Non-condensing vs. condensing boiler operation costs...

Skyline

The TriAngle Tube non-condensing combi-boiler had been replaced last September with Viessmann 222-F, B2TB combi-condensing boiler. In our digital age, where every data is collected and made available for consumption, swapping the boilers just prior to the heating season lends itself to compare operational cost for the same period. If for nothing else, to verify the much advertised savings, that condensing boilers provide. Well at least, that's how most companies/contractors sold this solution.

Over all, yes, the condensing boilers certainly will lower the operational, albeit not to the magnitude as advertised. Especially, if the increased electricity utilization for the condensing boiler is taken in to account.

Here's the last seven month energy utilization, observed in the same house/environment with different boilers:



That's an average of $12.56 savings with electricity utilization taken into account. Projection for one year savings results in $150.75, that doesn't even cover the yearly maintence cost for the condensing boiler. Maybe the next five month operational cost will decrease when compared last year and the operational cost decrease breaks even with the yearly maintenance cost, but that's a big if at the moment.

Don't take me wrong, I like my condensig boiler, it is quiter, provides more even heat and unlimited DHW. Even if I take into account the installation cost for the condensing boiler. Just don't believe the boiler company and the contractor advertised saving with the condensing boiler.

PS: Comparing the operational cost for different type of boilers is fair for the same house/environment.

Jamie Hall

The only thing I'd wonder is... was the actual load the same both years? heating degree days? Internal temperatures?

EdTheHeaterMan

Jamie Hall said:

The only thing I'd wonder is... was the actual load the same both years? heating degree days? Internal temperatures?

... and was the change in electrical usage attributed only to the heating appliance?

If there was an additional television, massage chair, electrical battery charger, or power tool included (as a Christmas or other Winter Holiday or Birthday present) in the higher electric usage sample. To follow up on Jamie's observation, In New Jersey (Statewide average. Your local numbers may vary) Over the last 5 years, there was an annual Degree Day total as high as 5171 and as low as 4551. That is a difference of 12% depending on what year you select. To get a more accurate statistic @Skyline should look up the actual month-by-month degree day history for his location and compare the actual monthly difference in the outdoor conditions from the two years selected in the comparison.

Electrical consumption will be harder to determine other factors. Without a record of the actual appliances that were online at the time of the comparison sample, There is no reliable comparison source. The proper comparison would be to have a Watt meter on the original boiler and a watt meter on the new boiler. The only way to get close is to find a boiler that is equal to the one removed in a neighbor's home and install a watt meter on that dedicated circuit to see how much electricity is used to dispense a given amount of gas heat into the building. I don't see that happening so the existing comparison must be relied upon with an asterisk next to the numbers (You know, as they do with the Stats of Baseball Players on Steroids).

Only the OP has the inside story on the numbers. With this new insight on what those numbers mean, a little more interpretation may make the actual savings greater or even smaller, once you look closer.

BOTTOM LINE...There is a valid point to be considered in his observations.

Mr.Ed

Skyline

Jamie Hall said:

The only thing I'd wonder is... was the actual load the same both years? heating degree days? Internal temperatures?

As stated in the O.P., we live in the digital age...

Here are the HDD for my ZIP code for the seven month period:

1. 2019 last three month and 2020 first four month: 5,566
   
2. 2020 last three month and 2021 first four month: 5,595
   

You can check your own area's HDD days here

The internal temperature had been set at 70F and the setback for the night is 68F for the three years listed above.

@EdTheHeaterMan

There had been no new appliances, TVs, etc. added to the household. After paying for the Veissmann boiler, do you really think that I could afford it? Just semi-kidding...

If anything, the lightbulbs had been replaced by LED lightbulbs, but that's about all of the changes I can recall, when comparing the last two years...

Hot_water_fan

Great analysis @Skyline !
A few questions:
How did the pandemic impact how much time was spent at home?
My utility uses therm factors, which can be substantial (I've seen 8% to 15%), does yours adjust the CCFs in anyway?
What size was the old boiler? Did it modulate?
Last, is the fuel cost just the natural gas portion or does it include monthly fixed costs? If so, did those change year over year? Your usage decreased much more than your cost decreased, so it might include monthly costs or your unit price increased (or both). All in, 2019-2020 was $1.49/CCF and 2020-21 was $1.69.

