Navien 210 CH NG Tuning help needed please

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Joe.b

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I am trying to tune this unit to keep my house warm. I can work on efficiency later.

I currently use 2 Nest thermostats that we had when we were oil based, I cleared out their learned patterns and started from scratch.

The Temp hit 12 and my house was at 68 when both zones are set to 72...

The house is an 1870's colonial with R-6 Siding and no insulation in the walls yet. Will be once I get the time to open the walls up and rehab the place. New Doors and a couple new windows... Slowly being replaced. 1800 sq ft and a 600 sq ft unfinished basement.

1st zone is 46 ft of baseboard with a 5K btu toe kick heater.
2nd zone is 36 ft of baseboard. I am thinking I should add another kick space heater on the second floor in the bathroom with a wall mount kit or more baseboard up stairs.

Thinking of adding an 11 K blower in basement on its own zone. And a 4th zone in my attic space as I redo the house.

Any ideas on how to tune this guy ? Or any tips. Right now here are the settings.

PS 17
Non well water
Return temp is set to 130 (140 doesn't seem to help any as it looks like the boiler temp fires at 165 most of the time but does spike to 185 at times.

Any other info and help is greatly appreciated.

-Joe
 

Jac04

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Joe-
Is the unit running constantly or is it cycling?

I'll defer to one of the experts here, like Dana, for the napkin math to figure out if you simply can't keep up with the heat loss.
 

Joe.b

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It is constantly running, very few times does it actually stop running... we use a ton of hot water and also keep the house pretty warm.

By cycling do you mean it completely stops burning ? If so that happens above 35 F below it is barely happens but from watching it for about 20 minutes I hear it cycle on and watch the boiler temp on the front jump to 165 for about 3 minutes then it throttles down to about 140.

I was watching the return temps on the pad and it says the return is at 135 to 138 when spiked to 165... other then that it hands at about 128 or so. I will have to watch it much more and note the times for cycling at this point.
 

Joe.b

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also I have an outdoor reset with a long cable that we disconnected because the house never got hot as well.

it was extended a bit and im wondering if the extensions that were added caused trouble with that also. Wondering if adding that is a better idea and just shortening the wires to make sure that there is little resistance to mess with the sensor.

Also does anyone know how to read the K factor chart if I decided to use that instead ?
 

Jac04

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I messed around with using return temp control and setting the k-factor on my CH-180. Neither seemed to work well. When using return temp, the unit would fire hard to get up to temp on a call for heat, then overshoot causing the unit to stop firing, then fire again and usually try modulate up & down quite a bit before the t-stat would stop calling for heat. The Navien factory k-factor curves are not very good IMO. Because you have to choose from a pre-mapped k-factor, I could never find one that would work for me and keep the house warm in all conditions. If you are having trouble just keeping the house warm, my suggestion is to keep the outdoor reset disconnected.

So your 'steady state' is about 140 outlet temp and 128 return temp?

With 82 feet of typical baseboard and 130F AWT you should be putting out 20500 BTU/hr to 24600 BTU/hr. ( 250 - 300 BTU/hr per foot of baseboard) That seems kind of low for the size of your house and the minimal insulation when the outdoor temp is low. Your 130F AWT is limiting your heat input into the house. What type of baseboards are you using?
 
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Joe.b

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It's copper baseboard aluminum finned standard slant fin cheap stuff.

I will try and check the values later when I get home. I may just set the unit to fire up 160 degree supply and see if that helps.
 

Jac04

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I may just set the unit to fire up 160 degree supply and see if that helps.
I was thinking the same thing. To get heat into the house get the supply temperature up and keep it there. When mine was installed they set the supply temp to 160F and walked away. I had very short burn times because the t-stat could be satisfied too quickly.

Do you have CPVC for the exhaust? According to Navien, you need CPVC if the supply temp is set to 140F or above.
 

Joe.b

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So any other info on this folks ? our weather is getting horrible and id like to figure this out.

I opened up the unit and found that the boiler was not set to 180 degrees. I bumped the # jumper and set it for cpvc the burner jumped to 175 immediately after restarting and seams to be doing better. house is 68 and its 10 degrees outside.

Guess I can see how it hangs in tomorrow when it hits -18 or so. Thanks all. Right now I re-connected the outside reset and am trying to figure out the K-factor thing.
 

Jac04

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Forget about messing with the outdoor reset. It will over-ride your controller settings, and if the temp sensor isn't reading an accurate outdoor temp it will result in setpoints too low. You have other things to worry about, like keeping the house warm as we see some of the coldest temps so far this season.

