Navien NCB 240 Issues?

[Dave 1804]

Hello,

I just had a Navien NCB 240 boiler installed to replace an old Weil Mclain152k btu boiler that was leaking internally and I have some concerns:


First some back ground. After the 6 day long install (was quoted 8-10 hours by installers that I now realize aren’t worth anything) of redoing the plumbing until I was happy with it and thought it conformed to install requirements of the unit, the boiler has been up and running for 2 days now (heating working ok? DHW working on and off depending on current well pressure (another problem and long story)).


First problem is unit is running constantly for 18-20 h each day according to the thermostat (NEST). I cannot believe this is normal and cannot find much information on these online aside from this forum. I’m concerned what will happen when the temp drops to single digit numbers.


Burning Approx. 6 gallons of propane a day.

120 gal tank*.80%max fill = 96 gallons (moved 10 increments over the two days (0-80)) 96/80=1.2 gal per increment = 12 gal/2 days (just got off work please tell me if you see an error in that math)

Second is I think this unit can run much more efficiently then it currently is and am wondering if anyone can help with proper tuning numbers? Also I have seen a lot of mention of the outdoor temp sensor, would this help out significantly in my case?


I have only had about 20 min per day to watch the unit operate and I don’t think it is short cycling but I haven’t had time to remove the cover to watch the burner, just going by exhaust and sound.


Approx. low of 32 and high of 50 each day low to no wind

maintaining a constant 72 deg (I take care of a 94 year old man that demands this temp or higher) in a 1800 square foot house from 1959 with r13 in walls and ceiling , single pane windows


154’ of aluminum finned copper baseboard in a single zone configuration


With unit running:


Space heating supply water temp: 138-142

Space heating return water temp ~126

Space Heating water pressure 23.9 psi

Pump over run time 40 min

Burner off temp 4

Burner on temp 5

Supply absolute max 180

Supply absolute min 104

Return absolute max 149

Return absolute min 80


Thanks in advance for any advice.

 

[Dana]

With a return temp of 126F most propane burners will be delivering efficiencies in the low 90s. With an outdoor reset temperature you could run it at much lower temperatures and achieve higher combustion efficiency, but more on that later.

If it's not keeping up with the load and running constantly at a fixed output temperature of ~140F you'll need to either raise the temperature or install the outdoor reset sensor and set it up to automatically adjust the temperature up/down with falling/rising outdoor temperatures.

At 140F out, 126 back the average water temp (AWT) of the system is about 133F, a temperature at which fin tube baseboard delivers about 250-275 BTU/hr per running foot. So the rate the heat is being emitted out of the 154' of baseboard is about 154' x 250 BTU/hr-ft= 38,500 BTU/hr when the burner is running, so it's surely duty-cycling. Propane contains 91600 BTU/gallon, and at 90% efficiency that's 0.9 x 91600= 82,440 /gallon. Per hour you're averaging 6gal./24 hrs = 0.25 gallons/hr, so the average output is about 0.25 x 82,440= 20,610 BTU/hr.

That's on the high side for a tight well insulated 1800' house at a ~40F average outdoor temp with a 72F outdoor temp, but with single-pane windows/no-storms, no foundation insulation and excess air leakage it's a credible number. At the cost of propane blowing a foot of cellulose in the attic and installing tight Low-E storm windows has very good payback.

If the heat load is ~20K at an outdoor temp of ~40F, (based on the reported fuel use & average outdoor temp), when the outdoor temps drop to about 10F you'll have to bump up the output temperature of the boiler for it to keep up. With outdoor reset you could set up the boiler to drop to 120F when it's 60F outside, and ramp to 150F at +10F, and it would be condensing most of the time.

There are some issues with the near-boiler plumbing that bears looking at. The tees at the in/out ports of the boiler appear to be slightly further apart than is ideal, which would be 4 pipe-diameters MAXIMUM. The distance of straight pipe both into and out of the tees are too close to the ell and pump. This un-favorable spacing puts more turbulence at the tees than is ideal, which doesn't adequatey separate the boiler loop flows from the radiation flows. This is tried & true standard min/max spacing:

The other issue is that the pump is pumping TOWARD the expansion tank, rather than away from it, which allows cavitation on the pump impeller, increasing turbulence and interfering with flow (and lowering pump lifespan.) Whether the pump is pumping toward the boiler or away from the boiler, the pump should be fairly close to the expansion tank separated by a straight section of pipe, and pumping away from the expansion tank:

This error is being further aggravated by how close the input side of the pump is to the ell, which is inducing turbulence at the worst possible location for the pump.