EBEBRATT-Ed

Bottom line for me is condensing boiler don't save any money unless they are condensing all the time. If they are installed in a condensing system, yeah you can save money over a non-condensing system

System, you have to look at the whole picture not just the boiler

Skyline

Hot_water_fan said:

Great analysis @Skyline !
A few questions:
How did the pandemic impact how much time was spent at home?
My utility uses therm factors, which can be substantial (I've seen 8% to 15%), does yours adjust the CCFs in anyway?
What size was the old boiler? Did it modulate?
Last, is the fuel cost just the natural gas portion or does it include monthly fixed costs? If so, did those change year over year? Your usage decreased much more than your cost decreased, so it might include monthly costs or your unit price increased (or both). All in, 2019-2020 was $1.49/CCF and 2020-21 was $1.69.

The pandemic had no impact on the time we spend at home. My better half has been working from home for the last decade or so and I joined her six, or seven years ego. We have our own small businesses and as such, there's only two temperature setting, day and night.

Yes, my utility company does have therm factors, but it had been pretty much the same in the past. The cost per CCF had been the same, take/give a penny here and there.

My old boiler was 120K BTU if I recall correctly, non-modulating.

There's a delivery charge that changes, by volume utilization and some yeearly/monthly increase for that. I'll check for it later.

The NG utilization is fine, with the boiler condensing most of the times, but you missed the electricity utilization increase, that offsets a substancial part of the NG savings.

@EBEBRATT-Ed

I don't disagree with you, but...

The system is a given in this case, the only thing changed is the boiler. If you are going to say, that in my system the condensing boiler is not the best choice, I'd agree with you...

Hot_water_fan

@Skyline gotcha! Pretty much apples to apples minus the delivery charge. If they jacked that up by $.20/CCF in one year, I'm sorry. Those fees only seem to move in one direction. Looks like you decreased gas usage/HDD by 22%, while total electricity usage increased by 6%. If all of that increase is due to the boiler, you're looking at an additional 40watts/hour for the time period, which seems reasonable.
I'm interested in if the installer calculated your heat loss - looks like it's around 30,000-40,000 BTU/h, which is probably why your savings exceeded the AFUE efficiency difference between the boilers, but the total $ aren't that substantial - your house is too well constructed .

Skyline

Hot_water_fan said:

@Skyline gotcha! Pretty much apples to apples minus the delivery charge. If they jacked that up by $.20/CCF in one year, I'm sorry. Those fees only seem to move in one direction. Looks like you decreased gas usage/HDD by 22%, while total electricity usage increased by 6%. If all of that increase is due to the boiler, you're looking at an additional 40watts/hour for the time period, which seems reasonable.
I'm interested in if the installer calculated your heat loss - looks like it's around 30,000-40,000 BTU/h, which is probably why your savings exceeded the AFUE efficiency difference between the boilers, but the total $ aren't that substantial - your house is too well constructed .

After further review...

It seems that the delivery charge is dependent on the magnitude of energy utilized. The chances are that the per CCF charges are adjusted based on the volume. For example, this is from the actual NG bill for January of last year:



This is the NG bill for January of this year:



The electricity utilization is the opposite tendency, pretty much coincides with initial image posted for seven month.

The more telling view is, when the first four month NG utilization for the last three years is collected:



Certainly, there had been price increases, as the overall "Cost/CCF" shows, especially for 04.2021. Saying that some of the cost increases masked the overall efficiency of the new boiler would not be wrong. Add to that the increased cost of electricity taking away some of the boiler's efficiency, the overall saving in the initial posting about the bottom line is pretty much "right on money".

Ha-ha... Four out of five contractors did the heat loss calculation by looking at the old boiler labels and rubbing their belly. Is it 120K BTU? Yes.... "Well, you'll need a minimum of 120K BTU boiler output..." The fifth one wanted to charge more than the yearly maintenance cost for the condensing boiler to do the calculation, but I wasn't going to pay him for reading the label, when I am not looking.

