Using PEX for manifold-to-system supply/return piping


Old 07-22-19, 07:44 AM
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Using PEX for manifold-to-system supply/return piping

My 1950s 1,500 sq ft ranch is fitted with 100’ of baseboard convectors, 75ft on the main floor & 25ft in the basement. The baseboards are double-pass convectors with ˝” copper pipework. There are 2 zones, main floor has 5 loops with one loop used for the basement.

The original installation featured four 9’ convectors mounted below the floor joists to warm the hallway and bedroom floors. 2 of these convectors were relocated to the basement walls during a 1970s finished basement project. This basement zone is now rarely used.

The house is equipped with reasonably effective storm windows, but the exterior walls are uninsulated. The attic is lightly insulated with plans to bring it up to current air sealing and R-value standards.

My heat loss calculations suggest the existing conditions would require about 60K btu.

The existing boiler is a 1970s era Burnham with an AGA rating of 210,000 in and 168,000 out. My heating season natural gas bills average $160/mo…OUCH!

My plan is to replace the boiler and direct fired water heater with a Burnham ES2-4 77K Btu boiler with outdoor reset and 30 gal HTP SuperStor indirect. At 5,200’ elevation, this boiler is de-rated by 12% to 67,760 Btu.

While planning the installation I have discovered a few indications of past leaks, especially in the old distribution manifolds. The brass supply and return manifolds looks like candelabras – 1” inlet with five ˝” outlet ports. The casting includes what appear to be butterfly valves. These valves, which I suspect were intended to throttle the flow thru the unequal lengths of supply piping, have leaked in the past with traces of corrosion evident.

Replacing these manifolds will require considerable pipework modifications with 3 or 4 els added to each supply and return pipe…in relatively tight positions. Alternatively, I’m considering using 2 Sioux Chief pre-fab 1” x ˝” copper manifolds with O2 barrier PEX to connect to the existing supply and return pipes. This would allow me to simply cut out the existing candelabra manifolds, solder PEX fittings to each pipe and make a clean, easy connection. Good idea…or, not?
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Old 07-22-19, 12:52 PM
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The pre-made manifolds work well as long as the take-off pipe sizes are of the correct sizes. The 1" is of the proper size for up to 70k DOE output.
I believe your heat loss is off a bit, probably more like 50k.
Oxygen barrier pex is OK to use

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