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aluminium or steel radiator?

roman

pfm Member
A quick question whilst you plumbers are convened:

I need to rejig a room which entails installing a vertical radiator no more than 570 mm wide including valves kicking out approx 5800 BTU's. I found a few steel rads costing rather a lot before discovering aluminium which appears cheaper. Are there any reasons to buy/not buy aluminium?

The remaining rads are steel, fed by a small combi boiler if that makes any difference. Any brands or reliable sellers would be handy as well as guidance on metal.
 
My first thought is corrosion, it seems some aluminium radiators have steel pipework which should make them okay.
 
Corrosion in any water-fed heating system is not what you'd expect from everyday experience as there is no oxygen, so straight-forward oxidation (corrosion, rusting etc.) does not occur. It is why steel rad's gain a bit of black sludge (mainly magnetic iron oxide) on the inside, over years, but rust like bar stewards if something like the bleed valve weeps. Besides, even ignoring any Al rad's, any normal system will very highly probably contain steel, cast iron, copper (held together with lead or, more recently, tin solder), stainless steel and brass.

Despite being called radiators, the things that go under this name actually heat a room primarily by convection. That being so, it is very hard to believe that some of the benefits claimed for Al rad's are actually anywhere near significant, even if they exist at all. It would not be the first time that a standard test poorly represents something in the real world - maybe the tests to calibrate rad's are another case?
 
Aluminium radiators are usually more expensive than their steel equivalents, but if you have found one which suits your purpose at a good price I don't see why you shouldn't just go ahead and fit it. Decent ones certainly look better than steel, which is why architects love them.
 
Not wanting to, er, generate any heat, but I have friends who tell me that their hifi sounded better when they junked a steel rad for an aluminium one. Their speaker cables ran right past the radiator, and the suspicion was that the ferromagnetic steel one drew a little energy out. An Al rad restored the dynamics.
 
Corrosion in any water-fed heating system is not what you'd expect from everyday experience as there is no oxygen, so straight-forward oxidation (corrosion, rusting etc.) does not occur. It is why steel rad's gain a bit of black sludge (mainly magnetic iron oxide) on the inside, over years, but rust like bar stewards if something like the bleed valve weeps. Besides, even ignoring any Al rad's, any normal system will very highly probably contain steel, cast iron, copper (held together with lead or, more recently, tin solder), stainless steel and brass.

Despite being called radiators, the things that go under this name actually heat a room primarily by convection. That being so, it is very hard to believe that some of the benefits claimed for Al rad's are actually anywhere near significant, even if they exist at all. It would not be the first time that a standard test poorly represents something in the real world - maybe the tests to calibrate rad's are another case?
One thing to remember is to keep the aluminium out of contact with other metals such as Fe, Cu, Pb as it has a high electrode potential -1.66V. If in contact with those other metals the aluminium will act as a sacrificial anode and corrode away fast thus protecting the lower potential metals from corrosion. In other words it forms a battery and the aluminium will dissolve and create the electrical current.

Lumps of zinc are often used to protect the iron hull of ships.

Cheers,

DV
 
Not wanting to, er, generate any heat, but I have friends who tell me that their hifi sounded better when they junked a steel rad for an aluminium one. Their speaker cables ran right past the radiator, and the suspicion was that the ferromagnetic steel one drew a little energy out. An Al rad restored the dynamics.

Did it improve further after warm-up?
 
One thing to remember is to keep the aluminium out of contact with other metals such as Fe, Cu, Pb as it has a high electrode potential -1.66V. If in contact with those other metals the aluminium will act as a sacrificial anode and corrode away fast thus protecting the lower potential metals from corrosion. In other words it forms a battery and the aluminium will dissolve and create the electrical current.

Lumps of zinc are often used to protect the iron hull of ships.

Cheers,

DV

I would assume aluminium radiators take this into account - domestic circulated hot water heating is either copper or PEX piping. If the aluminium radiator cannot be connected directly to copper piping one would assume this would be clearly pointed out. Maybe the couplings are brass, as is used to join galvanized pipe to copper to prevent corrosion.
 
One thing to remember is to keep the aluminium out of contact with other metals such as Fe, Cu, Pb as it has a high electrode potential -1.66V. If in contact with those other metals the aluminium will act as a sacrificial anode and corrode away fast thus protecting the lower potential metals from corrosion. In other words it forms a battery and the aluminium will dissolve and create the electrical current.

Lumps of zinc are often used to protect the iron hull of ships.

Cheers,

DV
While we are at it, make sure you keep any mercury away from aluminium.


This is weird and cool at the same time and the reason why you can't take mercury on an airplane.
 
Amalgams. Takes me back to when I was a Chemistry teacher. Aluminium is a highly reactive element and its the hard oxide coating that protects it from corrosion. The process of anodising builds up a hard thick oxide layer that can absorb dyes during the process. Salt water removes the protective coating and the metal soon starts corroding away. We used to see this at the seaside with those old big H aerials and after a few years the bits started falling off.

I used to demonstrate a mixture of aluminium powder and iodine. Nothing happens until you place one drop of water onto the mixture. We end up with a flaming volcano with brown/purple fumes ............. ah those were the days.

Wadda ya no! I found a whimpish version on the tube


Cheers,

DV
 
You need to be adding inhibitor with aluminium rads. Personally i'm not so keen on them. I prefer a system with steel rads, copper tubing and a boiler with stainless steel heat exchanger with absolutely no chemicals added. A Spirovent deaerator is an excellent product.
 
Worcester Bosch Heat exchangers are aluminium and Valliant use SS heat exchangers.

Don't know if WB still advise this but they used to recommend no higher than about 8.6ph (alkaline) in the system water.

See Ellenor's post re inhibitor.
 
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Worcester Bosch Heat exchangers are aluminium and Valliant use SS heat exchangers.

Don't know if WB still say advise this but they used to recommend no higher than about 8.6ph (alkaline) in the system water.

See Ellenor's post re inhibitor.
Yes. You need it mildly alkaline with Al to prevent serious corrosion but not too high because of scale formation. Typical tap water should be OK except during hot periods when sometimes a lot of chlorine is added to kill algae,

Cheers,

DV
 
Thank you all, that's some very useful advice. I'll look into if further. So far it appears aluminium is cheaper than steel, but the potential corrosion issues will probably decide the matter.

Cheers,

Roman
 


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