Andy Hall wrote:

It could be just a personal thing, but radiators above a certain temperature
I find unpleasant and best avoided; it seems to be something to do with
breathing in the hot air from around them so I was trying to avoid this in
future alterations. I understand that comfort level is affected by many
factors, including relative humidity and radiant heat emission from walls
and objects in the room, so personal comfort can no doubt be a complex
concept.

Yes, ditto. I find continuously warm rads much preferable to
intermittently scorching rads.

The radiant heat losses to/from the surfaces in the room have a
significant effect on one's feeling of comfort. You can usually drop
the air temperature by a couple of degrees in a room with UFH because
the radiant component of the heat emission is much higher.

If that's your only issue rather than having a more or less constant
temperature, you could resolve it quite easily.

For conventional boilers, radiators are run at 82 degrees flow and 70 return.
Radiators are sized for the room heat loss requirement to work with this.

Whilst this is true, the radiators are sized for the worst-case,
mid-winter, design conditions,
-5 degC or suchlike outside, which probably occurs for only 2% or 5%
of the time that the heating is on.

For the other 95-98% of the time, partial load conditions, the
radiators could operate at less than the 'classic design' 82 flow 71
return, whilst still putting out sufficient heat to offset the heat
losses. Similarly, if the system can vary the flow temperature, they
can operate continuously at lower temperatures, rather than
intermittent bursts of 82/71.

I was surprised by the amount of time my modified modulating system
operates at less than 100%; probably 90% of the time and I didn't
change any radiators. You will achieve worthwhile savings with a
condensing modulating boilers even without changing radiators.


If you install a condensing boiler, it *can* work at these temperatures -
they do to avoid mandating radiator changes. However, it will operate more
effiiciently at lower temperatures, so it is more typical to design for 70
flow and 50 return. Heat output is then about 30% less so the radiators
have to be larger. There is no reason why you couldn't extend this
principle further, use even larger radiators and lower temperatures.

In the extreme, it heads towards underfloor heating, where the floors
are huge radiators operating at 29 degC surface temperature.