replacing black pipe with pex

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Old 10-11-11, 06:07 PM
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replacing black pipe with pex

Hello,

I'm new to the forum.

I have removed the iron pipes from my 100+ year old house and replaced with 3/4 pex. The old system was a "branching" type, with one pipe coming from the boiler, then branching into three and then branching once more before reaching each radiator. I replaced that with two 1" copper manifolds with 3/4" outlets/inlets. Each radiator now has its own supply and return directly back to the manifolds (with valves).

My question is, do I need to replace the pump? It is not very old but it seems bigger than the ones I've seen in other manifold systems. I am not changing te size or number of radiators.

Please help - winter is coming!

John in Toronto
 
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Old 10-11-11, 06:51 PM
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What size boiler and what is the heat loss?
 
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Old 10-12-11, 06:49 AM
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The boiler is 117000 BTUs. As for heat loss - well it's a 2000 ft2 house with almost no insulation and some original windows. In any case, the heating was sufficient before I made the switch. I am just wondering if the change in piping will require a different pump.

John
 
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Old 10-12-11, 07:21 AM
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What's the pump manufacturer and model number?

Sizing a pump, if you want to do it in a theoretically correct way, is tricky - and much more info would be needed than you provided. I would leave the pump alone and see if it performs satisfactorily. If it's way oversized, there will be flow noise in the piping system. Changing the pump later wouldn't be a major task provided you have isolation valves on each side of the pump (otherwise you'd have to drain the system). If you don't have such valves, now would be a perfect time to install them - use full-port ball valves.

If you post some photos, we might get a better idea of your situation.
 
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Old 10-12-11, 12:34 PM
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It's an Armstrong (model E6312?). The following is written on it: 3.6 FLA, 1.75 SF, 4.7 SFA, 48 FR, 1/6 HP, 50 AMB.

I have 10 runs of 3/4" pex serving 10 rads in a 3 story house. The longest run is about 30'.

I ran the system and there was some noise. I also noticed the supply pipe was only lukewarm after a couple of minutes of running. Usually it heats up much faster.

John
 
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Old 10-12-11, 01:04 PM
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Your system is probably air locked. You'll need to stop running the pump before you damage it, and vent the air. Photos would help us suggest how if you are unsure. Show near-boiler piping, expansion tank, air elimination devices, and any fittings on the ends of the radiators. What does the pressure and temp gauge show on the boiler?

Couldn't find the model number at armstrongpumps.com

Did you use special oxygen barrier PEX? I hope so.
 
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Old 10-12-11, 05:14 PM
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I asked a heating guy to come over tomorrow. He converted my neighbour's place to pex. I did use the oxygen barrier pex, btw.

I will let you know what he says.

John
 
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Old 10-13-11, 05:11 PM
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So...it turns out that there are some air locks. I did everything correctly but I did not realize that dips in the line could trap air and cause problems. I am in the process of removing the dips and purging the system. The pump is a good size for the system. If you have any tips for me before I finish the job, they would be most welcome.

Will let you know how it goes.

John in Toronto
 
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