Tue, 21 Apr 2026 07:59:10 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125960#Comment_125960 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125960#Comment_125960 Mon, 12 Dec 2011 13:40:16 +0000 Ricochet
booklet that comes with the g'tee basically says 20C across rads , and thats it.

what is recommended ?

and as a subsidiary... the same bklt says to insulate your bath if it is cast iron or pressed steel, what do you chaps think?

thank you in advance for your help.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125964#Comment_125964 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125964#Comment_125964 Mon, 12 Dec 2011 14:08:09 +0000 JSHarris
Generally the return temperature needs to be as low as practicable for the required heat output from the rads. The reason for this is that it is the return temperature to the boiler that determines whether or not it runs in condensing mode - if the return temp is too high the boiler either won't condense or at least won't condense as efficiently. This can make a significant difference - the boiler efficiency rating will have been obtained with a fairly low return temperature.

Return temperature is determined by two things primarily, the flow temperature to the rads and the heat that the rads give out to the rooms. Increase the flow temperature and the heat output from the rooms increases as does the return temperature.

The most efficient way to set the boiler up is to use the lowest flow temperature you can whilst still getting adequate heat output from the rads. For example, at the moment I'm running my boiler at a 48 deg C flow temperature, rather than the 55 deg C I used to run it at, and am finding that the boiler burns for longer each time it fires, but runs with a lower modulation level (less gas being used). The return temperature is down around 35 to 38 deg C, so the boiler should be condensing very well and running at high efficiency.

If your radiators are undersized, then you may find that you have to increase the flow temperature to get the house warm enough. This will hit boiler efficiency quite hard, maybe by around 10% or more.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125981#Comment_125981 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125981#Comment_125981 Mon, 12 Dec 2011 15:23:05 +0000 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125996#Comment_125996 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125996#Comment_125996 Mon, 12 Dec 2011 16:38:41 +0000 RobL I'm pretty sure it's on it's lowest modulation most of the time, on the basis that if I turn down either the temperature knob on the boiler, or turn down the pump speed, then the boiler starts cycling (bad).
You can see that the flue seems to track the boiler return temperature +5C. I think that as the boiler power increases, it will still track the return temp, but with a higher temperature offset.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125997#Comment_125997 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125997#Comment_125997 Mon, 12 Dec 2011 16:39:17 +0000 RobL https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125998#Comment_125998 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=125998#Comment_125998 Mon, 12 Dec 2011 16:40:22 +0000 RobL https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126000#Comment_126000 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126000#Comment_126000 Mon, 12 Dec 2011 17:19:11 +0000 djh Posted By: tonydefinitely insulate the bath if you use it
Agreed. It's also surprising how much of the heat is lost by evaporation. So be generous with the bubble bath to create an insulating foam layer. Or add some oil to float on top and reduce evaporation.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126058#Comment_126058 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126058#Comment_126058 Tue, 13 Dec 2011 00:35:33 +0000 wookey
Interesting graphs. I've been wanting to get some data like that for ages and not got round to it. I'm surprised how low the flue temp is. I guess the whole point of this design is that the cool return water is used to suck heat out of the flue but I kind of assumed that meant it got it down to ~100C, not 43C. I suppose relative specific heat capacities have a lot to do with the effectiveness (water can take the heat out of a lot of gas/air)]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126063#Comment_126063 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126063#Comment_126063 Tue, 13 Dec 2011 08:03:22 +0000 JSHarris
Boiler manufacturers rarely seem to state the return temperature at which their claimed efficiency was achieved, which is a shame. My guess is that it will be pretty low, probably below 40 deg C. Mine is noticeably better with a return at around 35 deg C than it was when the return was running at around 45 deg C, although I'm struggling to get hard numbers on the actual gas saving.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126067#Comment_126067 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126067#Comment_126067 Tue, 13 Dec 2011 08:38:08 +0000 CWatters https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126211#Comment_126211 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126211#Comment_126211 Tue, 13 Dec 2011 21:07:58 +0000 RobL Our boiler is a bosch greenstar 24i, so pretty basic controls - just a temperature knob. I wish I could hobble it, so that no matter what it just stuck on its most efficient lowest modulation only.
I was pleasantly surprised by the low exhaust temps - the thermocouple is pushed right into the centre of the exhaust, through the inspection plughole (with all gaps sealed), so I'm confident it's right. It's a welcome contrast to the last boiler we had, which had an exhaust around 130C.
I used a 3 channel thermocouple based logger that I splashed out on (Extech SD200), £200, easy to use, don't need to leave a PC on, records to sd card.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126312#Comment_126312 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126312#Comment_126312 Wed, 14 Dec 2011 22:49:06 +0000 Ricochet
if you run th boiler at a lower temp doesnt this mean the temp diff to room temp is reduced and so the rad output is lowered?

