NAVIEN CH240 COMBI

JONMAC

I HAVE A PLUMBER THAT WANTS TO INSTALL A NAVIEN COMBI CH240 IN A HOUSE THAT HAS 8 ZONES.6 OF THE ZONES ARE AIR HANDLERS AND 2 ARE DOMESTIC WATER HEATERS.HAS ANYBODY HAD ANY EXPERIENCE WITH THIS BOILER/WATER HEATER DOING THIS MANY ZONES.HIS NET BTU LOAD IS 140,000-155,000.ANY FEED BACK WOULD BE APPRECIATED

Ironman

BTU Load

Does the house need that much heat? Has a heat loss calc. been done?



I just installed one 2 weeks ago. The boiler works great and switches to domestic priority very quickly. This one had one hydronic AHU hooked to it which was over-sized on the hydronic side - about 80k btu's. I piped it with a very short 1" primary loop and 3/4" secondary with about 30' piping and a 006 circ. that was internal in the AHU. The AHU pulled all the heat that the primary pump in the boiler could give it. In other words, the secondary return temp was the same as the primary. With the size of the secondary circ., the line sizes and a 30* Delta T, I estimated that the load was about 75K btu's. I don't think the onboard pump will give enough GPM's to get much more than that through the primary loop.



If you need more than that, you could possibly place another circ. in series, but you would have to wire it so that it's de-energized when the boiler switches to domestic because the 3 way valve would cause the additional circ. to "dead-head" when the valve switches.



I talked with Navien Tech support before the install and they said if there was only about 10" of piping between the AHU and the boiler that it could have been directly piped without pri/sec. or an addition circ. in the AHU. This obviously would have been inadequate for my job.



A call to Navien might be prudent as my experience indicates the onboard circ. is marginal.