Need Help Tuning Navien CH-180 ASME Mod Con Combi

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Dana

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This is the first mention of propane as the fuel- I had assumed you were on the gas grid. I don't have much to offer on your valve/pressure flucutation enigma, but I DO have a suggestion on a cheaper/better way to heat at least part of the house.

At CT-style propane & electricity prices heating with a better-class ductless air source heat pump would have about 1/3 the cost of heating with condensing propane. With any reasonably open floor plan you should be able to heat/cool at least one of your zones with a single ductless head (a 1-head mini-split), and you maybe able to do both reasonably with a one-head per floor approach. Though that works better for high-R houses, even if it's only covering your average winter load you'd be able to cut your propane use by more than 3/4, making it self-funding in short years on propane savings. A pretty-good high efficiency 1-ton like the Fujistu AOU 12RLS2 (or 12RLS2-H) would run about $3.5-4K (installed) and can deliver about 17,000BTU/hr @ +5F, more at higher temps. A 1.5 ton Mitsubishi MSZ-FE18NA puts out over 22,000 BTU/hr @ +5F and runs $4-4.5K installed.

Getting a handle on your room by room and whole house heat load would be necessary to size it correctly and pick a model that works, but it's almost a no-brainer type investment if you intend to stay there more than 3 years. For the broader picture, download and ponderthis short policy piece from last March. If you need or want climate specific performance information I can point you can get pretty deep into the weeds on it on the NEEA field metered test data. In a coastal CT climate they are nearly as efficient as ground source heat pumps if you get a decent one.
 

Jac04

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Thanks Dana. Looks like I'll probably stick with the Navien unit, assuming the buzzing gas valve can be sorted out. I'm 99% sure it is gas supply related. If I have any other propane appliance running (clothes dryer or garage furnace), the boiler has a lot of trouble firing. The plumbers put the boiler last in line on the gas piping - not good. I ran the numbers on the piping, and it is indeed undersized. I talked to the propane company, and they confirmed this as well. What's frustrating is that a while back the propane company actually called the plumbers to tell them that their piping was undersized and would cause trouble. The plumbers simply ignored them. So, think once I get the gas supply taken care of, I'll be in good shape.

With the supply temperature set at 130F and an overnight low of -5F I have found my limit. I left the t-stat set at a constant 69F all day yesterday & last night. When I woke up, the house was 67F with the heat on non-stop. Once the sun came up, the house warmed right up to 69F.
 

Dana

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It sounds like 130F covers you pretty well for all conditions then, given that the -5F anomaly is well below your 99% design temp. And yes, modulating burners are more sensitive to undersized propane plumbing, so fixing that will probably fix the mis-behavior.

I wasn't suggesting that you scrap the Navien for mini-splits. I'm suggesting that putting at least one decent sized mini-split would be cost effective in short years heating one large zone, and would provide high efficiency air conditioning too. A mini-split doesn't provide hot water, and is rarely a whole solution for heating in standard construction housing. A good one would use less than half the power of window air conditioners and are much much quieter. If sized for the cooling load it'll likely be big enough to handle your average heating load. While your cooling loads are too low to rationalize the upfront cost of a mini-split just for cooling, your heating fuel costs are very high and volatile, and the payback is short enough that even if you're planning to sell in 3-5 years you will have paid it off in propane savings, and have another selling point for the house. (If my 401K had that kind of internal rate of return I could have retired decades ago! :) )
 

MikeG88

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on a call for heat the burner will sometimes give 5-8 short 1-second 'bursts' of flame at start-up before it finally ignites and stays burning. Both Navien and the installer are stumped. They say they haven't seen this before.

I have the same problem with a Navien CH-210 (about 1 1/2 years old) Navien has had a local plumber put in a new Air pressure sensor, Install the newer hi temp computer board, and neither or those solved it so now I am waiting for plumber to install new burner rods to see if that fixes it. It is the only appliance on the propane line and pressure has been verified several times. And funny- it doesn't seem to happen when using DHW. I have also been instructed by the dealer the original plumber got it from to turn down the capacity, I currently have it down to 60% (at 100% and 80% it would go through the burner cycle the full 20 times causing an error 12 and shutting down). One of the tech at Navien's support line told me not to worry if it's not going the full 20 and erroring out, they don't seem to know what to do, just keep changing parts till it gets fixed or the homeowner gives up. Any luck in solving it at your end?
 

Paul Herrnson

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This is my first winter in a home with a Navien CH-240 ASME. Over the summer, I suspected the existing made no sense. Now I’m fairly sure of it.

I’m new to the forum and have little technical expertise but I’m good at following directions and tinkering. I can follow the instructions in the User’s Operation Manual.

I live in West Hartford, CT. The house has 4 zones, including a basement and sun room (where I set the thermostats at 55 F). In the other 2 zones, the thermostats are set at 60 F from 8am-4pm (when no one is home), at 64 F from 4pm -11pm, at 60 F from 11pm-5:30am, and at 64 from 5:30am-11am.

The water temp on the Navien unit is set at 115 F.

I’m looking for recommendations for the unit’s other settings, such as
1. The preheating setting
2. The room temperature setting (should I set this?)
3. The return temperature setting
4. The supply temperature setting
5. The K factor setting
6. The standby setting
7. The 24 hour timer (should I set this)
8. Capacity control of the whole setting (Heat Capacity Control)

Thank you in advance for the advice!
Paul
 

Dana

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Since you have at least some wintertime fuel use data to work with, first run at fuel-use heat load calculation against heating degree-day data using +6F as the outside design temperature, and 65F as the indoor design temperature. Given your thermostat settings, run the calculations using both base 50 and base 60F degree-day data. If it has been operating at a 115F fixed temperature, assume 95% efficiency on the boiler when making those calculations.

Measure up the radiation in each zone. If baseboards, the total length of the baseboard, but not the distribution plumbing. If radiators, estimate the equivalent direct radiation (EDR) square footage.

If you don't have the outdoor temperature sensor the K-factor setting is meaningless. If the house keeps up with the load at a fixed 115F output temperature and your heat emitters are fin tube baseboard there's nothing to be gained by going with outdoor reset control using the outdoor temperature sensor.

The minimum-fire output of the CH-240 ASME is about 19,000 BTU/hr, and at 115F out it may be short-cycling on zone calls if there isn't sufficient radiation on each zone which may need some setting tweaks to tame, or maybe it's already set up reasonably for that. Run the napkin-math on that when you have your zone radiation measurements ready, or, when you have a few hours to experiment, time the burn times and duty-cycle over the weekend with just the zone with the least amount of radiation calling for heat, by turning that thermostat way up, and the others way down.
 
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