My mistake. Are electronic room stats cheaper than bimetallic ones?
Your "real cheap solution" didn't do this. Ergo it wasn't a solution.
Which is relevent to me how, excatly? Am I buliding a new house or
This is a good start - ask me what I want first, before suggesting a
'solution'. I am glad you have learned something today.
Not at all.
I have gas fired central heating with a non-modulating conventional cast
iron boiler which is rated at about double the worst-case heat loss for
the house. I have a programmable room stat, with TRVs on 10 radiators
and one bypass.
How much would it cost to add individual time/temp control to the system
with a view to increasing efficiency without the disruption of moving or
If you recall, I mentioned that I had been looking at the CM67z and HR80
solution yesterday becasue it appeared to do what I wanted, although at
the price indicated I would want more - interfaces to house control
system, that kind of thing.
The CM67z sounds interesting to me as a way of retrofitting some measure of
individual room control to an existing system without a lot of plumbing and
wiring changes. The main drawback seems to me (apart from the batteries!) to
be the fact that each CM67z only controls 2 zones. So if you have (say) 10
rooms, and want each room to do something different by way of temperature
profile, you need 5 CM67z's - which could get a bit expensive.
I think that if I were to upgrade my system - which is similar to yours
except that I haven't got any TRVs - I would probably fit a 2-port zone
valve in the feed to each rad, and have each of these controlled by a
programmable room stat. [Ok, I would need 10 stats, but they could be a lot
less exotic than a CM67z]. Installing zone valves would not necessitate
converting to a manifold system (contrary to IMM's inference) as long as you
can get at the feed pipe to each rad in some suitable location. Bringing
them all together in a central point would simplify wiring up all the
volt-free contacts on the zone valves to control the boiler - but is by no
means essential. In my case, at any rate, all the zone valves could be under
the upstairs floorboards, and the only exposed wiring would be that going to
each room stat - which I would cover with small section white square
trunking until the room is next decorated, when I would chase it into the
Good point, although I'm not sure I have room under the floorboards to
house the zone valves, and having them exposed in each room would not
have sufficient WAF to obtain budgetary approval :-)
When I first saw the CM67z I considered 2 zones (being nominally 'living
rooms' and 'bedrooms'.) Clearly if one room calls for heat the whole
system will be switched on, but unless I *actually* zone the system that
will happen whatever I do. Battery life looks a definite disadvantage -
these valves must be making adjustements on a fairly regular basis. On
the other hand it would probably be simple to use a mains transformer
At the end of the day, if it starts getting too expensive I'd be better
off replacing the boiler, although that is no simple job either, given
the layout of the house.
I've been developing a system which includes this type of
functionality plus a great deal more. There are some commercially
exploitable aspects, so I don't want to expand on the details as yet.
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