature of 20°C. However, that's not the case. We have adjusted the watts on the rooms to represent what each room needs. Using our table above, we know that room B now needs 190 watts for a temperature of 8°C. However, this is what we want, not what will happen. The blue arrows below represent the internal heat loss from rooms A and D to room B.
To find out what will happen, we need to do some quick heat loss calculations: Each wall in our rooms is 4 metres by 2.5, that is a surface area of 10m2 and we are going to use a U-Value of 2 to represent the internal heat loss. So, 10 (surface area) x 2 (heat loss U-Value) x Temperature difference. If the TRV in room B is set to frost protection mode (7°C) and the rooms being heated are 20°C, then the temperature difference is 13°C. 10 x 2 x 13 = 260 Watts of internal heat is lost (along each blue line on our image), 520 Watts in total. So for rooms A and D to maintain 20°C, we need our original 500 watts + 260 Watts? The implication being that rooms A and D cannot get to our desired 20°C temperature. At most they can deliver 576 Watts and to reach our temperature we would need to turn the boiler up to compensate for this internal heat loss. So while Room B, set (by the TRV) to 7°C, would only require 190 Watts, due to internal heat loss, you would end up only hitting somewhere around say 17°C across all rooms.
Bear with us on this next part. However, 576 Watts is the radiator heat output when the room is at 20°C, if we were looking at the output when the room is at 17°C, for this same radiator, the radiator output would be 625 Watts. Room B was also stated to get 260 Watts from 2 rooms, 520 Watts in total when they are at 20°C. So we would assume that the temperatures of rooms A and D are higher than 20°C, meaning this heat loss is lower internally, but higher again on Room B’s external walls. Therefore, room B’s temperature cannot be 7°C, it must be higher, and its heat loss to the outside world must also be higher.
Hands up if you’re confused? Us too, mainly because this commonly used method and online advice just doesn't make sense! Basically, it seems that someone has taken two related estimates - room heat loss and radiator heat output - and defined that they work a certain way. But, there isn’t enough information there to determine that is how they work in general and certainly not to apply to a specific home. These calculations do not have the concept of time in the way that it relates to the problem in question - room energy. All the Room Heat loss tells you is the rate of energy loss when a room's internal temperature is at Y°C and outside it is X°C. All the Radiator Delta heat output tells you is the heat output when the room’s internal temperature is at Y°C and the radiator’s internal temperature is at Z°C. Therefore, if you drop Y in one calculation, you must drop Y in the other calculation. In fact, you would need a relationship of time between these two calculations in order to actually align what would happen in the real world. We can see this issue clearer if we use this common model. Let’s say we put 3 of the rooms down to frost protection mode (7°C) and 1 room stays at the requirement. What others imply is that our single radiator that is on in Room A will be required to provide roughly 1430 Watts of energy. In some cases they will even tell you that as the home required 2000 Watts in total for 20°C, this single radiator must produce this.
So when you calculate heat loss using CIBSE, BRE or BSI standards and methods, unheated rooms would be assumed at 10°C. We are doing 7°C (which makes the scenario worse for this model), but by turning off Rooms B, C and D, Room A now has an additional 2 walls of internal heat loss. So, using similar dimensions and U values as before: 10 (surface area) x 2 (heat loss U-Value) x 13 (temperature difference) = 260 Watts of internal heat is lost (along each blue line on our image), 520 Watts in total. Based on the calculations used to determine the model used here, room A can’t, in theory, lose more than 1020 Watts* per second while: it is -1°C outside, Room A is at 20°C, and all other rooms are set to frost protection mode. *The 500 Watts is already lost from external heat loss + the 520 Watts from the new internal heat loss = 1020 Watts total. So this is what people base saying “turning off a TRV means the boiler and radiators have to work harder” and that you shouldn’t do this. However, as we can demonstrate the calculations - the CIBSE, BRE and BSI calculations - that are used to determine heat loss and radiator output don’t directly translate to this scenario. Energy will do what it wants (move to the colder areas), not what the youtube video maker needs to suit their argument.
