Navien NCB-240E possible purchase

[DR-DEATH]

Hi,

New user here but I am looking for some professional advice. I am shopping for new hot water heaters and while I am at it.. interested in replacing our old nat gas boiler from 1985.

I am specifically looking at combi units and have had two companies come out to give me quotes and expect another two more before I make my decision but I have a few concerns.

So far none of these companies have ran a J load which I have read is usually important. I asked if they needed to measure base boards or anything to get a sense on how big of a boiler I need. Their response was that they provide the largest unit available as it will have no problem heating most homes. I am worried that an oversized unit will cause short cycles and lose any cost savings I was looking at anyway.

From what I understand these boilers need to be in their condensing stage to get the best bang for my buck which usually requires running at a lower temp around 140f. Current set up heats perfectly at 180... will heating at 140f really get the job done?

Here are the basics of my house:

Located in Southern New Hampshire so winters can be cold.

House was built in 1986. Concrete foundation and well taken care of. (in wall and attic insulation is good. Windows seal well and doors don't leak air.)

Three zones which include finished basement, first floor and second floor. Total of 1420 square feet. 710sqf on first floor, 494sqf second floor, and 216sqf finished part of the basement.

2 bathrooms but we only use 1 shower/small tub. 2 adults and one toddler. Using multiple hot water sources at one time shouldn't be an issue for us.

Basement has about 14 feet of copper/aluminum baseboard.

First floor has about 50 feet of baseboard. 15 in office, 35 feet in living room/dining room area. (one large open space with vaulted ceilings)

Second floor has about 36 feet baseboard. 5 in bathroom, 17 feet in bedroom 1 and 14 feet of baseboard in bedroom 2. (bedroom 2 is only 88 square feet.)

Browsing some past threads on this forum I have seen people saying short cycling won't be an issue with 50 or so feet of baseboard per zone. I definitely have less than that in 2 out of the 3 zones. I know the boiler can modulate based on out side temp but I do not know how that works with the baseboard lengths and zones.

My wife is a home 99 % of the time so we typically keep the house anywhere from 65-68 degrees during the winter. At night we set first floor and second floor to 60. Basement does not get used so it stays at around 45-70 degrees depending on if it's winter or summer. I have noticed when I use the heat with our current boiler the basement seems to have a hard time getting above 65 degrees even after an hour of the heat being on. ( I am assuming the baseboard is not enough OR short cycling if possible with an old atmospheric boiler?)

Anyways... I hope someone here can help me make the best decision possible because these things aren't cheap and the last thing I would like to do is drop 6-8 k on something that doesn't work as well as it should.

Thank you for any help. I will update this thread with quotes once I get them in email but so far prices are looking 6-8 k for Navien NCB 240-E installed.

 

[Leon82]

The 14 foot zone is going to be a thorn in the side if it runs alone. They don't modulate down as much as some of the firetube boilers out there.

During a 50 degree day the outdoor reset will set the water temp low and the baseboard won't emit the 16k or so btu the boiler puts into it. So it will shut off and restart. There are fans boards ignitors and flame sensors that will wear sooner with a lot of cycling.

I have my odr curve tet to 145 at 7 degrees and the house stays at 68 to 69 degrees and will shut off once solar gain adds some heat. I also set both of my zones to run together

But you should do a heat loss for yourself even if you use the slant fin app so you know where you are.

 

[Sponsor]

 

[NY_Rob]

First off, I’m not a professional and I'm not in the heating/plumbing trade... so nothing I saw should be considered as professional advise.
I came here a while ago looking for advice on replacing my old cast iron boiler with a modern boiler. The good folks here were gracious enough to dedicate their time to answering my newbie questions and educating me as to making a good choice for my boiler replacement that would be good fit for my home.
With the knowledge/advice I’ve gotten here and with online research- I think I have beginners basic understanding on the overall upgrade scene. So, here’s what I’ve learned so far….



With a mod-con… pretty much forget about the 5-8F nighttime setback. A couple of deg setback is possible, but with the low loop temps in a mod-con system it would take all day to recover from a 8 deg setback. You’ll see why it’s this way when you read the following…

Your return water temp has to be at/near 130F to just hit the very beginning of the condensing threshold- which means in a “standard” system that assumes a 20f temp difference between boiler supply output and return- your supply temp should be around 150F.
If you look at the efficiency curve chart- it indicates that you really want the return water to be closer to the 110F range- which would mean nearer to 130F supply temps.

