how do i drain an old cast iron house radiator?

Answer 1

There should be a drain in the back. If not, you would need a plumber to dismount and drain.

Answer 2

The best way to get water out of the heating system is to find your boiler and locate the inlet and outlet to the pipe that provides water for the heating system. Usually your boiler is in the basement, so if you open up the outlet and drain all the water out of your heating system, the radiator will be nearly empty.

But, BEFORE you do this, turn your boiler off. After you have turned it off (and your thermostat), open the outlet for the heating system while keeping the inlet closed. It is likely that very little water will come out. To get more water to come out, go to the radiator and open the valve to allow air into the system (this valve is about 1/2" diameter and sticks out an inch or two from the top of the radiator). Allowing air to enter the system will release the vaccum in the radiator and let the water drain out from the outlet near the boiler.

Once you're done, close the radiator valve, close the outlet, and open the inlet to fill the system with water. Go back to your radiator and open the valve (you will now be letting the air out, so the water can come back). Once water starts coming out of the valve, close it. Turn your boiler and thermostat back on, and you should have a functioning system!

It's getting harder to find a good plumber that knows how to maintain hot water heating systems like yours, but if you are able to find one, he's worth whatever labor cost he's charging.

Also, a note regarding one of the previous answers: STEAM heat is very different than hot water heat. If you have a system that uses steam (usually only commercial/institutional buildings), there will be A LOT of pressure in the system and any maintenance should be done by professionals due to the small tolerances involved.

Answer 3

Beyond the vent valve and disconnecting the unit from its plumbing, I suggest a check of the piece to see if it has a drain out plug. If it has one, it may be a square head, threaded "BOLT" that allows gravity to do the work for you.

The fact that they are steam powered doesn't mean they can't retain water. That may also be due in part to the release/vent valve thing on the plumbing line, which you might want to replace anyway.

With no offense to another answer, I've been involved with radiators in my younger days, and Paint sold specifically for the purpose is the way to go. Similar in properties to a car engine paint, it won't degrade.

Not knowing at all if your intent is to paint, I've done quite a few, and had to sand blast some that the home owners had applied latex, or enamels too, not meant for high temps.

You might also go beneath the radiator in the plumbing to find a drain out plug, especially if this is a chronic issue.

Steven Wolf

Answer 4

TURN VALVE OFF, BIG NUT THAT JOINS RADIATOR TO THE VALVE PUT A PAN UNDERNEATH AND USE PIPE WRENCH TO DISCONNECT. THERE IS NOT MUCH WATER IN IT SEEING THAT IT"S HOT STEAM THAT GIVES YOU HEAT!!! DO YOU KNOW HOW MANY TIMES I"VE HAD TO DO THIS TO PAINT ????????