So What do we do to solve this?
Let’s split this into 2 categories - planning ahead and working with what we have.
Planning Ahead
If you do a proper heat loss calculation for individual rooms, you should be accounting for heat loss internally. You will have some rooms, by design, at different temperatures e.g. the kitchen could be 18°C while the living room is 20°C. If those rooms touch, then there will be heat loss from the living room to the kitchen (because the kitchen is colder), which you need to account for when picking a radiator. So if you know you have a room that you either don’t want to heat all the time, or at some point, may not want heated at all, then when sizing a radiator for this room or an adjacent room you should treat that room as unheated. But, how do we do this?
- To size a room that is unheated/not heated all the time, we still measure that room temperature to 20°C or so, so that when you do want the heating on that radiator will work.
- Then to size a room that is heated but is next to unheated room(s), instead of assuming that all internal rooms heat to the same level, treat the unheated rooms at 10°C or so.
This will ensure that you can easily turn off the TRV without worrying about the other rooms having to work harder because your radiators are sized to cater for that. Larger radiators also mean lower boiler temperatures - yay! How do you know if a room will become potentially unused? The most common scenario for this is kids growing up and flying the nest. If you have 2 teenagers and a 3 bedroom house, then you know (hope!) eventually they will leave. So if you need to get new radiators, size them as though the two teenagers’ bedrooms are empty.
Working with what we have
The equations required to actually solve this are very complicated, we may build an app for it one day, but until then we need some simpler considerations. As mentioned before, these are our rules of thumb in order to lower our heating bills:
- Lower the boiler temperature as much as possible, there are caveats to this, so we have prepared separate advice around this in our Weather Modulation guide.
- Turn down TRVs in unused rooms as low as possible, or start with putting them ‘off’ (Frost protection mode) apart from in hallways and landings which should always be on.
- If your heating starts to struggle as the winter gets colder, the first port of call is to open up the TRVs instead of turning up the boiler temperature. You may only need to open the TRVs a small amount to achieve this as opposed to fully opening them, it would be a gradual process as the winter gets colder. You can gauge this by whether or not your room with the main boiler thermostat reaches the desired temperature.
- If the rooms in your home do not reach comfort temperatures after that, then turn up the boiler flow temperature.
- As the days become milder, then we reverse the process by turning down the boiler temperature and starting to shut off TRVs.
Now, what about your specific scenario?
Properties built after 2013
Do what you want really! You will probably be able to turn down your boiler a lot, as well as the TRVs in any room. The main issue you have is likely overheating in rooms, champagne complaint, unless your radiators are very small. One of the UKRads team has a property like this and they only ever use the downstairs radiators, the upstairs ones are never on. They can lower their boiler temperature, but for them, turning on the upstairs radiators even on the coldest days would just mean they need a fan to cool them down! This is also good heat pump territory; you would have good success here without needing radiators that were much bigger than what you already have in place. That gives you an idea of how much energy you are wasting with a gas boiler right now, in a property built after this date.
Properties built after 1990
Similar flexibility to the above, but some consideration around room location is a good idea (we cover this further down). An example, another of the UKRads team has a property in the south of England - open floor plan 2 bedroom flat with electric heaters. He occasionally uses the bedroom heater, but only ever uses the living room heater (which doubles as home office) if he has guests because he finds that generally, during the day it gets really good solar gains (heat from windows) as it has windows both all around the room and on opposite sides (L Shaped wrapped around the flat). Then in the evening, cooking does enough to heat that room. Once his flat is heated, it seems to take forever to cool down. If he did have a gas boiler, he would probably find he heats the bedroom and hallway in the evenings only, then the rest of the time there is no real need. The point being: the rules and considerations we have for properties built after 1990 are very different to before 1990. Prior to the 1990’s, housing regulations were a bit more varied in property structure.
