Are mod-con high efficiency boilers false economy Vs traditional cast iron over a longer time frame?

craigs2023

Hello and apologies in advance for the essay.

I have a 25+ yr old cast iron NG; chimney vented; HW boiler heating cast iron radiators, single zone tstat, 100 yr old well insulated house. Separate NG hot water heater. All work great - no complaints. I live in the northeast US so it’s a long heating season.

I will be finishing my basement next year and will need to remove the huge feed and return water pipes to gain head room. Will liikely change to pex home runs from a manifold. Will change and move the boiler as part of this project, but keeping the original radiators.

I have talked to a few local reputable heating guys and the general consensus is to move to a mod-con high efficiency wall-hung (Lochinvar or equivalent), and most also suggesting an indirect for HW.

What I am struggling with is, would I be adding a lot more complexity and cost over the long run for short term gains in efficiency - vs changing out for another CI boiler?

These are my (possible?) cons to a mod-con, compared with a traditional cast iron boiler

- Higher up front cost
- Shorter life span (15 yrs vs 20-30yrs ??)
- Annual expensive maintenance essential
- Parts more expensive and may be more difficult to source
- Unlikely to be running at 95% unless system is optimally designed and operated
- Cast iron radiators not optimal for low enough return temps for condensing
- More complex, so more likely to have issues/requiring service visits, more of a PITA. The current boiler has never caused any problems in 10yrs since we have lived here.
- I wonder if I ran the costs over a 30 yr time frame which one would come out ahead, with the least amount of headaches which is a big factor for me. No idea of course of future NG costs.

The current boiler is probably on borrowed time anyway so I want to decide on replacement before it breaks.

Am I being old-fashioned/too conservative? I am struggling with why not just get another CI.

Also, the current boiler is completely oversized (have to do heat loss calc) but I could size a new one back a lot and also get ODR to add some efficiency - maybe a direct vent model too; TRVs if the budget permits. Appreciating that efficiency won’t be close to a modulating boiler:

Would really appreciate any thoughts from the pros on this.

Thanks

GroundUp

With CI rads and good insulation, a mod/con can likely be condensing the entire winter. This can easily lead to 20-30% saved in fuel. Now whether the added maintenance and shorter lifespan maths out, that depends. Are you using 50 million BTU per year or 500 million? That 20-30% may be pennies and it may be thousands. I'm a big proponent of CI boilers with high temp emitters, but CI rads with good insulation are almost always a good candidate for a condensing boiler IMO. Just make sure the system is flushed well and employs a mag filter of some sort. As for the indirect, absolutely. You're easily saving 30-40% on fuel there when paired with a mod/con.

jesmed1

I'm not a pro, just a semi- informed homeowner, so I'm not going to try to influence you either way. But I will ask some relevant questions and share my take on our heating system, which is quite similar to yours.

Question number one is how long you expect to live in this house. On one hand, you ask "would I be adding a lot more complexity and cost over the long run for short term gains in efficiency..." What do you define as "short term gains in efficiency?" If you're planning to live in the house another 30 years, that's *long* term gains in efficiency. And you seem to be taking the long view, because you talk about running the cost comparison over a 30-year period.

On the other hand, then you talk about "the least headaches, which is a big factor." I'm pretty sure you already know from your research which type of boiler is likely to give you "the least headaches" over 30 years.

I've gone through a similar evaluation cycle with our 4-unit 4800 sq ft condo building that I maintain in the Boston area. I've looked at converting our 100-year-old gravity converted system to ATW heat pumps, condensing boilers, etc. What I keep coming back to is the proven history of the 25-year-old cast iron Weil McLain boilers we run (2 of them). They've been bulletproof for 25 years and have survived periods of benign neglect, minimal maintenance, and occasional maltreatment (before I got here, of course.)

Every other alternative I've looked at is more expensive up front and will need more attention and is more likely to fail and need expensive parts, some of which may not be readily obtainable. In a communal building like this one where I may not always be around to fix things, reliability and simplicity are key.

