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

[Arseniy M]

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!

 

[Dana]

In many ways the system design is easier with the UFT, since it's fire tube heat exchanger can easily handle the radiation flow rates. NHB boilers MUST be plumbed primary/secondary in most cases.

The UFT also comes internally plumbed with a dedicated secondary port for the indirect.

NY_Rob is also on L.I. and successfully DIYed a UFT in recent years, and has shared lots of setup tips on this forum.

 

[Sponsor]

 

[Arseniy M]

Hi Dana,

Thanks for responding. It is thanks to your articles that I did NOT blindly go with an NCB-240e last year when one Navien installer offered that to me. With a heat loss of just under 30kbtu/h @ 99% design temp, and 5 people in the house that boiler is almost the exact opposite of what we need. I'm a software engineer by the way, so I crunch through numbers well.

NY_Rob hasn't posted anything anywhere for a while, but I did read a lot of his (and your) posts. HTP schematic for direct piping with zone valves looks straight forward. Few things I don't quite understand, so I was just wondering if someone here could clarify.

1. Why are there 2 sets of purging valves in a row on the supply side?
2. If the system pump already has an IFC why is there a check valve on the return?
3. When would the differential pressure bypass valve be needed?

 

[Dana]

I'm not sure what the rationale is behind #1 &#2.

The pressure bypass valve is a good idea for systems using zone valves, since the flow through the boiler would otherwise stop when the last zone valve closed, leading to flash boil on the heat exchanger. Also when serving just one low flow zone it may be needed just to keep the flow through the boiler above it's minimum flow spec.

 

[DR-DEATH]

I have the taco 1816 with zone valves and almost identical basement situation with my HTP. Spent many hours watching the basement zone and the cycles last around 30-40 mins stand alone. Have heating cap. Set to 60% and ramp up feature enabled. Other than my possible failed HX... it’s been great lol

 

[Arseniy M]

Do you have it piped direct or primary/secondary?

 

[Dana]

I have the taco 1816 with zone valves and almost identical basement situation with my HTP. Spent many hours watching the basement zone and the cycles last around 30-40 mins stand alone. Have heating cap. Set to 60% and ramp up feature enabled. Other than my possible failed HX... it’s been great lol

Without the pressure bypass valve there is a water-hammer pressure spike when the last valve closes, which may not be a big deal if the gpm is low enough, but it's still easier on all the equipment to relieve that spike. Whether that's related to the HX failure is TBD.

 

[Arseniy M]

Would plumbing it primary/secondary alleviate the problem of pressure spike? Also, what commands the primary (boiler) pump to start/stop?

 

[Fitter30]

3/4" fin tube @ 165* 46 btu's a foot primary secondary does eliminate bypass valve and the plus is constant flow through boiler. Btu rating table link
https://www.google.com/url?sa=t&sou...FjACegQIDRAM&usg=AOvVaw2VvIGnP7muPVhLp5iSJSIA