Using the baseboard BTU chart- you’ll see that at 14’ of baseboard at 120F (split the difference between 130F out and 110F return temps) can only put out 190 BTU x 14’ = 2,660 BTU’s. There is no boiler that can fire down that low….

If you combine the 14’ basement and 36’ second floor zones into one 50’ zone (which would perfectly match your 50’ first floor zone) you can then use 9,500 BTU’s. With that in mind- you could use a high turndown mod-con like the HTP UFT-80W (or it’s clone- Westinghouse WBRUNG080W), with it’s 10:1 turndown ratio it can modulate down to 8K BTU at it’s lowest fire rate.

For the domestic hot water- you can use an indirect tank off the mod-con which will be more efficient than the combi boilers.

But as Leon mentioned above- you need to do a heatloss calculation before you do anything else.

 

[Dana]

A 36' stick o' fin tube can only emit about 7200-9000 BTU/hr at condensing temps. The 50 footer can only deliver 10,000-12,500 BTU/hr at condensing temps. That's fine with an NHB-080 or a UFT-080W, but sucks for an NCB 240, which has a min-fire output more than 2x that much.

The min-fire output of the NCB-240 is about 17,000 BTU/hr which is probably more than half your heat load at the -3F to +5F 99% outside design condition, and more than your mid-winter average heat load. A typical mid- '80s 1500' house would come in with a heat load under 25,000 BTU/hr @ 0F. Tighter homes of the era can come in under 20,000 BTU/hr, provided the foundation was insulated. (If it isn't already, it's worth insulating the basement even if you normally leave that zone off, but that's a different subject we can get into if you like.)

You have 100' of baseboard on the system total. Designers of the era typically installed 2-3x as much boiler as was needed, and set it up to run at 180F out 160F back or an AWT of about 170F, which emits about 500 BTU/hr per foot. So you only have enough radiation to emit 50,000 BTU/hr, and it's probably more than 2x oversized for the real load. It's fine to over size the high-fire output of a mod-con a bit, but the critical number is the low fire output, since that determines how much modulating and condensing can really go on.

To get a handle on your real heat load you can use the existing boiler as measuring instrument. I'm going to guess that it's something like a 3-4 plate cast iron beast with 60-80,000 BTU/hr of output, with a DOE-output/Input BTU ratio of about 0.80-0.82, but you should check the nameplate numbers on it. Ignore the IBR numbers etc, they're completely irrelevant for this task.

With some mid and late winter gas bills with the EXACT meter reading (not billing) dates, and a ZIP code we can better estimate the 99th percentile temperature bin at your location, and look up heating degree-day data from a nearby weather station. With that data and the steady state efficiency it's possible to determine the likely range (and an absolute upper bound) for the heat load.

Knowing the 99% load would be enough to estimate the average mid-winter load. If the average mid-winter load is lower than the min-fire output of the equipment it won't be modulating much, even if it's condensing, which cuts into both efficiency & comfort, and puts some wear & tear on the boiler.

Tankless combi boilers are rarely a good fit, but tank type combi units can work out well in low-heat-load multi-zone situtaions, since it's nearly impossible to short-cycle them.

But first, let's get a handle on the heat load:

Your ZIP- code=??

Mid winter fuel use with exact meter reading dates =??

Input BTU and output BTU of the beastie boiler=??

 

[DR-DEATH]

Dana,

Sorry I haven't been able to update this post quickly. I went ahead and had a Rinnai ruc98 installed for just domestic hot water. I am now looking at just doing a regular boiler replacement as from the sounds of it a combi didn't make sense.

I haven't been able to have a J load calc done but length of baseboard and home info is all in my first post. A quick calculator is estimating I need about 88k btus to heat my house.

Can you guys recommend the best high efficiency boiler for my current set up? Now that I don't need a combi I think I'll have a lot more options that won't short cycle etc. I am looking to keep the boiler price around $2500-3000 to leave cost for install and misc items. Have budgeted around 5k for this with labor.

 

[NY_Rob]

Take a look at the HTP UFT-80W:
http://www.htproducts.com/UFT-Boiler.html

 

[DR-DEATH]

Do you know the going cost for that boiler? I can't find anything online that gives me an idea on cost. They are located in MA so I like that too.

 

[Dana]

Do you know the going cost for that boiler? I can't find anything online that gives me an idea on cost. They are located in MA so I like that too.

The Westinghouse badged version of the UFT-080W runs about $1700 at internet pricing.