Did you set it to 160F supply and try that, or are you still using return temp control? If still using return temp control, change to supply temp control set to 160F and see how that works. Without doing the math, it seems you don't have nearly enough baseboard to take advantage of lower return temps (and trying to run in condensing mode). Your 130F AWT is limiting your heat input into the house. You need to get your AWT (average water temp) up to make use of the limited amount of baseboard that you have. You may even need to run higher than 160F supply temp.
 
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Dana

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With 82' of baseboard, and 165F output, 130F return for an average water temp of about 145-150F, you should be getting about 350BTU/hr per foot for typical baseboard. That's only 28,700 BTU/hr, which is nowhere near what you would have for a design heat load in an 1800' antique with only R6 siding for insulation- you're probably looking at a load 2x that. Don't know what the derating curves for the toe-kick heaters are, but they're probably only rated that high at an AWT of 180F (190F out, 170F back). Reality is probably no more than 6-7K out for the 11k unit, maybe 3K out for the 5K.

The fact that the delta-T is a whopping 35F means the radiation is under-pumped in it's current configuration. The installer SHOULD have been able to foresee that, and plumb it primary/secondary to preserve the flow rates on the radiation, and separate it from the flow rate of the Navien. If they just dropped the Navien into where the old high mass/low head boiler was plumbed to pump direct, the higher pumping head of the Navien is probably limiting the flow to the radiation, and the total pumping head may be too high for the Navien to get it's minimum flow requirements. This would be a serious limitation if they are using the internal primary loop pump that comes in the Navien as the system pump.

Take a look at the system plumbing diagrams starting on page 17 of the manual. You'll note that they are using a pair of closely spaced tees (spaced at 4x the diameter of the pipe) as the hydraulic separator, and that the secondary pump driving the radiation (the symbol with the black triangle pointed left) is it's own thing. If your system is plumbed differently (and I suspect it is), that's the fundamental fly in the ointment for getting more heat out of the boiler and into the radiation. What you have is a system design problem, not a boiler setting problem.

Not the problem, but definitely a problem:

The min-fire output of the Navien CH210 in condensing mode is 18,000 BTU/hr. For a zone with 36' of fin tube that's 500 BTU/ft, which takes an AWT (not output temp) of ~160F to balance with the boiler output, even at min-fire. And that's WAY above the condensing range, when running reasonable 10-20F delta-Ts on the radiation. The 11K blower zone will NEVER balance, since that's it's rating at 180F AWT, and would require temps well above what the Navien can deliver.

If you're going to keep the system all chopped up into zones, you either need more radiation, or more thermal mass to keep from short-cycling the boiler, even if you eventually get the radiation flow up to snuff for smaller, more reasonable delta-Ts. If you're going to add more zones, use high-mass radiators (you can get used radiators on craigslist on the cheap, sand blast them & paint 'em if you like), which will deliver the heat more evenly ( even when the burner is cycling on/off) , and will lengthen the burn cycles. The more radiator the better, if you're looking to get condensing efficiency out of it.

But first address the system architecture & radiation flow issues to get the delta-T down. It won't kill the Navien to short-cycle it for a season while you're figuring out how to treat the zone radiation/thermal mass issues, but you DO need to stay warm.

BTW: There is no location in MA predicted to hit -18F tomorrow, but there will be lots of negative single-digits. Pittsfield might hit low negative double digits, but it currently expected to "only" hit -9F, at about 4AM. Don't confuse wind-chill temp with air temp- only the latter is relevant to space heating.

It may be possible to insulate the walls on your house with blown cellulose without gutting the place, depending on what the wall stackup is, which will tighten it up considerably as well as insulating it. Also, is the R6 a continuous rigid foam sheeting under the siding (if yes, what type), or is it something like foam-loaded vinyl siding or something? How deep are the cavities, from the interior plaster to the (likely for that vintage) plank sheathing?
 

Jac04

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This would be a serious limitation if they are using the internal primary loop pump that comes in the Navien as the system pump.
Wow, didn't even think of that.

Joe indicated that he sees the supply temp throttle down to 140F when the return is about 128F after several minutes of running. I've seen this on my Navien as well when using return temp setting - supply temp goes way up in an attempt to hit return temp quickly, then it overshoots & throttles down. So I'm not sure his delta-T is as high as 35 degrees at 'steady state'.
 

