Replacement for 1960's era N.G. boiler....

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NY_Rob

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Hello,

Looking for some advice regarding replacing our 50+ year old natural gas fired cast iron boiler.
I’ve read many posts here over the last week to help educate me, I’ll include the facts and measurements I have made to help facilitate correct boiler choice, sizing, etc… when speaking with the heating contractor.

I’m considering a Triangle Tube Prestige Solo 60K boiler and a Triangle Tube Indirect 40 gal DHW heater.

Here’s the basic info….

Location: zip code 11720, Suffolk County, Long Island

House: 1964 build, 2”x4” construction “spalnch”- downstairs at ground level (Kitchen, dining room and den + mother/daughter apartment in built in converted garage) is on a concrete slab, four bedrooms plus full bath upstairs, and a living room on a mid level that’s over a unfinished 18’x11’ “quarter basement” where the boiler/utilities are located.
Upstairs windows were replaced in mid 1987 with Anderson sash windows. Downstairs/livingroom windows and patio door were replaced with Anderson casement windows in 1997.
House was vinyl sided in 2009 with ½” foam over original common Cement-asbestos siding shingles.

Current natural gas fired cast iron boiler- Hydrotherm HC-100 (most likely original from 1964- no safety controls at all!) Input 100,000 BTU/HR, Output 80,000 BTU/HR Net Rating 69,600 BTU/HR.
DHW is currently supplied vai stand alone GE brand gas fired 40 gal hot water heater.
Currently- from my latest “actual reading” gas bill- I’m using about 3 therms/day this milder winter.


Three zones baseboard/water fin heating ¾” copper pipe:
Upstairs- 46’ measured fin length
Downstairs 51’ measured fin length
Apartment 43’ measured fin length
Total length = 140ft

SQ Ft measurements not including “quarter basement”:
Upstairs 566 sq ft
Downstairs 590 sq ft
Apartment 400 sq ft
Total heated area 1556 sq ft

My shortest zone is 43’ and it seems that can use up to (43*560) 24,080 BTU/hr whereas the Prestige Solo 60K can modulate down to 16,000 BTU/HR so I shouldn’t see short cycling and should be in condensing mode?


So, with the above in mind, and assuming I go with the TT Prestige Solo 60…..
Will there be an issue if all three zones call for heat at once?
I’m hoping the Solo 60 is sufficiently sized to supply the 40gal indirect DHW heater?

Please feel free to ask as many questions as necessary.

Thanks in advance for all the help and great info available on this site!


Rob
 

Dana

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The Solo-60 would surely handle your loads. Make the indirect the "priority" zone and you'll NEVER run short on hot water.

16,000 BTU/hr into 43' of baseboard is 370 BTU/hr per running foot. That balances at about 145F AWT which is above the condensing range. (You need return water of 125F or lower to get condensing efficiency). At an AWT of 125F (130F out, 120F back) the baseboard only delivers about 250BTU/hr per foot, or (x 43'=) 10,700 BTU/hr for that zone. The Solo-60 is going to cycle a bit, and if you dropped to an AWT of 115F it would cycle quite a lot. A boiler with a min-fire output of less than 12K would be better.

If you went with HTPs UFT-80W it can modulate down to about 8000 BTU/hr in, or 7500 BTU/hr-out, and would have no cycling issues (and it has even higher output than the Solo-60 at the high end). Alternatively, Lochinvar's CDN040 can drop back to about 8500 BTU/hr out, and would also be just fine at condensing temps. It's high-fire output is about 38K though, so it's good to get a better handle on your actual heat load before committing to that one.

The 3 therms/day number is only relevant if you can also give the average outdoor temp during those days. I've had days this winter that averaged north of 50F, as well as under 5F. With exact meter reading dates and the fuel used it's possible to look up the heating degree day weather data for the meter-reading period and get a much more precise measure of your heat load. If you're at under 100 therms/month in winter probably even the smallest mod-cons will cover your heating load during a sub-zero cold snap, but it doesn't hurt to run the real fuel-use numbers and KNOW that it will.

