Shared pipe sizing

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Old 08-08-11, 07:30 PM
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Shared pipe sizing

I'm planning on adding a zone for an indirect water heater to my current 1 zone setup. I will be piping the indirect with 1" pipe and it will be wired for priority. The current zone is 3/4" and at most I will be adding 1 more 3/4" zone in the future. Is it ok to pipe the shared piping with 1" pipe since the indirect will be on priority?
 
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Old 08-09-11, 05:01 AM
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Yes it is OK. You can supply 2-3/4" zones off of one 1" pipe. What is the DOE output of the boiler?
 
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Old 08-09-11, 05:53 PM
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The DOE output is 100,000.
 
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Old 08-09-11, 07:37 PM
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Your boiler will probably be short cycling due to being over sized. A 3/4" pipe can carry about 40,000 btu's but may release less than that dependent on the amount of radiation. If the 3/4" loop has 50' of baseboard @ a water temp of 180f will get rid of approximately 30k btu's with a DOE of 100k. The indirect will give you a decent run time.
 
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Old 08-11-11, 07:39 PM
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I believe you are correct with the boiler short cycling. The boiler is only 10 years old so it is not going anywhere. The reason for asking the initial question about shared pipe size is that I was going to reconfigure the boiler to pump away from the boiler and add a good air eliminator. The 1" air eliminators seem to be significantly cheaper than a 1 1/2" model. If necessary I will go ahead and keep the shared piping at 1 1/2".
 
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Old 08-11-11, 07:58 PM
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I don't think keeping the 1-1/2 is going to prevent any short cycling... I think what rbeck is saying is that with two small zones pulling heat out of a 'too large' boiler that they won't be able to move the heat to the home as fast as the burners are putting the heat back into the water. It might be a bit 'ghetto', but you could leave most of the 1-1/2 in place and just reduce down to 1" for the rework, then back up again to 1-1/2.
 
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Old 08-11-11, 08:11 PM
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I was thinking about going from the current 1 1/2" supply pipe into a 1" air eliminator and continue with 1" into each of the pumps.
 
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