Dana

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If it's possible to set the thing up at a fixed output temp of 180F+, that's what should be done, then when it stabilizes measure the delta-T across the radiation (and across the boiler, if plumbed primary/secondary), which would be able to determine a lot. At the likely ~50K load and limited low-mass radiation it's going to take average water temps high enough that 130- 140F return temps won't be an option when it's this cold out. (It was -3F on my deck in Worcester this AM when I headed out the door which was well after sunrise, probably -5F for the low, which is cool enough, given that the 99% temperature bin is +5F.)

Who installed this thing?
 

Joe.b

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Weather wise it was -2 confused windchill with actual temp.

Got the output of the unit to 175 with the outdoor reset on. Using the supply temp and the k factor settings in the manual. The burner is on a solid 175 constantly as the bottom zone heat is never met. But the secondary zone is at temp. Which I would think is normal considering the lower level has a ton of air leaks. And I will be dealing with these hopefully when it warms up a bit.

The unit on the heat exchanger says 240... so it must have been a 240.

Page 25 on the manual is how it is setup.except 2 zones instead of 3.

I have a distinct feeling it is the lack of baseboard killing me here, the unit replaced an old oil fired unit which used 185 degree water above 20 degrees outside the unit does well and uses $120 in gas. But below it seems to struggle.

So would it help for me to add on the return a big old cast iron heater with the same pipe size ? I plan to open up one of the walls and add one of these soon. With the Wall install kit to add some heat to the front foyer area of the home.

https://www.emersonswan.com/ckfinder/userfiles/files/pop6.pdf

I figure its a quick fix to get more heat out of the zone, and I can still use it after we remodel.
 

Dana

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Lack of insulation is what's killing you on being able to heat the space more than lack of baseboard.

But lack of radiation is what's going to keep the thing from achieving condensing efficiency. Rather than just hack on it, starting with a room-by-room heat load calculation of the "after" levels of insulation & window upgrades etc.. Then start specifying the radiation requirements for each room & zone.

To get good condensing efficiency:

1: Install enough radiation in each room to be able to heat the place to at least 68F at the 99% outside design temp with 140F water temp (or lower).

2: Install enough radiation on each ZONE such that that the zone can emit at least 18,000 BTU/hr (the min-fire output of the Navien) at an average water temp of 120F or less.

3: (least critical) Try to balance the water temp requirements of each zone at the 99% outside design temp so that it's within 10F, so that the same reset curve/K-factor works about the same for each zone.

It doesn't have to be perfect, but it helps to be close. You'll probably have to over-radiate the smaller zones relative to constraint #1 so that it won't short-cycle the boiler (constraint #2), but as long as the main zones are pretty close in water temp requirements (constraint 3) it should run pretty well.

Fin tube baseboard sucks for low temp systems, and has very non-linear output characteristics below 120F AWT, making it a lousy choice. Panel radiators do much better, as do old-fashioned high-mass radiators, and since both emit a good fraction of their output as radiated heat, they're more comfortable at any temperature.

To figure out the output of old school radiators across temperature, use this document for reference. Panel radiators are usually specified at both 180F and 140F AWT, and you can interpolate, or use the nomograph on p2 in that old-school radiator reference to figure out how much they deliver at 120F or any other temp, since the output is very linear.
 

Joe.b

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I was hoping to slowly scrap them in favor of cast iron baseboard.

But maybe just over radiating the zone is a better idea. I can really use 3 or 4 of those toe space heaters in various locations around the first zone.

I would also love to radiate every foot of the outside walls and possibly add some to the inside walls as well.
 

Joe.b

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If it's possible to set the thing up at a fixed output temp of 180F+, that's what should be done, then when it stabilizes measure the delta-T across the radiation (and across the boiler, if plumbed primary/secondary), which would be able to determine a lot. At the likely ~50K load and limited low-mass radiation it's going to take average water temps high enough that 130- 140F return temps won't be an option when it's this cold out. (It was -3F on my deck in Worcester this AM when I headed out the door which was well after sunrise, probably -5F for the low, which is cool enough, given that the 99% temperature bin is +5F.)

Who installed this thing?

We had munihelps.org contractor do it, since we are in a muni here there was very few contractors that were willing to do the install. I guess that is because some gas companies actually help pay for it.
 

Mage182

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I was hoping to slowly scrap them in favor of cast iron baseboard.

But maybe just over radiating the zone is a better idea. I can really use 3 or 4 of those toe space heaters in various locations around the first zone.

I would also love to radiate every foot of the outside walls and possibly add some to the inside walls as well.

I have found that adding high mass radiation does far more than adding fan based heaters. Swapping out all my Multipak 80 fin tube for cast iron baseboard made a huge difference.
 
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