Understanding Thermostats

bpk101 · 18 Feb 2015

Hi,

I’m currently having a new radiator system installed as part of a full refurb of my victorian mid-terrace, but understanding TRV’s and Thermostats and what to get and where to put them is causing me headaches… I need to move quick as builders are waiting!

We’re having 5 x Acova column rads installed and a new Worcester Greenstar 38CDi Combi Boiler. I understand with any new build or refurb, TRV’s need to be fitted as well as a Room Stat, is this correct?

Given the complications that arise when having a TRV in the same room as a Room Stat, is my plumber allowed to fit a standard manual valve on 1 of the radiators, or do all 5 rads need TRV’s to comply with building regs?

If the latter… should I buy a TRV for the 5th radiator and disable it once he’s signed the work off? The TRV’s we want aren’t cheap(!) and I rather not buy one then have to tamper with it.

We were also considering a ‘smart’ thermostat like the Wave, Tado, or Nest but I’ve read so many mixed reviews about them I’m not sure I’m quite ready to part with the cash. Should we just get a standard digital room stat installed for now? Again I need to make some pretty quick decisions.

My builder seems to think if we installed a smart stat, then we'd still need to install a wireless digital theromstat which i presume is incorrect?

Thanks!

stem · 18 Feb 2015

The electric thermostat is there to shut down the entire system including the boiler when the set room temperature is reached. Bearing that in mind, its location is critical. If in the wrong location it could turn off all of the radiators when only part of the house is warm. This main thermostat with 'boiler interlock' is a requirement of the building regulations for energy saving purposes.

A TRV simply reduces the flow of water through the radiator as the room warms, to prevent the room overheating, but the boiler will keep running even if all TRV's are shut.

There should not be a TRV fitted to a radiator in the room where the main electric thermostat is sited.

The choice of the type of main thermostat is up to you, but you need one or the other, not both. A smart thermostat learns your heating pattern and can also allow remote control which may or may not be useful to you. But if you are not sure, have a simple electronic thermostat for now. They are fairly cheap £20-£40 and it can be easily be replaced with a smart stat later should you feel you need one.

bpk101 · 18 Feb 2015

Will my plumber be allowed to install a manual valve on that radiator? Or does building regs state all radiators need TRV's?

Here's a floor plan of my house with radiator positions marked in RED and a couple of options for thermostat placement marked in BLUE (the downstairs is fairly open plan).

Will either of these options work?

http://bpkersey.com/images/open-rooms-2.jpg

stem · 18 Feb 2015

bpk101 said:
does building regs state all radiators need TRV's?

The requirements relate to temperature control, so that rooms do not become overheated. An electric thermostat in a room where there is a radiator achieves the same thing as a TRV (and more). As per my previous post, the boiler interlock which can only be achieved by a room thermostat is the requirement of the building regulations, I believe TRV's in other rooms are still only a recommendation, not a requirement anyway, but I could be a bit out of date here.

There should be at least one radiator in the same room as the thermostat not fitted with a TRV. I would be concerned if your plumber is suggesting otherwise.

bpk101 said:
Here's a floor plan of my house with radiator positions marked in RED and a couple of options for thermostat placement marked in BLUE (the downstairs is fairly open plan).

The thermostat should be in the coolest area downstairs and by that I mean the last area to heat up. It also needs to be away from other sources of heat such as sunlight, open fires / stoves, kitchens etc., or be too close to a radiator. The orientation of the property can also have an effect, with a north facing aspect being cooler than a southern one. Looking at your layout, I would be inclined to fit a slightly smaller radiator than required in the hallway so that it doesn't heat up too quickly, and not fit a TRV on the hall radiator, then put the thermostat either in the hall, or in the top position shown in your diagram near the lounge as it will be shielded from any heat generated in the Kitchen and also the fire in the lounge. From the diagram of course I can't consider orientation and sunlight in the equation. You will know the coolest spot.

bpk101 · 18 Feb 2015

We don't know the coldest spot yet as we haven't moved in. I can tell you however that the lounge bay window faces north...

We've already purchased the rads. The hallway rad will be the correct size for that space (around 4500 BTU).

Any other thoughts on stat placement?

Gasguru · 18 Feb 2015

TRVs on all the rads except the hall. That one should be fitted with lockshield valves each end (ie. neither can be adjusted by the user). The room stat is installed in that area too and the hall rad throttled down to ensure the rest of the house has come up to temperature before that area finally shuts down the boiler with the room stat.

Since it looks open plan another option would be to fit lockshields to both the hall and dining room rads with the room stat located on the stair outer string.

Use quality TRVs...Honeywell or Danfoss. I don't rate Drayton. Use quality lockshields to BS2767 Part 10. These have a proper seal around the spindle and won't leak.

