Advice: choosing boiler and hot water heater

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MG NJ

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I'm so impressed with the outpouring of informed advice for everyone who asks questions on this site. Thanks for being here!

My problem is that my boiler broke this past winter in my 1969 split level house and the plumber put in a temporary fix, got me through the winter. So now it's time to decide. Lots of choices! Facts: baseboard heat, about 70 ft of baseboard on each of the 2 floors, no basement (slab house, New Jersey, not too bad winters, but damp location near water).
2 bathrooms, center of house above abs below each other, dishwasher. House 1850SF. Garage.

I was hoping for the Navien NCB 210 combination boiler/hot water but read so many things about what could go wrong that I'm nervous. The guy I have who I would go with to install that has 9 years experience with installing those and I asked about issues of water going cold, unit not working efficiently etc and he said to be honest, at first there were problems which they had to go back and fix but with experience (and using the specs in the manual) they now know how to do it well.

Another 2 choices (more expensive but keeping 2 separate wall hung units and still qualifying for the best Eco rebates):

Weill-McLain Eco80 + Navien NPE 210

Carrier BW9AAN000075 + same

I'm totally new. This is so confusing.

I also have estimates for conventional boilers too ( Weill M CGA4 88,000 BTU or Carrier BWB...96 78,000 BTU) with that Navien wall hung hot water unit.

Any advice you could offer would be SO appreciated. If you need a photo of my house I can post it.

Thank you!!
 

John Molyneux

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Here are my suggestions based on having gone through the same process you are:

1. You need to start with a heat loss calculation because the size of the boiler is one of the most important criteria. You can search this board to figure out how to do it yourself based on actual historic fuel use (look at various posts from Dana) or hire a professional, like someone who specializes in energy audits. Wild ass guess, but I'd be surprised if your heat loss is any higher than 30,000 - 40,000 Btu/hour. The smaller the boiler the better as long as it comfortably covers your calculated heat loss. If you go with a conventional boiler you probably want the smallest size they make, which will still be almost twice as big as you probably need.

2. The installer/installation is more important than the brand of the appliance. Get competing estimates. Another good site, heatinghelp.com, can help you find local installers that are up to date with how to design, install and, just as importantly, how to program/tune/setup the boiler for optimal performance. I expect homeowners almost never take full advantage of their new boiler if the installer walks away leaving everything at factory defaults. Ask what they know about tuning outdoor reset curves and return water temperature.

3. A properly sized and installed modulating/condensing boiler + an indirect domestic hot water tank is often said to be a top choice for performance and energy efficiency. I don't really know anything about combi's other than reading that it might be unlikely to find one that properly matches your heat loss (too big), so you would lose some efficiency. Also, for domestic hot water it certainly depends on whether you have minimal needs or have a couple teenagers in the house.

4. There are lots of highly-regarded brands, such asTriangle Tube, Lochinvar, Bosch, Energy Kinetics/System 2000, and HTC (not an exclusive list by any means). I chose my contractor based on price and expertise and who I simply liked the best, and they happen to focus on Bosch, which I'm very happy with. I ending up not working a couple of the contractors that looked at my job solely because they wouldn't install the smaller sized boiler I wanted (one said he wouldn't take the 'legal liability,' which was simply ridiculous).

5. Might be worth looking at a mini-split heat pump option.

6. I tend to think there's no perfect solution and that a lot of the decision-making process depends on your goals. I think efficiency is very important -- do you care about your household CO2 emissions? :). But budget is certainly important too.

7. You obviously need a new boiler but, with respect to energy efficiency and long term operating costs, insulation and air sealing may very well be the best bang for your buck. For example, you might actually be better off with a cheaper, somewhat less efficient conventional boiler and a better building envelope, which is another good reason to start with a professional energy audit.
 

rjbphd

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Stay away from Carrier boiler.. they are re branded Dunkirk ( known as Junkirk around here) boiler with higher price.
 

Dana

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Never heard of the Weil-McLain ECO-80, but there is an ECO-70, which is a nice fire-tube heat exchanger boiler The minimum input firing rate is ~14,000 BTU/hr, isn't as low as some others, which may be too high to operate in condensing mode, depending on the system particulars. If there is 70' of baseboard on every zone that's 14,000/70= 200 BTU/ft, which is fine, but if it's broken up into zones there are issues. It's time to do at least the napkin-math on the design parameters before you paint yourself into a corner.

