Rad temps

[chris watkins]

I know we have done this one before but will throw my two pen'ith in.
Domestic Heating Design Guide which has become the main work for modern design, recommends the use of 70 F - 50 R (21 C all rooms except for baths 22 C heated by rad's) when the heating system has also to heat domestic hot water. The reason is to keep the boiler in condensing mode (<53 C on the return) for as long as possible but still have a flow temp that can heat the domestic HW to the required minimum temp of 60 C.
If heating only, then any flow temp could be used, the lower the better, as the heat recovery on the flue gases get better the cooler the return.

I would be interested in peoples views on what the optimum temperature / size of rad / cost / space / efficiency of boiler ???

 

[doitmyself]

I've always used 82/71 never known anyone to use 90/70 think you must be mistaken on that one.

You may use 82/71, but I'm talking about the temperatures used to measure radiator outputs. According to all the sources I can find, BS 3528 required rads to be tested at 90/70/20. Unfortunately the BS is not online and I don't feel like shelling out £136 to buy an obsolete book.

Running a rad at 82/71 means that it will give out about 7% less heat compared to the 90/70 output and 18% more compared to the current 75/65 output.

As the return temperature needs to be less than approx 57C for condensing to occur, systems need to be run at 75C/55C. This reduces rad outputs by 15% compared to the 75/65 figure quoted in manufacturers' catalogues.

 

[zzzjim]

Judging temperature by touch test , make sure it has not old and got 5 thick coats of paint on it !

( can bear 50 deg all day long - but have soft skin ! )


Things have changed form OLD inefficient designs blasting out

timed surges of heat from big chunks of cast iron .