Help setting max space heat capacity for Navien NCB 240E

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Dobson

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I need some help understanding how to set my Navien NCB 240E. Most importantly, where I should set the max space heating capacity (50% - 100%). I have a 2,800SF house with 116 feet of fin-tube and 3 zones. I have the outdoor reset setup to the preset fin tube setting. Now, I see that my max space heating capacity is set to 100% which I'm sure is overkill for my home. This thing has been running terribly inefficiently and I'm trying my best to get it dialed in a little bit. Any help is much appreciated. Thanks!
 

John Gayewski

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Why don't you try turning it down and see how uppity like it? Then if you don't just turn it back.

Why do you think it's running inefficiently?
 

Fitter30

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Any condensing boiler is 95%+ efficient when return water temp is below 130° above 87%. Need some pic of the boiler, piping and pumps to see how it's piped. Fin tube doesn't really put out much heat under 120° supply. If water temp is set at 150° and if 70% keeps that temp it won't run at 100%. If you know the pipe and fin size can tell you how many btu at a temp or brand and model. Would like to know the supply and return water temps of the individual loops?
 

mrmackster

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I am not a plumber, but from my experience you can't really rely on the presets on the Navien unless things were designed perfectly. You will need to do load calculations for each zone, figuring out if your pumps are pumping the right GPM, figure out how many feet of slant fin you have, and then manually configure the outdoor research based on those inputs.
 

jac04

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The max space heating capacity only limits the max firing rate when the unit is trying to achieve its target baseboard water temperature. It will throttle back to whatever % firing required after that. Your issue is likely that you are running return temperatures that put you way out of condensing range. Are you producing much condensate?

My suggestion is to ditch using the preset outdoor reset. I used a custom ODR setting on my NCB-180E with baseboards, which is much lower than the factory preset. If you find that the lower temperatures can't keep up with your heating requirements under certain conditions, then use the "boost interval time setting" feature to compensate.
 
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