Choosing the correct gas wall mounted boiler for my needs

Discussion in 'Boiler Forum' started by Alaska_RockGirl, Mar 18, 2016.

  1. Alaska_RockGirl

    Alaska_RockGirl New Member

    Joined:
    Mar 18, 2016
    Location:
    Alaska
    Hello All,

    I've read quite a few of the boiler sizing threads and I'm pretty sure the bids I've received from 3 heating contractors are too big for my needs. But I wanted to get your opinion to confirm before I call to request bids on smaller models.

    I'm in Anchorage, Alaska. 1978 construction, end unit, townhouse-style condo, 1,096 square feet. One bathtub/shower, one dishwasher, in-unit washing machine. Originally electric heat, converted to gas boiler baseboard hot water heat in the late 1980s(?). My wall-mounted Weil-McLain AHE-60 boiler is in the dining room. The crawl space is not sufficiently sized for installing a boiler, so I am keeping it in the dining room, which is an outside wall. I asked about moving it to the utility room with the washing machine/Amtrol, but the contractors said it would be too expensive (though if I save money on the install by getting a smaller boiler maybe that will change).

    They also did not recommend a combi boiler and from the research I've done and the fact I'm planning on selling in the next 5 years I am in agreement at this time...though it would be nice to get rid of the space-hogging Amtrol!

    Three zones:
    Main floor: 43' fin baseboards
    Second floor: 31' fin baseboards
    41 gallon Amtrol hot water maker (new in 2009)

    I participated in an energy rebate program in 2010 and made a lot of upgrades- but not the boiler. The energy program featured a blower-door air changes evaluation along with R values, window to wall ratio, south facing window area. I brought my place up to a 4 star plus rating. My "coldest day" design heat loss is 34,000 BTU/hour.

    So far I've received quotes from three different heating contractors in town for five different units:
    1. Triangle Tube Challenger TCC85
    2. Lochinvar Cadet CDN070
    3. Weil McLain 97+70
    4. Navien NHB-80
    5. Dunkirk CHB-100

    Costs are ranging from $7,334 to $8,834 for boiler + install. Efficiency rates are between 85% and 95%.

    Based on the coldest day value of 34,000 BTU/hour and the fact that all the proposed boilers have an output of 65,000+ it sure seems like I should be looking at a smaller boiler. In the contractors' defense, I hadn't realized when I had the gentlemen out to bid that the upgrades I made to my home would affect the boiler sizing. It wasn't until I found this board that I realized there were more factors than just "what size I have now" to take into account.

    Hopefully I've provided enough details for a recommendation. Please advise, does a smaller boiler make sense, based on the information above?

    Thanks in advance!
     
  2. Leon82

    Leon82 Member

    Joined:
    Mar 13, 2014
    Location:
    Connecticut
    I believe they have a cdn 040 boiler also a whn 055
     
  3. Sponsor

    Sponsor Paid Advertisement

     
  4. BadgerBoilerMN

    BadgerBoilerMN Hydronic Heating Designer

    Joined:
    Mar 4, 2011
    Occupation:
    hydronic heating designer/contractor
    Location:
    Minneapolis
    Your baseboard will likely not handle more than 40mbuth output at 180F average water temperature.

    The main floor zone, likely runs most of the time, will need a maximum of 17mbtuh, or about the low-fire of an
    80mbuth ModCon. That is, under design conditions, so you will be bumping off the bottom of the boiler control and efficiency, along with reliability, will suffer.

    Of the units mentioned the Cadet is a good value and with a proper Manual 'J' heat load their CDN-040 is will likely confirm it to be the perfect fit with a low-fire input of just 9mbuth is one of the smallest and a good match for the Amtrol, if you must.

    http://www.lochinvar.com/_linefiles/CDN-04.pdf
     
  5. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    It's the minimum fire output that's important, not the max. The turn-down ratios differ:

    1. Couldn't find good specs on the TCC85, but it's minimum input is 23,000 BTU/hr which is well over half your 99% design temp heat load. Forget it.

    2. The Lochinvar Cadet CDN070 only modulates down to 14K-in/13K/out, and will will short cycle on zone calls at condensing temps.

    The CDN040 would be a better choice at 9K-in, and would probably do just fine if it's big enough to cover your heat load (which it does, if the calculated 34K is right.)