i have ahot water cyl to consider.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126318#Comment_126318 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126318#Comment_126318 Wed, 14 Dec 2011 23:16:58 +0000 RobL Yes, rad output is lower. But you can see from my graphs, that in our case the main stat kicks in & out to regulate air temperature - so in the steady state case all will be well. If I increased our boiler temp, it would just spend less time on & more time off, and the boiler would be less efficient, but comfort levels would be the same.
Higher temp boiler does give a faster warm-up time, and a decent hot HW cylinder.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126491#Comment_126491 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126491#Comment_126491 Thu, 15 Dec 2011 20:54:37 +0000 alec
Almost all boilers accept these, but many Worcester bosch boilers do not.

The benefits of these controls are longer burns, lower temperatures, more comfortable room temperatures, and lower gas bills...]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126509#Comment_126509 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126509#Comment_126509 Thu, 15 Dec 2011 23:41:50 +0000 Ricochet cheers ,
john.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126618#Comment_126618 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=126618#Comment_126618 Fri, 16 Dec 2011 21:24:18 +0000 alec https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=128056#Comment_128056 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=128056#Comment_128056 Fri, 30 Dec 2011 09:50:32 +0000 Ricochet i asked Worcs Bosch about 'controls' but they do not have any dedicated ones for the non combi boilers .]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=128058#Comment_128058 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=128058#Comment_128058 Fri, 30 Dec 2011 10:06:02 +0000 JSHarris
The return needs to be below 55 deg C for the boiler to start condensing and the lower you can get it the better, as it probably won't be fully condensing until the return is down at around 40 deg C or so. My return temp is around 38 deg C, with a flow temp of 48 deg C and the boiler efficiency seems to have markedly improved over the old regime I had of running it at about 55 to 60 deg C flow temperature. I get longer boiler burn times, but with a lower flame modulation (the boiler burns noticeably quieter) and the cooler radiators still seem able to keep the house warm, albeit with a slower response time (not a problem for me as the heating is on all the time normally). So far the system has kept the house warm with night temperatures dropping to around -4 deg C outside, so I'm hopeful it will be OK if we get a spell of prolonged cold weather.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=128130#Comment_128130 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=128130#Comment_128130 Fri, 30 Dec 2011 17:29:30 +0000 alec
Radiators are balance for no other reason that distributing heat effectively through a building...just throttle back the rads nearest the boiler and make sure they are more open the further from the boiler...

I have seen figures suggesting that poorly balanced system (nothing to do with the delta T) waste up to 15% of heat... one can see why if the rads nearest the boiler are getting all the flow....]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=128154#Comment_128154 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=128154#Comment_128154 Fri, 30 Dec 2011 21:42:27 +0000 Ricochet
i wil reduce boiler flow temp to 60c and see how hw cyl copes

thanks]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=131827#Comment_131827 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=131827#Comment_131827 Tue, 24 Jan 2012 21:52:48 +0000 martin.n For extra fun I have a probe cylinder stat on the RETURN pipe which i set high B4 to bed, and then turn down when/after I get up at same time as turning the boiler stat down. When the probe stat is satisfied it breaks the wire to the roomstat. Result is that during the day and eve the boiler runs for 5 or 10 mins, then off for 10 to 20 mins, i.e. avoid very short cycling and get more condensing. Temperature chosen varies depending on how cold outside, and if I get it right the roomstat is always calling for heat and I get a pretty even heat in the rooms as by the time rads have cooled right down the boiler fires again. favourite return temp is 40 degrees.
I guess that with a lightweight fan flued boiler (whether or not condensing) short cycling is not such a problem as with heavy square flue or chimney flue ones.
My son has a Worcs Bosch on which we took the optional clever roomstat/sensor which turns the boiler down as target room temp is approached, again reducing short cycling and incr condensing. Has to be wired, it can't be that clever with a wireelss roomstat.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=132949#Comment_132949 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8266&Focus=132949#Comment_132949 Wed, 01 Feb 2012 13:15:16 +0000 alec
the are not available in the UK except through a boiler manufacturer...

at the end of the day whilst the institutions that write our regulations are wedded to heating appliances that are either on or off there is no stomach for getting these controls to market...]]>