size of replacement rad with fins

[very_pointy_ears]

Hi,

How much more output would you get from a single finned radiator compared to an unfinned one of the same size?

I want to replace an old 1740mm x 700mm unfinned single radiator with a new 1800mm long finned single radiator. I'm already resigned to having to change the pipework slightly. What height should I buy? I've seen 450, 500 or 600mm as possibilities.

The heat output of the old one was just about right - I just want something a bit less ugly now that we're redecorating. I figured we could get a lower one if it was finned - I just need to know how low.

The room is open plan to the stairs and landing so I'm presuming that using the usual radsize calculators wouldn't be quite so straightforward.

 

[gas4you]

Approx 40%

 

[kevplumb]

keep one thing in mind
if a rad is to big you can turn it down if its to small you cant turn it up

 

[very_pointy_ears]

Approx 40%

Is that meaning you get 40% more output from a finned rad, so if I started off with a 700mm high rad, I could go to 700 / 1.4 = 500mm high?

Kev - yes, good point!

 

[htgeng]

Approx 40%

Is that meaning you get 40% more output from a finned rad, so if I started off with a 700mm high rad, I could go to 700 / 1.4 = 500mm high?

Kev - yes, good point!

If you want to be really energy conscious, go for a double finned of the same width and 600mm high. If you have a condensing boiler, all well and good. If you don't it will pay back when you do get one.

Ive got a mega 2metre double finned under the lounge window. The return temp to the boileris usually lukewarm. The boiler is almost always running in condensing mode. All the other rads in the house are either double finned or double with single fin.

I don't like these little dinky rads they fit in newbuilds. Apart from killing condensing mode cos they have to run at 80c, they just look daft. Longer and wider is better, no pun intended.

Buy the rads from B&Q if you want cheap, but don't buy their TRVs which are sh*t. Get some danfoss RASc's.

 

[very_pointy_ears]

Thanks.

We're recently had to have the outlet temperature of our boiler turned down because it was slamming when it clicked off so I guess this is going to help efficiency too. We certainly noticed a difference in the heating. For starters, the en-suite doesn't get stifling any more and I no longer burn my bum on the towel rail if I catch it getting into the shower

I understand the principles of latent heat of evaporation etc so I won't be asking for a lengthy explanation of how and why etc but I am intrigued about how running at 70C rather than 80C can make that much of a difference to how much it runs in condensing mode (I do have a condensing boiler).

What is condensing, exactly, is it water? I assume this is a by product of the combustion process? Is it that a condensing boiler would tend to condense this back down to water, putting the regained heat (mostly from change of state I presume) into the heated water instead of chucking steam out of the flue? I'm interested to know how running at an outlet temp of 80C would stop this working so much. I'm not challenging what you say - I'm genuinely interested.

I don't buy rads from B&Q

 

[TicklyT]

My understanding is that for the boiler to condense, and recover the latent heat of evaporation from the water vapour generated in the combustion process from the flue gases, the heating return circuit to the boiler needs to be maintained at a lower temperature than is desirable with a non-condensing boiler, where condensation in the heat exchanger may cause problems.

The return temperature can be reduced by throttling the flow rate or reducing the flow temperature. Either way, the radiator temperatures will be lower.

If the radiator temperatures are lower, you need either a larger or more efficient radiator to provide the same heat output.