 

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[Dave 1804]

Thanks for the info, the primary loop is prebuilt and came from navien for the unit.

The house has non low e storm windows

As for the pump configuration I'll see if I can make them fix it. And they are apparently providing the outdoor reset to me now.

I'll post more details after I get off work and have a chance to reread all the above.



Thanks

 

[Dave 1804]

Thank you Dana for your very informative post.



If i under stand the above correctly, with my space constraints it would be best to remove the pump from its current location and reposition as shown below leaving approx. 5.5" on either side of it or should i move it closer the right giving more straight pipe from the expansion tank?

 

[Dana]

Putting it where you have it sketched is fine, but if you can add a bit more to the stub between the tank and pump it would be ever so slightly better (the 10 diameter rule. Looks like you have maybe 5 diameters as-is.) The pump is 6-3/8" flange-to flange (not counting the parts screwed to the plumbing. If the plumbing section can be shifted a bit to the left to allow the full 10 diameters between the pump & air-scoop/tank, and at least a 6" straight run coming into the air-scoop it'll scavenge air more quickly . If you have to cheat one vs. the other, having the longer straight shot into the pump takes priority over a longer straight shot into the air scoop.

 

[Dave 1804]

As for the pump output side, would it be OK to run it right into an elbow with 1-2"of strict pipe giving me approx. 12" between the scoop and pump inlet
Or do I need a 10x pipe Dia (1.25" pipe) on that side as well?

 

[Dana]

It's fine to be pumping toward an ell at short distance, but it should never be pumping away from an ell at short distance (the way it is now).

The reaoning: When pumping toward an ell the turbulence induced by the ell is downstream of the pump, in the pipe. It's only problematic if the turbulence is occurring on the water entering the pump, interacting with the impeller. The expansion tank behaves as something of a shock-absorber, but you're asking more of that function from the tank if you put an ell too close to the input side of that tee (the air-scoop), so at least some straight pipe ahead of the tank is a good idea, as well as the ~10 diameters between the tank and the pump. (The teeing off to the tank creates it's own turbulence too, but it's tiny compared to that induced by an ell.)

With some low-mass higher-head boilers it's preferable to pump toward the boiler, but that's less critical. The worst that happens pumping way is that you may hear some flash-boil sizzle, the solution to which is to raise the system pressure a few psi. The 23.9psi reported is already quite a bit more than would be required to suppress that symptom, and is way higher than most residential systems would ever need, (is this a 5 story house?). Setting it up at 12-15 psi (measured when no pumps are running, with the system warm, not smokin' hot) is probably the right starting point. If the boiler stays quiet when running after that with no sizzles pops or bangs, it's enough pressure.

 

[Dave 1804]

Thanks again for the very informative post Dana.

Dana, do you by chance know anything about 1950's jacuzzi bros. inc deep well pumps? I'm trying to identify the one i have because i need to find an adapter plate or change it out due the new boiler (dhw pressure issue)



Hopefully i will get the company back up here in the next day or two to fix these issues.

 

[Reach4]

Dana, do you by chance know anything about 1950's jacuzzi bros. inc deep well pumps? I'm trying to identify the one i have because i need to find an adapter plate or change it out due the new boiler (dhw pressure issue)

Franklin Electric bought them, but I doubt you will find what you are looking for. Submersible, or 2-pipe jet? http://franklinwater.com/search/?query=jacuzzi seems to be jet related.

You might ask here: https://terrylove.com/forums/index.php?forums/pumps-and-tanks-well-forum-blog.4/

 

[Dave 1804]

The company will be back a few days after Christmas to fix my concerns and add an exterior temp sensor and better flow control on the 3 returns for balancing purposes ill post some updates then.

i also created a post for my well pump issue that this new boiler has brought up if anyone is interested or has any input. ( boiler requires 40 psi to make hot water)

https://terrylove.com/forums/index.php?threads/need-to-identify-old-well-pump.63731/

Thanks again for all the helpful reply's