Should we install TRVs? Do they save energy?

[DIYNotIan]

Hi all

My partner and I (and dog) live in a semi detached/3 bed house. No kids. We have 9 rads. We prefer cooler houses (16-18c) and have next to no heat in our bedroom. We spend the majority of our time in two of the bedrooms (one is a music room, one a study) and the lounge. This can vary. We both work different hours (so often in the house alone).

We are on oil and currently have no room thermostat. Some rads have TRVs, some don't. The ones we do have look quite old, and one of them is not working (rad on full permanently).

We are trying to decide whether to install new TRVs on all rads (bar one) or not. What we would like to know is, if all TRVs were to reach their set temperature and switch off (leaving the last one on so the pump has somewhere to send the water) would this result in any saving in energy/oil??? Similarly, if 4 rads were switched off and 4 rads set to "3", would this save energy/oil compared to all rads being on max???

Many thanks

Max

(PS - we need our system to be serviced soon regardless [drain down, inhibitor] so wondering if we should get the TRVs fitted at the same time).

 

[Gas2Air]

Forget the TRVs fit a thermostat.

 

[CombustionGuy]

Room stat is a must that will help trv can save money if used correctly ( keeping room doors shut)

 

[DIYNotIan]

Thanks for the replies guys.

But to be honest I still feel none the wiser about what I'm actually trying to find out, namely:

....if all TRVs were to reach their set temperature and switch off (leaving the last one on so the pump has somewhere to send the water) would this result in any saving in energy/oil??? Similarly, if 4 rads were switched off and 4 rads set to "3", would this save energy/oil compared to all rads being on max???

I've read in some places that if less radiators are calling for heat, the water returns to the boiler hotter and the boiler therefore fires less as a result. On the other hand, I've also read quite a few people who say that TRVs are not really about saving money. I'm still not sure which is correct and to what extent (if any) the boiler would be used less if only two or three rads were calling for heat rather than all of them. Until I know more about that, it is hard for me to decide what the pros and cons are of TRVs versus Room stat. I can totally see why room stats are preferred and recommended ahead of TRVs. I'm just not sure that the reasons are as valid and relevant in our case and circumstances.

So any further thoughts and opinions would be great.

Cheers

Max

 

[Burnerman]

Use both, but prioritise on the room thermostat......the TRV's will regulate each individual room, so even if the room isn't used often, it can be heated up quickly enough by opening the TRV. Its usual for bathroom towel rails etc to be on all year round.
The boiler thermostat will control the boiler demand - if the TRV's are largely closed down, then the boiler will be off for longer periods.
John

 

[DIYNotIan]

Thanks for the Burnerman.

Aside from the points you raise RE room thermostats, when you say:

if the TRV's are largely closed down, then the boiler will be off for longer periods.

...can I clarify whether you mean that having no room thermostat but TRVs which are turned down/off for some radiators does in fact save energy (and energy = money)??? That's in essence what I am trying to find out, and if it is the case it would be most helpful to know to what extent it is the case.

I do appreciate what people are saying about room stats. But I do think our circumstances are different to most. In terms of money saving, we only spend around £300 a year on oil. So £200 (approx) for a wireless stat set up would take a few years to "pay for itself". For now, I just want a better understanding of how TRVs change the amount the boiler has to work (and therefore how much energy/money is used). Armed with that knowledge, I can then re-evaluate our options (including room stats) and take it from there....

Cheers

Max

 

[ALEC1]

TRVs save a limited amount of energy, and how much will depend on the anti cycling strategy of the boiler software.

They work by reducing flow through radiators which raise the performance of other radiators.

 

[DP]

TRV will shut the radiator that it is fitted to when if the room is heated by sunlight, you breathing on the TRV, fire being on in the room or whatever external applied that acts on the TRV. At this stage the boiler is not even switched on.

Now you fire the boiler to heat the radiators. Radiators start shutting down and boiler starts modulating, might even switch off for a short period of time unless you want the boiler to become a boiler and turn water to steam
But rest assured, with warm house, boiler is still using gas pumping out heat. With room thermostat fitted, room thermostat shuts the boiler down until the room the stat is fitted in, drops below the set point.

Idea of fitting a room thermostat is to switch the boiler off. Idea of fitting TRVs is to reduce the load on the boiler as rooms attain set temperature. There will be rooms with rads fitted with TRV that will at all times be set to 5- don't see the point of fitting a TRV in this case.

 

[Burnerman]

I can't really help you with the maths or statistics Max - just maybe practicalities.
If your property has just TRV's it will take a long time for them to become operative when the house is very cold, and therefore the boiler will be on big time......with a thermostat in the hall for example being half way up the wall it will respond to room temperature quicker, and its dead easy for you just to turn the thing down yourself if the temperature is comfortable.
If you have rooms that are seldom used then the TRV (or conventional valve) can be turned down or off until the demand is there.
If you want me to say TRV's or room stat, the choice must be the room stat - I look at TRV's being a convenience rather than an energy saver.
Regarding a wireless system - I had a Honeywell one fitted to my Heatslave 12/14 oil boiler. Totally hopeless. When the temperature set was getting close, the boiler would be switching off and on all the time, which isn't good for an oil combi. Back to the simple wired one for me.
John

 

[chantelle]

Turn off the radiators you don`t use, in the rooms that are not used...FFS!

 

[Blagard]

If you fit TRV's they will allow water into the radiators at low temperatures typically around 10C so may not shut off a radiator 100% You need to look at the brochures for them to find the operating range. They can only be shut off completely with a "decorators" cap that replaces the thermostatic head.

They will save energy to the affected rooms but there are other factors to consider. There is a natural flow of heat in a house from warm areas to cold. A cold room will be taking heat from adjacent warm spaces due to gaps around the doors or open doors or through the thin internal walls. Without a room stat the boiler simply keeps cycling for the entire programmed on period driving at least one rad full blast. The only way to stop this process is to shut down all the heating when a designated area reaches the right temperature and this is why a room stat should be considered the primary source of control.

It is not practical to calculate the actual saving TRV will give without full construction knowledge, air leakage tests and a detailed knowledge of your movements, the temperatures you want (i.e. with a minimum of around 10C) and then it would be just a good guess.

Without doubt the room stat properly sited will have a significant effect. This you can be sure of. The ones with programmable heat levels would be even better so you would not have to tweak it manually for different times of day.

 

[Richardthe3rd]

From another highly respected forum. The OP is only spending £300/year on oil. So I'd advise turning the central heating off completely, that'll save......eh, 300 quid & you'll not need to incur further costs!!
You're not an Aberdonian are you?

 

[tiptoptrump]

Hi Max
If you look at it simply.
The radiator you have with the broken TRV is on all the time your heating is on. (Do you open the window if it gets too hot in that room?)
Lets say the output of that radiator is 1000W when perfectly balanced, then it is kicking out 1KW of energy every hour it is on. If you have your heating on for 3 hours per day then it is kicking out 3KW. That energy has to come from somewhere (your oil) If you had a working TRV on that radiator and it reached its set temperature and shut off the heating to that room after 1 hour then you would only be using 1KW for the same period of heating. Fitting a working TRV will therefore save energy. As everyone here has already said, fitting a thermostat with a boiler interlock will stop the boiler cycling and save you even more. Oh and in doing all of this you can also control your rooms to whatever you are comfortable with.
Mick