Navien NHB-80 vs. HTP UFT-80w.

ArseniyM

I originally posted this on terrylove but did not get much input so here it goes again:

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Hello everyone!

After a significant amount of reading/research I'm looking for opinions on the following two mod-con boilers as possible replacements for my existing oil-fired beast:

1. Navien NHB-80
2. HTP UFT-80w

The house is a typical Long Island split-level. Currently heated by an over-sized Burnham KV74 with a coil for DHW (about 20 years old).

3/4" baseboards ~ 105' feet total. Currently 2 zones (3 separate loops). Since this is a split-level, I can't really say upstairs or downstairs so I'll give breakdown this way:

1. Ground level -> 22' (has its own thermostat) -- 200sq. ft.
2. Middle level -> 42' (has a thermostat) -- 600sq. ft.
3. Top level -> 41' (no thermostat) -- 500sq. ft.

The plan is to use an indirect for DHW. Most likely HTP SSU-30LB.

Everything is currently pumped by 2 Taco 007-f5 circulators. The middle and top levels start off as 1" and then it splits (while still in the basement) into two 3/4" separate loops as mentioned above and they run in opposite directions. After they complete their respective circles they re-join to become 1" again and back to the boiler.

The minimum firing rate for NHB-80 and UFT-80 is 8,000 btu/h. The 22' will most definitely short cycle when it's the only zone calling for heat (at condensing temps), so the plan is to run a single ECM pump (Taco Viridian 1816 or Grundfos Alpha 2) in constant pressure mode and use zone valves which should allow me to open both the ground level and the middle level loops when the ground level is calling for heat. The plumbing is already there, so this should be an easy change. 99% design temperature for my area is 15*F. According to my calculations, I should be able to condense most of the heating season. The long term goal is to finish the basement and make it a separate zone with enough radiation to emit 8,000 btu/h at condensing temps -- about 35 feet or so. The basement is about 600sq. ft. (underneath the middle level), about half of it is below grade.

As I mentioned I'm located on Long Island (Nassau County) and it looks like locally there's more support for the Navien, but to be honest I'm leaning towards the HTP.

If anyone has first-hand experiences with either one (the good the bad or the ugly) please do tell.

Thanks very much, and stay safe during this difficult time!

fenkel

Both are only as good as the installation... both can (will)have issues sooner or later..
Weve installed a few htp ufts and had no issues...
The uft boiler is a medium mass boiler..a little more water in it..
Might not short cycle as much..
Id install a 20 gallon htp buffer tank with the uft boiler.. ( no short cycling)
The uft boiler has a nice post purge setting for both idw and central heat..has a anticycling function...
They just came out with a new boiler called the elite ultra.. has a 15 year warranty... search this site for installation pictures of that boiler..

GroundUp

Unpopular opinion, but I'd say neither until you have an accurate heat loss calculation completed. You say your calculations show you'd be able to condense most of the year but didn't list that data so it's tough to say whether or not a mod/con is going to suit you well or not. With that said, I do really like the UFT and have installed dozens with zero trouble (save for one, that's been constant trouble) on low temp radiant floor systems. If the SWT runs over 140 (typical for baseboard, but not always), I will usually stick with a conventional CI boiler like a Weil McLain CGA/CGI or Slant Fin VSPH depending on the application. Sometimes a 5% trade in efficiency is worth 20 years of maintenance free operation. Regardless of boiler though, I'd look into a buffer tank as well. The mod/con don't like to run extended periods on low fire and it will cause HX issues with time. Perhaps something like a TurboMax reverse indirect?

ArseniyM

GroundUp said:

Unpopular opinion, but I'd say neither until you have an accurate heat loss calculation completed.

Since I have a habit of keeping receipts of my oil deliveries, I did a fuel-use calc a while ago, can't remember the exact number, but it was definitely under 30kbtu/h. The sticker on my 20-year old boiler says 82% efficient, but in reality it's probably 72% -- so that's what I used. The < 30kbth/h figure also includes DHW.

I thought that mod-cons LOVE to be run nearly continuously at the lowest possible input. This is where they shine, no?

GroundUp

ArseniyM said:

GroundUp said:

Unpopular opinion, but I'd say neither until you have an accurate heat loss calculation completed.

Since I have a habit of keeping receipts of my oil deliveries, I did a fuel-use calc a while ago, can't remember the exact number, but it was definitely under 30kbtu/h. The sticker on my 20-year old boiler says 82% efficient, but in reality it's probably 72% -- so that's what I used. The < 30kbth/h figure also includes DHW.

