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HW Radiator Piping Options?

jkatzjkatz Member Posts: 3
Hello, I would like to get another opinion on this question: We are using new replacement slenderized tube radiators for a hot water system. (6 tube, various sizes). We see on the cutsheet/catalog page that the recommended piping is to use the bottom taps for both supply and return. While this makes sense, we have a few upfeed radiators, where due to existing conditions, the plumber cannot fit the elbow so close to the rad. to use the bottom connection on both ends (limited by ex. radiator enclosures). Question is, what would happen if we did the following, Supply in the top, and Return out the bottom (on opposite end of course). I suspect it would work similar, but curious if anyone has experience with this before? In addition, Contractor has asked if they can use Top supply, and Top Return, however, in my opinion, this could derate the radiator quite a lot? DO you agree? Appreciate any help anyone can provide.


  • JohnNYJohnNY Member Posts: 2,432
    The one thing you don't want to do is "top supply, top return".
    The hot water will skate across the top and never mix with the cooler water below. Let the water move diagonally through the radiator one way or another or across the bottom like the manufacturer suggests. Two bottom connections will allow the water to enter and due to buoyancy changes, will rise to the top and back down and out. Just don't over pump it. All good!
    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is the Boilers and Hydronic Heating Systems Course Instructor at NYC's Mechanics Institute, a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
    John also oversees mechanical installations and maintenance for metro-area clients with his family's company, Gateway Plumbing and Heating along with his brother/business partner.
  • jkatzjkatz Member Posts: 3
    Thank You for the response!
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