I've been looking at dividing my CH into zones. To do this I would need to retrofit a thermostat into each zone (amongst other things). All the thermostats I have seen so far require the cable to enter directly from behind. The problem is that I don't really want to start chasing walls and having to redecorate. I was hoping there might be a model where I could run the cable down the wall in truncking until such time as I want to redecorate but I cannot find any models like this. Are there any?
I know I could go wireless but they are more expensive.
4/5ths of bugger all. A mechanical room stat only uses power when it's calling for heat (for the internal compensation resistor) zone valves on= ly use power when they are open, mine are plated at 6W. A receiver for a wireless stat or a wired programmable stat is probably less than a coupl= e of watts.
So lets say 5W for a the stat 24/7 =3D 43kWHr/year or about =A34.30 or r= oughly a quarter the cost of a decent TRV...
The usual trick is to run trunking down to the thermostat and then chisel into the plaster at the end of the trunking behind the thermostat so that the damage is not seen.
Personally I would not allow trunking at all in my house. Add the cost of the cable and trunking and wireless may be a viable option. You can use a mixture of wired and wireless thermostats if you want to.
Also, if using honeywell stats, you can only synchronise the wireless ones which is good to limit boiler cycling if a small zone comes on out of sync with larger ones.
I assume the same will be the same for other manufacturers unless they use some kind of wired communications link.
4/5ths of bugger all. A mechanical room stat only uses power when it's calling for heat (for the internal compensation resistor) zone valves only use power when they are open, mine are plated at 6W. A receiver for a wireless stat or a wired programmable stat is probably less than a couple of watts.
So lets say 5W for a the stat 24/7 = 43kWHr/year or about £4.30 or roughly a quarter the cost of a decent TRV...
And the 6W electrical heating of the thermostat is not wasted. It just helps heat the room.
I have heard of compensation resistors but don't really know what they do. Is it something to do with hysterisis by the resistor generating heat when a current flows through it? Do you need a neutral connection to the stat for the resistor or does the current flow through the load? I haven't seen any stats with neutral connections.
Do all dial type thermostats have these resistors? If so, does this mean that these thermostats can only ever be used to switch mains ac, as I presume they need a minimum current to heat the resistor?
I upgraded my room thermostats to digital ones and they are battery powered. So they add nothing to the electricity bill, though I will incur a charge when I have to replace the batteries. I have wondered whether it might be possible to power the thermostats from some sort of DC supply, possibly using something like a burglar alarm supply with lead-acid battery back-up?
These digital stats can switch any voltage so they could be used to switch small DC voltages if you wanted to use some fancy home automation system.
My controller draws a current, I don't know how much, but I doubt it is much. That's a digital one too, but even a clockwork one would need a power supply so there's no escaping that.
My valves are also rated 6W. You can get motorised ones that only take power when switching between on and off but I didn't know that when I bought mine.
Thanks but for some reason the manufacturers say that they should not be fitted onto patress boxes. Why? Is it because it makes them stick out more and are more likely to be knocked?
Also called the "accelerator resistor". What it does, it warms up when the thermostat is in the ON state. This in turn heats up the bimetallic sensor to well above room temperature, causing it to turn the thermostat to the OFF state. Then the sensor cools down, and since it was much warmer than the room it cools off quickly, and so it soon turns itself on again.
Thus the resistor reduces the dead-band (or hysteresis) of the thermostat. That's the theory. In practice their performance is rather poor.
You need a neutral connection for the accelerator resistor to work *at*
*all*.
I think that all mechanical thermostats whose switching function is performed by means of a bi-metallic strip will have accelerator resistors. I have a feeling that some digital stats may have a knob to twiddle to set the temperature - in which case these *wouldn't* have accelerator resistors.
If so, does this
Just for the avoidance of any possible confusion, the load switched by the stat doesn't go through the resistor but is in parallel with it. Nevertherless, the spec of the resistor is such that it will only get warm if fed with mains voltage, so if - for example - the stat was used to switch a 12v circuit, the accelerator resistor would be totally ineffective.
Not absolutely true. The 24v thermostat on my previous heating system had an adjustable series resistance which had to be set to suit the load current, something like 0.4A for the gas valve.
I am puzzled. The only dial thermostat I have is on the HW cylinder and that only has live and switched live. The old CH thermostat that I replaced also only had these two wires.
They probably didn't have an accelerator resistor. For thermostats that do, the accelerator resistor is connected (in parallel with the load) to the neutral line.
You can use such a thermostat without connecting the accelerator resistor, but then you don't get the benefit of it - such as it is.
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