So where I keep ending up is that it's not worth us trying to wring more efficiency out of our systems by converting to more expensive, more complex, more failure-prone systems. When we need a new boiler, it's going to be another cast iron 86%, probably another Weil McLain, but a smaller one to match our actual heat load.

YMMV. I'm sure you will hear good arguments for going the other route too.

Jamie Hall

You are posing a very tough question -- and one to which I personally think there is no definitive answer. Let me give you my impressions on your questions, though -- all of which are quite valid.

- Higher up front cost
This is quite true; significantly higher
- Shorter life span (15 yrs vs 20-30yrs ??)
This may not be as true as it once was.
- Annual expensive maintenance essential
Absolutely. And will be more expensive, though how much more expensive is questionable.
- Parts more expensive and may be more difficult to source
This is absolutely true. There have also been problems with many of the parts being specific to a particular maker and sometimes a particular model, and may be come difficult to impossible to source after several years, or if dealers change
- Unlikely to be running at 95% unless system is optimally designed and operated
- Cast iron radiators not optimal for low enough return temps for condensing
These two depend very much on how much oversize your radiation is in relation to your actual heat load. If the radiation is significantly oversized to your current heat load, you will be able to run lower temperatures and use the condensing more of the time. This will improve average efficiency, though you won't achieve the 95% except during those times you can run the water temperauture low.
- More complex, so more likely to have issues/requiring service visits, more of a PITA. The current boiler has never caused any problems in 10yrs since we have lived here.
Absolutely true
- I wonder if I ran the costs over a 30 yr time frame which one would come out ahead, with the least amount of headaches which is a big factor for me. No idea of course of future NG costs.
This is your big -- and unknowable -- variable: future fuel costs. Can the expected, conservative 5% savings in fuel costs outweigh the additional maintenance cost and lost opportunity cost from the additional capital expense. If you can figure that one out, let me know.

Redbaran

An interesting topic with regards to cast iron lasting 30 years is: what will be available in terms of new products in the next 10 - 15 years? Who knows, but like most things HVAC has seen some pretty amazing technological improvements in the last 10 - 15 years. I worked with my Dad when I was younger; at 80 he is still puzzled by boilers that you can hang on the wall... For every gallon of flue gas condensate produced you save about 8,000btus. There are products that "sit" in the middle of traditional cast iron boilers and low mass wall hung modulating condensing boilers. Take a look at the Viessmann CU3A - it's floor standing, high mass, fully modulating and condensing. No need for primary secondary piping, low loss headers, etc. That being said, qualified installation and the service that follows is key; so look for a contractor with a good history of installing such products if you find comfort "in the middle" of traditional and wall hung.

Hot_water_fan

Ha quite the question! It’s interesting thinking about timelines - is 5-15 years of extra lifespan 15 years away important? That’s really hard to know - things change and a forever home becomes someone else’s home. Awhile back someone posed a question to the effect of “why don’t manufacturers make a boiler that lasts centuries?” And it gets back to the same answer - do people care about timelines that long? Seems to be no. 

ethicalpaul

Higher up front cost

This one is even worse than it seems. If you were to leave that money difference invested, the up front cost difference gets worse and worse (or better and better, depending) as every year passes. This also holds true for the maintenance dollars, year after year.

I love new technology for a lot of things, but there are two things I think I'll never do: replace a steam system, or buy a mod-con

jesmed1

Here's another thought. Have you considered an Energy Kinetics EK1 Frontier? Again, I'm a homeowner not a pro, but many pros here have high praise for the Energy Kinetics. The benefits for you are that it's higher efficiency than a standard cast iron boiler, but it's non-condensing, so you don't get the problems associated with a condensing boiler. If you get the stackable EK1 Frontier, you get a compact system with a 40-gallon water tank for your hot water.

https://energykinetics.com/system2000-quietest-most-efficient-boiler/

So that might be the best of both worlds for you: higher efficiency with the good reliability track record of the Energy Kinetics, without going to a condensing boiler that brings more problems. And the stackable design is more compact than a traditional cast iron boiler with an indirect tank.

