Cast iron efficiency facts.

[solutions]

Was trying to find some older style radiators for a customer. Closer to 70s with a big tube like round top with little inset welded end caps with bleed valves threaded in to the center of the welded round tube cap. Dtarted looking at sites selling cast iron rads and came across some clestly " unbiased"efficiency "facts" about cast iron radiators.
Check this page out.
Are Cast Iron Radiators An Energy Efficient Radiator?

 

[steadyon]

The thermal conductivity of cast iron is broadly the same as low carbon (mild) steel. However, because cast iron radiators have thicker walls, it takes longer for the temperature on the inside to become (virtually) the same as that on the outside. Thus it appears to heat up more slowly, and will also cool down more slowly. But the amount of heat given off by the surface remains the same as for steel, so its overall efficiency in transferring heat from hot water to a room is the same as carbon steel. It is no more, or less, efficient as a radiator material than steel.

Cast iron radiators normally have a much higher water content than modern steel radiators. Thus there is more water in the system. This has to be heated, and any loss of this heat other than in gainful space heating, represents a loss of efficiency. Thus a high water content system is very likely to be less efficient than a low water content system.

 

[doitmyself]

came across some clestly(??) " unbiased"efficiency "facts" about cast iron radiators.
Check this page out.
Are Cast Iron Radiators An Energy Efficient Radiator?

I really liked this "claim":

Yes the boiler will benefit from cast iron radiators because the temperature of the water that is returning to the boiler is hotter when cast iron radiators are on the system as opposed to modern steel radiators. As the cast iron radiator will hold its heat better and for longer the water in the system will return to the boiler hotter making the boiler more efficient providing better energy efficient heating.

Does that mean that condensing boilers with return temperatures below 55C are a waste of time??

 

[solutions]

I really liked this "claim":

Yes the boiler will benefit from cast iron radiators because the temperature of the water that is returning to the boiler is hotter when cast iron radiators are on the system as opposed to modern steel radiators. As the cast iron radiator will hold its heat better and for longer the water in the system will return to the boiler hotter making the boiler more efficient providing better energy efficient heating.

Does that mean that condensing boilers with return temperatures below 55C are a waste of time??

Yeah that was one of my favourite parts.
Crazy thing is while searching for other sites I came across forums referencing that site as evidence of cast iron radiators superior efficiency.

Complete rubbish.

 

[gassafe]

I've not clicked the link but always found the odd cast iron rad on any job to take ages to heat, I often see them with modern danfoss 15 trv too which must throttle back the flow on them big things!!

 

[AWheating]

load of tosh.

 

[newcastle phill]

Aw beat me to it !

 

[Whyme]

I got shouted down massively a few years ago on here saying they weren't as efficient as modern convector rads..By certain folk.

 

[solutions]

The problem with the website I linked too is it is deliberately misleading and factually incorrect. However the term efficiency and the many facets of efficiency and people's understanding of efficiency doesnt help. In simple terms neither can be more efficient than the other as they can each only give out the energy that is put in. But the speed with which they react and how well they disperse the energy put in to them in to a room as well as there overall size are all important factors that effect comfort.
The increased water volume makes cast iron radiators slow to react and any system they are on slower to respond overall. They radiate heat rather than convect it so heat from them remains more localised to their location. Cast iron absorbs and dissipates heat more slowly so I am not sure how that might affect return temperatures to the boiler certainly modern he condensing boilers lose efficiency with high return temperatures, but then again the increased water volume would have provided greater efficiency for longer when the boiler fires and the whole system is cold. The boiler will also have to fire for so much longer to heat the unnecessarily large volume of system water although all of that energy will end up in thr home it msy raise temperstures beyobd comfort levels as cast iron radiators continue to heat a room long after the Trv has shut the flow down.
The way I see it cast iron radiators simply are not suited to the way modern systems are designed and intended to operate. Their only purpose is to achieve a certain aesthetic. If you want that look you have to accept that the system will likely not be as efficient as it could be with modern convectors. Contrary to the opinions of the cast iron radiator selling website.

 

[Best]

I fitted a couple of cast iron rads in a nice cottage that I was doing all the heating & plumbing.
All the other rads were the Quinn rads that are a cast iron lookalike, but light steel.
All look impressive, but people living there say the cast iron 2 are better because they give out great heat, but also because they keep the room warm for a few hours after heating is off.
Hard to say if the benefits out way the slow heat up & large water content, but got to admit the long lasting heat in the winter can be an advantage. Bloody heavy things though and expensive! I couldn't hardly budge them when moving them slightly into exact positions. Guess they are like Agas, - very expensive, possibly inefficient, but highly desirable, things for the upmarket home for rich customers. Let's face it, - If a house is up for sale, the big selling points are the luxury features, - like it has an Aga, or Cast Iron rads, or a swimming pool, but not of it has normal boring efficient rads.
What would you choose? A Ferrari or a nice efficient Fiesta? :smile:

 

[solutions]

I fitted a couple of cast iron rads in a nice cottage that I was doing all the heating & plumbing.
All the other rads were the Quinn rads that are a cast iron lookalike, but light steel.
All look impressive, but people living there say the cast iron 2 are better because they give out great heat, but also because they keep the room warm for a few hours after heating is off.
Hard to say if the benefits out way the slow heat up & large water content, but got to admit the long lasting heat in the winter can be an advantage. Bloody heavy things though and expensive! I couldn't hardly budge them when moving them slightly into exact positions. Guess they are like Agas, - very expensive, possibly inefficient, but highly desirable, things for the upmarket home for rich customers. Let's face it, - If a house is up for sale, the big selling points are the luxury features, - like it has an Aga, or Cast Iron rads, or a swimming pool, but not of it has normal boring efficient rads.
What would you choose? A Ferrari or a nice efficient Fiesta? [emoji2]

Perhaps sadly the Fiesta would be my choice. Form follows function but function wins over form.

 

[Sparkgap]

I've not clicked the link but always found the odd cast iron rad on any job to take ages to heat, I often see them with modern danfoss 15 trv too which must throttle back the flow on them big things!!

Let's guess: old CI rad, single pipe system, somebody puts on a modern TRV to control it? :biggrin5:
Did a big old manor house four years ago with about 50 new CI rads throughout, TRVs etc, fully pumped system. Worked a treat and looked the part! As said elsewhere, the only issue is the greater water capacity in the system taking a little bit longer to heat up.