Choosing a mod-con boiler

[Davie]

I'm looking at boiler options for my new hydronic system, and here's a list of what makes my local supplier deals with:

• Lochinvar
  
• Navien
  
• NY Thermal Inc. (NTI)
  
• Raypack
  
• Thermo 2000
  
• Viessmann
  
• Weil-McLain

Speaking with them, they were trying to convince me to go for a Navien NHB 110 or 150, even after I told them my requirements are 58,460 btu/h. Seems to me that the NHB 80 is better sized for my needs--right about 1.4x oversize, and the same minimum fire (8,000 btu/h) as the NHB 55.

Anyone have any thoughts on the NHB or the other brands above? I've heard some of them mentioned here, but don't know enough about any of these to really know what I'm comparing. From what I've read here, I would have gone for HTP or

 

[Dana]

How did you come up with the heat load number?

With a mod-con there is no need to use the ASHRAE 1.4x multiplier, which is there primarily to be able to use set-back strategies with on/off non-modulating boilers. With a mod-con tweaking the reset curve and keeping it at a constant temperature uses less energy than set-backs, which would need a higher, less efficient water temp to deliver reasonably short recovery ramps back to temperature.

The Navien NHB-080 boiler is just fine for a 58K design load. Stick to your guns on that. If they support that product well that's your choice. The higher impedance water-tube heat exchanger means in most systems it would have to be plumbed primary/secondary, but the pre-engineered hydraulic separation manifold they sell for it makes it relatively easy to get right, even if it's not as forgiving as low-head fire-tube heat exchangers.

Lochinvar is a high quality vendor with lots of bells & whistles to tweak for the boiler controls. The KH-085 (0r wall-hung WH-086) or KHN/WHN-086 stainless fire tube boilers would be a good fit.

The Weil McLain ECO-70 fire tube stainless boilers are a bit simpler and would cover your specified load too, but doesn't . Whether it works for you depends on how much micro-zoning you're going to do.

The NTI Trinity Tft 85 stainless fire tube boiler would do it too, but has an even higher minimum modulation level, but would be fine for a 1-2 zone system.

I'm less familiar with the others.

 

[Sponsor]

 

[Davie]

Thanks Dana, that's super helpful.

I calculated the heat loss with CoolCalc and also on paper with heat loss equations. CoolCalc gave me 56,020 and the paper calcs gave me 58,460.

The system has 3 zones: two in the low 2ok's and the third between 9k and 14k (depending on the calculation method). So I like the sub 10k turndown option that the Navien and Lochinvar offer for that third zone.

Wall mounted seems appealing to me. Is there any advantage to the floor mount?

 

[Dana]

Like most online freebie calculators coolcalc tends to shoot higher than reality by a double-digit percentage even with aggressive input assumptions, so there's no need to upsize the boiler from their numbers. You might be even be able to get there with a 50K boiler, but with 10:1 turn down ratios 70-85K boilers are fine.

Floor mounts can be installed in a wider range of locations (such as not next to a wall) for ease-of-plumbing convenience, but beyond that the differences are cosmetic. If wall-mounting on an exterior foundation wall that is currently not insulated, build out and insulate a section of wall for mounting the boiler so that you won't need to move it all if you decide to insulate the whole foundation (highly recommended, in locations as cool as Toronto.) There are multiple threads on this site on how to do that without going into the mold-farming biz.

Be sure that all of your zones have enough radiation to emit the full minimum-output of the boiler at condensing temperatures. That may require upsizing the radiation for the third zone, if it's design load is only 9K, but maybe not if it's design load is 14K. If it's load is that high when it's -18C outside it'll be about half that when it's +3C outside, and your outdoor reset curve is sending cooler boiler water. The napkin math on that lives here.

 

[Jac04]

Anyone have any thoughts on the NHB or the other brands above?

I'll give you my honest opinion on the Navien unit. I have a NCB180-E (combi heat & hot water unit), which uses the same basic heat exchanger as the NHB. It is a neat little unit, but I'm not sure they have all the heat exchanger reliability issues worked out.