I did the heat loss calcualtion by myself and "this old house" is about avarege, maybe a bit better, when it comes to heat loss. Yes, the boiler is oversized, if you just look at heat. Add the DHW to the boiler and the 120K BTU is about right.

One thing I can say, I am no plumber, rather a computer guy. I did learn about heating, radiators, DHW, etc., prior to getting the new boiler and a much, much more afterward. Had I known as much as today, I'd have a non-condensing combi-boiler, even if I like what I have...

EBEBRATT-Ed

@Skyline

I was just saying that for a condensing boiler to save much money it has to be connected to a system that will allow it to condense. I think you have proved that

Steamhead

Skyline said:

......... that doesn't even cover the yearly maintence cost for the condensing boiler.

This has to be taken into account as it is part of the total operating cost. How much was it?

Hot_water_fan

Yeah I think a non-condensing would have been best likely if you had gone right sized with either an indirect or a gas tank water heater. Thanks for posting the bills: I noticed that you used about 1 CCF/Day during the summer. I'm not sure how the boiler's efficiency compares to the old's for DHW production, but subtracting out 1 CCF/Day for everything but space heating does improve your CCF/HDD to a 30% reduction (it also makes the original 120k btu boiler even more oversized). It's not great compared to the annual maintenance and increased electricity, but still substantial! There are higher heat load houses out there that can learn from your experience here - the electricity use would increase less in comparison if your heat loss was 70k for example.

Tom_133

Just curious which gas boiler that is non-condensing would you have gone with? There are very few on the market.

Robert_25

Great analysis.  Thank you for sharing.

Hot_water_fan

One really important takeaway from @Skyline 's experience is to run a usage based heat loss calculation before the quotes come in so you can appropriately evaluate realistic savings. This installation ended up saving a good chunk of gas (22% -30% based on the proportion of gas unrelated to the boiler), but if the top line usage number is botched, the bottom line number will be too.

MaxMercy

Everything I had read up until I replaced my boiler three years ago said a condensing boiler wouldn't save enough to justify it's cost, it's yearly maintenance, AND it's 1/2 to 2/3 shorter lifespan - as a strait replacement.

I replaced my vertical tube steel boiler (close to 30 years old and still running) with a cast iron Slant. If this lasts as long as the builder spec steel boiler did, I won't be around to worry about replacing it again. Plus, with its AFG, Taco circ controls, and Hydrostat, I won't be more than a few hours without heat as everything is available on the shelf locally, including big box stores if it's a night or weekend (which is when they seemed to be programmed to fail).

But what I would LOVE to see is a direct comparison of two identical houses in the same area - one with a conventional CI boiler and one with a condensing boiler system designed so it condenses most of the time. I'm sure at that point, the savings would be much greater with the condenser, but I still wonder if the 1/2 life or less of a condensing boiler plus the additional maintenance would offset the fuel savings cost.

mattmia2

EBEBRATT-Ed said:

@Skyline

I was just saying that for a condensing boiler to save much money it has to be connected to a system that will allow it to condense. I think you have proved that

I think that the way we control most systems is quite dumb. I think that most systems would happily run in in condensing mode most of the time but the way we control them doesn't allow that to happen.

Usually we just control DH on/off. Since we do that, the boiler controls have no way of knowing if the heat call has lasted an hour and a half because the outdoor reset curve is matching the load or because the space isn't getting up to temp or someone just had a door open for 20 minutes so we usually have algorithms that increase the swt every 10 or 20 minutes until it forces the call to end. Same thing for the start of the call, can i take my time on low fire to get up to the swt or do i need to max fire then go off on high limit because there isn't that much demand in the system?

