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  1. #1
    Join Date
    Nov 2009

    Default Hot room caused by Cast Iron Radiator


    I have a small cape with a 2 zone hot water system, 1 up stairs, 1 downstairs. The 1st floor zone is all copper baseboard except for 1 Cast Iron Radiator in the Master Bedroom. The radiators are piped in series using 3/4 Pex and Copper. The 1st floor thermostat is in the hall, right outside the master bedroom Door. The problem is that the Master bedroom is 2 - 4 degrees warmer then the rest of the house, and I believe throwing off the thermostat. The thermostat is set to 70, the rooom gets between 70 and 74. The rest of the house is about 68.

    After much reading, my plan is the following:

    1. Move the Thermostat to a more central location on the first floor. I have an Ideal spot in mind.

    2. I am thinking up setting up a bypass loop for the cast Iron Rad by bridging the supply and exit pipes on the rad, and putting a 3 way zone valve at the exit connection. I would be installing a thermostat in the master bedroom to drive the zone valve. I would set the zone valve to open the bypass when my set temp in the master bedroom is reached.

    I guess I am hoping someone can confirm my theories to the best of thier abilities, or sent me in the right direction.

    Thanks all for looking, i look forward to any and all opinions and suggestions.


  2. #2
    Join Date
    Feb 2008

    Default Re: Hot room caused by Cast Iron Radiator


    I agree with your BASIC idea in item #2 to connect a bypass pipe to bridge the existing supply/return piping (this would be done in the cellar,assuming you have under floor access to the piping)---but there is a simpler & much less expensive way to do this instead of a zone valve.

    A standard way of doing this is to bridge the piping in the cellar (is this 3/4" copper tubing??) & install a MONOFLO TEE (diverter tee) on either the left side or the right side of the bridge-- a SHUTOFF VALVE (ball valve or standard radiator shutoff valve) would be installed on either the right side or left side of the radiator in the bedroom for easy access.

    The MONOFLO TEE costs $15, the BALL VALVE costs $8 (a standard radiator valve would cost more like $60)---if you intend to do this yourself, you would have to be able to cut & solder copper tubing (or connect PEX, if it's PEX).

    The thermostat should be left where it is for the time being---the problem seems to be solely in the bedroom with a cast iron rad that is putting out too much heat---the method above would allow you to control the amount of hot water that flows thru the rad & thus control the bedroom room temp.

    Consult the diagram of a monoflo piping system at the site below & focus on just the first radiator---note that the BYPASS PIPE you install in the cellar would have to create a tee at the supply riser and the return riser for the bedroom radiator so you could install a monoflo tee on either the left side or right side of the bypass---an ordinary tee fitting would be installed on the other side---sometimes monoflo tees are installed on BOTH sides of the bypass to increase water flow, but one is almost always sufficient.

    Monoflo tees work on the principle that flowing water in a pipe will TAKE THE PATH OF LEAST RESISTANCE when approaching a tee bypass (like traffic on a freeway will take an alternate bypass road in a traffic jam)---the monoflo has an internal restriction that forces the water to take the path thru the radiator----the ball valve controls just how much water is allowed thru the rad.

    Also Google "Diverter-Tee-Hot-Water-Heating" (with quotes) to get an excellent article by Dan Holohan on diverter/monoflo tees---notice in the piping diagrams in this article how the radiator(s) in the diagrams "stand above" the series piping once the bypass pipe is installed--so that the main water flows thru the series piping circuit, & some is "diverted" thru the rad by using a monoflo/diverter tee valve.

    Please advise if you want more detailed info on a diy install.
    Last edited by NashuaTech; 11-19-2009 at 09:44 AM.

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