Condensing boiler or Cast iron??

[hammer49]

The knowledge on this site is amazing,but am still confused.I have a high ranch built in 1966 in NY 10990 zip code.I currently have a Weil Mclain CGM-5-PI 140000 input btu D.O.E 115000 capacity net I-B-R 100,000. the boiler is old and probably oversized for the house,it short cycles alot.i did vinyl siding, new windows and foam insulation in the attic about 10 years ago.a separate hot water heater.the house is 2400 sq ft. built on a slab with the back of house 3/4 under ground and a attached garage on the other side of the house.I have 3 zones for heating. zone 1 is the 3 upstairs bedrooms. zone 2 is the upstairs living rm,kitchen,and bath rm. zone 3 is the downstairs a den,bath rm, boiler room and bedroom. we enter the house from downstairs but mostly use just the upstairs. baseboard heat zone 1 is 43ft of baseboard. zone 2 is 41 ft of baseboard. zone 3 is 60 ft of baseboard. on 3 separate circulators.I have a regular chimney not lined. I had someone came and due a heat loss calculation and basically said i need only a 70,000 btu boiler. what would be the best way to heat my house efficiency? go with a regular cast iron 85% efficiency boiler like a burnham ES2-4 or a condensing modulating boiler or any other boiler so fit. Also when i do put on the downstairs zone and the boiler is already hot and the cold slab zone hits the boiler does this do damage or condensation in the burner and chimney OR cause its a cold start boiler is this alright. There are a lot of smart people on this forum i read alot. Thank you

 

[NY_Rob]

Your situation is very similar to mine when I started researching mod-con vs. cast iron back in Feb, even our total length of fin tube is only off by 4'.
https://terrylove.com/forums/index.php?threads/replacement-for-1960s-era-n-g-boiler.64707/
I suggest you read through that thread because I had many of the same questions you probably have- and most of my questions got answered there.

In the end- I went with a HTP UFT-80W mod-con... but you have to do the math to make sure "fits" your system.

 

[Sponsor]

 

[Dana]

With the shortest zone being 41' of fin tube, have enough base board on each individual zone to run a modulating condensing boiler that has a minimum firing rate of 9000 BTU/hr (input) at condensing temperatures, which is a good thing. Hold the line at 11,000 BTU/hr as the biggest min-fire for any modulating condensing boiler choice, but 9K or under would be a slam-dunk. A Lochinvar CDN040 , HTP UFT-080W (also sold as the Westinghouse WBRUNG-080W), or NTI Trinity TX51 would all be good choices, provided they still covered your 99% heat load with some margin at their respective high-firing rage. But of those, only the UFT-080W /WBRUNG 080W can deliver the calculated 70,000 BTU/hr (but I'm skeptical that your heat load is really that high even at -15F, let alone your 99% outside design temp. The napkin math on mod-con boiler sizing is explained here.

You don't have enough baseboard on any individual zone to run a ES2-4 (or even an ES2-3) without cycling. The ES2-4's DOE output is 89,000 BTU/hr. When only zone 1 is calling for heat that would be 89,000/41= 2171 BTU/hr per foot. The most you'd get out of fin-tube baseboard is about 800 BTU/hr per foot at the maximum operating temperature of that boiler, so the thing would just cycle on/off at less than a 50% duty cycle. The ES2-3's output is 59,000 BTU/hr which would be 59,000/41'= 1439 BTUhr per foot, which is still WAY over what the baseboard can emit.

Since you have a heating history on the place, run a fuel-use based heat load calculation, which uses the old boiler as a measuring instrument, and that will put a stake in the ground for the lowest maximum firing rate it would take to heat the place.

For calculating the heat load, the 99% outside design temp for Warwick NY is about +11-12F (NYC's is +15, Newburgh's is +10F) . If the fuel use calc comes up with something different than the calculated 70,000 BTU/hr, trust the fuel use calculation. A heat load of 70,000 BTU/hr @ +10F for a tightened-up 1966 rancher would be 4500-5500 square feet of conditioned space, which is one hell of a ranch house! Even if the 70K recommendation was based on a 1.4x oversizing factor (a 99% heat load of 50,000 BTU/hr), that would imply a 3300-3800' house, still pretty big for a mid-60s ranch house. A tightened-up 2400' ranch house would typically come in between 30,000-35,000 BTU/hr @ +10F, which means with 70K of boiler output you'd be good down to about -50F before it begins to lose ground. That's fine if you moved the house to Fairbanks, AK, but seriously oversized for Warwick.

But run the numbers. I'd be surprised if even the Lochinvar CDN040 didn't cover your actual heating load.

Any 85% efficiency boiler would require a new flue liner, which would be about as expensive as the plastic venting for a mod-con, maybe more. The WBRUNG 080W or UFT-080W runs about $1700 at internet pricing, which is cheaper than the $1900 they want for the ES2-3, and it's about as simple to install.

