Flex, and especially for signal/control like this, is normally considered perfectly OK for fixed wiring, so long as the slightly higher mechanical damage risk is addressed - so it may need a bit of trunking if it goes up the wall or along the skirting surface wired or something rather than clip direct- though in new build I rather hope it has conduit or capping behind the plaster.

I'd not blink - the regs certainly permit it. The 0.75mm may be a bit thin if that is the only CPC to something that needs one, depends on the fuse or breaker, but that is normal rules, and the thinner floppier stuff is probably a better match to the sort of terminals on small 'stats. - avoids  the 'tail wagging the dog' problem.

Mike

Hi Mike

Thanks for your reply. Yes most will be either in conduit in a plastered wall or concealed above a plasterboard ceiling so mechanical damage won’t be much of a concern. I just wanted to hear other people’s opinions before I carried on but I think I’ll go with the flex, should even make connecting into the heating manifolds a bit easier too

thanks again

Peter

Baldyhugh said:

I Am currently first fixing a new build property and the heating designer has specified 0.75mm 4 core cable to the room stats

It doesnt sound like that person is a heating designer. That many zones will undoubtedly be inefficient, expensive to install and expensive to run. Current thinking is to have a maximum of 2 zones, preferably one, and design the heat emitters to be suitable for the environment, with only one thermostat to control the lot. Once it is set up, the temperature should be stable in all the rooms, thus allowing the boiler to modulate as required, and run at a low output to make it more efficient.

Having multiple zones means the boiler will be on and off constantly, adding up to more cost in running it (starts ups are the biggest waste of gas/electric), it'll be at full temperature for a few minutes, then will shut off abruptly, until the next zone calls for heat, and it goes through the sequence again. Its a really bad design.

That many zones will undoubtedly be inefficient, expensive to install and expensive to run.

I beg to differ. Per room zoning is quite popular these days, especially with underfloor heating as the heating circuits tends to be about room sized. Heating demand can easily vary between otherwise similar rooms - e.g. one gets the sun on a bright day and another doesn't; or just the occupants have different preferences for an ideal temperature (or for opening windows). If boilers can't modulate adequately itself a buffer tank or heat store (again increasingly popular these days, to combine multiple heat sources, including solar thermal and wood burners) solves that problem.

   - Andy.

alanblaby said:

Current thinking is to have a maximum of 2 zones, preferably one, and design the heat emitters to be suitable for the environment, with only one thermostat to control the lot

That presupposes two things: (1) that the external walls are well-insulated and that the internal ones are not; and (2) the householder wants the same temperature throughout the building.

I have old-fashioned radiators with TRVs. Are room stats not similar? The boiler will be shut down only when all of the room stats are satisfied. Surely there must be overlap between the different zones, or one might think of it like diversity in a distribution board.

P.S. If that is a house, it must be a big one.

Well, sort of. Currently, the best way to control a modulating boiler(or any heat source), is to have it running slow and long. This works for heat pumps and boilers. Zoning is basically making the boiler turn on and off regularly. This is quite inefficient, causing an inrush to fire up, and over-run when it turns off, as well as wear and tear on the parts.

To eliminate that, the house, and individual rooms should be designed to the correct temperature. Of course, if the heat is on permanently, you would think that the heat will be the same throughout the house, but, if designed correctly, the bedrooms should still be 2 or 3 degrees below the living room etc, as the thermostat is set up for one room, then all other rooms are adjusted as an offset of that room, so once the living room is at 21 degrees, the bedrooms should be at 18 degrees. There will be some crossover, but in tests, it has been shown that when set up correctly, the required temperatures are met most of the time.

What we are missing in this Country are heating designers. The typical gas boiler fitter did heat loss theory in college, then hasnt even thought about it for years, so if a boiler is faulty, they invariably fit another of the same rating. The customer is happy , as the new boiler works well, and gives out the heat, but, they dont realise they are paying higher bills forever, as their boiler/heat source isnt running at its most efficient level.