DHW has the same problems, is it just a small demand from hand or dish washing where i just need to be above the indirect storage temp or is it a big demand that i need max swt as fast as possible like a shower or filling a tub.

archibald tuttle

EBEBRATT-Ed said:

Bottom line for me is condensing boiler don't save any money unless they are condensing all the time. If they are installed in a condensing system, yeah you can save money over a non-condensing system

System, you have to look at the whole picture not just the boiler

boiling it down i agree, although if they condense some of the time they save some money. but I am in total agreement that the rush to condensing boilers (especially combi units) is completely overdone because most installed base of emitters are not designed for condensing temps although they may be acheived by outdoor reset in shoulder seasons and none of the combi units are designed to condense when making hot water which seems exceedingly stupid when you think about it since that is a question of heating 40 or 50 degree water. only phds could come up with a system to do that that presents 140 or degree water to the boiler. yes the finish wants to be 120 or 125 and that's closer but it still is on the margins of condensing. I would never put in a combi unit. high stack temps just the wrong combination.

archibald tuttle

Hot_water_fan said:

Looks like you decreased gas usage/HDD by 22%, while total electricity usage increased by 6%.

this is a better analysis than on the dollars because of changing prices but @Skyline , what kind of emitters do you have? My guess is that there might be some condensing reflected in shoulder season with ODR and algorithmic operation but that some savings are due to the load matching and lower stack loss without condensing.

If you aren't condensing a lot, then the maintenance could be less frequent. still want to do it but maybe every couple years. just saying. what is your venting? PE? I may have missed advances that can make hot water with lower temps in combi/condensing units, but when boilers that ought to cost a $1500 start costing 3 grand i loose interest. Still think I'd rather see a decent modulating boiler, don't really care if it condenses and a separate DHW setup (again, the non-condensing are bomb proof and last forever and are load matching so I'm not saying that just for condensing purposes although those design for condensing get really low stack temps that make venting a dream (ditto condensing furnaces although it seems like we only talk about hyrdonic here. mentioned scorched air is worse than listing prices in these posts . . . ))

PC7060

Following the advice of @hot_rod, I configured the condensing boiler I installed last November for ODR range of max water temperature of 120F at 10F outside temp and minimum water temp of 86F at outside temp of 68F. The return water temps are alway less than 110F and usually in range of 95F which should have boiler running at the highest rated level of efficiency of the boiler.  

During the 3 coldest months of the year the fuel usage decreased around 30% with savings in range of $40-50. I’ve recently noted a much higher % reduction in fuel usage during the spring season largely due to elimination of the heating cost  of keeping the 30 gallon tank of the old boiler at 180F. The reduction in cost during this period is about the same as the colder month so overall it’s around $300 a year.  The fuel usage also includes the DHW indirect added with the new boiler. A non-monetary but significant note is the long heating cycle have made the house much more comfortable.

So at a rough guess the fuel cost savings pay for the annual maintenance even with the additional cost of the DHW. 

Skyline

Thank you everyone for your comment and suggestions.

"This old house" has CI radiators in one zone, baseboard in the other zone and the exhaust vented through the chimney via PVC pipes.

As for the system... Pretty much everything that can be is using NG, like stove, dryer and DHW, are using NG. The boiler is a 4' x 5' room with two doors in a ranch style house. The house had a combi-boiler previously and made sense at the time to choose and condensing combi-boiler. I did look at the Weil McLain CGt-5 Boiler and probably should've got that instead, that was about 20-30% less than the condensing boiler.

The only changes made last year is replacing the boiler. Comparing the two boilers' operating cost is fair, in my view, even if the rates for the energy increased. After all, that what I have to pay, not what the rates were last, or previous years.

Nonetheless, here's the updated first seven month utilization for the new boiler, with the cost calculated via last year's rate for the same period:



My thermostat set to 70F and yes, I could set it at 68F to save some on the utility bill. As someone smart stated in one of the posting, "Do you want comfort or savings? You can't have both..."

As @archibald tuttle has stated, the condensing boiler works the best at shoulder seasons. In the heart of the winter month, the boiler saves about 6% on average And please don't start me on the boiler's frost protection that runs most winter nights and sometimes for days. The savings on NG is pretty much lost with the increased utilization of the electricity. If you look at the system as whole, the electricity utilization should be accounted for as well.