HTP's should be in the same range, but you'll probably have to call for pricing.

 

[NY_Rob]

It was under $1'700 at the local plumbing supply house.

 

[DR-DEATH]

The Westinghouse badged version of the UFT-080W runs about $1700 at internet pricing.

HTP's should be in the same range, but you'll probably have to call for pricing.

Not bad at all. Any preference on which one to do if both are same price? Also, not sure if this is against the forum rules but by any chance you guys know a decent installer located in southern New Hampshire? I have the company that installed my rinnai system but as far as I know they don't sell these two boilers and may not want to support them.

 

[NY_Rob]

I would stick w/the actual HTP branded unit.
If there happens to be a warranty issue- you can deal with them directly vs. Westinghouse.

In fairness, I did dial the support number for the Westinghouse branded boiler (when I was looking to buy) just to see who answered- it was HTP support, and the address listed on the Westinghouse literature is the address of the HTP headquarters. So, it's pretty clear who's supporting the Westinghouse branded UFT boiler... but it's still better to go with the HTP brand in any case.

 

[DR-DEATH]

Gotcha. That makes sense. One more question,
I am fairly certain 80k btu is enough for my house but just in case would I lose any efficiency by buying the 100k btu unit just to be safe? I know it's a few hundred more but that's not a big deal. I just want to make sure it won't short cycle with my small zones.

 

[NY_Rob]

You won't lose efficiency, but if the 100K boiler has a 10:1 turndown like the 80K boiler has that means it's minimum output is 10K BTU's
You have to make sure you shortest zone can adsorb 10K BTU's otherwise it will short-cycle.

My "shortest" zone is 160' long but only has 43' of fin-tube, so at 120F average water temperature (130 Supply, 20F Delta, 110F Return) it can only put out 8,385 BTU's. If I used a boiler with a 10K BTU minimum on that zone- it would short cycle at those temps.

 

[Dana]

Gotcha. That makes sense. One more question,
I am fairly certain 80k btu is enough for my house but just in case would I lose any efficiency by buying the 100k btu unit just to be safe? I know it's a few hundred more but that's not a big deal. I just want to make sure it won't short cycle with my small zones.

What NY Rob said. It's less "safe" to oversize than to right-size it (to the extent possible). An 80K condensing burner is more than adequate for more than 19 out of 20 houses in North America, including those in central AK or on Hudson Bay. Unless you have the leakiest 5000' house in New Hampshire, it's enough.

If you have a heating history on the place it's pretty easy to caluculated the heating load base on fuel use and weather data using this methodology.

It's worth running the napkin-math on the radiation (per zone) to avoid short-cycling modulating condensing boilers.

 

[NY_Rob]

DD...
As Dana mentioned in post#4:
"You have 100' of baseboard on the system total. Designers of the era typically installed 2-3x as much boiler as was needed, and set it up to run at 180F out 160F back or an AWT of about 170F, which emits about 500 BTU/hr per foot. So you only have enough radiation to emit 50,000 BTU/hr, and it's probably more than 2x oversized for the real load. It's fine to over size the high-fire output of a mod-con a bit, but the critical number is the low fire output, since that determines how much modulating and condensing can really go on."

The above can't be ignored. If your measurements are correct- the 100K boiler is way overkill and that is the fastest way to kill a mod-con boiler.

 

[NY_Rob]

Even with the 10:1 turndown of the 80K boiler you'll have to combine your 14' and 36' zones (or use a $$$ buffer tank) to satisfy the minimum 8K BTU output.

 

[Dana]

Even with the 10:1 turndown of the 80K boiler you'll have to combine your 14' and 36' zones (or use a $$$ buffer tank) to satisfy the minimum 8K BTU output.

The basement zone is the 14 footer. Basements have very different heat loss characteristics than upper floors, and aren't really good for combining with upper floors- it'll never balance reasonably over all seasonal changes.

But if the boiler isn't oversized for the rest of it, calls for heat from that zone will almost always overlap with calls for other zones and almost never the only zone calling for heat. It certainly isn't worth adding a buffer tank. If it seems like it short cycles a lot, it would be easier and cheaper to add another 25' of baseboard, making it comparable in radiation size to the other zones.

