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?

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?