    3. Minimum input on the Weil McLain 97+70 is also 14K in (like it's Lochinvar cousin) , still not great- it'll short-cycling on a 31' stick o' fin tube at condensing temps.

    4. The Navien NHB-80 will modulate down to 8000 BTU/hr in, so it's not going to be a problem, and would give you fast hot water heating recovery.

    5. Min fire input on the Dunkirk CHB-100 is 31K- take whomever recommended that piece of junk outside and whup 'm! ;-) (Lose their number- seriously!) That's a really lousy-high minimum firing rate even for domestic hot water, and the thing would require expensive stainless steel exhaust venting.

    The only contender on the list worth considering is the Navien NHB-80. At 8K-in/7600 BTU/hr out going into 31' of baseboard it' s ~250 BTU/hr per running foot of baseboard, which would balance at an average water temp of about 125F. If you gave it 120F boiler output with 115F return it would cycle some with just the small zone calling for heat, but it wouldn't short-cycle. With 34,000 BTU/hr of load and 74' of baseboard you'd need to have the outdoor reset function working, raising the temp to 170F on design day, but it'll do that just fin. With 120F output

    HTP's UFT-08oW has the same modulation range as the NHB-80, would be simpler to install than the Navien, and the boiler itself is priced comparably. (The Westinghouse-badged version the UFT-080 is the WBRUNG-080W and slightly cheaper than Navien at internet pricing.) Both the Navien and the UFT series boilers are built in Korea by reputable manufacturers. HTP's support is pretty good in my area, but have no idea what their support is like in Anchorage (or Navien's local support, for that matter).
     
  6. Alaska_RockGirl

    Alaska_RockGirl New Member

    Joined:
    Mar 18, 2016
    Location:
    Alaska
    Thanks so much! I am going to call the contractors today and see if they have smaller boilers to offer and go from there. Well, maybe not the Dunkirk guy...

    It's good to know that the Navien NHB-80 would work. I don't know what other brands are supported in Anchorage, I only got bids from 3 of the 30+ contractors in town. And the three that visited didn't measure baseboards or anything like that, just looked at what I had, asked about the number of zones, and measured the boiler space on the wall. Given as I'll be spending a chunk of change, maybe I'll get a few more bids now that I know what questions to ask and what information to offer.
     
  7. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    Key things to let them know are:

    * The smallest zone has only 31' of fin-tube on it, and you're interested in getting condensing efficiency without short-cycling the thing into an early grave on zone calls during the shoulder seasons, so a min-fire output well under 10,000 BTU/hr is a critical feature.

    * You have a Manual-J that indicates a design day heat load of 34,000 BTU/hr. (Did they specify the outdoor design temperature in that calculation? The 99% temperature bin according to ACCA data at the airport is -9F, at Fort Richarson it's -13F. ASHRAE disagrees, putting it in the -20F range. Using a design temp lower than -20F would be silly since you'll be up-sizing from there anyway.) If you go by ASHRAE standards there is no need to oversize by more than 1.4x. That means anything with more than (1.4 x 35,000 BTU/hr =) 47,600 BTU/hr of output is already overkill, but fine as long as the minimum modulated output is low enough to not short-cycle at condensing temperatures.

    * You have a 6-7 year old indirect HW heater that would be fine to keep in service.

    It's worth calling back the Lochinvar folks with this info and asking about the CDN040. It's oversizing factor is pretty slim if the calculations were done at -10F or so, but still OK. If the load calculations were done using -20F or colder it's low oversizing factor isn't an issue.

    It's worth considering condensing tank-type water heater combi options, and moving the Amtrol along, since the footprint is about the same, and the thermal mass of a tank-type combi system makes them fairly short-cycle-proof. The ability to deliver 170F or higher heating system water when it's cold out would be important for one of those.
     
  8. Alaska_RockGirl

    Alaska_RockGirl New Member

    Joined:
    Mar 18, 2016
    Location:
    Alaska
    Dana, thanks, I'll use those exact points. The only problem with a tank-type combi system is it would involve moving the boiler to the utility area, but I was kind of considering that anyways. I'll ask the question and see what answers I get.
     
  9. Alaska_RockGirl

    Alaska_RockGirl New Member

    Joined:
    Mar 18, 2016
    Location:
    Alaska
    Well the second round of boiler/combi estimates has gone relatively well.