1: If you have a heating history on the place, calculate the whole-house heat load using these methods.

2: Measure up the radiation by zone, and make sure you won't short cycle the boiler using this methodology. (There are a handful of other boilers that would work on the left inset sidebar of that blog page.)

In general, the lower it can modulate, the lower you can run the water temps for higher efficiency without short cycling. The ECO-70 can work, but an NTI Trinity TX51 or HTP UFT-80W might be a better choice. (The UFT-80W is also relatively inexpensive and easy to install.)

Rather than a separate tankless with a monster-sized burner for the hot water, an indirect tank operated as a zone off the boiler almost always delivers better service, supporting higher flow, and without needing to upgrade the gas distribution plumbing (or even your meter!) to support the bigger burner.

The condensing fire-tube UFT-080W should be simpler and cheaper to install (and way more efficient) than the CGa-4, which is way oversized for your heat load- so oversized it would not even hit it's modest AFUE numbers. It's even too big for the single zone radiation (by at least 2x), and would do a lot of cycling on zone calls, calls that wouldn't necessarily overlap. If going with that series, the CGa-25 is almost certainly the best fit, but that should become obvious once you've run the fuel-use based load numbers.

[edited to add]

BTW: Nice dog avatar! Reminds me of a sweet pit bull my mother had back in the '90s.

74843.jpg
 
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MG NJ

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Thanks so much!!!
Weirdly the Save Green people I called (the agency offering the rebate) said their home energy audit is done AFTER I install the new system!? I thought that makes no sense because I thought the audit would help me make my choices.
So I guess I need someone to do the audit and who would that be?
 

MG NJ

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That last one was thanks to John. Reading the other replied now...

Here are my suggestions based on having gone through the same process you are:

1. You need to start with a heat loss calculation because the size of the boiler is one of the most important criteria. You can search this board to figure out how to do it yourself based on actual historic fuel use (look at various posts from Dana) or hire a professional, like someone who specializes in energy audits. Wild ass guess, but I'd be surprised if your heat loss is any higher than 30,000 - 40,000 Btu/hour. The smaller the boiler the better as long as it comfortably covers your calculated heat loss. If you go with a conventional boiler you probably want the smallest size they make, which will still be almost twice as big as you probably need.

2. The installer/installation is more important than the brand of the appliance. Get competing estimates. Another good site, heatinghelp.com, can help you find local installers that are up to date with how to design, install and, just as importantly, how to program/tune/setup the boiler for optimal performance. I expect homeowners almost never take full advantage of their new boiler if the installer walks away leaving everything at factory defaults. Ask what they know about tuning outdoor reset curves and return water temperature.

3. A properly sized and installed modulating/condensing boiler + an indirect domestic hot water tank is often said to be a top choice for performance and energy efficiency. I don't really know anything about combi's other than reading that it might be unlikely to find one that properly matches your heat loss (too big), so you would lose some efficiency. Also, for domestic hot water it certainly depends on whether you have minimal needs or have a couple teenagers in the house.

4. There are lots of highly-regarded brands, such asTriangle Tube, Lochinvar, Bosch, Energy Kinetics/System 2000, and HTC (not an exclusive list by any means). I chose my contractor based on price and expertise and who I simply liked the best, and they happen to focus on Bosch, which I'm very happy with. I ending up not working a couple of the contractors that looked at my job solely because they wouldn't install the smaller sized boiler I wanted (one said he wouldn't take the 'legal liability,' which was simply ridiculous).

5. Might be worth looking at a mini-split heat pump option.

6. I tend to think there's no perfect solution and that a lot of the decision-making process depends on your goals. I think efficiency is very important -- do you care about your household CO2 emissions? :). But budget is certainly important too.

7. You obviously need a new boiler but, with respect to energy efficiency and long term operating costs, insulation and air sealing may very well be the best bang for your buck. For example, you might actually be better off with a cheaper, somewhat less efficient conventional boiler and a better building envelope, which is another good reason to start with a professional energy audit.
 

MG NJ

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Ok - thanks Dana! I will find someone who knows what you mean to help me figure this math out (I'm a HS English teacher ;) I have a plumber I'm in contact with who has been writing up these proposals. I'll give him these particulars and see what he says.

The house is 2 zone (upper and lower floors each have a thermostat). The house is mainly summer use and some weekends through the winter, but expect to possibly retire there. No teenagers but I like a long shower! Generally no 2 people are showering at the same time. Maybe a dishwasher and a shower.

