Looking at getting a new condensing boiler etc, already gleaned plenty
of info from previous posts (thanks everyone), just a couple of
1. Is there a rough way of calculating the output of older rads
without convectors, although the majority are newer rads with
convectors there are a few older ones without. I'm trying to get an
approx value of their output but can't find any sources. For example
with a double panel/no convectors can I take the average output of a
double/double and divide by 1.5 or something? Not looking for exact
figures, just a rough idea. I don't really want to replace them, the
look in good condition and it seems silly to throw out something that
is in good working order. The rads without convectors that I am
looking at are:
2200x700 Double panel
750x700 Single panel
1750x500 Double panel
2. In the case of a modulating condensor, are there intelligent CH
thermostats that, rather than just calling for heat or not, can say to
the boiler I need x amount of heat? At present I have a CM67, is there
any changes you can make to this to make it more suitable for a
modulating boiler? It seems silly having a thermostat that only turns
the boiler on or off, when with a more intelligent control the boiler
could just modulate down to the current heat loss for the house. Maybe
I am getting a bit too anal here, just interested really.
Thanks in advance.
On 22 Sep 2004 12:13:13 -0700, email@example.com (Mary Hinge)
Very approximately, a double panel radiator has 1.7x the output
of the equivalent single panel (both without fins.
If you look up the data sheet for the Myson Premier HE there is a
single panel, no fin version. For sizing, simply scale the
dimensions, Apply the factor above and then multiply by 0.9
because the data sheet numbers assume a higher operating temperature
than is used in the UK in practice.
Left to its own devices, a modulating, condensing boiler will modulate
downwards automatically as the heat requirement falls. The simple way
to do this is with TRVs on all radiators except one. Then as the
flow and heat load fall, the boiler will detect it and reduce power.
A CM67 can control the boiler by pulse width control - basically
varying the on/off ratio for heat demand. This is effective for
conventional boilers because in effect it "modulates" the temperature
of water to the radiators. The objective is to prevent overshoot of
room temperature. With a condensing boiler, you really don't
want this action to happen to the same degree because it is not as
good as letting the boiler do it. Therefore, the operating window
should be set as small as possible.
The situation that you want is for the rooms with TRVs to come up to
temperature, and then shortly after that for the room with no TRV and
the thermostat to reach its set point and for the boiler to be turned
off altogether. It's not so useful to have the CM67 turning the
boiler on and off in an attempt to control it, if the boiler is
already modulating down on its own.
Some boilers have the ability to accept an input from a room
thermostat which is able to give it a modulating control as a digital
signal of the value required rather than a simple on/off.
For example, on my boiler, a MAN Micromat, you can optionally connect
a Landis & Staefa QAW20 room controller.
Normally these are intended to run with a zoned automation system in a
multi-occupancy building with central boiler, but will drive this
boiler quite happily. The boiler also has input for an outside
temperature sensor which affects the boiler operating curve and
control points. It is possible to set the relative sensitivities of
the boiler to the internal temperature control input and external
control input in order to optimise power level with temperatures.
The main problem is that there are no standards for these, and when
available, they rarely support subzoning.
The Worcester-Bosch Greenstar, for example, can have a proprietary room
thermostat that sends an analogue signal to the boiler. Very nice, except
that (a) it isn't programmable and (b) you can have only one zone using the
Thanks for the answers guys.
I couldn't find a single panel, no fin version of the Myson Premier HE
in the tech specs PDF on the Myson web site, don't suppose you have a
link at all?
As I am probably going for a Worcester Bosch or Glow Worm I think I
will stick with my treasured CM67. Are there any changes to the std
CM67 config that might be worth making for a condensing boiler (my
guess is no). I have always had my min burn time set to 5 mins as
without that I found it had a tendency to fire the boiler for only a
minute or so quite often, setting the min burn time high stopped that
without any noticeable temp overshooting.
So far have contacted three "heating engineers" regarding fitting the
boiler, not suprisingly they have each recommended a different boiler
for exactly the same reasons! (ie the other two being "unreliable").
All three guys are pretty clued up so I guess in the end it is as much
down to personal preference as anything else.
Here's one for Stelrad:
To decode, P1 is a single panel without convector, K1 is a single panel
with convector, P+ is a double panel with a convector on one panel only
and K2 is a double panel with a convector on both panels.
FWIW, I prefer the look of the P+ as it is a bit slimmer than a full double
convector. http://www.discountedheating.co.uk/ have a good site that lets
you see what's available and are a useful price guide even if you don't buy
On 24 Sep 2004 05:12:19 -0700, firstname.lastname@example.org (Mary Hinge)
Send me an email and I'll reply with a PDF as an attachment.
You may need to play with the cycle times and also to reduce the size
of the proportional control window.
One factor that affects it is the thermal characteristic of the house
- i.e. whether it heats rapidly with the heating starting or whether
it has a larger thermal inertia.
Really, you will need to experiment a bit with the settings.
If you post some makes and models you will get some opinions on that.
To email, substitute .nospam with .gl
"Mary Hinge" wrote
| So far have contacted three "heating engineers" regarding
| fitting the boiler, not suprisingly they have each recommended
| a different boiler for exactly the same reasons! (ie the other
| two being "unreliable"). All three guys are pretty clued up
| so I guess in the end it is as much down to personal
| preference as anything else.
Alternatively they may be recommending whichever boiler is giving savings
stamps on new monogrammed overalls or a trip to Ibiza.
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