    1. Triangle Tube guy refused to consider other options and continues to promote the Triangle Tube listed above. He doesn't think the Lochnivar CDN40 would be sufficient and he has nothing nice to say about Navien.

    2. Original Navien bid guy wouldn't call me back.

    3. Navien NCB 240 was bid by three other companies- one said it was quieter than the Intellihot, so if I kept the boiler in the dining room he'd recommend it for that location.

    4. Navien NHB-55 bid by two companies- I had asked them to bid a combi or a boiler so I had the comparison.

    5. If I moved the boiler the recommendation was an Intellihot i200x. But that bid is coming in $4,000 above the Navien NCB 240 and I just can't justify the extra expense in moving the boiler in the current real estate market in Anchorage. Simply having a new boiler/combi will put my place heads above the others, but a similar unit in my building just sold for $10,000 less than I paid for mine so the extra $ just don't make sense.

    So I'm leaning towards the Navien NCB-240. Ditch the Amtrol- which means more room in the utility area. Leave the combi in the dining room, enclose it with cabinets. Combi would be on the south facing wall, so would have to locate the outdoor reset under the deck to make it most efficient.

    The NCB-240 input/output seems big, when compared to what I was looking at for boilers, but apparently our year round 38 degree F water needs a lot of heat to get it up to comfortable levels.

    Is the NCB-240 a good choice? I reviewed the boards and it seems like there are some users who have had issues.

    Thanks again for your assistance! This is such a valuable resource because I get a different opinion from every bidder.
     
  10. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    The min-fire input to the NCB-240 is 18,000 BTU/hr. At condensing temperatures that's about 17,000 BTU/hr out, which is literally half your design-day heat load of 34,000 BTU/hr. (OK, it could theoretically modulate SOME of the time, if you had enough radiation per zone, but you don't, really.)

    Putting 17,000 BTU/hr into a zone with 31' of fin tube is 550 BTU per foot, which balances at a boiler output of about 180F, which is well above condensing temperatures. At condensing output temperatures the fin tube won't be able to emit 17,000 BTU/hr into the room, and the thing would just cycle on/off during a continuous call for heat, putting wear & tear on the ignition components and cutting into efficiency by blowing away heat with every ignition cycle & flue purge. If you don't care about condensing efficiency it can be made to work if programmed for a fixed output of 180F without short cycling, but it's not exactly ideal. The high min-fire ignores the suggestion that"...a min-fire output well under 10,000 BTU/hr is a critical feature".

    Tankless hot water heaters/combis don't deliver nearly the hot water heating performance that you need if you have more than 2 showers going at a time, and the high min-fire output means it can't be run in high efficiency condensing mode (ever) for space heating. But you only have one shower, and the NCB-180 would cover the water heating loads, but it only modulates down to 14K in, which is still too high for your smallest heating zone. I don't know of any tankless combi-heaters out there with sufficiently low minimum fire input to not short-cycle on your 31' baseboard zone.

    The NHB-55 (or NHB-80) + Amtrol would still be a better solution, since it can deliver high flow on the domestic hot water, and modulates down to under 8000 BTU/hr out. The NHB-80 is probably a better choice than the NHB-55 (and probably only about a $100-200 cost adder) since it has the same sub-8K minimum fire output, but still delivers enough heat at high fire to run a 24/365 shower at 2 gallons per minute, and the Amtrol would have noticeably faster recovery times after filling a tub. But if it's more than a $200 quote difference the NHB-55 can clearly do it, recovery on the Amtrol after a tub fill would still be slightly faster than a standalone tank heater.

    The Intellihot i200x would be a lousy choice at any price, since it's min-fire input is nearly your calculated 99% condition heat load. It would neither modulate nor condense in space heating mode and would have a difficult time regulating the domestic hot water temperatures at low tap flows (trust me on this, I had a tankless with a 30K min-fire input for 15 years.)
     
Similar Threads: Choosing correct
Forum Title Date
Boiler Forum choosing correct pump Aug 21, 2011
Boiler Forum Choosing a mod-con boiler Sep 27, 2018
Boiler Forum Advice: choosing boiler and hot water heater Jul 28, 2016
Boiler Forum Choosing a reliable boiler May 18, 2016
Boiler Forum Help choosing a control system and manifolds for Hydronic Heating Jan 8, 2014

Share This Page