Quick one - Typical Maximum Radiator Temperature

[Chris_J]

I've balanced my CH system using one of those IR thermometers, resulting in all of my rads heating up together quite nicely.

I've adjusted the valves down to the settings I require, but one or two of the radiators I need on full setting.

Typically speaking, what would be the maximum temperature the radiator should heat up to, on a presurised system?

I'm reading 72-74C at the top of the rad, but I thought this should be more like 80C?

Cheers.

 

[Terrywookfit]

What is the flow temperature?

Should give you a clue!

 

[Chris_J]

Yeah, what I mean is a typical safe maximum. Obviously, 100C is way too hot which would result in scalding and damage to PVC pipes etc.

I want to know how hot the rad should get before it is deemed "too hot".

Cheers

 

[D_Hailsham]

I want to know how hot the rad should get before it is deemed "too hot".

The National Health Service has produced a guide for Hospitals called "Safe hot water and surface temperature" which decrees that radiator temperatures should not exceed 44°C. Their main concern is the elderly and vulnerable people. Manufacturers, such as Stelrad, produce radiators which meet the NHS standards, their LST range. This however is at the expense of a loss in output of up to 20% for the same size radiator.

I've adjusted the valves down to the settings I require, but one or two of the radiators I need on full setting.

Do you mean that you have thermostatic valves on your rads and you need to leave some on full open to make the room hot enough? If so, this would suggest that the rads in those rooms are not large enough for the heat loss from those rooms.

If you are achieving a temp of 72-74°C at the top of the rad, you are doing fine. Radiators outputs are quoted for flow temp 75°C, return temp 65°C and Room temp 20°C; the so called 75/65/50 standard (50 is the difference between the average rad temp, 70°C, and the room temp).

If you are concerned about the radiators being too hot due, say, to small children or elderly relatives, you could always install radiator covers; but you will loose as much as 30% of the heat from the radiator. You get less heat loss (about 10%) if your rad cover looks like this in cross section:

 

[ChrisR]

Is the boiler a condenser or not?
IR thermos don't work on shiny metal so get som paiintout if necessary, but take the temps at
the boiler flow pipe
inlet to your biggest radiator
outlet from that
return pipe into boiler
Then work out how much heat you must be losing under the floor. Can be horri fying

 

[D_Hailsham]

Then work out how much heat you must be losing under the floor. Can be horri fying

I agree A couple of years ago I retired and moved to a smaller house. I could not understand why the rads in the new house never got to more than about 60°C so I started investigating. The boiler output was 15kW and the rads came to about 13kW so, allowing 2kW for hot water, the boiler should have been up to the job and providing a flow temp of 75-80°C. As all the pipework was buried, either under a floor or within a dry lined wall, I could not determine exactly how the system had been installed, so I made some educated guesses. and calculated that nearly 5kW was being lost in the pipework.

 

[Chris_J]

Did a bit of messing around today. As you say Chris, I noticed how the IR thermometers don't work on shiny metal! Won't work on the copper flow and return pipes from the boiler, but work fine on the rads and PVC pipes.

Anyway, I'm getting 83C flow temp at the boiler and 80C at the inlets to the rads, resulting in about 74C at the top of the rad. This is from a 24kw non-condensing combi boiler.

The controls valves I have are not thermostatic, so I've closed down valves in rooms I don't need much heat, and just cracked them open. In my front room, I have a knocked through double size room with exposed wooden floors, so I have the two rads serving the room on full power.

They were running at about 65C before, and the room didn't get comfortable. Makes a huge difference now, and the thermostat picks up the heat to shut down the boiler in good time.

Appreciate your input guys.

Cheers

 

[Gasguru]

Don't waste your time with a cheap IR thermometer...get one with an adjustable emissivity setting. You can then calibrate it (inconjuntion with a thermocouple) to work on different surfaces. With experience your hands are just as effective.

 

[Chris_J]

I think the one I have has adjustable emissivity, but never really played about with it. I bought it a while back to use for tuning those little 2-stroke engines, but seems to work well on most things. I can get some scary readings when I point it at my log stove!