Rate of heating in a living room?

[Mossop]

If a radiator has been correctly sized for a room and the boiler is adequate and fully functioning, at what rate of C/Hour would you want a living room to be able to heat up at?

Thanks.

 

[ShaunCorbs]

Shouldn’t be running the heating temp at 75dc

max you should do for a condensing boiler is 65 ideally lower the better

 

[John.g]

The other few rads are still open when I took the last measurements. I could easily take these again with these other few rads closed off again.

I need to double check that the boiler was running continuously at 75 C with both valves open in order to be 100% sure , but certainly on the various occasions I looked in at the boiler it was running continuously,

OK, the reading taken with the vertical rad throttled in might indicate that the boiler may not be running continuously as you are only getting a flow temp of 63.8C but that makes sense to me as that rad is emitting 1.7kw vs 2.4kw unthrottled.
I would suggest reducing the boiler temp to 60c again (original e setting) and reopening the vertical rad valves fully which will still give 1.7kw but only as long as the boiler is running continuously which we now know is dependent on those few other rads being on.
Or you may decide to shut them (extra rads) off and put up with a further reduced vertical rad output (due to cycling) and/or install another rad in that room. Also installing another rad may mean that you can shut off the other rads and get the heat where you really need it.

 

[John.g]

Shouldn’t be running the heating temp at 75dc

max you should do for a condensing boiler is 65 ideally lower the better

Yes, I have a SE (non condensing) boiler and because I have a a lot of TRVs installed that even with a boiler temp of 75C I regularly get down to a return of 40/45C, no real advantage with a SE boiler, mine runs with a fairly constant flue temp of 230C and hasn't changed much in 15 years.
There is a lot of emphasis put on getting the (HE) boiler to condense, condensing only begins at a flue gas temp of 55C so even a boiler return temp of 50C will have very little condensing benefit, you have to get down to return temps of 35/40C to get real condensing benefit, the real, easily got benefit of the condensing boiler is that it takes no effort to get down to say 75C flue temperature with a ~ 7/8% increase in boiler efficiency based on my 230C temperature, above,

 

[Mossop]

I would suggest reducing the boiler temp to 60c again (original e setting) and reopening the vertical rad valves fully which will still give 1.7kw but only as long as the boiler is running continuously which we now know is dependent on those few other rads being on.

I'll maybe set the boiler to 60 C, switch off the other rads on the other level. Leave on, as originally, only the rads on the same level as the main rad and determine with certainty if cycling is occurring.

 

[John.g]

What size approx. are the other two? rads you had on to stop the cycling?, just trying to see can we determine what the minimum boiler output is.

 

[Mossop]

WBosch have informed me that the minimum central heating rated output for my boiler is 7.2 kW.

The other rads which I had on on the other level, are:

Double panel radiator: 42" x 23" (107 cm x 58 cm)
Single panel radiator: 47" x 28" (119 cm x 71 cm)
Acova column rad: (60 cm x 62 cm) 3540BTU 1037W according to manufacturer

I have now switched off all 3 rads above which are on the other level, and looked at the boiler where the cycling has returned.

Below the rads on the same level as the main rad in question are open again just slightly at their lockshields. So it's just the main rad in question which is on, the "other " vertical rad, and the other two 1980/90s panel rads. So back to the original setup. The boiler is set to 60 C for all below.

With the lockshield on the main rad in question open only slightly the boiler cycle times (in minutes) were as below:

0:00 On
0:02 Off
0:05 On
0:09 Off
0:09 On again
0:12 Off
0:15 On


With the lockshield on the main rad in question open fully the boiler cycle times (in minutes) were as below:

0:00 Off
0:02 On
0:04 Off
0:07 On
0:14 Off
0:17 On
0:18 Off
0:22 On

With the lockshield of the main rad in question open full, the flow has a temp of 59 C with a drop of 3.3 C. The "other" vertical rad has a flow of 61.4 C and a drop of 6.5 C. The other two 1980/90s panel rads have flows of 63 C and drops of 14 C. (The boiler sometimes ranged up to 65 C itself which explains some 60+ C temperatures here).

With the lockshield of the main rad in question open only slightly, the flow has a temp of 48.7C with a drop of 5 C. The "other" vertical rad has a flow of 61.9 C and a drop of 10.1 C. The other two 1980/90s panel rads have flows of 60 C and drops of 12 C.

 

[John.g]

Your total heating load is ~ just above the minimum output of the boiler so you will get continuous cycling when running on the 4 rads downstairs, you really can't do anything about this.
I would increase the boiler temp to 70C and note the cycling on/off times, this is with main vert rad valves full open, the other vert rad as is and remaining rads as is, if the boiler on time averages 3 mins then you will be doing well IMO.
Also see can you can range rate the boiler from the user menu, this means that you can reduce the boiler maximum (but not the minimum) output from its present 30 kw to say 10 kw or the next lowest setting, this won't affect the hot water output but should cause reduced cycling and more consistent radiator temperatures, if this option is not available then it should be possible to get it carried out at the next service. You can ask WB if this range rating is available on this model.