Repipe supply & return gravity feed system

hello 

I am planning to convert my 2 pipe hot water heating system to a manifold homerun. I will run 1/2 oxygen barrier pex to and from each radiator back to the boiler. The main purpose of the project is to get rid of the low hanging 1-1/2 black iron pipes in my basement. My main question is, can I keep the expansion tank/circulator/low water cutoff in the same location. I basically would like to sweat 1-1/4 manifold above the gate valves on both the supply and return piping (about 2-3 feet above the boiler) . I included a picture for comments. Any advise would be greatly appreciated  

I follow your logic completely. Your idea is sound. In the redesign of the near boiler piping I recommend Pumping away from the expansion tank as Bob recommends Furthermore the expansion tank should be located on the supply pipe (Hottest pipe) on the system with an air vent located there also A Microbubble air vent works best like Sparco-vent or Spiro-vent or any or the other brands available. Of course your PEX tubing will only move about 1.25 GPH to each emitter. If you have any large radiators that require more than that you might need to do that one in 3/4" PEX. How to know if your emitters need more than 1.25 GPH? as a rule of thumb, 1.25 GPH will move a maximum of about 12,500 BTU per hour. A radiator that can emit (is rated at) 10,000 BTU/Hr will have more than enough heat delivered by 1/2" PEX tubing. If a radiator can emit 20,000 BTU/Hr. then 1.25 GPH can only deliver 12,500 BTU/Hr the 1/2" pipe can not deliver all the heat needed to reach the capacity of that radiator. The space served by that radiator may not get enough heat. If however you feed that heat emitter with 5/8" or 3/4" PEX, more heat can be delivered to the radiator. Bottom line... Are any of your radiators so big that they have 6 legs (2 legs at each end and 2 in the center)? If not then you probably can use 1/2" PEX on all of them

hot_rod said:

Hard to tell exactly which way things are flowing. Ideally you want the circulator to be pumping away from the expansion tank connection. It's fine to pump into the boiler, as long as the tank connection is up stream. Maybe that is how it is now? as the pressure temperature gauge is usually in the supply pipe. What I don't see is a good air separator? You could get a vertical style, install it above the lowered circled gate valve, assuming that is the supply out of the boiler. A step further would be to add a motorize mix valve to provide some outdoor reset. And consider a delta p circulator upgrade if you zone those home runs, or TRV them. What size is the boiler or what is the total GPM you need for the radiators?

hot_rod said:

Better picEdTheHeaterMan said:

hello 

I am planning to convert my 2 pipe hot water heating system to a manifold homerun. I will run 1/2 oxygen barrier pex to and from each radiator back to the boiler. The main purpose of the project is to get rid of the low hanging 1-1/2 black iron pipes in my basement. My main question is, can I keep the expansion tank/circulator/low water cutoff in the same location. I basically would like to sweat 1-1/4 manifold above the gate valves on both the supply and return piping (about 2-3 feet above the boiler) . I included a picture for comments. Any advise would be greatly appreciated  

I follow your logic completely. Your idea is sound. In the redesign of the near boiler piping I recommend Pumping away from the expansion tank as Bob recommends Furthermore the expansion tank should be located on the supply pipe (Hottest pipe) on the system with an air vent located there also A Microbubble air vent works best like Sparco-vent or Spiro-vent or any or the other brands available. Of course your PEX tubing will only move about 1.25 GPH to each emitter. If you have any large radiators that require more than that you might need to do that one in 3/4" PEX. How to know if your emitters need more than 1.25 GPH? as a rule of thumb, 1.25 GPH will move a maximum of about 12,500 BTU per hour. A radiator that can emit (is rated at) 10,000 BTU/Hr will have more than enough heat delivered by 1/2" PEX tubing. If a radiator can emit 20,000 BTU/Hr. then 1.25 GPH can only deliver 12,500 BTU/Hr the 1/2" pipe can not deliver all the heat needed to reach the capacity of that radiator. The space served by that radiator may not get enough heat. If however you feed that heat emitter with 5/8" or 3/4" PEX, more heat can be delivered to the radiator. Bottom line... Are any of your radiators so big that they have 6 legs (2 legs at each end and 2 in the center)? If not then you probably can use 1/2" PEX on all of them

hot_rod said:

Hard to tell exactly which way things are flowing. Ideally you want the circulator to be pumping away from the expansion tank connection. It's fine to pump into the boiler, as long as the tank connection is up stream. Maybe that is how it is now? as the pressure temperature gauge is usually in the supply pipe. What I don't see is a good air separator? You could get a vertical style, install it above the lowered circled gate valve, assuming that is the supply out of the boiler. A step further would be to add a motorize mix valve to provide some outdoor reset. And consider a delta p circulator upgrade if you zone those home runs, or TRV them. What size is the boiler or what is the total GPM you need for the radiators?

Yes an air purger is best located at the hottest point to work efficiently. But no reason the expansion tank needs to be at that point. The expansion tank, and the circ on the return to that type, low pressure drop, boiler is fine. And they live, maybe longer and happier, in a cooler fluid on the return. The fill valve also wants to be at the expansion tank connection, the PONPC. A Webstone purge/Ball Valve, shown in this drawing at the circ would be a great purge point for the entire system and isolation for the tank/ fill valve and one side of the circulator.