Cast Iron Radiators

Richard Nelson

In changing over a gravity system to a new loop system. After cuting out all of the large pipes (because they hung to low.) Is there a rule of thumb. Supply goes to the top of the radiator and out of the valve at the bottom. Or supply in the bottom of the radiator and out of the bottom. There is a mix in my house of both styles.

Mike T., Swampeast MO

Cast iron radiators should NOT be installed in a one-pipe loop! Rads down the loop will run progressively colder, have significantly less output and you'll RAPIDLY run out of usable heat alltogether.

You can use a one-pipe diverter tee system, but these must be VERY carefully engineered and it's extremely unlikely that the radiators will be properly sized. Radiators in diverter tee systems must be sized to deal with the gradually reducing supply temperature available as the "chain" progresses. Unless this was one of the rather rare one-pipe gravity systems, the radiators will NOT have been sized this way and you will have poor results.

Doesn't really matter where you place the supply/return pipes as long as they're on different sides of the radiator. If you put the supply at the top and install the hand valve there, it makes for adjustment without stooping so far and is also ideal should TRVs ever be installed. Best to use the old piping locations as the alternate location plugs are VERY difficult to remove.