Here's my experience: My old Navien CH180 failed the heat exchanger in 4 years - it failed due to corrosion from the condensate. The acidic condensate ate right through the outer aluminum casing of the heat exchanger. Now I have a NCB, which was installed under warranty (still had to pay a bunch of $ for installation). It has a slightly updated heat exchanger design which is basically the same as the NHB you are considering. The problem now is that I have metallic sediment in the condensate trap, which appears to be an indication that the stainless steel part of the heat exchanger is deteriorating. The heat exchanger is 400-series stainless, which is magnetic. The "technical" support people from Navien are completely clueless about how these condensing units operate, especially the basics of the heat exchanger design in condensing boilers. So, if I want this issue addressed, I will have to spend hundreds of dollars to get a "Navien Service Specialist" to come out to look at it. But, I'm under a parts-only warranty because the new unit only comes with the remainder of the original unit's warranty. Very frustrating.

Now, with that said, I really have no idea how long this thing is going to last, but it doesn't give me a confident feeling.

The plus side to this unit is that parts are readily available and reasonably priced. I bought a fairly complete set of spares for my unit just to have them on hand.

 

[Dana]

Thanks Dana, that's super helpful.

I calculated the heat loss with CoolCalc and also on paper with heat loss equations. CoolCalc gave me 56,020 and the paper calcs gave me 58,460.

The system has 3 zones: two in the low 2ok's and the third between 9k and 14k (depending on the calculation method). So I like the sub 10k turndown option that the Navien and Lochinvar offer for that third zone.

Wall mounted seems appealing to me. Is there any advantage to the floor mount?

I'm surprised a local supplier in Toronto wouldn't carry Laars(?). The 80K version of the FTHW series is pretty-good Korean fire tube heat exchanger boiler (manufactured by Kiturami) that can usually be pumped direct rather than primary/secondary (unlike the Navien water-tube boilers). It doesn't have as many bells & whistles/programming levels of a Lochinvar, but it's not a stripped down feature-free item by any means. A nearly identical Kiturami boiler under the paint is sold by HTP & Westinghouse in the US, and fairly popular in my area.

The Laars version has the option of an internal pump, unlike the HTP/Westinghouse version, but the latter has a two supply & return ports pre-plumbed to make installing an indirect water heater easier. Compare the diagram on p8 (p10 in PDF) of the Laars document with Figure 5 of the HTP document (p16). All of the major components are identical.

This boiler should be easier to install correctly than a Navien, and substantially less expensive than a Lochinvar (TBD). Since Navien & Kiturami compete head-to-head in their domestic market it may be the case (or not) that the same suppliers might not carry both in Canada. But since Laars HQ isn't very far away (Halton Hills), local support in the Toronto area should be pretty good.

[edited to add] Upon closer inspection the Laars FTHW80 has only a 5:1 turn down ratio not 10:1, unlike it's HTP cousins, with a ~15K minimum output.

 

[Davie]

Be sure that all of your zones have enough radiation to emit the full minimum-output of the boiler at condensing temperatures. That may require upsizing the radiation for the third zone, if it's design load is only 9K, but maybe not if it's design load is 14K. If it's load is that high when it's -18C outside it'll be about half that when it's +3C outside, and your outdoor reset curve is sending cooler boiler water. The napkin math on that lives here.

I reread your article on GBA, and did the math for my situation. Checking out WeatherSpark, it looks like my median wintertime temperature is around 27F, and using that number for my load calcs, I get zone values of ~12k btu/h for the two larger load zones and between ~5k and 8k for the smaller zone. At +3C (I appreciate the metric conversion), it's a different story--as you suggest. Right about at that halfway point.

All of this leaves me a bit confused, I must admit. Let's say I'm sizing the radiators in the basement to emit 14k btu/h at 140F AWT at design conditions. When the load is half that, I get that my load is only 7k btu/h for the basement, but I can't turn the boiler down to 7k. (Although once the output efficiency is calculated, and the thermal mass of the cast iron rads is figured in, maybe we're close?). But how do I figure out my actual heat output capacity at the outdoor reset-controlled AWT? Or do I reverse engineer that and insert it as a point on a custom outdoor reset curve?

E.g. At 140F AWT my EDR per square foot is 90 btu/h. To get 45 btu/h/sq.ft., it looks like I need about 117F AWT.

Testing for condensing efficiency, I determined that at an AWT of 130, the house gets 7/9 as much heat output as it does at 140F. Using 7/9 of my delta T at design conditions (Indoor temp 70F minus outdoor temp 1F = 69F; 69F x 7/9=54F; 70F-54F=16F), I determined that my outdoor temperature at that load would be ~16F. Does this math add up? Am I right that this means anytime the temperature is above 16F I'll be in condensing territory?