(That's one great doggie, yep - sweet boy who loves the car as you can see!)



Never heard of the Weil-McLain ECO-80, but there is an ECO-70, which is a nice fire-tube heat exchanger boiler The minimum input firing rate is ~14,000 BTU/hr, isn't as low as some others, which may be too high to operate in condensing mode, depending on the system particulars. If there is 70' of baseboard on every zone that's 14,000/70= 200 BTU/ft, which is fine, but if it's broken up into zones there are issues. It's time to do at least the napkin-math on the design parameters before you paint yourself into a corner.

1: If you have a heating history on the place, calculate the whole-house heat load using these methods.

2: Measure up the radiation by zone, and make sure you won't short cycle the boiler using this methodology. (There are a handful of other boilers that would work on the left inset sidebar of that blog page.)

In general, the lower it can modulate, the lower you can run the water temps for higher efficiency without short cycling. The ECO-70 can work, but an NTI Trinity TX51 or HTP UFT-80W might be a better choice. (The UFT-80W is also relatively inexpensive and easy to install.)

Rather than a separate tankless with a monster-sized burner for the hot water, an indirect tank operated as a zone off the boiler almost always delivers better service, supporting higher flow, and without needing to upgrade the gas distribution plumbing (or even your meter!) to support the bigger burner.

The condensing fire-tube UFT-080W should be simpler and cheaper to install (and way more efficient) than the CGa-4, which is way oversized for your heat load- so oversized it would not even hit it's modest AFUE numbers. It's even too big for the single zone radiation (by at least 2x), and would do a lot of cycling on zone calls, calls that wouldn't necessarily overlap. If going with that series, the CGa-25 is almost certainly the best fit, but that should become obvious once you've run the fuel-use based load numbers.

[edited to add]

BTW: Nice dog avatar! Reminds me of a sweet pit bull my mother had back in the '90s.

74843.jpg
 

NY_Rob

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Regarding shower usage.... I have the HTP UFT-80W boiler with a 30gal HTP Superstore Indirect hot water storage tank- 1" piping for the indirect heating loop.
I use low flow shower heads- with that in mind I have seen the boiler fire up, satisfy the demand for hot water and actually shut down (and stay shut down- not cycle) while someone is still taking a shower. Since the boiler sets the DHW/indirect as a priority zone it commits all 80K BTU's to domestic hot water heating vs. 30-40K BTU's usually supplied by stand alone hot water heaters.
 

Dana

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It's 5th grade math with a bit of 7th grade pre-algebra thrown in, but if you can use a computer spreadsheet and the internet it goes faster. This is not the sort of approach most plumbers are into, and goes against a whole bunch of archaic rules of thumb and other bad habits endemic in the trades, but it's the right thing to do. Hydronic heating design is more than an exercise in plumbing, and optimizing modulating condensing boilers for the load and the radiation is (sadly) still pretty rare among HVAC contractors. Read the heat load calculation blog piece- it's neither cummings nor Salinger, but the concepts not particularly tough to grasp (if a bit dry.)

Basically, if you compare the average temperature to the average fuel use over a period it's possible to infer the rate of heat input (=heat load) required to maintain temperature at any arbitrary outside temperature.

The heat load at the 99th percentile temperature bin (= the temperature where only 1% of all hours in a year fall below the number) at your location is the code-required standard for heating system minimums is the relevant temperature at which the load is calculated. There is an industry standard that the optimal upsizing of the heating system above that load number is a factor of 1.4x for most residential systems. Any more than the buys no more comfort, and much more than that results in lower efficiency. AFUE testing presumes 1.7x oversizing, which is about the limit at which a cast-iron boiler will deliver average efficiency reasonably close to it's steady state efficiency. Any more than that the standby and cycling losses start to add up.

If you want to share a couple of mid winter gas bills with the EXACT meter reading dates, your ZIP code (for outside design temp and weather history date purposes) I'd be happy to run the load numbers for you on this forum.

If you don't have a heating history on the place (though it sounds as if you do), you can hire a RESNET rater or engineer to run a Manual-J type heat load calculation on the place.

