Repiping Steam Radiators to Hot Water

Unknown

OK Patrick, I got ya now, that type-of valve is not very common here. Thanks.

Patrick Suiter

Repiping Steam Radiators to Hot Water

I was at a job site where existing steam radiators were being converted to hot water. Pneumatic thermostats controlled normally open valves on each radiator. A new reverse return piping loop was already complete, with take-offs from overhead mains on three floors. The CI push nipple style radiators were re-used, having a new high side air vent installed on each. The contractor said the "correct" piping for this conversion was to install a supply side valve on the high side, pushing water down to a return outlet on the low side. That certainly made the conversion easier, since each radiator had a control air tube at the high side inlet from the original steam valve. I am not sure if this arrangement is okay, not so good, or irrelevant. Comments?

Patrick Suiter

Repiping Steam Radiators to Hot Water

Okay, experts: Please offer your sage advice...

I was at a job site where existing steam radiators were being converted to hot water. Pneumatic thermostats controlled normally open valves on each radiator. A new reverse return piping loop was already complete, with take-offs from overhead mains on three floors. The CI push nipple style radiators were re-used, having a new HIGH side air vent installed on each. The contractor said the "correct" piping for this conversion was to install a supply side valve on the HIGH side of each radiator, pushing water down to a return outlet on the LOW side. That certainly made the conversion easier, since each radiator had a control air tube at the high side inlet from the original steam valve. I am not sure if this arrangement is okay, not so good, or irrelevant. Comments?

Brad White_9

OK, I'll bite...

I see no clear advantage or disadvantage to either way; the differences are mostly academic that I can see.

If you supply top on one side and return bottom of the other, you will get pretty even flow through each of the tubes/columns. Essentially a reverse-return flow pattern. The advantage I see is that the hottest water sees the warmest leaving air as far as the convective portion goes. Also, the gravity effect of descending cooler water is enhanced. Like I said, big deal.

If you reverse this, supply low and return high, this has been traditional in coils for it forces the air out and up. (Really thin advantage, you are venting it all out anyway!). You also get the reverse-return even-flow effect. To a lesser extend you are pre-warming your incoming air and the top water will be cooler than the other way, so you do not have as high a delta-T between water and air before the send-off.

Yawn.

There may be other advantages and I will stand by for others.

Unknown

Patrick

You lost me a bit with the word "pneumatic", I`m going to assume you mean TRV`s on each rad. Not moving the "inlet" lower and the "return" higher(since its overhead), could cause "air-binding" problems, but seeing as how he installed vents(auto I hope), it should work. But that`s alot of vents!

Patrick Suiter

Brad, the yawn says it all. I appreciate your comments. This project will go live any day...soon to provide its own answers.

Patrick Suiter

Actually, small VP525 valves were on the steam inlets before. I don't know what was used as a replacement on the water conversion. The pneumatic tube from a Reverse Acting stat would be easily connected to a valve at the same location. I wasnt' sure about air trap issues. going from high to low and back up to overhead mains.