A nearly identical Kiturami boiler under the paint is sold by HTP & Westinghouse in the US, and fairly popular in my area.

...

This boiler should be easier to install correctly than a Navien, and substantially less expensive than a Lochinvar (TBD). Since Navien & Kiturami compete head-to-head in their domestic market it may be the case (or not) that the same suppliers might not carry both in Canada. But since Laars HQ isn't very far away (Halton Hills), local support in the Toronto area should be pretty good.

I haven't found a local supplier of Laars (strange, I agree, given how close I am to their HQ), but I'm looking at the HTP now, with the 10:1 turndown. I have contacted their sales rep. to see if I can find a local supplier, because they also seem to be hard to track down locally for some reason. I certainly like the idea of a simpler installation, and jac04's experience is not too encouraging.

 

[Davie]

I'll give you my honest opinion on the Navien unit. I have a NCB180-E (combi heat & hot water unit), which uses the same basic heat exchanger as the NHB. It is a neat little unit, but I'm not sure they have all the heat exchanger reliability issues worked out.

Here's my experience: My old Navien CH180 failed the heat exchanger in 4 years - it failed due to corrosion from the condensate. The acidic condensate ate right through the outer aluminum casing of the heat exchanger. Now I have a NCB, which was installed under warranty (still had to pay a bunch of $ for installation). It has a slightly updated heat exchanger design which is basically the same as the NHB you are considering. The problem now is that I have metallic sediment in the condensate trap, which appears to be an indication that the stainless steel part of the heat exchanger is deteriorating. The heat exchanger is 400-series stainless, which is magnetic. The "technical" support people from Navien are completely clueless about how these condensing units operate, especially the basics of the heat exchanger design in condensing boilers. So, if I want this issue addressed, I will have to spend hundreds of dollars to get a "Navien Service Specialist" to come out to look at it. But, I'm under a parts-only warranty because the new unit only comes with the remainder of the original unit's warranty. Very frustrating.

Now, with that said, I really have no idea how long this thing is going to last, but it doesn't give me a confident feeling.

The plus side to this unit is that parts are readily available and reasonably priced. I bought a fairly complete set of spares for my unit just to have them on hand.

Thanks jac04,

It's great to hear from someone who has a Navien product.

How long ago did you have the new NCB180-E installed? I'm curious how soon you started seeing the metal in the condensate trap. I have to say I'm not too keen on embracing a condensing boiler that can't handle its own condensate.

And as far as spare parts that you have on hand, did you purchase the Navien Spare Parts Kit (30018664A)? What specific parts are in that kit? I don't see the details on Navien's site. I did find something that made me wonder if it is mainly electrical components (transformer, fan motor, PC board, flow sensor...). If the heat exchanger corrodes through again, is there any way to fix that specific issue, other than replacing the whole boiler?

I'm feeling a bit conflicted as Navien was identified by my local supplier as the better supported option (between them and Lochinvar), but between the primary/secondary installation, and your condensate issues, I'm not feeling confident.

 

[Jac04]

I had the NCB installed in September 2017, and I saw metal in the trap in February 2018. I cleaned it out a few times before that, right after installation, but never checked to see if it was metallic.

I put together my own spare parts kit. I got things like thermistors, 3-way valve, dhw flowmeter, hi-limit switch, o-rings, air press sensor, ignitor, ignitor transformer. I didn't get a fan blower, but I might pick one up. Just a little leary right now. I have a bunch of spares for my CH unit including a fan blower, but they are worthless now.

The heat exchanger carries its own part number, but Navien doesn't supply it individually. So, if the heat exchanger fails, then the whole unit needs to be replaced.

 

[Davie]

I had the NCB installed in September 2017, and I saw metal in the trap in February 2018. I cleaned it out a few times before that, right after installation, but never checked to see if it was metallic.

I put together my own spare parts kit. I got things like thermistors, 3-way valve, dhw flowmeter, hi-limit switch, o-rings, air press sensor, ignitor, ignitor transformer. I didn't get a fan blower, but I might pick one up. Just a little leary right now. I have a bunch of spares for my CH unit including a fan blower, but they are worthless now.

The heat exchanger carries its own part number, but Navien doesn't supply it individually. So, if the heat exchanger fails, then the whole unit needs to be replaced.