Then, in order for a condensing boiler to actually extract the heat of vaporization from the exhaust by condensing at least some of it's water, the entering water temperature at the boiler (the water coming back from the baseboard) has to be ~125F or less. The baseboard delivers less than half the amount of heat at those condensing temperatures than it does with 180F water, and it might not be able to keep up with the 99% load at a condensing temperature, but ideally most of the rest of the heating season hours it will. (I expect in your case it would.) But if boiler's minimum firing rate is much higher than the baseboard can emit at condensing temperatures the boiler will cycle on/off during calls for heat, which cuts into both efficiency and boiler longevity. Ideally the boiler would have a modulation range low enough to run nearly continuously any time the outdoor temperature was below 60F, but they don't. But if you size it right it still should run VERY long cycles for the vast majority of the time. If it short cycles in condensing mode you're giving up at least 10% of the efficiency, and taking years (or even decades) off the boiler's service life.

Similarly with on/off cast-iron boilers, the amount of baseboard on any given zone is ideally enough to emit the full burner output at some boiler temperature to keep it from cycling on/off during continuous calls for heat from the thermostats. The upper bound of the output of most baseboard for the CGa series operated at it's maximum temperature is about 750 BTU/hr per foot ove baseboard. The CGA-4's output is 88,000 BTU/hr, so the minimum amount of zone baseboard that balances reasonably with the output of that boiler is 88,000/750= 117 feet. Your zones aren't even close to that. The output of the CGa 25 is 44,000 BTU/hr- half the output, which needs only half the amount of baseboard per zone, or about 59 feet. You have 70', so you're good.

Cast iron boilers are damaged if the return water temperatures at condensing temps, but with a total of 140' of baseboard and 44,000 BTU/hr of boiler output the average water temp will run about 135F when both zones are calling for heat, so the return water would still be ~10F above the condensing hazard zone. Most cast iron boilers would be installed with a bypass branch to feed a bit of boiler output into the return water stream to protect it from condensing water temps. But the question would be whether 44,000 BTU/hr enough to cover your 99% heat load. A fuel-use based heat load calculation based on your existing boiler's performance would tell.

The existing boiler's output is probably on the order of 85-100,000 BTU/hr out (maybe more?), but you probably only need 25-35,000 BTU/hr to keep the place warm. Most plumbers would just install something roughly the same size as what worked before (which is probably why they picked the CGa4), and that's almost always a mistake. If you can find the model number (which I could look up the specs on) or ratings plate on the boiler, the input BTUs and D.O.E. output BTUs numbers are useful to have for running the heat load calculations, but assuming 80% efficiency is a reasonable guesstimate for a generic atmospheric drafted cast iron boiler made anywhere between 1968 and 1998, and the calculation would be an upper bound for anything that old.
 

MG NJ

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Hi!
OK Here's what I've got:
heater1.jpg


I just read your entire article "Sizing a Modulating Condensing Boiler" and am now wondering a few things:
1. If this is a house I use only sporadically in the winter and all summer, does it even make sense to go for a condensing boiler because it sounds like (to me, completely new to all this language) it only operates well "on average." If I just come in for 2 days every 3 weeks all winter, then does it even make sense not to have just a conventional boiler?
2. I wonder now if the condensate running down the exhaust pipe (which is an old asbestos pipe) is due to the oversized boiler in this house?

My zip is 08005; and here's a bit of historic data (the coldest month in the winter before last - it hardly makes sense to me to use the current data from this past very mild winter, but I can get that to you as well):

Feb 5 - Mar 9 2015: used 122.9 therms (114 cu ft used x 1.078 BTU content) Avg temp this month 26, prior year this month 30.

Does that help? I'm now going to read more in those links you have above (mind you, I'm reading everything 3x because I reallllly don't get it ;) No joke. Last book I read was by George Eliot. This stuff is Greek to me.

THANK YOU, THANK YOU, THANK YOU!!!
 

MG NJ

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How have you seen your bills change compared to what you had before this combination boiler?

Regarding shower usage.... I have the HTP UFT-80W boiler with a 30gal HTP Superstore Indirect hot water storage tank- 1" piping for the indirect heating loop.
I use low flow shower heads- with that in mind I have seen the boiler fire up, satisfy the demand for hot water and actually shut down (and stay shut down- not cycle) while someone is still taking a shower. Since the boiler sets the DHW/indirect as a priority zone it commits all 80K BTU's to domestic hot water heating vs. 30-40K BTU's usually supplied by stand alone hot water heaters.
 

