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Re: Replacing Steam Radiators with H/W baseboard

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Posted by joe on May 21, 2006 at 12:30:37:

In Reply to: Re: Replacing Steam Radiators with H/W baseboard posted by Steve Kelleher on May 21, 2006 at 01:21:36:

My brother had the same problem as you regarding installing 1/2" piping up and down from the basement to the second story. He had me ask Heatpro a question or two regarding this.

Heatpro suggested using the old steam piping as chases for the new 1/2" tubing. We did find a problem with this however, because of the sizes of my brother's steam piping. Heatpro also advises on his websites that the hole containing the hot water piping must be about 1/2" greater than the piping, to allow for expansion. My brother's old steam pipe risers are all 1" and 1-1/4". To put two pieces of pex piping into either 1" or 1-1/4" piping does not permit the extra 1/2" that Heatpro recommends. If your piping is bigger than that, you can use the old steam pipe as a chase with enough clearance for expansion. You can also use one 1" or 1-1/4" old steam pipe for only one supply or return pipe.

There was also another issue of support if these old risers are to be used as pipe chases. The risers in my brother's house are literally supported by the elbows in the basement and the basement piping. He has three stories. If we disconnected every radiator on each story of an old steam riser, the pipe would be solely supported by the piping in the basement. There are no pipe rests or clamps in my brother's house to support these old risers on each story. The entire basement piping supports the risers going up through the house. When converting to hot water, we will remove all that big 3" overhead piping in the basement, that is secured to the overhead beams with heavy chains and clamps, that supports the risers throughout the house. Without this support, the old 1" riser will drop until it rests on something like the foundation wall. If a straight peice of pipe with its opening rests on the foundation wall, you can run the pex down and it will terminate at the foundation wall. To lift that pipe up and turn the pex into the foundation wall, you would need to support that old heavy pipe with pipe rests on each story to prevent the pex from getting crushed. If the old pipe terminates against the foundation wall with an old elbow attached to it, then the pex can be turned out into the basement.

If your riser is 2" and is well supported to act as a pipe chase after being disconnected from the overhead steam piping in the basement, then you can run two 1/2" lines through the pex. A house your size may only have 1" or 1-1/4" risers. Be careful to check that.

Me and my brother decided to remove the old risers and use the holes as chases for the new piping. A few holes we wont use because it may be 6" away from the corner of the room and 1" away from the window. We are patching up those holes and moving our new piping about 5" over, so that we can make a little vertical box in the corner of the room.

Heatpro's heating estimation will give you the btu requirements for your rooms, which then determine the number of baseboard feet you will need. You can refer to slantfin's website for ratings (BTU / ft) at different temperatures. After calculating this stuff a few different times, I found that the feet of baseboard required almost always correlated to the lenght of the exterior walls. For example, if you have a room that has 13 feet of exterior wall and the other walls are interior, the lenght of baseboard required was about 13 feet. With a room with one exterior wall at 14 feet and the other at 16 feet, the lenght of baseboard required was about 30 feet. If I was installing baseboard rated at 180 degrees, I would not even waste my time doing calculations. I would know that the amount required is roughly equal to the amount of exterior wall.

Remember what Heatpro said about optimal water temp for the condensing boiler is about 140 F. I cannot find baseboard ratings for 140F. Furthermore, based upon the rule of thumb, (which may be valid or invalid) that I need an equivalent in feet of about the lenght of the exterior wall at 180, I could conclude that I would need even more baseboard feet to run my system at 140. That may be alot of baseboard. Remember what Heatpro said about cast iron radiation at 140 F, and that the existing cast iron radiators could likely heat the room at
140F. You may want to consider eliminating some of your cast iron radiators.

Heatpro had also advised me to install the supply branch in the top of the radiator and the return branch in the bottom of the radiator. I noticed on my old cast iron radiator that I have a thing that looks like a screw above the top 1-1/4" threaded opening of the radiator, which will be my supply. Someone told me that it is not a screw it is a tapping for 1/8". I will try and remove it and put my air vent up there, just above my supply line. Also if the supply has an elbow entering the top, you can install a special elbow with an air vent installed on it.

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