Daveinscranton

I am a hobbyist not a pro.  I have a couple thoughts.  If you have enough radiation to make use of a mod con, at (mostly) low temperatures, it may make sense.  If you do the work yourself as entertainment, it may make sense.  Mod cons seem to want nice clean water with attention to water chemistry.  They like to be dialed in.  The default settings seem to be for the arctic, which I understand.  A warm house doesn’t generally make for manufacturer complaints.  Setting one up for maximum efficiency takes a bit of time.

It bothers me to see any computer stuff, or sensitive computer like stuff, around temps that cycle from near room temperature to cooking in a cabinet that contains a boiler, maybe as high as 180 degrees.  Again and again and again.  Has to be awful for circuit boards.  I run my mod con rather cold.  I also monitor the computer board temperature which never gets over 80 degrees F in my application.  The one I have runs at (an assigned) max of 31%.  It could be lower I think.  I added magnetic separators etc.

These are the things I would worry about.  If I had to pay for the installation, and wanted a mod con, I would find the best installer I could find.  I would do the same with cast iron.

 I guess I would worry a bit about very old plumbing and new technology.

EBEBRATT-Ed

This one has not been decided yet and mod cons have been around for 20 years or so. I don't think it will be decided upon in the near future.

Both have pros and cons.

You would think with mod cons that sooner than later the cost of mod cons and their parts would come down a bit but that may be wishful thinking.

john123

could we start to put some numbers on these choices
is 40 years reasonable for the ci wm
is 18 years reasonable for a lochinvar wall hung with good maintenance
what is the cost of the ci weil maclain--100,000 btu?
what is the cost of a comparable lochinvar mod con wall hung ---125,000 btu
what is the installation costs of each
what is the estimated annual maintenance of each

i have a friend who ran a standard 80% boiler for 40 years without any service or maintenance whatsoever, with one circulator change at 25 years. then it died!--completely died like the one hoss shay. it would be easy to compare this costing over the next 40 years with the costing of a mod con wall hung along with parts, maintenance, service, LESS FUEL SAVED over the next 40 years and get the answer!

but we need the numbers

i think this comparison could be done if we had some input

ethicalpaul

We can't talk about the installation or maintenance prices here, it's against the rules and it varies by geography anyway. The boilers you can get the prices of with google.

craigs2023

Thanks for all of the responses. 

Given that the key driver behind the boiler change is moving it for renovating a basement, it does nudge us towards HE mod/con - better air quality etc as the basement will be the kids playroom. 

Otherwise, I would just wait for the current boiler to fail and replace with something similar in the same spot.

Can’t really use the chimney to vent in the future given the planned layout. So, if I want to use a traditional CI, I would need to use a power vent?- and they seem to be somewhat problematic and noisy? Am I off base in this?.

I need to look at the viessmann cu3a that someone recommended as a compromise but I think they are $$$

I am just outside Boston so lots of boilers here. But with Mass Save incentives of $10K it seems like everyone I know is tossing out the boilers/hydronic and replacing with heat pumps or hyper-heat minisplits, with plans to add solar in the future. I hate the look of minisplits and really like radiator heat - my wife would probably like to get rid of the radiators for cosmetic reasons. I do feel like a dinosaur at times. 

We already have high velocity AC - works great but a little noisy - and I suppose we could change the condenser to a heat pump and see how that goes, but i would miss the radiator heat. Maybe we will make that switch when the condenser dies as a back up to hydronic or for shoulder seasons.

I love the fact that our CI boiler needs nothing, a service every two years, and it chugs along, but given the reno plans it might be time to make a change  But I know I will be as frustrated as when I look under the hood of my newer car.