Properties built before 1990
In this scenario, we definitely need to think about room location and whether or not turning down or off (frost protection) a TRV, is a good idea overall. As a general note, if you have a heat pump, you probably wouldn’t turn TRVs off. It is also very difficult to say as a gut shot rule that any property built before 1990 should get a heat pump to save money - it's possible in some and impossible in others (rising costs). In these properties, we need to think about the location of the unheated room when deciding to turn the TRV off.
Golden Rule - We need to ensure that our room with the main boiler thermostat is protected (this will always be Room A in the scenarios). If we don’t protect the boiler thermostat room, it will never reach our desired temperature, and so, never trigger the boiler or the pump to turn off. Scenario 1 – The unrealistic property example most commonly found in explanations While this property is unlikely to ever exist (i.e. to access a room you have to go through another room) if it did, then we could turn off Room D (put the TRV in frost protection mode) without worrying about things too much. Our boiler is controlled by Room A and protected by Room B and C, so turning off room D shouldn’t be too much of an issue for our Golden Rule above. You could also try turning down room B and C a little bit, see how it works for you.
Scenario 2 – Lets have an entrance hallway! Bungalows often have a central hallway connecting all the rooms. Therefore our first question is: does the hallway have a radiator? Hallway has a radiator – Room A has our boiler thermostat, so really we only need Room B and the Hallway on to heat to 20°C, that should be enough to protect Room A. However, you would probably find that Room B can also lower a bit, but the hallway should stay with the same or even a higher TRV target temperature. Hallway does not have a radiator – Room E can be Turned off without too much concern, it would have a low impact and it’s quite a distance from Room A. Room C and D can probably be lower than 20°C on the TRV, but probably not all the way into frost protection mode. Room B can probably lower a bit as well. Ideally, if you get the opportunity, add a radiator to the hallway!
Scenario 3 – Upstairs Vs Downstairs So A is in the bottom left now, showing our room with the main boiler thermostat. Rooms A and B are downstairs, C and D are upstairs. Do you have insulation between floors? Yes – Rooms C and D can be turned off, room C might be better just lowering the TRV, Room B can be lowered a bit too. No – Room D can be turned off, room C could just be turned down a bit and Room B can be lowered a bit too.
So, now you can see from these 3 scenarios that it’s about protecting the main room. The other rooms may lower in temperature a bit, but we always want to protect the room with the main boiler thermostat.
Scenario 4 – My boiler thermostat is in my hallway The good news is that you definitely have a radiator in the hallway, but being realistic, you don’t want your main boiler thermostat in the hallway. Part of your heating requirement is the room heat loss via construction materials and part of it is air change rate - this is the warm air naturally looking for an exit from your home. Another part is the energy required to raise the room temperature, this is not something people often account for. The heat loss is energy lost when the room is at the desired temperature and the radiator output is the heat output when the room is at the desired temperature. But, you still have to heat the air in the room. If your thermostat is in the hallway then every time you open that front door, you lose all that energy! We can prevent this in other rooms by having internal doors closed before opening the front door, but this is not often possible in the hallway. It is also going to have a high air change rate due to the door, even when closed, leading the heat to find its way toward the colder weather. So, what you would likely find is that just by moving the thermostat to say your living room, your energy usage will go down. You may have to change the valve types as well because the room with your main boiler thermostat should not have a TRV, it should have manual valves, but swapping valves over is usually a very easy job. So the question is, do we really want our hallway at 20°C like the rest of the house, or do we want to take the edge off and prevent drafts? If the latter, then it should not have the main boiler thermostat in place.
North South Divide
Do we have any geographical considerations? Well yes and no, in the south, turning down TRV and boiler temperatures has less of an impact, because while you get cold weather, it varies within a few days to being milder again. There is generally a long period of consistent cold, but it does not last as long. In the North however, this variance of temperature is not as flexible the further up you go. So there is quite a solid argument that TRVs are not the most helpful item for saving money when you are up in the Highlands of Scotland. Instead, you may be better off leaving all your radiators on high TRV temperatures and just managing with the boiler temperature, even if you have a well structured building. But for most of England, Wales, Northern Ireland and lower parts of Scotland it's fine to follow the advice in the previous sections.
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