MG NJ

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Never heard of the Weil-McLain ECO-80, but there is an ECO-70, which is a nice fire-tube heat exchanger boiler The minimum input firing rate is ~14,000 BTU/hr, isn't as low as some others, which may be too high to operate in condensing mode, depending on the system particulars. If there is 70' of baseboard on every zone that's 14,000/70= 200 BTU/ft, which is fine, but if it's broken up into zones there are issues. It's time to do at least the napkin-math on the design parameters before you paint yourself into a corner.

1: If you have a heating history on the place, calculate the whole-house heat load using these methods.

2: Measure up the radiation by zone, and make sure you won't short cycle the boiler using this methodology. (There are a handful of other boilers that would work on the left inset sidebar of that blog page.)

In general, the lower it can modulate, the lower you can run the water temps for higher efficiency without short cycling. The ECO-70 can work, but an NTI Trinity TX51 or HTP UFT-80W might be a better choice. (The UFT-80W is also relatively inexpensive and easy to install.)

Rather than a separate tankless with a monster-sized burner for the hot water, an indirect tank operated as a zone off the boiler almost always delivers better service, supporting higher flow, and without needing to upgrade the gas distribution plumbing (or even your meter!) to support the bigger burner.

The condensing fire-tube UFT-080W should be simpler and cheaper to install (and way more efficient) than the CGa-4, which is way oversized for your heat load- so oversized it would not even hit it's modest AFUE numbers. It's even too big for the single zone radiation (by at least 2x), and would do a lot of cycling on zone calls, calls that wouldn't necessarily overlap. If going with that series, the CGa-25 is almost certainly the best fit, but that should become obvious once you've run the fuel-use based load numbers.

[edited to add]

BTW: Nice dog avatar! Reminds me of a sweet pit bull my mother had back in the '90s.

74843.jpg

Yes, it's 2 zones for the house: upstairs & downstairs separate.
 

Dana

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Hi!
OK Here's what I've got:
View attachment 35468

I just read your entire article "Sizing a Modulating Condensing Boiler" and am now wondering a few things:
1. If this is a house I use only sporadically in the winter and all summer, does it even make sense to go for a condensing boiler because it sounds like (to me, completely new to all this language) it only operates well "on average." If I just come in for 2 days every 3 weeks all winter, then does it even make sense not to have just a conventional boiler?
2. I wonder now if the condensate running down the exhaust pipe (which is an old asbestos pipe) is due to the oversized boiler in this house?

My zip is 08005; and here's a bit of historic data (the coldest month in the winter before last - it hardly makes sense to me to use the current data from this past very mild winter, but I can get that to you as well):

Feb 5 - Mar 9 2015: used 122.9 therms (114 cu ft used x 1.078 BTU content) Avg temp this month 26, prior year this month 30.

Does that help? I'm now going to read more in those links you have above (mind you, I'm reading everything 3x because I reallllly don't get it ;) No joke. Last book I read was by George Eliot. This stuff is Greek to me.

THANK YOU, THANK YOU, THANK YOU!!!

Greek? I thought it was written in Hindi! :)

A condensing boiler isn't necessarily more expensive to install than a cast iron boiler these days, and on it's worst performance day will be 10% more efficient than a typical cast iron boiler installation. If the indoor temperature while you're away is something like 50-55F you should be able to beat the rated AFUE of a condensing boiler by a few percent with just about any amount of radiator, but with a cast iron boiler the standby losses at such a ridiculously low duty cycle means you wouldn't even come close to hitting it's (already 10-15% lower) AFUE numbers.

It doesn't matter how cold it was this winter vs. some other winter, as long as the place was being heated to some reasonable temperature during your fuel use sample period. It's performance during the sample period is sufficient to infer the approximate heat load at any arbitrary outdoor temperature, but you're only required by code to meet the load at the 99th percentile temperature bin (only 87 hours per year are colder than that temp.) In ZIP 08005 the 99% outside design temp is in the low to mid teens. Trenton's 99% bin is +15F, Atlantic City's is +13F, so let's go with +13F.

Between 5 February and 9 March 2015 it use 122.9 therms, in a boiler that is ( 100,000 BTU-out/ 125,000BTU-in =) 80% efficiency, so it delivered at most (0.8 x 122.9 therms x 100,000 BTU/therm= ) 9,832,000 BTU into the house.

