Thermostats with TRVs

[Multiplex]

It seems fairly common knowledge that a thermostat should not be placed in the warmest room in a house, and should also not be placed in a room with TRVs. But in our brand new house the builders did just that!

Does anyone know if this is actually against building regulations?

The TACMA guide says it should not be done:
http://content.honeywell.com/uk/homes/Technical/Regulations/TACMA.pdf

But the regulation document itself (is this the right one???) is so wishy-washy it doesn't seem to make any regulations at all!!

http://www.odpm.gov.uk/stellent/groups/odpm_buildreg/documents/downloadable/odpm_breg_600288.pdf

Does anyone know if I can approach the builder to get them to fit a wireless thermostat, because they won't do anything if they can avoid it.

Simon.

 

[kevplumb]

take the head off the trv where the stat is

 

[Multiplex]

Hey you sound like our builders!

This room has two radiators in it and is on the second floor. The kitchen downstairs has just one radiator and is always cold. What we need is the thermostat to be in the hallway downstairs which even colder than the kitchen!

Simon.

 

[kevplumb]

not sure if its against the regs but its deffo bad practice

 

[blahblah]

As a temporary fix, turn the room stat up and turn the trv down in that room so the stat isn't satisfied. The boiler should continue cycling and allow the other rooms to come up to temp and shut off according to trv settings. Problem then is boiler will keep on cycling so try and find a happy balance.
The stat should indeed be in the warmest area of the house - but by design, the rest of the rooms should already be up to temp prior to the stat being satisfied. Hallway or main living area is usual (and recommended).

 

[blahblah]

PS. Contrary to building regs if new build or replacement boiler.

 

[croydoncorgi]

As a GENERAL RULE - yes, it's not smart to have a TRV and wall stat fighting it out in the same room.
BUT there ARE exceptions, especially when you're working with what's there, not an ideal situation!

The purpose of the roomstat is to make sure that the CH system switches ON when there is heat needed SOMEWHERE in the house and OFF when the WHOLE house is at the desired temperature(s). The roomstat is therefore usually sited in the COLDEST area of the house.

But if the roomstat is NOT in the coldest part of the house AND shares a room with a rad with a TRV, you can still make the whole system work perfectly well.

Proceed as follows: with the roomstat and the nearby TRV set on max, set up ALL the TRVs EXCEPT that one to give the desired temperatures in the OTHER areas of the house. Then go back to the room with the roomstat. If just that room is still too hot, REDUCE the setting on the TRV until it's cool enough. Then adjust the roomstat down until it 'clicks' and the whole CH system switches off. You may need to fiddle a bit with the 'key' TRV and roomstat settings to make sure the whole system switches on when SOMEWHERE needs heat and off when EVERYWHERE is at the right temperature. The key points to remember are that the roomstat affects the whole house and that to make OTHER areas of the house WARMER you should first turn the 'key' TRV DOWN, NOT the roomstat up!

And once you've got everything set up right, leave it alone!

Another tip: if other parts of the house get cold in REALLY wintry weather, instead of increasing roomstat and TRV settings, it's usually easier to SLIGHTLY increase the temperature setting on the boiler. Remember that ESPECIALLY in the case of condensing boilers, the LOWER the temperature setting on the boiler, the better, so turn it back down when the weather warms up.

 

[Multiplex]

Thanks for the responces. Since this house was only built a few months ago this shouldn't really fall under any exceptions...

Where does it say in the building regulations that new houses must have the thermostat in a zone without TRVs? I'm really struggling to find any building regulations that spell this out...does anyone know where to find them?

Simon.

 

[ChrisR]

I doubt very much that you'll find that. According to some advisers a trv in a room with the stat is correct - you set the trv temp just above the stat setpoint. Then, if any additional heat , perhaps from a warmer room, gets to the radiator it'll turn off. Bit of a thin argument if you ask me.

As has been explained or at least implied above, you can have a roomstat anywhere. As long as the system is balanced correctly and the rads the right size relative to the rooms' requirements.
You have to make sure that the room with the roomstat is the slowest to heat up so the others all get to be controlled by their trv's. So it makes sense to use somewhere other than your living room.

Before TRV's were commonplace it was seen by some as best practice to put the roomstat in the living room, because that's the room you spend most time in!

 

[PEDANTICVINDICTIVEMAN]

If you want a laff phone your local building inspecter who inspected the properties and ask him, you wont find out anything but it will be a laff hearing him/her fumble and mumble not knowing what he is talking about.

 

[blahblah]

Croydon- I think we're getting mixed up with or coldests and warmests. I said warmest by design, ie zone to be heated to warmest (or its equal).
Multi-
Building Regs 2001 Part L- room stat (or programmable) in main zone and trv's on all rads in second or further zones.
CHeSS 2002 (Energy Effeciency Best Practice in Housing- Central Heating System Specification )- trv's on all rads except in rooms with a stat.

 

[croydoncorgi]

Croydon- I think we're getting mixed up with or coldests and warmests. I said warmest by design, ie zone to be heated to warmest (or its equal)

Nope! I'm happy with what I said.

In practice, it really doesn't matter where the main thermostat is sited so long as:

- its setting is satisfactory for the room it's in,
- it does not get heated up too quickly so that it switches off with other parts of the building left too cold (eg. by being too close to a rad, or by being in a room which heats up too quickly compared with the rest of the building.)
- it is not sited outside the influence of the system it's controlling, or in room with a heat source that is switched off too soon independently (eg. a rad with a TRV), or is set so high, so that one way or another it never reaches its switch-off temperature.

The advice given in ChESS and elsewhere NOT to site a roomstat in the same room as a rad with a TRV is a simple way of avoiding just one type of problem where the roomstat never reaches its setpoint.

The trouble with TRVs is that they may work so well holding each room at the desired temperature that the occupants overlook the main thermostat staying on and wasting fuel cycling the boiler and heating up the plumbing.

PS. If the original question was in fact looking for a stick to beat the builder with, I doubt you'll find one. Key objective of new control standards is to make CH systems work efficiently. If you follow the advice given (except 'taking the head of the TRV '- sorry Kev!) it will do that, unless the roomstat has been installed in a place with such extremes of temperature (see above) that it cannot control the heating effectively. To be honest, I can't quite see why you want to make such an issue out of it.

 

[blahblah]

Not trying to make issues but discussing the query and responses. I thought at first we were saying the same things in a different way, and to some extent I think we are. But I can't get my head around the idea that you could put the stat in a room you want at say 18c then expect to have areas at 21c?

 

[croydoncorgi]

Simple.

With roomstat set to 18, turn TRV in 18 degree room DOWN until temperature in 21 degree area reaches target. If whole system still turns off before 21 degree areas satisfied, reduce TRV in 18 degree room some more.

 

[blahblah]

Unless I'm being really thick (which is not beyond the realms of possibility) surely that means you don't achieve the desired temp in the stat room and if you did the rest would get cold again?