Radiant Loop Using Cast Iron Radiators
Hello All. I am Installing a new hydronic radiant heating system in an existing home that is currently "gutted" of most drywall and interior finishes. The home is two stories, about 22 years old, and built with modern materials and methods. I have decided to use cast iron radiators for the emitters and each floor will be its own independently controlled zone on its own loop using a reverse return, 2 pipe system. I have already done a thorough heat loss analysis and sized the radiators required for each room. The loop for the first floor will be in the basement with the supply and return to each radiator going up through the floor. The loop for the second story will be run along/though the second story floor joists between the first floor ceiling and second story floor with the supply and return for each second story radiator going up through the second story floor. The piping for the first floor loop (in basement) will probably be copper, and the loop for the second story will have to be pex since I am going to have to drill each floor joist and "fish" it through each one 16" O.C. My question is: in this scenario how does one get the water from the supply loop up and into the radiators? The floor joists in both cases are 2x10s so the supply water will have to be pushed up about 15 inches into the radiator and radiators are 25" tall so approximately 40" of elevation difference. My guess is If I use regular tees for the supply and return to each radiator the water will never exit the supply loop. How is this typically done? Thanks in advance for any responses.
I will add I have sized and installed several radiant concrete floor slabs that work flawlessly but I have never messed with these cast iron radiators yet.
Comments
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Maybe you could post a sketch because I don't understand your question. The water does not need to be lifted the system is a closed loop. You need a minimum of 4psi at the highest portion of the system. Maintaining 12-15 psi at the boiler should accomplish this.
But I don't think I am understanding your question.
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I think your question is, if you plumb all the radiator supply and return risers with standard plumbing tees off the supply and return loops, will there be enough pressure differential to force the supply water to leave the supply loop at each tee, rise 40" to the top of each radiator above the loop, and drop back down into the return loop 40" below the top of each radiator.
I think the answer is yes, because that's basically how all old cast iron radiators were originally plumbed, except that the second floor rads had longer risers feeding them from the basement instead shorter risers from another loop under the second floor. Those risers from the basement to the second floor are typically hidden inside interior walls. That's how our second floor radiators are plumbed. So if you can site all your second floor radiators on convenient interior walls where you can run long risers inside the walls, you don't need to drill through all the joists on the second floor to run another loop.
The longer risers from the basement to the second floor rads actually help circulation, because they establish a long gravity-assist loop where the long column of colder water in the return wants to fall, and the long column of warmer water wants to rise. So those long risers actually help your flow to second floor rads.
I'm not an expert, so take that with a grain of salt. Pros like @EBEBRATT-Ed will give you better guidance.
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In 2 pipe reverse return the water has to exist the supply pipe because the only way for it to get to the return is thru the radiators. The issue you will run into is balancing. You may want to figure some sort of thermostatic head for each radiator.
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See attached section view of second story. Radiators will be 10 and 12 section with the exception of one room will have an 18 section unit. Second story will have a total of 8 (possibly 9 if I decide to place one in the large landing/hallway) radiators with a total heat load of 28,500 BTH/hr at 99% design temperature.
Correct. Your first paragraph is essentially my question in a nutshell. Thanks.
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I don't know why this was not obvious to me lol. The second I read your reply it made sense to me. The water has to flow through the radiators in order to get back to the boiler…….Duh. OK. my next question would be and you have somewhat eluded to is balancing. Since all the radiators of a given loop are on the same elevation the majority of the water will want to flow through the radiator with the least amount of pressure drop which in this case (I would assume) would be the smallest one installed in the system. How is this overcome or would the difference be negligible since they are all about the same size?
For more information. The loops for each floor will essentially trace the exterior walls and all the radiators will be placed along exterior walls under the windows. Thanks. All good information so far.
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I would still encourage you to put the second floor rads on interior walls away from windows. You can put them on adjacent interior walls nearest the windows. That way you can run risers all the way from the basement through the interior walls, without having to hack your way through floor joists all the way around the second floor perimeter.
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The balancing is easy. Presumably each radiator will have a valve… either a hand valve or a TRV. If it's a hand valve, just… close … it part way if the room is too hot…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
What type of boiler are you using? If it is a mod con, the boiler room piping needs to be considered.
Here is a basic RR with actual balance valves. Those could also be the angle valves on each radiator or a more sophisticated TRV which would give you individual temperature control at each radiator. That could be helpful for rooms that are not used 100% of the time, set them at lower temperatures. T
TRVs act as both a zone valve and temperature control valve.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
My plan is to use an outdoor wood boiler on a constantly running loop to and from the house. The primary loop in the boiler room will be connected to the outdoor wood boiler loop via a flat plate heat exchanger and the secondary loops will be the aforementioned first and second story reverse return loops as well as possible a heated floor in the master bath and future emitter of some type in the garage. I plan to use primary/secondary pumping in the boiler room….
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I'm guessing that you will have a backup boiler to the OWF? If so there are any number of ways to pipe multiple heat source, multiple heat emitter systems.
Some piping and control ideas here. From mild to wild.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Reverse return is inherently self balancing. Yes it will have to be tweaked a little.
I would prefer the rads on the exterior walls where most of the heat loss is.
If you calculate the BTU/HR of each rad and figure out the flow required it should be fine. You could also use a manifold system with balancing valves or thermostatic operators.
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The main advantage of reverse return piping is that it is effectively self balancing. The length of the pipe circuit is the same for every radiator, so the only difference is friction within the radiators themselves; and this is generally negligible.
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Bburd0 -
Yes. I am installing ductwork for air conditioning and the cost difference between an air handler and a propane furnace is almost negligible so I will be putting in a propane forced air furnace as backup for the OWF or for if we travel and nobody is around to feed it wood. Thanks for the link.
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