Taking the weather data from station KNJBARNE5 on degreedays.net, using 60F heating/cooling balance point for base temperature (assuming you kept it at least 60F during that period), it logged 1089 heating degree days. Using base 65F it logged 1267.6 HDD.

So using base 60F that's 9,832,000 BTU/1089 HDD= 9028 BTU/HDD, or (/24=) 376 BTU per degree hour.

At base 65F it's 9,832,000 BTU/ 1267.6 HDD = 7756 BTU/HDD, or 323 BTU per degree hour.

Assuming a 99% design temp of +13F and a balance point of 60F, that's (60F - 13F =) 47F heating degrees, which at 376 BTU per degree hour becomes an implied heat load of (47F x 376BTU/degree-hour =) 17,672 BTU/hr @ 13F outside ~65F inside. To project what it would be at ~70F inside, add another (5 degrees x 376=) 1800 BTU/hr, for a whopping, 19, 552 BTU/hr .

If the balance point is 65F, that's (65F - 13F= ) 52F heating degrees, which at 323 BTU per degree hours implies a load of (52F x 323BTU/degree-hour = ) 16,796 BTU/hr @ +13F outside, and ~70F inside.

Unless the place was unoccupied and you were keeping it at 50F or something, your heat load is likely to be under 20,000 BTU/hr which is about right for either a fairly small house by current standards (say 1000-1500 square feet), or a somewhat better than current code-min 2000-2500', house, or a tightened up house somewhere in-between.

If you kept the house at some lower temp, say what that temperature is/was.

How many zones, and what type/how much heat emitter (radiator or baseboard etc) do you have on each zone? Since you have a 100,000 BTU/hr -output boiler installed, I'm going to guess that if it's baseboards you have between 125' and 200' of baseboard. If it's cast iron radiators it'll take some measuring to come up with a radiation estimate. If the existing radiation is sufficient to deliver the full 100,000 BTU/hr output of the cast iron beastie without cycling, it should be able to run a modulating condensing boiler at condensing temps even at the coldest hours of the year, and would be able to run almost any small mod-con boiler without short cycling, but let's measure it up, eh?

With a ~17-20K heating load ideally the boiler would be able to modulate down below 10,000 BTU/hr so that it's not cycling at the average winter load too.
 

MG NJ

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Hi Dana,
Most days it's between 50-55 because it's a summer place. When we come down we kick it up to 68. There are 2 zones, up and down, Zillow says it's 1824 SF. We have a conventional brick fireplace (where heat just goes out :( and eventually I guess I'll get a wood burning insert). It's 64 ft of baseboard fin on the bottom floor (which has an unheated garage) and 111 ft upstairs. It's your typical 1968 big rectangle with the center entrance, six steps up/six steps down, concrete slab, new insulated American Craftsman Home Depot Vinyl crank open Windows (about 5 years ago). The upstairs has new insulation, not downstairs.

I'm inquiring about an estimate for the WeilMcLain Eco70 and a Rinnai RL94.
 

Dana

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Assuming the indoor temp averaged 55F for that period, it's better to use 50F as the temperature base. Using degreedays.net data it adds up to 787.7 HDD.

9,832,000 BTU/787.7 HDD = 12,482 BTU/HDD , or 520 BTU degree-hour.

So for (50F - 13F= ) 37F heating degrees, and a load of 37F x 520= 19,240 BTU/hr @ +13F outdoors, +55F indoors. To project the load at 70F we have to add another (70F - 55F =) 15F heating degrees, or (15F x 520=) 7800 BTU/hr, for a total of (19,240 + 7800= )

27, 040 BTU/hr @ +13F out/ +70F in.

At ~15 BTU/hr per square foot of conditioned space that's a very realistic load for a somewhat tightened up 2x4 framed 1800' house with new-ish windows and at least R19 in the attic. The ideal sized cast-iron boiler would have an output of no more than 1.4 x 27,040 = 37,856 BTU/hr, which would make even the CGa-25 somewhat oversized (at 44,000 BTU/hr out) , but it would still hit it's AFUE numbers if the house were occupied continuously, but won't if you keep the place at 50-55F most of the time.

With 175' of baseboard for a 27,000 BTU/hr load that's 154 BTU/hr per running foot, which typical fin-tube baseboard can emit at an average water temp (AWT) of 110F, which is WELL into the condensing zone. You can probably just set up the mod-con for a fixed temperature output of 120-125F for an AWT of 115F, which should deliver 95% + efficiency with most mod-cons.