I'm guessing your heat load a +15F is about 20,000 BTU/hr, which would also point away from the Solo-60, since it would nearly always by cycling rather than modulating with load. Your average mid-winter load is probably less than the 15,000 BTU/hr condensing output of the Solo-60, but probably more than the output of the CDN040 or UFT-80W. The latter boilers could run nearly continuous burns in winter at high efficiency, whereas the higher min-fire output of the Solo-60 means it would have to cycle.
 

NY_Rob

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Thanks for the valuable info Dana.
Regarding actual gas usage... over last Jan (2015) which was by all accounts brutal around here- I used 180 therms from Jan 1/2015 to Jan 29/2015. Pretty close to 6 therms/day average.

I'm not acquainted with HTP boilers... there's not too much info out there on the UFT series either.
 

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The UFT series is fairly new, but HTP has been in the condensing gas-burner biz for decades now. They're a local New England company headquartered in MA, but have pretty good distribution & support in several parts of the US. (One of the hydronic designers/installers I know who gave raves on the Solo-60 for years is now waxing poetic over the UFT boilers.)

Downloading daily base 65F HDD data from weatherstation KNYCENTE9 at Steward Circle in Centereach, from 1-28 January there were 918 HDD. Burning 180 therms in an 80% boiler delivers at most 180 x 0.8= 144 therms of heat into the heating system. So...

That's 144/918= 0.1569 therms/HDD. At 100,000 BTU/therm that's then 15,690 BTU/HDD

With 24 hours in a day that's 15,690/24= 654 BTU per degree-hour.

The 99% outside design temp for almost all of Long Island is +15F, and the presumptive heating/cooling balance point of 65F (which is why that's the HDD base), means you have 65F-15F= 50F heating degrees. The implied load is then

50F x 654 BTU/degree-hour= 32,700 BTU/hr @ +15F

The coldest temperature of the past 20 years in Centereach NY was on Valentines Day this year, when it hit 0F at about 7AM. At 0F (a 65F delta) it would take 65F x 654= 42,510 BTU/hr, which is above the output of the CDN040, but still WELL within the output of the UFT-80W.

For only 1556 of heated space that's a ratio of 21 BTU/hr per square foot, which is fairly high, which means you may have some big gaps in the insulation (is the foundation insulated?) or some big air leaks such as big single pane windows or other heat leaks. If you can peel 4-5K off the heat load the CDN040 would be nearly ideally sized, if you're wary of the UFT-80W.

Mind you, the 32.7K number is an upper bound, and the likelihood of a 3x oversized mid-60s Hydrotherm delivering 80% efficiency is very low, but it's probably doing better than 65%- your real heat load is still over 25K, and may be as high as 30K.

ASHRAE recommends oversizing of ~1.4x for non-modulating boilers as the efficiency /comfort compromise sizing, so were you to replace it with another cast-iron beastie the upper size limit would be on the order of 30K x 1.4= 45.8 KBTU/hr
 

Leon82

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Lochinvar has a new khn floor mount firetube with 10 to 1 turndown.

Althogh the 055 and 085 have similar min fire rates because the 055 is not full 10 to 1
 

NY_Rob

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Dana I'm sorry if I wasn't clear, but that 180 therms usage was for jan 2015, not jan of this year if that's what the calculations were based off. Jan of 2015 was the coldest month we've seen since I moved here in 1991 IIRC.

Here's the latest billing/consumption data I have available from my gas supplier..
LDC Actual Period Gas Used: 164 Therms 12/30/2015 to 1/27/2016 (29 Days)
The average daily high was 41f this billing period.


Overall I think this house is pretty tight for a 1964 build. I'm on budget billing- my gas bill is $75/month and the delivery charge is $63/month for total of $138 monthly or yearly total of $1656... that's with the 1964 boiler.

Also, if it makes a difference... even though the "apartment" baseboard actual fined tube length is only 43' the loop length of 3/4" pipe out from the boiler through the radiators and back to the boiler is about 170' total... it's at the far end of the house from the boiler.

Thanks again for all your assistance!

