Further to my successful attempts to remove the brass valves in my old cast iron rads, I have been unsuccessful in removing the iron bushes these valves were mounted in. Now I'm having a bit of a dilemma;
I can keep trying to get the iron bushes out, using more leverage and heat, but seeing as the rads are about 80 years old I'm thinking they're going to be well and truly seized. I don't want to break the rads getting them out. I can fit bushes within bushes to bring the inlet down to 1/2", ready to take a standard valve, but the rads are currently plumbed for gravity feed - ie connections top and bottom at one end. Is it possible to plumb them in to a ring in this manner, or will the efficiency be affected? If so by how much?
To remove the bushes try soaking around them with 3 in 1 oil and leave overnight. This will (may) work its way into the threads and ease extraction. Otherwise heat the rad around the bush not the bush itself the rads iron will expand and ease extraction.
It is actually better with flow top, return bottom, gravity or pumped.
Hot water entering via the flow is at the top of the rad. Air moving across the rad from the floor, will move across the slightly cooler parts of the rad at the bottom and gradually pick up heat from the rad as the rads temp gets hotter the further up the air goes.
Flow doesn't matter for a pumped system, but return from the bottom is best so the return draws the cooler water out of the radiator. With return at the top, you will be drawing off the hot water which floats to the top; you will be relying on turbulance inside the radiator to get the heat to the rest of the panel. With return from the bottom, hot water entering the radiator floats to the top and expells the cold from the bottom, more rapidly heating the hole radiator. Generally, you want a temperature drop across a radiator, and you get a temperature gradiant top to bottom anyway, so you might as well use this to obtain your temperature drop. Flow can be top or bottom -- if it's at the bottom, the hot water instantly rises to the top anyway in just the first couple of vertical channels.
Interestingly, I notice that with flow and return at the bottom, when another zone kicks in and dumps a load of cold water into the heating circuit, the existing hot rads stay hot and you just get a cold flow across the bottom between the inlet and outlet, until the boiler gets the new volume of water back up to temperature.
I bought some bottom-entry radiators (as opposed to regular side-entry). One of the entries is piped to the top internally before is joins the rest of the radiator. The instructions did actually hint the flow should be at the bottom and return from the top connection, but I deliberately ignored this and did it the other way round, and I'm glad I did. I can only assume the instructions said this so any air would be flusheed out of the radiator automatically, but as I don't have any air in my system, that really was of no consequence. When heating comes on, you get the heat filling the whole width of the radiator working from the top down. If I had done it the other way, I rather imagine I would get one warm end where the pipework is, and then a longer time before the heat made it to the far end of the radiator.
No so. In general the flow in a pumped system is on the bottom for convenience and cosmetic appeal. The work better, pumped or not, when the flow is on the top of the radiator.
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