Thermostat placement and TRV advice

[elsmandino]

Hi there.

I am upgrading my current central heating system with a wireless thermostat and TRVs (non-motorised).

I have the following rooms with radiators (it is a bungalow):

2 in the livingroom
1 in the master bedroom
1 in the second bedroom
1 in the kitchen
1 in the bathroom (a towel warmer)
2 in the hallway
1 in the office

I fully appreciate how TRVs work but now have a couple of questions:

1. Do you put a TRV in a bathroom? I assume not as quick fluctuations in heat (from bath/shower) will mess it up.

2. Do rooms with 2 TRVs need to be on the exact same number? Again, I think they probably do.

3. I understand that the room with the thermostat cannot have a TRV in it. However, which room should the thermostat go in?

I cannot work out whether it should go in the room that needs to be kept the warmest (and most often used) or should it in fact go in the coldest room in the house.

Any pointers would be much appreciated.

 

[Murdochcat]

In general the thermostat should be in the hall, not close to a radiator or draft

 

[stem]

I have often been called to look at a system where the householder claims the there is a fault with the thermostat/s. Generally in my experience I usually find.

40% operator error or misunderstanding of how the system works
50% poor installation and location of the thermostat / TRV's which will vary from property to property
10% worn or faulty thermostat

So here's a guide with regard to the thermostat location, it can be tricky because in some homes there is no perfect location.

Tips for Room Thermostat Location:
The room thermostat should be in a room that is not effected by other sources of heat such as an open fire, cooking equipment, or direct sunlight etc. It should not be somewhere drafty or too close to a window, especially if it's one that is opened in the winter.

Secondly it should be in a cool room, ideally the last room in the house to warm up. That way, the other rooms will be warm enough, (but not overheated because of their TRV’s) before the room thermostat switches the entire heating system off. To achieve this, it may involve downsizing the radiator in the actual room where the thermostat is located.

The radiator in the room with the thermostat installed should not have a TRV fitted. Otherwise the TRV can interfere with the correct operation of the room thermostat.

The thermostat should be mounted about 1.5 metres from the floor, and not close to, or above a radiator.

Preferably it should not be on an outside wall, (although if you have well insulated walls, this is not quite so crucial.)

It should be in an area where air can circulate easily, not in a corner, or hidden behind curtains, or furniture.

For the bathroom if there's a radiator generally I would expect a TRV to be fitted, with the possible exception of a towel warmer as they don't usually emit much heat into the room. [about one third of the output of a similar sized radiator and even less when covered in towels] TRV's work fine in a bathroom they will still regulate the room temperature when the bath / shower are used. Some older systems or solid fuel systems need to have at least one radiator that does not have a TRV fitted as they serve as a heat leak. This is often the bathroom radiator.

The TRV's in the same room don't necessarily need to be on the same setting. Some people set one slightly lower so that it shuts off slightly before the second one, but much depends on how well insulated the room is, whether one being off will create a cold spot, and if one radiator is sufficient to maintain the set temperature on its own once it's reached. So this will probably be trial and error.

 

[elsmandino]

Thanks ever so much for this - extremely helpful.

Does look like I am going to have to do a bit of planning/testing, before I proceed with this.

It does make perfect sense to put the thermostat in the coldest room - as you say, all the warmer rooms can then also be accurately controlled with the TRVs.

I need to do some temperature testing, then, because I need to identify which room is going to the "coldest" one and thus the one with the thermostat and no TRV.

My guess is that our office is the coldest area, usually. I say usually because we sometimes use that room for drying clothes (as it is the smallest) with a dehmudifier in the winter. The dehumidifier may well then mess with the TVR as it does warm the air, slightly.

The other thing that I need to remember is that my house only has roof insulation in parts (I am hoping to put in 270mm this year) the areas that are insulated only have 100mm.

I might find that once I have put insulation everywhere, the coldest room may well suddenly become one of the other rooms.

I guess that I should buy a temperature sensor and just see what the coldest room actually is. Bar my office, it may well be the corridor, as it only has a small window.

The corridor does, however, have two radiators in it - one either end. What I might do is try and put the thermostat at an equal distance between them and (given that neither will have a TRV on them), turn the heat down to ensure that the corridor is indeed the coldest space in the house.

 

[ericmark]

3. I understand that the room with the thermostat cannot have a TRV in it. However, which room should the thermostat go in?

I cannot work out whether it should go in the room that needs to be kept the warmest (and most often used) or should it in fact go in the coldest room in the house.

The idea is to put it where it will be on the most, the TRV will stop a room over heating, but can't stop a room under heating, also when summer arrives nice to have heating auto stop, so being in a cool room means heating less likely to run on a warm day. The other points is should not be in a room with alternative heating, like a kitchen, or a room with large windows so heated with the sun, and also not in a room with outside doors, following the above rules no room satisfies the criteria so intend to fit a second wall thermostat in parallel with first, and will have TRV's in room with thermostat.