And that had been my initial point, if you take into account both utility bills, you really don't save that much with condensing boiler. Is it better saving however little it might be, than increased cost? Well, yes, but at what initial cost? Then we didn't even discuss life expectency for the condensing boiler and it's yearly maintence cost.

For most systems, condensing boilers are a scam and contractors should know that...

Hot_water_fan

I don’t think the boiler is a scam, it’s saving a significant amount of energy plus you can always fiddle with the outdoor reset, with a heat loss so small you probably can condense more than you are. The issue seems to be expectations. How much gas did you believe/did installers tell you you’d save? Both % and number. You used 736 CCF before. A chunk of that (say 50 CCF) isn’t boiler related. DHW efficiency might be similar between the boilers, but let’s leave that out for now. If you saved 50%, that’s 343 CCF, about $515 at $1.5/CCF. Would you have been happy at that savings amount?  

archibald tuttle

@PC7060 what emitters do you have that can handle a design temp of 120 degrees? totally agree with @Hotrod about the temperatures needed to take best advantage of condensing boiler, and you may have attended to this problem, but for most houses they don't have emitters that can keep them comfortable at 120 degrees in shoulder season never mind when its cold out. Most are designed with emitters that could heat the house at design temp at 180 degrees. Because of old fashioned overkill, maybe 150 would work with less of a setback motif and 120 would get you by in like kind in shoulder season. But unless you've got bill gates size house that won't justify a condensing boiler. But everyone wants a silver bullet, one discrete change and everything is good to go (to be fair this can be precipitated by failure of old boiler although I have repeatedly seen professionals telling folks to replace perfectly good boilers that just need some serious TLC with condensing boilers spurred in part by you and i a the insanse rebates that you and I are paying for–the nutjobs have finally caught their tails and now want the rebates to go just for heat pumps. what a great idea, worked out so well in Texas I can't wait til they try that somewhere where we really have winter) when the hard work to be done is careful insulation. And then vastly more emitters before you go changing your boiler. That's where to spend your money.

Skyline

Hot_water_fan said:

I don’t think the boiler is a scam, it’s saving a significant amount of energy plus you can always fiddle with the outdoor reset, with a heat loss so small you probably can condense more than you are. The issue seems to be expectations. How much gas did you believe/did installers tell you you’d save? Both % and number. You used 736 CCF before. A chunk of that (say 50 CCF) isn’t boiler related. DHW efficiency might be similar between the boilers, but let’s leave that out for now. If you saved 50%, that’s 343 CCF, about $515 at $1.5/CCF. Would you have been happy at that savings amount?  

Maybe scam is too strong and deceptive would be a more suitable word. That applies to both the boiler manufacturers and contractors as well.

The boiler manufacturers pretty much switched over to condensing boilers, it's hard to find non-condensing boilers, even more rare is the traditional CI boiler. Of course it makes a difference for them, if the boiler last 20+ vs 10+ years. Especially, when the parts are hard to come by for the condensing boilers by the end of its life.

The contractors push for the condensing boilers, where there are incentives to do so. Give you an example...

About 5-6 years ego my Triangle Tube non-condensing boiler had the LWCO sensor failed. My preferred contractor, all-in-all a nice guys, came and replaced the sensor for less than 2 "C" bills. We discussed possible replacement at the time and he recommended Navien condensing combi-boiler. I did not go for it at the time, but last year when I had to replace my Triangle Tube boiler, he gave me a quote for IBC boiler. You may think that this is just anecdotal, but three out of five contractors gave me a quote for IBC boiler. The funny part is that all three of them stated different BTU ratings. Obviously, I stayed away from the ICB boilers...

My expectations had been higher for the possible savings, based on the manufacturers and contractors statements. Mind you, I am not looking at a single aspect of the saving, rather the overall saving for the system with current rates on the utility bills. That had been the base for comparing two different time period, including heat, DHW, stove, dryer, etc. The roughly 5% overall savings for the seven month period really not that great, at least not to the level that had been stated by manufacturers and contractors. Especially, if the saving doesn't even cover the projected yearly maintenance cost.

