Rad temps

[smhstu]

Hi allGot a custard who thinks that there's something wrong with a few rads cause there not hot enough, I mean they put there hand on and it doesn't take the skin off so they think it's not hot enough, even though there not cold!
So what is the temp of a rad supposed to be when boiler on full.?
I just want to go in with the correct info.

 

[SimonG]

Pinch the rad and if you can't hold it for ten seconds it's too hot. Just as a rule of thumb.

 

[Keefy]

Pretty sure it's 82 degrees on the flow and 71 on the return. Can anyone clarify?

 

[dancinplumba]

Pretty sure it's 82 degrees on the flow and 71 on the return. Can anyone clarify?

depends on what design temp drop is of system. is room not getting hot enuff ?

 

[smhstu]

Room temp is ok but they have a towel rad in the kitchen which is scalding hot they think all rads shoul be like that!

 

[tamz]

You could try balancing the system

 

[REDSAW]

Pretty sure it's 82 degrees on the flow and 71 on the return. Can anyone clarify?

what, at the boiler?
65-55

 

[doitmyself]

Got a custard who thinks that there's something wrong with a few rads cause they're not hot enough. So what is the temp of a rad supposed to be when boiler on full.?

Which boiler is it?
What is the flow temp setting?
What controls do they have?

The surface temperature of my rads currently is about 50C and the house is lovely and warm at 21C. The only time I get higher temperatures is first thing in the morning when the house is heating up from 'cold', i.e approx 15C. (I don't keep the heating on overnight; it's just well insulated.)

If it is a very old boiler, the rads will have been sized for a 90C flow/70C return. That changed in the 1990's to 75C flow/65C return. Modern condensing systems should be sized for a 75C flow/55C return. The output of a radiator is dependent on flow, return and room temperatures.

 

[albabe]

Design Temperatures.
82C Flow. 71C Return. Christian terms 180F / 160F.
Room Temp 21C (70F)
These are used to test radiator outputs.

 

[doitmyself]

Design Temperatures.
82C Flow. 71C Return. Christian terms 180F / 160F.
Room Temp 21C (70F)
These are used to test radiator outputs.

NO they are not.

BS EN442, which all rad manufacturers have to adhere to, require the rad to be tested at 75C flow, 65C return and 20C room. That has been the case since 1997. The now obsolete BS3528 tested radiators at 90C flow, 70C return and 20C room.

 

[albabe]

Well done, I've been out of it for a while, as you have pointed out. However, heating design calculations were based on 82 / 71 / 21.

 

[doitmyself]

However, heating design calculations were based on 82 / 71 / 21.

How long ago was that?

If that was the case, why didn't rad manufacturers publish the relevant data? I've never seen any data using those temperatures.

 

[albabe]

Hmm!
They did I worked with the test house at BSRIA - Bracknell on the tests.
I'll find the data.

 

[doitmyself]

They did I worked with the test house at BSRIA - Bracknell on the tests.
I'll find the data.

So why did BS 3528 require testing at 90/70/20? Or are you talking about prior to 1977?

 

[markfxy]

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

 

[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 .