Thu, 30 Apr 2026 07:39:08 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7864#Comment_7864 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7864#Comment_7864 Fri, 12 Oct 2007 20:26:37 +0100 mitchino https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7872#Comment_7872 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7872#Comment_7872 Fri, 12 Oct 2007 22:29:28 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7875#Comment_7875 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7875#Comment_7875 Fri, 12 Oct 2007 23:15:16 +0100 nigel
The safest way is to compare to known ones and then to make an allowance for error such that you oversize the rads.
Providing you have trv's you are better of oversizing the rads as they will assist in the operation of your condensing boiler by working at a lower temperature.
Also be careful as the rates output of a radiator is stated at a defined water temperature these are often higher than you would choose to run a condensing boiler at in order to optimise condensing operation. A condensing boiler needs a return temp of 55 or less to condense whereas non condensing boilers had to have a higher return temp to prevent condenstation and corrosion in the cast iron heat exchanger.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7880#Comment_7880 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7880#Comment_7880 Fri, 12 Oct 2007 23:51:15 +0100 tony https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7896#Comment_7896 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7896#Comment_7896 Sat, 13 Oct 2007 16:40:04 +0100 nigel
You dont seem to understand that radiator systems for non condensing systems require lower output radiators because they are designed to run at a higher temperature. With a condensing boiler you need higher output radiators and run them at a lower temperature. Hence my suggestion is unlikely to be belt and braces just good design and far less less wasteful than running a condensing boiler that will never condense.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7899#Comment_7899 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7899#Comment_7899 Sat, 13 Oct 2007 17:48:11 +0100 tony
I would rather see cash spent on air sealing, insulation than heating for that matter too]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7904#Comment_7904 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7904#Comment_7904 Sat, 13 Oct 2007 19:04:33 +0100 nigel Posted By: tonythe system can be adjusted so that it will run in good condensing mode for the majority of the time without changing the radiators for bigger ones.

44

How?]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7907#Comment_7907 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7907#Comment_7907 Sat, 13 Oct 2007 21:55:10 +0100 tony
This is exactly the same as if it was colder out side with bigger rads and the boiler set higher.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7911#Comment_7911 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7911#Comment_7911 Sat, 13 Oct 2007 22:48:45 +0100 nigel
Quoted from the technical director of ideal standard

"The fact remains that a high-efficiency boiler will only condense when the system allows it to do so, crucially, when the return temperature is maintained below 50°C. However, commercial and industrial heating systems in UK buildings can be as much as 20 to 30 years old, and many cannot easily adopt condensing technology — either through design or suitability. With the replacement boiler sector accounting for 70% to 80% of all commercial boilers installed, careful consideration must therefore be given to overall system design before choosing either a high-efficiency or standard-efficiency boiler for a replacement project.

So what factors do installers need to take into account before making the right selection for their end-user customers? The main consideration is the flow and return temperatures that commercial buildings are designed on. To maximise the benefit of a condensing boiler, for example, the system must be designed for 60°C flow and 40°C return. However, most of systems are designed on 82°C flow and 71°C return, and if this is overlooked, the rated output of the appliance can significantly reduce by as much as 8%."


So following your logic and assuming a system design temperature drop of 11c the max flow temperature you could have would be 61c at an average system temp of 56c the heat available would be reduced by 60% which wont be enough to keep a building warm so even in mild weather your idea would not work.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7955#Comment_7955 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=751&Focus=7955#Comment_7955 Mon, 15 Oct 2007 14:25:03 +0100 Mike (Up North)
You should check the spec radiators are quoted against, it should be EN442. Radiators are now are quoted now at Delta 50 which means a water flow temperature of 75deg in and 65deg out, so average = 70deg so compared with a room at 20deg its 50deg (Mean Temp Difference). It used to be Delta60, which would have had a much higher flow temperature (85 to 75 = average 80 ) so gave a greater output. The output depends not only on the temp drop within the radiator (a heat exchanger) but the relative difference between the two sides i.e. the rad to room, as well as other things like convection, conduction, radiation etc, surface finishes etc (btw chrome emits less than flat white). This is not linear; there are standard conversion factors for this. Going from D60 to D50 loses about 20% output. However, if picking from a manufacturers brochure, they should be quoting D50 anyway so pick the one that is right according to the heat loss estimate for the room. Or on the other hand, as in your case, simple compare size to known and trusted sources/brochures and work from there. I say trusted because ostensibly they should all be about the same, but the same size radiator in different catalogues does not always seem to have exactly the same output. I believe this is because they do not actually calculate/test for every shape/size combination some are done on a size ratio so may not be as accurate but probably close enough.

Cheers,]]>