NCB-240E with DHW - what is inside pump for?

[theMezz]

Just had a combo boiler installed
NCB-240E with DHW - what is inside circulating pump for?

Maybe for DHW?

This unit replaces a CH-240 that has no inside circulation pump. Should I get DWH faster at the facets ?

Thanks

 

[Samat]

I believe all Navien have a internal pump. My CH210 has one. That’s why you have a primary and secondary loop

 

[Sponsor]

 

[theMezz]

I believe all Navien have a internal pump. My CH210 has one. That’s why you have a primary and secondary loop

What does it actually do?

 

[Samat]

I don’t know physics of it but it circulates the boiler water through the primary loop and the secondary loops (your heating zones) pump the hot water off of it to the radiators and return it back to the primary loop. It’s probably there to make sure water is always flowing through the units heat exchangers while it is firing. It also continues to run water water through the primary zone as the unit is purging before it shuts down

 

[Jadnashua]

A primary/secondary loop will help prevent cold water shock to the heat exchanger, too, since some heat will get exchanged with the returning, potentially much colder water from the heating loop. It should also help prevent boiling the water in the heat exchanger since the pump will be circulating it at least in that loop independent of the main heating loops.

 

[theMezz]

I would think that the regularly external circulating pump would do that. Odd that they have a second internal pump also added in the loop.

 

[djdavenport]

I think Navien strongly recommends that your combi is piped primary/secondary, which mean you need two pumps, the one in the unit itself and an external circulator pump. That system allows the two loops to work independently of each other, such that the demand of the radiators in the house on the secondary loop does not affect the flow through the heat exchanger which is driven by the internal pump. That way you are always assured that the temperature and flow through the combi itself remains within the operating parameters. (For a lot more information, Google the term "closely spaced tees" and it will explain how a P/S system works.) I think some people, if they're only operating one zone, have opted to go direct and simply use the internal pump as a system circulator, but if your system is multi-zone, you're asking for trouble. Not an expert, but that's what I've been able to glean about the process.

 

[theMezz]

I have one zone - so effectively I have two pumps - one inside the navien case and one outside.
Sounds redundant to me and adding one more point of failure.
I wish I was smarter and can understand their logic
Thanks - I appreciate your time and will use your Google term suggestion

(the guys that installed it had no clue!)

 

[djdavenport]

So, the supply side of the heater comes out of the combi and goes straight to the second pump? IOW, they are in series? I don't know if maybe the installer thought that the internal pump wasn't sufficient to provide adequate flow to the system and needed to add another locomotive to the train, so to speak. Not sure that it hurts anything, but also not sure you need it. Somebody here will know.

 

[theMezz]

I do not think they are hooked in series
hard to tell - the internal pump is packed in the unit

 

[djdavenport]

Take a look at this diagram (sixth one down) which shows a single zone with its own circulator pump. Notice the closely spaced tees. That is the typical P/S install. Does your unit have that? Or does the supply come straight from the unit into the external pump?

https://www.navieninc.com/app/W1siZiIsIjIwMTgvMDgvMjMvMTkvNTgvNDQvYjJmN2U0NGEtNjZmMS00NjhlLWJhNGYtZjZkZjUxMjNjNjQ1L05DQi1FIEFwcGxpY2F0aW9uIERyYXdpbmdzLnBkZiJdXQ/NCB-E Application Drawings.pdf?sha=9333d3f42dfea666

 

[Dana]

The internal pump on an NCB boiler drives the primary loop on the heating system side. Installers who don't understand what that is, and how it is different from the external you have no business installing one of these. If there is no hydraulic separator and the full radiation flow is being driven through the Navien it might not last all that long, and the pumps are indeed in series with one another. The internal pump guarantees the proper flow through the heat exchanger, which is not designed to take the full flow of the radiation, which can be much higher.

The radiation circulators drive a loop which intersects with the boiler loop, but at a low enough resistance at the point of intersection that the flows don't interact very much. That intersection point is called a "hydraulic separator". The pre-engineered manifold Navien sells for these is one type of hydraulic separator, but it's fine to install something else.

This is a completely different function from the pumps inside the tankless water heaters with internal mini-tanks or recirculation pumps.

 

[willsheeler21]

The internal pump on an NCB boiler drives the primary loop on the heating system side. Installers who don't understand what that is, and how it is different from the external you have no business installing one of these. If there is no hydraulic separator and the full radiation flow is being driven through the Navien it might not last all that long, and the pumps are indeed in series with one another. The internal pump guarantees the proper flow through the heat exchanger, which is not designed to take the full flow of the radiation, which can be much higher.

The radiation circulators drive a loop which intersects with the boiler loop, but at a low enough resistance at the point of intersection that the flows don't interact very much. That intersection point is called a "hydraulic separator". The pre-engineered manifold Navien sells for these is one type of hydraulic separator, but it's fine to install something else.

This is a completely different function from the pumps inside the tankless water heaters with internal mini-tanks or recirculation pumps.

Wrong! This is straight from there info (Integrated boiler pump for space heating and DHW. No need for an external boiler pump saving installation time, space and costs.).

 

[Fitter30]

Wrong! This is straight from there info (Integrated boiler pump for space heating and DHW. No need for an external boiler pump saving installation time, space and costs.).

What does it actually do?

Built in circulator is for steady gpm though heating exchange for constant flow primary side of the primary / secondary side of a piping system. Has nothing to do with DHW. Any brand of a condensing boiler/ water heat holds very little water 1-2 gallons. Where a cast iron boiler might hold 5-7 gallons. So if there is a water flow issue unit trips on high temp more than a couple of times good possibility that the heat exchanger is trash. Where cast is a little more forgiving. Condensing boilers aren't 95% efficient if return water temp is over 140°f above 87%. Can you pipe a condensing water with the factory pump yes would i NO.

 

[GReynolds929]

Wrong! This is straight from there info (Integrated boiler pump for space heating and DHW. No need for an external boiler pump saving installation time, space and costs.).

Unless you have a reference to back up what you are saying you are wrong.

 

[Fitter30]

Unless you have a reference to back up what you are saying you are wrong.

First page after cover good for 100'

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ebirdsall.com

 

[GReynolds929]

First page after cover good for 100'

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ebirdsall.com

I was referencing @willsheeler21 comment about the on board pump being used for DHW. It is not, it is only for the boiler side. Proven by your linked drawings and all my available literature.