Thanks again.

You make a good point about amassing spare parts when you don't know how long the unit will last. It's frustrating that the heat exchanger alone can't be swapped out.

I was thinking about your situation last night, and I wonder: did you see metallic sediment in the trap before the CH failed? If the condensate is corroding the stainless, would it create an identifiable metal particle? I'm not a chemist, and I'm not totally clear on what the products of a stainless-acid reaction would be. If it were corroding iron or steel, I would imagine seeing flakes of rusty iron in the trap, so maybe it's the same with the stainless.

 

[Jac04]

did you see metallic sediment in the trap before the CH failed?

Yes, but here's the weird part: The CH unit always had grey colored condensate with a dark grey/black sludge in the trap. When I had the condensate drain into a white bucket, the bottom would be covered in a thin layer dark grey sludge after a few days. The sludge smelled like aluminum(if you've ever wet sanded or polished a piece of aluminum you know that the smell is distinct). So, metallic, yes, but aluminum and not magnetic. When the CH exchanger failed, it was the outer aluminum casing that corroded through.

With the new unit, I was soooo happy that the condensate was perfectly clear until I found the magnetic sediment. The sediment never creates an orange color if you dump it onto a paper towel and let it dry. But, my experience with 400-series stainless (I have a few 409 stainless exhaust systems on cars) is that it creates a dark colored corrosive product, especially around the welds when new, almost like a weld slag. Hmmm, that has me thinking ... am I just seeing some weld slag coming off the internal welds of the heat exchanger? The amount of sediment seemed to go way down over the summer, but the unit was only running for hot water.

 

[DrS1]

I'm surprised a local supplier in Toronto wouldn't carry Laars(?). The 80K version of the FTHW series is pretty-good Korean fire tube heat exchanger boiler (manufactured by Kiturami) that can usually be pumped direct rather than primary/secondary (unlike the Navien water-tube boilers). It doesn't have as many bells & whistles/programming levels of a Lochinvar, but it's not a stripped down feature-free item by any means. A nearly identical Kiturami boiler under the paint is sold by HTP & Westinghouse in the US, and fairly popular in my area.

The Laars version has the option of an internal pump, unlike the HTP/Westinghouse version, but the latter has a two supply & return ports pre-plumbed to make installing an indirect water heater easier. Compare the diagram on p8 (p10 in PDF) of the Laars document with Figure 5 of the HTP document (p16). All of the major components are identical.

This boiler should be easier to install correctly than a Navien, and substantially less expensive than a Lochinvar (TBD). Since Navien & Kiturami compete head-to-head in their domestic market it may be the case (or not) that the same suppliers might not carry both in Canada. But since Laars HQ isn't very far away (Halton Hills), local support in the Toronto area should be pretty good.

[edited to add] Upon closer inspection the Laars FTHW80 has only a 5:1 turn down ratio not 10:1, unlike it's HTP cousins, with a ~15K minimum output.

I'm interested, what is your opinion of the Rinnai boilers like the E85SR vs the HTP/Westinghouse you mention. (http://pdf.lowes.com/installationguides/766156009327_install.pdf)? Also, how about the Noritz brand?

 

[Dana]

I don't know a lot about the Rinnai boilers, but it's a bit like comparing apples & pears. The Rinnai has higher head a water-tube heat exchanger (similar to Navien's boilers) with a 6:1 turn down ratio, the UFT-series HTPs are higher volume/lower head fire-tube boilers with a 10:1 turn down. For a system with multiple zones or a higher pumping head the Rinnai would need to be plumbed primary/secondary (Like Navien, they sell a pre-engineered hydraulic separator designed for their boilers to make it harder to screw that up), most fire tube boilers can be pumped direct over a wide range of if you do the math.

Noritz used to sell re-branded Kiturami boilers similar to HTP's UFT series (also manufactured by Kiturami.) I haven't really followed their evolving offerings. Kiturami is a first-tier Korean boiler & water heater manufacturer that competes head to head with Kyung Dong Navien in their home country, but has taken a different strategy for the export market, leaving the sales distribution & support to local companies such as Noritz, HTP, Laars, etc, whereas Navien has developed their own distribution & support networks here.

Rinnai is a first-tier Japanese vendor, and at least as of a handful of years ago was still the world's largest manufacturer of gas burning appliances.

How well supported any of them near YOU will vary.