Why are radiators made of cast iron

[krw]

Oxides of copper and aluminum are not porous, either (oxidation stops quickly). Rust is.

[Ed Pawlowski]

wrote

Where is the heat wasted? If the house is constantly losing heat on a cold day, the heat from the radiator is just helping to maintain it for a longer time between cycles. The perfect system it to balance the heat loss with the heat makeup of the radiators to maintain a perfect temperature all the time.

[Doug Miller]

Oxidation of iron stops pretty quickly, too, as long as it stays dry.

[Nonny]

The cast iron radiators are most likely used on a single pipe system, along with an open sump. Air is introduced at the sump and if the water isn't treated, it can cause excessive rusting. Yes, closed systems are different, though.

[krw]

Heat loss is proportional to the temperature difference. If you leave the difference higher, longer, the loss is more than it would have been if the temperature came down more quickly. Nothing for nothing.

The higher the temperature (difference) the higher the loss.

[krw]

We are talking about hydronic and steam heat systems.

[Ed Pawlowski]

OK, that is true and complies with the laws of physics. But where is the waste? If I keep my house at 70 with copper, I use the same heat as keeping my house at 70 with cast iron, cast aluminum, or hollow chicken bones. 70 degrees is 70 degrees and it takes the same Btu to maintain that temperature over outside ambient no matter the source.

Only way you'd have waste from the higher heat loss is if the temperature inside overshot the thermostat. That is the fault of system design or bad equipment, not the heat transfer material. Cast iron allows for a nice steady heat.

I don't see any loss.

[Doug Miller]

Yes, and there -- in closed systems, at least -- oxidation stops pretty quickly, too, as soon as the oxygen is used up.

[chaniarts]

hmm. webster at

1b doesn't agree with you. i think you need to take it up with them :)

[chaniarts]

really? aluminim oxide can be formed as a powder, which is pretty porous. never had a pinhole in copper pipe show green, and still leak?

[Doug Miller]

Nice try. It says "comparable coating". Copper oxide and aluminum oxide aren't even remotely similar to rust.

[harry]

Unfortunately not true. Due to the dissimilar metals in the system, electrolytic corrosion takes place without oxygen, the results are black iron oxide and hydrogen gas. Due to the development of condensing boilers made of aluminium/ stainless steel the problem is worse than ever. Chemicals to prevent this are vital in such a system.

[harry]

Not true. Well maybe in America where things are still primitive.

[harry]

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hak

lshak

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There are such things as one pipe steam heating sytems where the steam pipe is run to fall back from the radiators to the steam boiler. The condensate runs in the opposite direction to the steam flow (in the same pipe) back to the boiler. I think they were popular in America at one time I think. It's a simple sytem but control is poor and noises are often generated. The steam pressure is low, the boiler is usually cast iron and extremely inefficient.

[harry]

I ran a huge sytem personally before I retired. Steam raised was used to generate electricity. The exhaust steam from the turbines was used for heating with direct steam radiators. The pressure in them was 0.6 bar (absolute) ie -8psi in your parlance.

[harry]

:

ote:

lshak

illshak

on.- Hide quoted text -

The hall marks of efficiency are the three T's. Time, turbulence and Temperature difference. The lower the temperature of the heating medium (ie water in this case), the greater the energy transferred from the burning fuel to that medium. For an excercise, explain the other two T's.

I had a look round the last time I was in America. Appalling. You are thirty years behind European standards.

[harry]

The loss arises through the overshoot. If you have a sytem that can exactly matches heat requirements its possible to make very significant savings.10-15% would be pretty typical.

[Doug Miller]

obviously you're not worth responding to.

[Tony]

Yes, that's what I'm talking about. With steam coming out some of the radiators. It's always above atmospheric pressure, not much, I think 2 to 5 pounds. Pipes clang away. I worked at a place that had that heat about 25 years ago and while I was there he had a new boiler installed. The old boiler was very inefficient, originally coal converted to oil. The new boiler was about 1/4 the size and paid for itself in about 3 years.

[Tony]

In the house I grew up in my father had to open up a wall to find a leak. A leak in a copper pipe, lot's of green. I think it went way past the point of a pinhole and couldn't seal itself anymore.