Rob
 

NY_Rob

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Thanks to Dana's post I used my most current data with the correct HDD dates for my area..
Gas Used: 164 Therms 12/30/2015 to 1/27/2016 (29 Days)
HDD's for my area for the same period = 898
Using 80% efficiency for my 1964 boiler

I come up with 19 BTU/hr per square foot for my 1964 house.

FWIW- the old boiler is standing pilot and doesn't have a flue damper- so maybe it's less than 80% efficient?
When I run my gas usage numbers for 70% and 75% efficiency for the old boiler- the BTU/hr per square foot calculation changes quite a bit.
At 75% efficient it comes in at 17.9 BTU/hr per square foot
At 70% efficient it comes in at 16.7 BTU/hr per square foot
 
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NY_Rob

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Lochinvar has a new khn floor mount firetube with 10 to 1 turndown.

Although the 055 and 085 have similar min fire rates because the 055 is not full 10 to 1
Interesting, thank you.
I'll have to look into these as well.

Rob
 

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The error from the standing pilot and lack of flue damper is pretty small on a mid-winter fuel calculation unless the boiler way beyond ridiculously oversized. But the age of the boiler means it's probably in the 70-75% efficiency range due to corrosion on both the fire side and water side of the heat exchangers. A competent tech with a combustion analyzer could tell you with some precision what it's steady-state combustion efficiency really is, not that it will change the boiler choice here.

At ~3x oversizing it's AFUE efficiency is probably going to be 8-10% lower than it's steady state efficiency, but that doesn't affect the fuel-use/HDD calc on a mid-winter billing period. It's clear that your design heat load is well under 30,000 BTU/hr and over 20,000 BTU/hr.

The Lochinvar KHN-055 dials back to about 8000 BTU/hr out at condensing temps. It's not the 10:1 turn down like the others in that series, but it's still good match to your loads. You'd only bump it up to the KHN-085 if you had VERY high domestic hot water loads or something, (say a big spa tub with a 100 gallon indirect HW heater that needed to have reasonable recovery times.)
 

NY_Rob

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Thanks Dana and Leon82...
I got quotes from a local supplier on the Lochinvar 055 and 085.
I don't know the policy regarding price talk here.. but the 085 was only $150 higher than the 055.

Seems both the 055 and 085 modulate down to the almost (8.3k vs. 8.5k) the same rate- is there any efficiency hit/disadvantage in in getting the 085 over the 055?

I have a reputable local tech coming to my house Sat morning to look over the situation and get a better handle on my load requirements.

Another tech I've known for almost 20 yrs now is very high on the Bosch Greenstar line.
He likes the warranty and says parts are easy to get. The Greenstar 57 modulates down to 12.9k which may also hit my goal for the smallest (43 fin ft) zone.
The Greenstar 57 is also about $1k less than the Lochinvar boilers.
 

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If your true heat load is ~25K, a boiler with a min-fire output of 12K is going to be running a LOT more burn cycles per season than one with an output of 8K. The Greenstar 57 isn't a terrible choice, but the UFT-80 or the small Lochinvars are better at your low load.

To balance 12K of output with a 43' baseboard zone takes an AWT of 130-135F, which would be at the very beginning of the condensing zone. To balance 8K of output with a 43' zone takes an AWT of ~115F. That's the difference between 90% efficiency and 95% efficiency. If you ran the Greenstar 57 at the same 115F AWT it would be cycling on/off during a continuous call for heat, whereas the smallest UFT or KHNs would still be modulating.

There's no particular down side to the -085 vs. the -055, and it WOULD make a noticeable difference in how quickly an indirect hot water heater recovers. With the -085 you'd even have enough burner to run a 24/365 shower (if you didn't have to heat the house too), but not the -055. If endless-shower capability is worth $150 to you, go for it! Mind you, the UFT-80W has about the same high-fire output as the KHN-085, and would deliver the same hot water heating performance (for probably LESS than the KHN-055.)