That's the system I have and by now fully aware of that the actual saving is dependent on the heat emitters, heat-loss rate, comfort level, etc., could be improved at yet another substantial cost, but that's not going to happen. Mind you, the only thing changed is the boiler. The contractors should had been aware that as well, instead of "just hang one on the wall and you'll love it..."

PS: Oh, look, no images...

archibald tuttle

@skyline it isn't hard at all to get cast iron non-condensing boilers, both traditional atmospheric gas and power boilers that you can buy bare or if you get a good deal buy the oil version and throw the burner away and put a conversion on. I think most guys favor the featherweights cause they don't have to man handle the old stuff and it maybe feels backwards putting that in or god forbid fixing what is there, although from what you said you had a noncondensing low mass combi kind of thing so the parts on older ones can be a nightmare, cost and acquistion. I kept heatmakers running maybe 20 years and i keep munchkins going now (principally non condensing operation despite condensing capability) by buying old ones for parts units. The endurance follow ons drove me crazy with tech problems although it was theoretically a nice package. I get if you can't work on them and don't want to spend most weekends in the basement that you were looking for something new and you were perfectly set up to be sold on a condensing combi - indeed because of the 'difficulties', i.e. weight and size and venting of the alternatives, the fuel savings should have almost been a secondary consideration, but I don't let silly things like weight and seize and venting stop me.

So you were perfectly set up as a candidate for a condensing combi because, in combi's it is less likely to find noncondensing albeit most of the condensing installations are only marginally condensing so you can think about them just as load matching versions of the older units. Sounds like your room is not too big but you could get a non-condensing boiler that fits so it depends also on the venting (even side vent kits for the power boilers although i don't like them as much and they amount to adding the more moving parts that you are avoiding by not going to the 'higher tech' low mass boilers). And you would have needed to add DHW separately which is smarter anyway. You could use an indirect, but they are expensive and take up space in small room. I'd go with a takagi on demand (my own preference from experience, i'm sure other folks may have a different favorite). I prefer the noncondensing for price and reliability but the condensing ones work pretty well. I make that decision based on venting. You probably aren't going back to ground zero given your sunk cost so this is just a theoretical discussion but putting that out there so folks can whack away at this mole :-).
.

Hot_water_fan

You can still probably improve your savings by lowering the outdoor reset curve, give it a try. CCF percentage wise, I think your savings are reasonable and significant. Sounds like the contractors, by not doing an easy and free heat loss (which is dividing a few numbers since you have historical usage), really overstated the $ savings. That’s on them! They would installed an oversized non-condensing boiler too, with all the inefficiency that brings. I understand what you mean by total savings including electricity, but I think 6% more electricity which you can’t even isolate as just the boiler isn’t that bad. 

One way to think about it is: your heat loss is about 25k btu. Would you rather your heat loss was 80k? Same boiler, same 25% savings, but now you’re saving $700 dollars. The modcon pays for itself! But you’re paying almost $3k for gas 😂

PC7060

@archibald tuttle - My house had couple advantages which enabled the conversion to low temperature circulation.  The house configured with large Eastwood cast iron radiators in every room.  It was built in 1928 (post influenza pandemic) so the radiators are all generously sized to heat home even with windows open. The exterior cladding is stucco so air infiltration is very low for a house of its age. 

Conversions to improve efficiency: Before the house was re-stucco’d in the 1980’s by previous owner, rock wool was pumped into the walls. I’ve had to open up several wall and those installer did a very good job. 

For my part, the finished area to attic transition was sealed to block air flow from the open cavity interior walls; the thickness of the floor increased to 11” and dense pack insulation was pumped in to get around R45 insulation.  

I demolished a poorly built and very leaky (air and water) 400sft addition  from the 40-50-60s (think Johnny Cash Cadillac).  The addition consisted of a series of transitions from small porch to large porch to enclosed porch to enlarged kitchen; all of which encapsulated the previous iterations.  

We added 1200 sft addition which is well insulated with spray foam and is heated with vintage radiators.  

Which brings me to Ed’s (@EBEBRATT-Ed) previous point “ “you have to look at the whole picture not just the boiler”. 

