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Reducing pipe size on hot water radiators

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MikeG
MikeG Posts: 173
in THE MAIN WALL

My son is reinstalling 2 cast iron radiators on a hot water system. They were removed for remodeling. Previous owners in the 80s removed all but 3 and put in finned baseboard. The 2 rads are on a west wall, good location. The original piping was convoluted. The rads are 38"L x 19"H x 7"W, 22 sections. In the crawl space there are Taco monoflow tees. The original iron pipe was 3/4". Can I use 1/2" Pex-Al. I know it's rated high enough for the Temps he is running. It will make life a lot easier getting them back in service. They were capped of fo a couple years. Just looking for ideas, options etc. I have the pex, fittings and tools. Thanks. Mike

Comments

  • pecmsg
    pecmsg Posts: 7,561

    if your running 1/2” why not just run 3/4”?

  • Steamhead
    Steamhead Posts: 18,915
    https://forum.heatinghelp.com/discussion/comment/1905536#Comment_1905536

    Agreed. Especially with Monoflo tees- ISTR Taco called them "Taco-One Venturi Tees". The reduced pipe size will create too much resistance and water won't flow through the rads like it should. Don't reduce the pipe.

    Co-Founder, All Steamed Up, Inc.

    Semi-retired

    Baltimore, MD, USA

  • MikeG
    MikeG Posts: 173

    The short answer is I have a lot of 1/2" Pex-Al. I didnt want to get a bunch of 3/4 " if I didn't have to. Each take off is less than 2 feet. It's easier to make a sweep into the radiator union ells over trying to put iron pipe back. These two radiators set about 6 feet apart under windows. I'll have to see what size the main pipe is. The third radiator is on the same main pipe in a different room and was 1/2". That one we put back. All the finned baseboard comes off the monoflow tees when they removed the original radiators. I'll see what he wants to do.

  • PC7060
    PC7060 Posts: 1,959
    edited 9:47PM

    Buy oxygen barrier three-quarter inch PEX. It’s not that expensive and there’s no need for P – AL – P.

    if you want to use the half inch lines, do dedicated runs to each radiator

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