With only 100' of baseboard in the whole house, even if you ran the boiler at 210F you'd be freezing during cold weather if your heat load was truly 88,000 BTU/hr. That would be 880 BTU/hr per foot of baseboard- which it can't deliver at hydronic heating temperatures, or even 215F steam. With 220F pumped hot water and a high pumping rate you might be able to get that much heat out of it. Consult the output ratings of a typical baseboard heat emitter. For a 1420 square feet of conditioned space (that includes a basement), that would be a whopping 62 BTU/hr per square foot of conditioned space, which would be the heat load ratio of my 2x4 framed antique when it's -200F outside (a temperature that has not been seen in this location since the earth was formed, and about 70F lower than the all time recorded low temperature at any weather station since record keeping began.) Suffice to say, the 88K-BTU number being spit out by the calculator you were using is simply ridiculous.

For a reasonably tight 2x6 framed 8os vintage house the above-grade floors should come in under 15 BTU/hr per square foot @ -5F, and the basement even less (quite a bit less if the foundation is insulated.)

 

[DR-DEATH]

The basement zone is the 14 footer. Basements have very different heat loss characteristics than upper floors, and aren't really good for combining with upper floors- it'll never balance reasonably over all seasonal changes.

But if the boiler isn't oversized for the rest of it, calls for heat from that zone will almost always overlap with calls for other zones and almost never the only zone calling for heat. It certainly isn't worth adding a buffer tank. If it seems like it short cycles a lot, it would be easier and cheaper to add another 25' of baseboard, making it comparable in radiation size to the other zones.

With only 100' of baseboard in the whole house, even if you ran the boiler at 210F you'd be freezing during cold weather if your heat load was truly 88,000 BTU/hr. That would be 880 BTU/hr per foot of baseboard- which it can't deliver at hydronic heating temperatures, or even 215F steam. With 220F pumped hot water and a high pumping rate you might be able to get that much heat out of it. Consult the output ratings of a typical baseboard heat emitter. For a 1420 square feet of conditioned space (that includes a basement), that would be a whopping 62 BTU/hr per square foot of conditioned space, which would be the heat load ratio of my 2x4 framed antique when it's -200F outside (a temperature that has not been seen in this location since the earth was formed, and about 70F lower than the all time recorded low temperature at any weather station since record keeping began.) Suffice to say, the 88K-BTU number being spit out by the calculator you were using is simply ridiculous.

For a reasonably tight 2x6 framed 8os vintage house the above-grade floors should come in under 15 BTU/hr per square foot @ -5F, and the basement even less (quite a bit less if the foundation is insulated.)

Your reply somewhat confuses me. I'm reading it as I won't get 95% condensing efficiency with the HTP 80 with my set up and I'll have issues or???? will the HTP 80 be capable of using my existing baseboard and effectively heat my house without short cycling, it will just have to run at 180 degrees as 140 condensing temps won't cut it?

I also asked my current plumber if he would be willing to install the Westinghouse or HTP and he said: "

The track history with the HTP has not been the most stable. They did have a lot of problems with that boiler when it first came out. If you are looking for the best I would highly recommend this boiler.


http://www.viessmann-us.com/en/residential/gas-boilers/condensing-boilers/vitodens-200-w.html


This is by far the best boiler on the market". Any thoughts on that response?

 

[NY_Rob]

Ignoring the 14' zone for now- Your second shortest zone has 36' of fin-tube, to be at 94% efficiency you need to have 100F return water. With AWT of 110F that 36' of fin tube can only radiate 5,760 BTU's. The smallest Viessmann from the above link can only modulate down to 12K BTU's. How would it not short cycle on that zone that's only putting out 5,760 BTU's?

To prevent short cycling on the 36' zone at 12K BTU minimum boiler output you'd have to supply 150F water, 140F AWT and hope for 130F return- but if you look at the chart in an earlier post- 130F return water is just at the cusp of condensing mode at 86% efficiency.

With an 8K BTU minimum boiler output your supply would be slightly over 130F with a return near 120F which is in condensing mode and very near the 8K min output of the boiler.

 

[DR-DEATH]

Ignoring the 14' zone for now- Your second shortest zone has 36' of fin-tube, to be at 94% efficiency you need to have 100F return water. With AWT of 110F that 36' of fin tube can only radiate 5,760 BTU's. The smallest Viessmann from the above link can only modulate down to 12K BTU's. How would it not short cycle on that zone that's only putting out 5,760 BTU's?

I mentioned that to my plumber and he said if the system is piped correctly with a low loss header I wouldn't have any short cycling issues. I have no idea what a low loss header is so idk the truth behind that.