Zman

For those who missed the reference, https://www.youtube.com/watch?v=Hb9F2DT8iEQ
I still laugh when I go to put in the bolts and "all the holes are gone".

archibald tuttle

@PC7060 so a nice installed base with overkill emitters and insulation details well managed. That is a really good setting to get something out of condensing boiler. especially if its not a combi it keeps nice low stack temps for reliable plastic venting. although you probably don't have bad heat loss for the square footage either so you have savings but they still probably don't cover the life cycle costs of condensing vs non-condensing.

@Zman of course you can do it one piece at a time, but a condensing boiler is far from the the first piece to do.

Zman

archibald tuttle said:

@Zman of course you can do it one piece at a time, but a condensing boiler is far from the first piece to do.

I think that one went over your head....

archibald tuttle

Zman said:

archibald tuttle said:

@Zman of course you can do it one piece at a time, but a condensing boiler is far from the first piece to do.

I think that one went over your head....

might have since you get shorter as you get older . . . but i figured you were talking . . . eer singing . . . about the system as a whole vs. what you get one piece at a time . . .

Zman

PC7060 said:

@archibald tuttle - My house had couple advantages which enabled the conversion to low temperature circulation.  The house configured with large Eastwood cast iron radiators in every room.  It was built in 1928 (post influenza pandemic) so the radiators are all generously sized to heat home even with windows open. The exterior cladding is stucco so air infiltration is very low for a house of its age. 

Conversions to improve efficiency: Before the house was re-stucco’d in the 1980’s by previous owner, rock wool was pumped into the walls. I’ve had to open up several wall and those installer did a very good job. 

For my part, the finished area to attic transition was sealed to block air flow from the open cavity interior walls; the thickness of the floor increased to 11” and dense pack insulation was pumped in to get around R45 insulation.  

I demolished a poorly built and very leaky (air and water) 400sft addition  from the 40-50-60s (think Johnny Cassk Cadillac).  The addition consisted of a series of transitions from small porch to large porch to enclosed porch to enlarged kitchen; all of which encapsulated the previous iterations.  

We added 1200 sft addition which is well insulated with spray foam and is heated with vintage radiators.  

Which brings me to Ed’s (@EBEBRATT-Ed) previous point “ “you have to look at the whole picture not just the boiler”. 

archibald tuttle

@Zman got it, i was being too cerebral when it was right in front of me

PC7060

Love the video @Zman!  One of these days I’ll get better at checking spelling before I post. 

@archibald tuttle - the cast iron units would have required much more near piping to ensure the return temps going back to boiler were above condensing temps.  Plus the built in indirect water heater controls streamlined installation.  

Basically, any system is a matter of selecting options that achieve the desired goal while mitigating the downsides.  

My primary goal was long low temp heating cycling to improve comfort; gas water heater to replace electric; direct exhaust venting and fresh air intake along with reduced energy cost. The direct venting and intake were important consideration because it allow me to avoid installation of a fresh air makeup system per IRC 2015 “M1503.4 Makeup Air Required”. 

 I’m happy with the results.

Skyline

Hot_water_fan said:

You can still probably improve your savings by lowering the outdoor reset curve, give it a try. CCF percentage wise, I think your savings are reasonable and significant. Sounds like the contractors, by not doing an easy and free heat loss (which is dividing a few numbers since you have historical usage), really overstated the $ savings. That’s on them! They would installed an oversized non-condensing boiler too, with all the inefficiency that brings. I understand what you mean by total savings including electricity, but I think 6% more electricity which you can’t even isolate as just the boiler isn’t that bad. 

One way to think about it is: your heat loss is about 25k btu. Would you rather your heat loss was 80k? Same boiler, same 25% savings, but now you’re saving $700 dollars. The modcon pays for itself! But you’re paying almost $3k for gas 😂

Well, the supply temperature that is required to achieve a given room temperature depends on the heating system, outdoor temperature and the thermal insulation of the building that is being heated. The outdoor reset curve controls the boiler's maximum temperature, that by association controls the RWT.