I thought that mod-cons LOVE to be run nearly continuously at the lowest possible input. This is where they shine, no?

I suppose that's a viable enough source for loss, if you can narrow the usage down day by day. Average loss of 30k might have actual design loss of 100k or more so monthly average will do you little to no good. Mod/cons do love to run continuously, but not at low fire especially with a 10:1. A 3:1 is a different story but 10 will cause trouble with the HX over time. What temp water does your BB system use currently? Depending on element used, your 105ft of element is capable of producing in excess of 60k with 180 degree supply water so if the loss is indeed 30k at design, your assessment may very well be on point. I surely don't mean to discredit your research, just making sure we're on the same page is all.

ArseniyM

Decided to calculate again based on last winter's deliveries. This winter was very mild. Here it goes:

Delivery 2018/12/27 -- 126.2 gallons
Delivery 2019/02/01 -- 213.4 gallons
Delivery 2019/03/06 -- 193.8 gallons

Design temp for my location is 15*F.

Assuming that the tank was filled to capacity (275 gallons) all three times means that between 2018/12/27 and 2019/03/06 the boiler burned through 213.4 gal + 193.8 gal = 407.2 gallons.
The house is kept at 70*F. No setbacks unless we go away for more than a couple of days -- which we didn't last winter.

I know we are using about one tank-full per year for DHW. The period above covers 70 days. So (275 gal / 365 days) * 70 days ~ 53gal of the 407.2gal went towards DHW.

407.2gal - 53gal = 354gal -- is the amount of number 2 heating oil that went into the heating of the house.

Using DegreeDays I downloaded and summed up the daily base 65*F and 60*F heating degree days (HDD) for the nearest weather station for the period above -- 2203.7 & 1853.8 respectively.

My KV74's nameplate shows an input rating of 136kbtu/h and 82% efficiency, let's assume that this is in fact true. So the actual output is about ~ 112kbtu/h. Number 2 oil gives off 139,600 btu/gallon so the net amount of heat that was delivered into my baseboards:

354 gal x (112,000btu/136,000btu) = 290.28 gal
290.28 gal x 139,600 btu/gallon ~ 40.523 million BTU (MMBTU).

40.523 MMBTU / 2203.7 HDD is 18,389 BTU per degree-day. With 24 hours in a day, that’s an average of 766 BTU per degree-hour at a balance point of 65*F.
40.523 MMBTU / 1853.8 HDD is 21,859 BTU per degree-day, and with 24 hours in a day that’s an average of 911 BTU per degree-hour at a balance point of 60*F.

A balance point of 65*F with design temp of 15*F is a difference of 50*F degrees, and the implied heat load is then 50*F x 766 BTU/F-hr = ~38,300 BTU/hr.
At a balance point of 60*F there are 45*F heating degrees, and the implied load is 45*F x 916 BTU/F-hr = ~40,995 BTU/hr.

These numbers need to be adjusted for the actual efficiency of my KV74. Who knows. Realistically I'm probably in low-mid 60's.
Which would bring the load down to around 30kbtu/h.

The boiler has an old-school aquastat on it where LO is set to 155 and HI is set to 180*F. The temperature gauge reads significantly higher. So I'm not sure what to trust, but assuming that I'm getting about 600btu/h per linear foot -- 105*600=63,000btu/h. I know, there's not enough radiation to deliver the full rated output of my existing boiler at an SWT of 180*F, but it is what it is.

Like I said, the plan is to finish the basement and add enough radiation to satisfy the 80kbtu/h firing rate of the Navien or the HTP (or whatever else).

Zman

The sizing question always gets interesting with small loads. The turndown rate on both units is so low that I think sizing matters less.
You are asking a Ford vs Chevy kind of question. Pick the one with better local support and be done with it.
I prefer HTP (and Chevy) for no good reason.

ArseniyM

Zman said:

The sizing question always gets interesting with small loads. The turndown rate on both units is so low that I think sizing matters less.
You are asking a Ford vs Chevy kind of question. Pick the one with better local support and be done with it.
I prefer HTP (and Chevy) for no good reason.

That's what makes it so difficult -- can't afford a Lochinvar, but I'd probably go with a Ford (Raptor)

wesPA

Lochinvar does make their Noble boiler in a boiler only option, previously was a combi only. 10-1 turndown. Not as many control options as the Knight, but depending on your needs, can be a good option. I have had the combi (using it for boiler only at this point) for 3 heating seasons and have been happy with it so far