The min-fire input of the ECO-70 is 14,000 BTU/hr so at 95% efficiency it would be delivering 0.95 x 13,300 BTU/hr into the system. When only the 64' zone is calling for heat that would be 13,300/64'= 208 BTU/hr per running foot, which 64' of baseboard would fully deliver at an AWT of ~120F. If you're running it at an AWT of 115F and ONLY that zone is calling for heat it would cycle some, but the cycle times would still be pretty long, with a high probability of overlap from the other zone most of the season. It would not short cycle itself into lower efficiency (or an early grave) at that temp. The ECO-70 has an "outdoor reset" function that ramps the boiler temp up/down in response to outdoor temperature, but since you have enough radiation to cover even the 99% design load at condensing water temperatures it wouldn't buy you more than another 1% or so in average efficiency, and it would take some tweaking to get it dialed-in. At an AWT less than 115F the output of fin-tube is also non-linear and hard to model well too, which makes the tweaking-in process even longer.

The HTP UFT-080W would be a viable (and possibly cheaper) alternative. It's minimum modulated output is lower too, so it would really NEVER cycle on/off during a continuous call for heat, even with just the smaller zone active.

Again, an indirect fired tank operated as a "priority zone" is going to be a better solution than a wall-hung tankless, and is probably going to be cheaper to install too. The 199,000 BTU/hr burner of the RL94 would likely require upgrading the gas plumbing inside the house- it's nearly 2x the burner of your existing boiler (!), whereas the ECO-70 would not. With the ECO-70 serving both loads there would be no issues of pressure drops on the gas lines causing pressure drop problems interfering with burner modulation, which is a very common problem with 199K tankless units unless there is a dedicated 1-1/4" gas line (no tees off to other appliances) from the meter /regulator to the tankless. An indirect tank can deliver 2-3x the instantaneous flow of a tankless, and a 40 gallon indirect with a 70K boiler behind it would serve up 1.5-2x the first-hour gallons you'd get out of a typical 50 gallon standalone hot water heater.

Sh0rt of an air tight wood burning insert (which is a good idea, BTW), either a chimney balloon type plug or a gasketed top-sealing flue damper works pretty well for limiting the parasitic losses of the fireplace, and the "cold hearth" drafts near the fireplace when there's no fire burning.

chimney-balloon.jpg

lock-top-8-in-x-13-in-energy-saving-chimney-damper-42.gif

A chimney balloon is cheap, but bit of a PITA to deal with if you use the fireplace very often. The gasketed top dampers are sometimes a PITA to install (as a DIY-er) but much easier to deal with once it's installed. But if the plan going forward is a woodstove type insert, that's really a superior solution.
 
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NY_Rob

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How have you seen your bills change compared to what you had before this combination boiler?
I've only had the UFT-80W in service for one full gas billing cycle so far, and since it's summer it's only being used for domestic hot water currently.

With that in mind- the current gas bill shows about 20% less gas used this July with the new boiler vs. July of last year when I had the old system. I would think my hot water demands this July vs. last July are very close as my family size/needs haven't changed since last July.

My old hot water heater was a standard atmospheric stand alone gas fired hot water heater that was probably close to 80% efficient vs. the UFT-80W that is rated at 96% efficiency when in condensing mode. I have seen condensate running into the neutralizer on domestic hot water calls, so it must be condensing some of the time anyway.

So, in a nutshell... my gas bill for the same period last summer is about 20% lower with the new boiler vs. my old system.
 
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MG NJ

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Super, thanks for your feedback!! I'm getting close to getting this and making a decision. It's so hard bc there are so many choices!
 

Dana

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An ECO-70, is fine.

The UFT-080W, or NTI Trinity TX51, or Lochinvar CDN040 would all work just fine too, with a somewhat lower (=good) modulating range.

A tankless is generally not a good option unless you simply don't have the space for an indirect tank.

An indirect operated as the "priority zone" is the best bang/buck for 19 out of 20 houses heated with boilers. With a condensing boiler behind it the efficiency is comparable to a tankless, but without the quirks & limitations (and without the expense of a gas line upgrade required) of a tankless:

teaserbox_4207439323.jpg


When you're not there you can turn the aquastat controls on the indirect all the way down to off (or install an in-line switch) and let it stagnate at room temperature to limit standby loss.
 
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