 

[hammer49]

Thank you very much Dana I will run fuel use base calculation and read the napkin base math for mod-con boiler and get back to you here with the results.Your a Genius! and NY_Rob i read you whole post thats what gave me the idea to ask this question.very similar i know.much appreciated. Thank you again

 

[Dana]

Another rule of thumb (but a very dangerous one to use ) is that most mid-60s houses were built with boilers 3x oversized for the load after some retrofit air sealing & insulation, including replacing the single-panes with code-min replacements. Using that method 115,000 BTU/hr of DOE capacity divided by three would be 38,333 BTU/hr of actual heat load, which is on the high side (but not ridiculously high side) for a 2400' 2x4 framed house at +10F.

 

[hammer49]

Something is puzzling my mind after reading those articles about mod-con boilers..I know the water returning to the boiler now on this old system is somewhat hot probably 160 degrees or a less. So if i get a mod-con boiler the hot water going to the baseboard will be around 125 to 135 degrees, so the return water can be lower and condense and the baseboard will not be as hot as if it were 180 degrees and not put out as much heat. so am guessing that it will take longer to heat up and stay comfortable. Don't mind me if this is a stupid question but i don't know much about mod-con boiler. Only know how the old cast iron ones work. So i guess it will burn at a lower fire rate for a longer period of time and save on fuel that way, and not cycle as much. Just trying to learn,'' if you know how something works you can fix it''. Going to read up more on how these boiler work.Thank Again

 

[hammer49]

My natural gas Bill doesn't give me therms it just gives me CCF and I used 160 CCF's for January and February.so I converted it and got 1.6 therms.this can't be right? My boiler nameplate shows 140,000 input btu/hr.DOE heating capacity 115,000 and NET I-B-R rating is 100,000 btu/hr.I got 13.04 mm btu .i couldn't get the degree day to work for me.Am still not sure if I did it right.

 

[NY_Rob]

^ that's one of the reasons deep nighttime setback isn't used with mod-cons... it would take too long to recover in the morning with 130f water in the radiators. It's also one of the reasons mod-cons will circulate water up to 20+ hrs/day and a good reason to look into ECM circulator pumps that consume up to 85% less electricity then conventional electromagnet circulators.

Once you get to condensing mode- you're wringing the last 10-12% of energy out of the natural gas due to the latent heat released when the water vapor in the natural gas changes to liquid water (phase change). FWIW- burning 100,000 BTU's of natural gas (methane) produces a little over a gallon of water.

 

[NY_Rob]

Maybe your 160 CCF has (x100) somewhere in there on the bill?
That would give you 16,000 CCF which equals roughly 160 therms (http://www.kylesconverter.com/energy,-work,-and-heat/cubic-feet-of-natural-gas-to-therms-(u.s.))

My gas usage with my old cast iron 80K BTU boiler was:
Actual Period Gas Used: 164 Therms, 12/30/2015 to 1/27/2016 (29 Days)

 

[Jadnashua]

Many mod-cons can adjust their outlet temperature based on the 'need' of the system and the outside temperature, so, it might exceed the nominal 130-degree temperature that would be your normal steady-state value. Ideally, the boiler would run full-time with just the right outlet temperature. A constant temperature means a steady state, and more comfort. A lower temp also means less thermal gradient, and loss to the outside.

 

[hammer49]

thanks for the input guys. I just called my gas company and they said 1 ccf equals 1 therm. so if that is right I used a 160 therms for the coldest period between Jan 21 and Feb 19 of 2016.and I set my thermostat back at night from 69 to 64.but still can't get the degree day working for me to finish figuring this fuel load calculation.my because am using a iPad.maybe I should try it on a PC.

 

[NY_Rob]

^ you can use Excel, or even better use paper and a $4 calculator so you can track your steps.
What are you using for your old boiler efficiency figure?
I split the difference between 70-75% for the efficiency number for my 50 year old cast iron beast.

 

[Dana]

Taking weather data from station KNYWARWI5 on Warwick Old Ridge Road, in Warwick, throwing out either the first day's or the last day's heating degree days (since you don't know what time of day they took the meter reading) you have either 732.8 or 739.2 HDD (base 65F).

160 CCF is 16,000,000 BTU, and assuming 80% efficiency (0.8 x 16,0000=) 12,800,000 BTU went into the heating system. Assuming a worst-case rounding down to 732 HDD, that's 12,800,000 BTU/732= 17,486 BTU/HDD. With a 24 hour day that would be (17,486/24=) 729 BTU per degree-hour.

Assuming 99% outside design temp of +11F (it's probably warmer than that) and the presumed heating base of 65F as the heating/cooling balance point that's (65F-11F=) 54 heating degrees, and implied load of 54F x 729 BTU per degree-hour= 39,366 BTU/hr.