2. Do rooms with 2 TRVs need to be on the exact same number? Again, I think they probably do.

I used cheap eQ-3 TRV heads with bluetooth cost me £15 each in 2019, and they can pair together so both radiators work as a pair, however found that electronic heads work better anyway, so no real need to pair them.

1. Do you put a TRV in a bathroom? I assume not as quick fluctuations in heat (from bath/shower) will mess it up.

The shower room/toilet is the only room in main house to have a non programmable TRV head, the bathroom does not have a TRV but this is because the towel rail is thermo syphon and acts as a by-pass for the boiler to cool.

But it depends so much on the home, first house hot air so does not count, second open plan, had TRV's to stop bedroom over heating, but down stairs one wall thermostat did all.

Mother house was first where we had a problem, mainly due to bay windows heating living room too fast, so was the first house where we used Energenie TRV heads, the main advantage was easy to set the lock shield valves, they show target and current, clearly current should not exceed target, so if it did the lock shield closed a bit, new owners did not want them, so put old mechanical back, and once the lock shields were set, the old mechanical worked A1, however how do you know what temperature the TRV is set at when it just says *123456 ? needed TRV in degrees C to set lock shield in first place.

This house two faulty Energenie made into one good one, so three of the old Energenie still working, five eQ-3 with bluetooth and one Kasa (TP-Link) to replace the damaged Energenie, non linked to the Nest Gen 3 wall thermostat (load of rubbish) and 5 mechanical still in used, 4 in the flat under the house, which can be isolated with motorised valves. Just fitted new double glazing and waiting to see how it all works before buying second wall thermostat.

The dinning room is at moment not used, as is the office, so those two TRV's turned off, the craft room turned on when required, the bedrooms only turn on at 10 pm, and the living room turns off at midnight and back on at 8 am, I say off, really turns down to eco setting. The main wall thermostat turns to comfort at 8 am and to Eco at 12:30 am.

2 in the hallway

That I see as a problem if using hall way for the wall thermostat, what I want is when hall door opened, the TRV's detect the cold blast of air and turn off for 15 minutes I have set as window open inhibit, so can unload car without heating street, then the TRV will fully open to reheat hall, but at 17ºC it starts to close again so as not to over heat hall and cause other rooms to get cold, and the wall thermostat is set to 20ºC and being higher up on the wall it will turn off the boiler as the house heats up.

Heating bit is easy, it is the cooling where it all falls over, the hall was cooling faster than the living room, so living room would get cold before heating turned on again, hence considering second thermostat in living room. The Nest Gen 3 also does timed DHW, that bit is OK, so second will only do room temperature. They all need to be either battery powered, or from same FCU as the boiler, so with a power cut heating will continue to work from the battery back up and solar panels. Flat is hit and miss, don't use it in winter so not worried about it.

I will admit the TRV's in this house with a simple on/off boiler don't work as well as they did in mothers house with a modulating boiler, with a modulating boiler everything works analogue, turning boiler up/down, turning TRV's up/down, nothing turns on/off except the on/off timer. So her radiators were in the main warm, never hot or cold, this house with oil, radiators get hot and cold so a larger hysteresis in temperature.

In 2019 when I first set my house up, at £15 each could not see point in not having programmable TRV heads.

 

[Harry Bloomfield]

The room thermostat should be in a room that is not effected by other sources of heat such as an open fire, cooking equipment, or direct sunlight etc.

Sometimes that can be a desirable effect. The default location for our wireless stat, is in the hall, which has a radiator without a TRV, it is also the coldest areas in the house. In winter, when we settle down for the night, in the living room, we now light the living room gas fire - and take the stat in there with us. That causes the CH system to shut down, for the evening, saving a bit of gas. The house stores the already accumulated heat for several hours, so it is not a problem.

 

[stem]

That's why every case may be different, not only because of the building but also the occupants personal preferences. Doing that suits you, others may find that the bedrooms and bathrooms were too cold for them when retiring to bed if the heating had been off during the evening. And instead of moving the thermostat in and out of the living room every evening, the same thing could be achieved by setting the central heating programme such that is switches the heating off in the evening and just use the gas fire in the living room instead.

About 20 years ago on newbuild estate near me the room thermostat was installed in the living rooms which were at the back of the house, (no other heating source in that room) which had large patio doors into the garden. The properties on one side of the road where the living room was south facing warmed up with the winter sun and the thermostat switched the entire heating system off leaving everywhere else cold. For the properties on the other side of the road it worked perfectly well.