Adding basement radiators to two pipe system

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Bcarlson78248

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I have a Buderus gas boiler with a 1940-vintage two pipe system that uses 1" main pipe and 1/2" feeder pipes to supply four 1st floor and four 2nd floor radiators (total of 8 radiators). The system works well to heat the house evenly (630 square feet/floor, located in the DC area).

I want to replace an end section of the 1" main pipe with 1" PEX (end of the line: only feeds two radiators) and move the PEX up higher so it runs through the joists to get better head room. As part of that change I would also like to add one or two basement radiators to the system. I will probably use a Runtal or Myson radiator for the basement, but I have not bought anything yet.

Do I just need to add T's to the new 1" PEX supply and return pipes and connect them to the new basement radiators, or is there more to the installation? Will the existing pump push enough water down to the basement radiators, or do I need to do something to ensure they will heat properly?

Thanks,

Bruce
 

Dana

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It sounds like your system is implemented with mono-flow tees to the different parts of the house, but operated as a single zone? Those tees are not simple tees- they are designed with internal features to impede flow on the 1" to direct a portion of the flow to the local radiator loop, and it sounds like somebody did the heat-loss and flow math to achieve pretty good temperature balance room to room.



You can still add the basement radiators, but use thermostat controlled by valves rather than mono-flow tees. The characteristic changes in heat load with outdoor temperature of basements are very different from that of upper floors, and that nicely tweaked room-by-room temperature balance you have upstairs cannot be reproduced for the basement with mon0-flow tees . But if the basement radiator flow is controlled by a room thermostat controlled valve (or by an adjustable valve on the radiator itself) it will be reasonable. You may have to install a ball-valve between the tees that you partially close to assert sufficient back-pressure on your new radiator loop to get enough flow into the radiators, but as long as the ball vavle doesn't impede flow too much you'll still have pretty good flow & temperature balance on your existing loops.
 

Bcarlson78248

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Your comment about mono-flo T's is where my confusion begins, since I didn't think a two pipe direct return system with all supply and return pipes lower than the radiators would need mono-flo T's. Mine are all cast iron pipes and its hard to tell what kind of T they are.

A little more about my current system
- My two pipe system is routed in the shape of two U's, with the 2nd pipe running within the U of the other.
- The boiler is at one corner of the U and it supplies the outer pipe. The inside pipe is the return to the boiler. Each radiator connection is a T off the supply and a T off the return. There is about 3-4 feet between the supply and return connections for each radiator ( but they are also into two different pipes).
- The boiler has two radiators almost right above it (1st and 2nd floor) and the other six radiators are two at each other corner of the house.

I have disconnected (and capped) the supply and return lines for one side of the U (the side opposite the boiler) to get rid of a low hanging pipe that blocked a window. I could just rerun the lines with PEX and reconnect, and I would have the same system as before. I assume it would still work fine for the 1st and 2nd floor since I have not changed anything other than the type of pipe.

Then I need to look at options for connecting a basement radiator:
1 - T into the supply and return lines running in the floor above and connect the radiator. However, will the water flow down to the new basement radiator? Would a scoop T work to direct some of the water downward? I think most of the new radiators also have an option to use a thermostatic valve to control flow, if needed.
2 - Put a manifold at the point I disconnected the old pipe on one corner of the U, and split the supply pipe into a 1st/2nd floor run for the existing radiators and a basement run for the new radiator. That should increase the flow on the line running to the basement radiator, and I would have the option of adding a thermostat or even a zone pump in that line.

I appreciate any help and suggestions, but keep in mind that I am also trying to keep the approach fairly simple.

Thanks,

Bruce
 

Tom Sawyer

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Honestly, you start messing with a monoflow system and you can screw things up pretty fast. I'd leave that to a professional.
 

Dana

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If it's 100" iron plumbing, they aren't monoflow tees.

Are there valves in series with each radiator to adjust the flow through the radiators? With a ladder topology of radiator-branch rungs, with the supply and a return pipes as the side rails, the closest radiator to the boiler would get most of the flow unless the flow can be throttled back with a valve. With valves on each branch it's possible to tweak them all to achieve good room-to-room temperature balance. But if you're adding basement radiators you still have the issue of having different heat loss characteristics, which means there is no ideal flow balance that works just as well at 50F outdoor temps as it does at 15F.
 
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