I suspect quotes for the UFT-80W would be comparable to the GreenStar 57, not as expensive as the KHN. They've gone out of their way to make the UFT's easy to install configured as a direct pumped 1-pump system on the heating end with separate ports supporting an indirect HW heater, whereas Lochinvar pushes hard at plumbing it primary/secondary no matter what. (IIRC they void the warranty if pumped direct.) It's worth finding out if there's an installer in your area.
UFT-big1a.jpg
 

NY_Rob

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Thanks again Dana for all your help...
Does it make a difference in the calculations that my smallest zone (which happens to be farthest from the boiler) with 43' finned tube radiator has a total loop length of 150'-170' (rough measurement)?
 

NY_Rob

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Unfortunately, when looking at the UFT-80W, seems the closest NY rep is upstate in Buffalo- an 8hr drive from my LI location.
 

NY_Rob

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Dana,
How about the Lochinvar WHN055?

Very reasonably priced.


55,000 BTU/HR input
5:1 Turndown
SS Fire Tube heat exchanger
5:1 Turndown


5:1 turndown would mean 11,000 min fire rate.
 

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the whn 55 its a wall hung vs floor Mount. I would imagine at some point they will update them to offer more turndown.

I have the whn 55 but I set my large and small zone to run together 95 ft total. I don't know the price difference between the 2 but the smaller min fire would work better for the 40 ft zones
 

NY_Rob

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...I don't know the price difference between the 2 but the smaller min fire would work better for the 40 ft zones
The Lochinvar KHN055 with the 10:1 turndown (8,300BTU/HR) is about $1k more expensive then the Lochinvar WHN055 with 5:1 turndown (11,000BTU/HR).
So we're looking at $3,600 vs. $2,600 for the boiler, plus another $1,100+ for the indirect water heater +install.

If it's helpful- presently I have two zones.
-The (apartment) 170' loop with 43' of baseboard is on one zone with it's own cir pump and t-stat.
-The other two loops (upstairs and downstairs) with 51' and 46' of baseboard (total loop length unknown) are physically joined together as one zone with one cir pump and one t-stat.
 

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Pumped direct you can probably run the whole heating system with a single Taco VT2218 smart pump & zone valves, at about 10% of the pumping power used, which becomes important when running modulating condensing boilers that go nearly continuously. With the Lochinvar they'll make you run 2 pumps in a primary/secondary configuration.

You can probably tweak the WHN055 into serving a 43' baseboard zone at mid-90s efficiency without too much cycling, but it'll cost you an extra pump and more plumbing time relative to the UFT-80W.
 

Leon82

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With the lochinvar you can delay the inevitable with the control but you will still cycle with the 45 ft zone
 

NY_Rob

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So all in all, it seems the lochinvar KHN055 with minimum 8,300 BTU/hr output or the lochinvar KHN085 with minimum 8,500 BTU/hr output would be the best fit for my existing system without going to extremes to fit it to my needs.
I don't mind spending the extra $1k for the 10:1 turndown units if it will run as the manufacturer designed and it's right-sized for my needs.
 

John Molyneux

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Thanks Dana and Leon82...
I got quotes from a local supplier on the Lochinvar 055 and 085.
I don't know the policy regarding price talk here.. but the 085 was only $150 higher than the 055.

Seems both the 055 and 085 modulate down to the almost (8.3k vs. 8.5k) the same rate- is there any efficiency hit/disadvantage in in getting the 085 over the 055?

I have a reputable local tech coming to my house Sat morning to look over the situation and get a better handle on my load requirements.

Another tech I've known for almost 20 yrs now is very high on the Bosch Greenstar line.
He likes the warranty and says parts are easy to get. The Greenstar 57 modulates down to 12.9k which may also hit my goal for the smallest (43 fin ft) zone.
The Greenstar 57 is also about $1k less than the Lochinvar boilers.

I have a Greenstar 57 and I really like it. But if I had to do it over again I'd get something with a lower min-fire. My initial heat loss estimate was approx. 30,000. We did some insulation and air sealing that we calculated (and subsequently confirmed) would bring it down to 24,000 or so. I have an abundance of CI radiation and can run the system at very low water temps. I'm not sure that getting an extra 4,000 BTU on the lower end is a huge deal, because the Bosch doesn't cycle excessively, but I can tell the current setup isn't fully optimized for operations during warmer weather. I have a 30-gal indirect and we've never run out of HW.
 
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