older/newer GCH radiator efficiency?

In principle, the convection you're relying on now to distribute the heat from the radiator, that's moving air, and it's pretty quiet. Suggesting human hearing is not infinitely sensitive.

If you make the radiator large enough, you should be able to match the fan-driven performance. With a large enough radiator, the exhaust water temp will be the same as the room air temp. That should be the limit.

Paul

Yes, "rads further away" wasn't a good choice of wording. In fact ALL the other rads get a bit more flow because the total system resistance increases when you restrict flow in any radiator, thus driving the pump a bit further up its pressure/flow curve. This in turn causes a bit more flow in all the other rads.

Phil

and also not necessarily ideal from the system point of view since the boiler probably can't lift the water temperature from ambient room air temperature to target flow temperature in a single pass.

This subthread was discussing the use of a 'silent' fan. I'm quite aware that you might expect air currents formed by convection from a domestic radiator to be inaudible.

Of course they glow. Pretty much everything glows.

Just not necessarily in the visible spectrum. (And IIRC glass reflects most long-wave infrared to help keep it in the house.)

Andy

First silent fan I made I could hear nothing at all with my ear as close as possible to the spinny bit in a silent room. I'd say that's good enough once inside a box. Naturally you'll have your own ideas.

NT

So you've no idea where any inefficiency occurs in that radiator, but still want to make silly comments. Mmkay.

Yup. But it's not the rad being inefficient.

That blocks loss from heated air, but not from the steel mountings.

NT

The definition of energy efficiency has not changed. Nor has the looser usage of the word efficiency in other contexts. Some people believe anything.

NT

I take it you're not an engineer then. Or an ignorant one.

Hint: try turning a desktop fan round by finger & see how noisy it is. No wind noise.

NT

Of course. And any suitable engineer knows that fan noise output depends on speed among other things. It is odd that some 'engineers' do not realise that fans can be slowed enough to be inaudible.

FWIW you could do a slight bit better by wetting the metalwork at the outflow end. Evaporation could cool the outlet to slightly below ambient. Fairly pointless though.

NT

And precious little movement of air. It won't be very efficient!

Oh boy. Time to state the utterly obvious...

1. The fan turned by finger demonstrates that fans can be silent.
2. Yes you will need more speed to make it useful.
3. There are suitable fan designs and suitable motors that run at suitable speeds to get a useful silent end result. Clear enough for you yet?

You've already been told why it isn't 100% efficient but choose to ignore it.

Now try measuring with a sensitive device. Not your ancient ears. ;-)

another fact-free reply

No you've not come up with any inefficiency in such a rad. That's cos there isn't one.

Really?

I worked in broadcasting. All studios are air sealed against noise. So if in use for more than a short time, require ventilation. And despite this being an extremely expensive part of the structure, and done by experts in that field, none is totally silent.

But I'd guess in your world, the laws of physics don't apply. Hence you talking about 100% efficiency too.

Oh well yes, even I could do that. Doesn't make me (or you) an engineer. Or the room meaningfully warmer.