Navien NCB 240H - Any thoughts?

tabeth

Hi everyone,

A long while ago I had the NPE 240A installed. It's handled my hot water needs quite well, considering I'm in a situation where there are 3 bathrooms, 2 dishwashers and 2 washing machines.

My boiler is shot, and I had someone come out to look. The person who came out to look recommended getting the NCB 240/110H. I had considered the combination boiler before when The NPE 240A came out, but when I did research then, it didn't make sense. Since then significantly more baseboard has been added and the 240H has a lower (13K BTU vs. 18K BTU) minimum for heating.

With that being said I decided to measure all of the baseboard and follow some of what I've read on here to decide.

I have three zones:
Zone 1 - Living room area: 84ft of baseboard + 5ft of what seems to be something else (not a radiator), but maybe an in-wall cadet?

Zone 2 - Bedrooms: 83ft of baseboard

Zone 3 - Basement + apartment: 55ft of baseboard.

Total: 232ft of baseboard. Assuming 200 btu/ft @ 120F this should give us 46K BTU/hour. Well above the minimum that the 240/110H needs of 13K. It seems the only potential issue is if the basement zone is running by itself. During the winter, the basement is naturally cooler so the basement is more likely to be run. However, from experience usually at least one other zone is running so at a minimum we're looking at 55 + 83, or 138ft of baseboard active at any given time.

In my situation does it make sense to get rid of my NPE 240A and (dead) boiler and get this combi unit? Apparently it was released just last month so I haven't seen many reviews. I'm also willing to add another 10-15ft of baseboard in the basement as there are a couple rooms that could be warmer. My zip code is 02169

Zman

What size, model, and age boiler is presently heating your baseboards? What water temp are you running?
Measuring your baseboard heaters per zone only gives you part of the story. You really need to do a room-by-room heat loss calc and compare your heat loss of each space to the available radiation. Slant Fin makes a nice app for this.
I think you will likely find that some of your rooms will heat well with 120 degree water where others will require much higher temps.

EBEBRATT-Ed

You need to do a heat loss of the house. Download the Slant Fin app. Measuring the baseboard may get you close but a heat loss is more accurate.

I would be cautious about Navien, they don't seem to hold up well if not maintained yearly. All Mod Cons need regular service but Naviens seem to be loosing heat exchangers

tabeth

Zman said:

What size, model, and age boiler is presently heating your baseboards? What water temp are you running?
Measuring your baseboard heaters per zone only gives you part of the story. You really need to do a room-by-room heat loss calc and compare your heat loss of each space to the available radiation. Slant Fin makes a nice app for this.
I think you will likely find that some of your rooms will heat well with 120 degree water where others will require much higher temps.

So I used the app and you were right. All but 4 rooms could be heated with 120F. With the remainder I'm thinking of just adding more baseboard since they're generally cold even now.

Is there a nice way to calculate the break-even on cost to add more baseboard and have a more efficient boiler vs. replace with inefficient boiler and save on baseboard?

mattmia2

Depending on how far undersized it is, you could potentially run an outdoor reset curve that keeps it in the condensing range most of the time and only uses a higher swt on the coldest days. If those rooms aren't balanced, adding more emitters to those rooms could make them a lot more comfortable but there are other ways to balance most systems as well.

In reality you likely won't see any monetary benefits to a mod con once you factor in increased maintenance and shorter life, not that there isn't something to be said for matching the boiler to the load with modulation and outdoor reset and reducing fuel consumption.

plumbbob

many problems with navien units heat exchangers and 3 way valve look into lochinvar noble combi much more reliable