Dunkirk DKVLT-075 vs Navien NHB-80

[n0chance]

Hi,

I have a baseboard water heat system that currently heats by oil. I am looking to convert this to gas (and still have a separate electric water heater for running water).

I received a quote from a vendor stating i qualified for a home energy rebate to

1. Get my attic insulated
2. Install a Dunkirk DKVL-075 (which later they said they want to do Navien NHB-80 instead)
3. Final cost for equipment and service: $9,000 ($14,000 - $1,000 discount incentive - $4,000 new jersey rebate)

At first they said they would install a Dunkirk DKVL-075, and then when the financing went through, they wanted to change it to Navien NHB-80. I'm not sure if I'm getting a good price on this, or if I'm being bait and switched?

Any thoughts on the 2 units and price?

Thanks!

 

[Dana]

The price of the boiler is but a small fraction of the installation cost- most of it is in the system design and plumbing. If the warranty, service & local support between the two is similar, the NHB-80 is probably preferable, due to it's lower minimum modulation rate (8,000 BTU/hr in vs. 15,000 BTU/hr) which means it can modulate more even at lower loads or smaller zones, with fewer burn cycles per season, which means higher as-used efficinecy and less wear & tear on the boiler. If your whole-house heat load is say, 30,000 BTU/hr @ +15F (Trenton's 99% outside design temp), the Dunkirk would be cycling on/off rather than modulating during your average winter temp, whereas the Navien can modulate with long nearly continuous burns even at 50F or higher.

$14K is on the high side for simple boiler swap out of a cast iron boiler for a mod-con, but the particulars of the work can change it dramatically. If it's broken up into zones and needs a whole zone manifold and pump/zone-valve upgrade to work reasonably it's different than if it's a simple single zone boiler swap.

How much baseboard do you have (broken down by zone, if multi-zoned) and what is your design heat load?

 

[Sponsor]

 

[n0chance]

How much baseboard do you have (broken down by zone, if multi-zoned) and what is your design heat load?

I currently have 3 zones in a split level house. I'm not sure of the exact details, but in my 2 roof areas in the splitlevel they would do insulation, it is 498 sqft + 700 sqft.

There was a breakdown in a proposed measures:

• Gas Hydronic Boiler 95% AFUE = $8,000 | SIR 3.14
• 15" Blown fiber glass * 700 = $1,125 | SIR 0.85
• 15" Blown fiber glass * 498 = $1,125 | SIR 0.6
• Hatch 2 inch Polyisocynaurate = $125 | SIR 1.12
• Hatch 2 inch Polyisocynaurate = $125 | SIR 1.12
  
• Shell Test & Seal = $2,500 | SIR 0.7

Total: $13,000 | SIR 2.4

Any other opinions?

 

[Dana]

OK- the boiler installation is $8K, not $14K, which is fine, a credible and rational number for a simple mod-con boiler installation without a lot of re-zoning, etc.

From your orignal post there was no indication of the rest, which is a substantial amount of non-heating-system work.

If the total amount of conditioned space is 1200-2400' broken up into 3 zones you definitely want a boiler that modulates down to under 10,000 BTU/hr, which means the NHB-80 would be a good choice. Another good choice would be HTP's UFT-080W (which is also sold under a Westinghouse nameplate as the WBRUNG 080W, at an attractive list price. An advantage to the UFT/WBRUNG 080W over the NHB-80 is that in 9 systems out of 10 it can be pumped direct without much tweaking, rather than primary/secondary. The result is that it uses substantially less electricity. Navien's installation documents are fairly insistent about primary/secondary architecture (and they sell a pre-fabbed hydraulic separator for that purpose), though a decent hydronic designer doing the math it too could be pumped direct. With modulating boilers that run nearly continuously the pumping electricity use becomes relevant.

If any of the zones have less than 35' of fin-tube baseboard even the NHB-80 or UFT-080W will cycle rather than modulate when the water temps are low enough for condensing efficiency. If they went with the DKVL-075 the minimum would be ~55'. It's worth measuring and adding up all the baseboard lengths on each zone now, since upgrading the radiation is usually cheaper if done in combination with the boiler installation rather than going at it piecemeal later.

Was means "SIR" in this context?

The 1200' of R50 fiberglass at $2500 works out to about 4 cents per R per square foot, which is a competitive price, and $125 for a sealed insulated hatch is also reasonable. The $2500 of air sealing & testing may or may not be a good deal, depending on the details (including whether there is maximum air leakage or minimum percentage reduction guarantee.) Either way, air sealing is a critical first step prior to insulating, and if they're using blower-door and infra red imaging guided air sealing the prospects of getting it right are very good, and at $2500 in a house with complicated framing (as many split-levels are) it could be the best bargain on the list.