two pipe direct return system

Bart_5

Thank you Steamhead. I appreciate the feedback you've given me. I'm going to take your advice on the radiator connections and I've also ordered a couple of books (and a brick for the wall) on Dan's site including the "EDR" book. Best regards.

Bart_5

balancing a two pipe direct return system

A customer of mine has a two pipe direct return system on the first floor zone of their heating system. The zone has four large cast iron radiators and a kick space heater. Some years ago they had a fifth radiator removed and installed the kickspace heater. Now they would like the fifth radiator reconnected because the kitchen does not get enough heat. They tell me that the kickspace heater works ok but that when the fifth radiator was connected in the past it never heated well. It will be the next to last radiator on the system. Can I use ball valves on the supply side of the first three radiators to throttle the flow so that more hot water is forced down the main to the last radiators? I would like to put these ball valves in the piping in the basement ceiling.

Steamhead

Was this

a converted gravity system? If so, pipe sizing is critical, even if the system now uses forced circulation.

One common mistake when moving or changing radiation on this type of system is reducing pipe sizes. Gravity systems used large pipes to keep friction loss to a minimum. If you reduce the pipe size to one radiator, it won't get much flow because the water will go to the other radiators where the friction loss is less. Toe-kick heaters don't perform well on this type of system for the same reason.

Pay close attention to the pipe sizes of the various radiators when you go back. I bet you find the problem there.

Bart_5

two pipe direct return system

Thanks steamhead. Yes, I believe this is a converted gravity system. Some one ran 1" copper supply and return mains and tied in these very large radiators with 3/4" copper. I would imagine the original mains and radiator connections were larger. I was wondering if I reconnect this fifth radiator could I do anything so that it will heat better than it did before?

Mike T., Swampeast MO

Do you mean that the mains have been completely replaced in 1" copper? Or just the near boiler mains?

ALL of the radiator branches replaced in ¾" or smaller?

Steamhead

OK, this will be a bit more complicated

with five 3/4" branches off a 1" main I can see why that last rad won't heat. Do you have the EDR ratings for these radiators? If they're less then 100 square feet or so you can feed all of them with 1/2" runouts, and the system should go into balance.

Bart_5

two pipe direct return system

Thanks Mike T. and steam head. Mike T.--Yes, all of the old supply and return mains have been removed and replaced with 1" copper and all the connections to the radiators are made with 1" x 3/4" copper tees. Steamhead--- I don't know how to get the radiators EDR ratings. Can you tell me how to do that? By what your telling me, could't I try installing 3/4" ball valves on the supply line to each radiator and throttle these valves to simulate what you said about changing the connections to 1/2"? or even put 3/4" ball valves on the return sides as well?

Steamhead

EDR ratings

can be found in Dan's book "E.D.R.", available on the Books and More page of this site.

You could put in valves to throttle the flow but there's always a chance someone will mess with them. Far better to set it up in a tamper-proof way. Assuming the rads are small enough, you could simply replace the first two or three feet of each runout with 1/2-inch. That should be enough to do it.