That's a load/area ratio of (39,366 / 2400'=) 16.4 BTU/hr which is a credible number for a tightened up 2x4 rancher, but on the high side, and it presumes the boiler is shiny-new and really hit's it's efficiency numbers (not likely.)

Given that the boiler is 50 years old and 3x oversized, even if the nameplate input/output efficiency is 80% (probably is), the real as-used as-aged efficiency is likely to be closer to 70%, which brings the implied load down to (39,366 BTU/hr x 70/80 =) 34,445 BTU/hr.

That's a load/area ratio of about 14.3 BTU/hr per square foot of conditioned space, which is also a credible ballpark.

Reality is probably slightly less than that, but this tells you that even a 40K-50K BTU/hr boiler has margin. Anything over 1.4x the smaller number (1.4 x 34,445 BTU/hr= 48,223 BTU/hr) would be overkill, not really necessary, but OK as long as the minimum modulated output was low enough to not short-cycle on zoned calls.

You have 144' of baseboard, so at the calculated 34,445 BTU/hr load it would only need to deliver( 34,445 BTU/hr/ 144'= ) 239 BTU/hr, which typical fin tube baseboard would be able to do at an average water temperature of 125F-130F, which is on the warmer edge of the condensing zone, but still condensing. Odds are the room-to-room zone-to-zone balance isn't perfect, and you would in fact need a slightly warmer water temp to keep up when it's 11F outside, but it will probably still be condensing a bit if you dial in the outdoor reset curve. So with the curve dialed in, even on design day it should be delivering 90% efficiency, and at your seasonal average outdoor temps it'll be in the mid 90s.

A more detailed discussion on sizing mod-con boilers can be found here.

 

[BadgerBoilerMN]

Shutting down the ancient chimney can save 3-5

5%. Modulation, another 5-10.

Sizing the boiler's low-fire to the high heat load zone will assure reasonable cycling and adding an indirect-fired water heater will give you a 95% unified gas-fired appliance.

All ModCon boilers now feature outdoor reset and it works on fin-tube baseboard saving fuel with a minimum combustion efficiency of 86%. That will only happen in the coldest week of the year if properly installed and programmed.

 

[hammer49]

I really appreciate all the help here guys,now to pick the best boiler.I liked the HTP UFT 080 but from what you calculated it its to big for my house and Lochinvar is borderline.so I hate to ask but which boiler would be the best for my situation. Thanks again for everyone that helped me. NTI Trinity TX51 57,000 BTU/h ?

 

[BadgerBoilerMN]

Remember, it is not the input of the ModCon but the low-fire output that is most critical in designing a multi-zone system. To wit, the UFT 080 is fired from 8-80mbuth input (10-1 turn-down) so the low-fire output is just 7680.

I have one in my design studio...brilliant.

 

[Dana]

The TX51 has enough on the high end to cover the load (with margin!), and modulates down to ~7100BTU/hr-in or ~6750 BTU/hr- out, and would be as-good or better than UFT-080W. But it isn't dramatically better, with only a ~1000 BTU/hr difference in the modulation level at the low end. You have sufficient baseboard on each zone to not short-cycle the UFT-080W in condensing mode.

I don't have any insight into the pricing on th TX51, or how good local support is in your area.

With the UFT-080W you can drive to HTP's headquarters in MA in less than a day's round trip from Warwick to toss the thing through the front window if you don't get adequate support & service on the thing.

NTI's headquarters are in St. John, New Brunswick, so you'd have to stay over a night (or take your private plane) to pull the same antics with them.

But really it comes down to the competence & integrity of the installer. Now that you know which boilers make sense, call the distributors to refer a local installer in your area- they know better than anyone who is wasting time on tech support lines with questions already covered in the manual or bringing in bogus warranty claims, and who is installing them by the dozen with minimal support needed.

 

[hammer49]

Dana your point well taken. And BadgerBoilerMN loves his. No need to fly to New Brunswick better to stay local.Well gentleman I love this site i learned alot.I thank you again for your help in my dilemma.I will makes some calls hopefully there is some good installers with competence & integrity in my area.

 

[Dana]

The Badger rarely finds a mod-con he can't love, so you can't go by that completely.

I actually kinda like New Brunswick this time of year- the leaf color is peaking about now, and the fly-over of VT/NH/ME would be awesome! The TX51 is light enough and small enough to fit into a Cessna 172 or Piper Cherokee, eh?

 

[hammer49]

Lol. found some good reading material on this site.
http://energy.gov/eere/buildings/do...logy-solutions-new-and-existing-homeshydronic.
A lot of interesting stuff on setbacks with modulating boilers. Building America case studies very interesting. Browse around that site interesting stuff .
also was thinking about running another zone to my garage which is insulated to help with low temp return water if that would help or buffer tank?