Weissmann manual shows outdoor reset curves for different emitters:



That's all well and swell, but depending on the outdoor reset curve settings, the efficiency of the boiler drops substantially for different emitters:



There still might be some room for additional savings, albeit that will result in increased electricity utilization due to lower water temperatures and longer heating cycles. Not to mention that in my neck of the woods, 20-30F or more fluctuation in outdoor temperature is not unusual in the winter. In which case, efficiency might be out through the chimney, unless one frequently adjusts the heating curve, like I did. At least for awhile, until got tired of it...

To increase a given air mass temperature with the system from say, 68F to 70F like in my case, may require the same/similar amount of CCF. No clue how to calculate that...

I didn't isolate electricity utilization for the old boiler either and that had been indicate as "Includes all electricity/gas utilization" in the spreadsheet.

I can actually measure the actual electricity utilization for the boiler two ways, Kill-a-Watt and the UPS, both of them within 5W with each other; these were the average utilization for the different boiler cycles:

1. Frost protection: 140W, or 0.56KWh for per four hours of protection cycle
   
2. Single zone active: 180W, or 0.72KWh per four hours of heating cycle
   
3. Both zones active: 210W, or 0.84KWh per four hours of heating cycle
   

Obviously, the longer the cycle, the more electricity is utilized. Especially in the case of frost protection cycle, that sometimes ran 10 - 14 hours, that resulted in 1.4 to 1.96KWh respectively. As a reminder, my heat emitters are CI radiators and baseboards in "this old house".

Could I squeeze out more NG saving at the expense of increased electricity utilization? It's probably possible, but may not really be worth for the efforts. And no, I have no intent to change the heat emitters, or my comfort level...

Hot_water_fan

Let's make this simple:
Which curve are you using?
Are all the rooms comfortable when it's cold outside?
I'm not suggesting you change comfort expectations or heat emitters - only lowering the temperature supplied to them to meet your actual heat loss.

JDHW

@Skyline
Those power consumption figures seem really big to me. (I am in UK) but my condensing boiler (30kW) takes a max of 23 watts and the three zone pumps are about 7-10 watts each. Have you got really long pipe runs and a big pump(s)?

Regards
John.

Skyline

Hot_water_fan said:

Let's make this simple:
Which curve are you using?
Are all the rooms comfortable when it's cold outside?
I'm not suggesting you change comfort expectations or heat emitters - only lowering the temperature supplied to them to meet your actual heat loss.

Currently, the curve is set to 1.8; the outside temperature is between 45 - 65F. The return water temperature flactuate between 90 -115F. The rooms are comfortable and the thermostat is set @70F.

This setting is from last month and about to drop it down some, once this cold snap ends. The curve is generally changed at least once a month, or more frequently depending on the weather forecast, to keep the RWT below 115F.

@JDHW

Well, those numbers show up on both, Kill-a-Watt and the UPS for the condensing combi-boiler (37kW in the US) when it is running.

My boiler has two internal pumps; one for the three stage pump for heating and one for the DHW. In addition, each zone has its own circulator. Here's the technical specs for the three stage pump from Veissmann:



The two zone circulators are rated 40W max, each.

I guess everything is bigger in the US, including but not limited to the utility bills...

Hot_water_fan

So your internal pump alone uses more electricity than my AC's blower! This is one reason I'm so intrigued by the Vitocrossal 300.

TAG

Nice writeup Skyline. For another take. Buderus cast Iron gas boilers were rated at 85% ... started using them back in the early 90's. Bumping up to a condensing wall boiler never made sense when projecting fuel use -- even 20 years ago with high NG rates. They made even less when the projects were finished and all the building upgrades typically resulted in lower than expected fuel use. My office was one of my first projects and the boilers have been untouched other than having to replace the vent dampers -- 28 years! My stone Victorian is at 22 years. Saving a couple hundred in fuel a year -- then having to maintain and replace a system is not cheaper.

Did have to use a Viessmann 200 in my newest as there was no room for anything else --

Hot_water_fan

@TAG Important to remember that rated AFUE is only useful to compare across similar, properly sized boilers - once you get turndown ratios and bad heat loss calcs, it's not as easy as saying 85% vs. 95%.