Yes, TRVs work just as a room stat. It's not efficient. Even modulatiing boilers can struggle with constant on/offs.  If they are modulating, rather than putting out 20kW, they can put out 4kW (I actually dont know what gas boilers modulate down to, HPs usually, can go down to a third of their rated value), but to keep the modulation down to a low level output, they want to be on at the low rate for a long time, rather than being turned on and off regularly, which is what zoning does.

A lot of this has come from heat pump research, gas engineers have realised the same principles apply to their gas boilers too, so gas boiler modulation is now common, and one open zone is the way to achieve the best performance and efficiency, with a single stat and no TRVs. To do that, the whole system needs to be designed properly, and time needs to be taken to set it up, as the heat loss survey, upon which the design is based, is a semi accurate guess in most houses, so tweaking is required to make it work correctly.

Currently, the best way to control a modulating boiler(or any heat source), is to have it running slow and long. This works for heat pumps and boilers.

Alternatively run the boiler full whack for a decent length of time, then shut it down completely. Running a gas boiler at part load tends to reduce efficiency as overheads from heat loss, pumps etc tend to be much the same whenever the boiler is running, so are proportionately higher at lower outputs. In my home system, in winter, it tends to run full blast (i.e. just below condensing temp) for about 15-20 mins (to recharge the thermal store), then is shutdown for maybe 4 to 6 hours. The UFH then gradually draws down that heat as needed. Thermal store is off the bathroom, so heat 'loss' from that is a useful contribution to space heating.

To comply with building regs I think there needs to be per-room temperature control of some sort these days (even if only a TRV).

    - Andy.

alanblaby said:

A lot of this has come from heat pump research, gas engineers have realised the same principles apply to their gas boilers too, so gas boiler modulation is now common, and one open zone is the way to achieve the best performance and efficiency, with a single stat and no TRVs. To do that, the whole system needs to be designed properly, and time needs to be taken to set it up, as the heat loss survey, upon which the design is based, is a semi accurate guess in most houses, so tweaking is required to make it work correctly.

Alan, thank you.

My boiler is far too old to modulate, but I have considered having a smaller one just for hot water in the summer. Better still would be PV panels to drive the immersion heater.

We don't heat all of our rooms all of the time. I feel sure that houses used to be divided into rooms because of heating, and heat loss.

What is the current thinking on heating staying on all the time v just morning and evening please?

Thanks Alan, interesting ideas. Once set up, It sounds like there would be no user input. Normally on radiators, there is a lockshield valve and a manual valve (or TRV), for users to adjust. If, in this example, a user was able to turn off one or two radiators, this would surely have an effect on the balance of the system, so that possibly the reference room radiator, in the room with the thermostat, would experience a different flow from that which it was commissioned for, and an effect on any temperature difference, between eg bedrooms and lounge, which were designed for.

The OP, Peter, mentioned manifolds in their second post, so I assume they are wet UFH manifolds, one on each floor. 

As Andy said Approved Document L book 1 

"5.20 For heating systems in new dwellings, or when a heat generator such as a boiler is replaced in an existing dwelling, each room should be provided with thermostatic room controls. These should be capable of being used to separately adapt the heating output in each room served by the heating appliance. Where justified in accordance with paragraph 5.21, heating may be controlled for each heating zone rather than individual rooms."

But that doesn't preclude anyone from designing something different, as long as it is no worse than full compliance.

Edit; the building regs have hummed and ahhd about TRVs. They were once required, then when Boiler Plus came along they dropped the requirement, then last year they are back in, along with (one of the four) boiler Plus measures. 

I have UFH in my flat, I tend to leave the  thermostat at room temp all year round, but then I have cats who don't go out much ;)

OlympusMons said:

The OP, Peter, mentioned manifolds in their second post, so I assume they are wet UFH manifolds, one on each floor.

This is a big house, so possibly >1/floor.

IIRC, step-daughter's house has 8: 3 on the ground and first floors, and 2 on the top. The house is circa 200 m².

I can see the point in not heating the guest bedrooms, but if they are going to warm up due to heat below and to the side, the economy may be trivial.

BTW: IIRC, we used 4 core flex for the stats. (Hubby's choice, not mine.)