Are you sure about the radiator positions in the living and front bedrooms? It looks an old house and you will get a noticable temperature drop near the windows (which is normally the best position). Whatever you do don't place the TRVs behind doors or in the corners. Radiators stuck behind doors is normally the sign of a cheap job

Less pipework to run, less boards to take up.

Guitar_man · 18 Feb 2015

A manual thermostat such as a honeywell and a mechanical clock on the boiler is best.
Forget the wifi carp, plumbers like them as no wiring involved, and the wifi never works, you may even get your neigbours stat turning off your boiler. My 2c.

Dan Robinson · 18 Feb 2015

Jimbo320 said:
A manual thermostat such as a honeywell and a mechanical clock on the boiler is best.
Forget the wifi carp, plumbers like them as no wiring involved, and the wifi never works, you may even get your neigbours stat turning off your boiler. My 2c.

And not worth 0c I'm afraid. But thanks anyway

stem · 19 Feb 2015

Jimbo320 said:
mechanical clock on the boiler is best.

Which will only provide you with one or two on /off periods per day, the same every day and the hot water and heating will have to use the same times. Then when it fails, the boiler manufacturer will tell you it's obsolete. Electronic programmers have lots of flexibility, several different on / off time for each day, and many have nice features such as automatically changing time when we move from BST to GMT. A holiday setting that can turn the heating on just before you get home, and if it's remotely mounted they all use the same backplane and can be swapped in an instant with any manufacturers replacement if they fail.

Jimbo320 said:
Forget the wifi carp,plumbers like them as no wiring involved

Unless it's part of the boiler, they still have a separate receiver that needs to be wired in using exactly the same connections as a wired thermostat, it's just that the length of cable is shorter.

Jimbo320 said:
and the wifi never works.

"Never" eh, that's a sweeping statement, which is incorrect. I know of lots that do work. OK, there can occasionally be difficulty with communication between the thermostat and receiver, usually due to incorrect installation / location. Having said that, my personal preference, would be for wired, but just because it's simpler and no batteries to change. Usually it's the householder that wants wireless installing because the don't want to have their walls chopped out if they can avoid it.

Jimbo320 said:
you may even get your neighbours stat turning off your boiler

It's a slim chance, but you may. If you do, simply selecting a different frequency will sort it.

bpk101 · 19 Feb 2015

Gasguru said:
TRVs on all the rads except the hall. That one should be fitted with lockshield valves each end (ie. neither can be adjusted by the user). The room stat is installed in that area too and the hall rad throttled down to ensure the rest of the house has come up to temperature before that area finally shuts down the boiler with the room stat.

I had thought of putting the room stat in the hall... but had heard draughts from the front door might interfere with it. Is this true? Or is the hallway definitely the best spot for the stat and if so where?

It's a very narrow space with only option being above or next to the hall radiator (not good) or opposite it (also very close).

Gasguru · 19 Feb 2015

Why can't you have a single zone of the hall and dining room rads (with lockshields either end) and the room stat secured to the stairs outer string.

If the draught is excessive from the front door then fit a draught strip.

Remember it's all a compromise and will never be perfect. A perfect system would have so many controls and complexity that it would never pay for itself.

bpk101 · 19 Feb 2015

Gasguru said:
Why can't you have a single zone of the hall and dining room rads (with lockshields either end) and the room stat secured to the stairs outer string

The outer sting is all fully flush doors for under stair cupboards.. there's no 'wall' there.

Agile · 19 Feb 2015

Best place for room stat is the space where you live!

Apart from teenage daughters sitting in the hall using landline no one wants to live there!

Modern wireless types can be carried around wherever you go. [ Not the Nest though which needs to be plugged in most of the time as its power consumption is too high for batteries! ]

Tony

Gasguru · 19 Feb 2015

A room stat in the living room will shut the system down too early when the log burner's in use....so the positioning is also down to other additional heat inputs to the house.

Carrying around a wireless stat is down to lazy installers not screwing it to the wall...contrvenes Part L. Corrupt manufacturers put a stand on them knowing they'll sell more

stem · 19 Feb 2015

Agile said:
Best place for room stat is the space where you live!

Agile said:
Modern wireless types can be carried around wherever you go.

I'm surprised at those recommendations.

1. There is a log burner in the place where they live. Put the thermostat in there and as soon as it's lit, all of the heating in the rest of the house goes off. This is why it should be in a cool place the last one to heat up. The TRV's will take care of the other rooms and keep them comfortable.

2. Moving it around??? So it could end up in a room where there's a TRV on the radiator set at 18 degrees. With the room thermostat set at 21 degrees it would never reach the set temperature and switch off. I've seen it happen more than once when I've been asked to look at someone's thermostat that "isn't working". Putting it out in the garden would achieve the same thing.

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Understanding Thermostats

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