I will take a look at the pro recs on here but please let me know if there are good recs for just west of Boston. This will likely be a next summer job. We plan on staying in the house for ever so I want to get this right and I know that whatever direction I go the right installer is probably 90% of the final product.

Thanks

Paul Pollets

A cast iron boiler will outlast the mod con and have less yearly maintenance costs. I'd put TRV's on the radiators and put the boiler on an outdoor reset control. All boiler controls and pumps or electronics have a 10-15 year average life expectancy.

tim smith

I have ran 10 yr costs on ones we installed and maintained very year and it really is a crap shoot. With the added maintenance on water tube or firetube boilers, along with the expense of part replacements. It pretty much wiped out the savings for residential boilers. Commercial was better as their usage is much higher and maintenance not that much more than residential. Some mfrs have less part replacements than others and that helps on the cost benefit ratio. But still with the lower lifespan it makes me think, are we really ahead of the game. Only thing is the carbon output for the difference in gas usage. Maintenance and repair are appx 1.5 to 2x what an atmospheric boiler would be. So doing the math says something.
My .02 worth
Tim

craigs2023

Thanks for the responses 

Given that the main reason to change the boiler is to move it as part of the basement reno, i can see why nudging towards HE mod-con makes more sense, even at the higher complexity. If we were not doing this, I would just wait for the CI to die and replace it with something similar at the same location.

Pros of HE:
- Don’t want to use chimney to draft due to future basement layout. Moving mechanicals to back room, so venting out side makes sense

- To stay with direct vent CI boiler, I would have  to use power vent(?) which would add complexity, cost to run, and noise…. I don’t know if any of these are true/significant
- Cleaner air in basement, given that it will be young kids playroom?
- Smaller footprint … not really a factor
- Efficiencu 
- I need to look into the Viessemamm cu3a that someone recommended

We are outside of Boston so lots of boilers here. Although it seems that everyone I know is ripping out hydronic and replacing with heat pumps/hyper heat mini splits. Considered it but I hate the look of mini splits and I prefer radiator heat. Maybe I am a dinosaur.

All said and done, the cost of new hydronic including all pex home runs etc will be around the same cost of adding a new ducted HVAC but I don’t think I can deal with the construction in the main living areas, and much prefer radiator heat than forced hot air.

I should mention that we have high velocity Unico AC that works great. Did give some thought to changing condenser to heat pump for heat and AC , but it is little noisier than we would like for all winter, not sure if it would keep up, and prefer radiator heat. We may make this change whenever the condenser fails, and use it for shoulder seasons or as back up.

We are planning to stay here for ever so that is why we need to get it right. I know that the installer is more important than the system so we will look on the find a pro tab, and open to recs … will likely be done next summer. 

On the other hand, I love that my CI boiler is serviced once every two years and just chugs along. and I will definitely miss that.

Thanks

nde

Overall if you want reliability and easier fixing go CI otherwise you are lucky to get 10 years on the new wall hung junk. Any savings are negated by shorter lifespan, cost of annual maintenance. Carbon footprint may be wash or even plus to CI as producing three junk iterations of a "efficient" boiler to same one CI seems dumb to me....but people lap em up. Must think they look cool. I know installers who no longer install them now based on such a poor track record and angry customers.

PeteA

The only thing I don't see mentioned here is the life of the production runs of the fancier mod/cons. How long do the manufacturers have to keep making parts available during and after model changes? I was actually going to ask a very similar question because I am also anti-bells and whistles and want something that has the best chance of being repaired for many years into or past the typical life span of the equipment. I have to imagine that with the typical CI boiler that as long as the heater core doesn't leak that there isn't a component on them that couldn't be swapped out to keep the heat on for years to come. I am just not into this super sophisticated stuff that seems to not only last a shorter amount of time but they are such heavily reliant on proprietary parts that once something goes bad, the whole thing needs to be replaced.
I have a Quietside that was installed in my home in Pennsylvania years before I bought the house and the company doesn't even exist anymore, so no parts are available anywhere, no tech manuals are available for troubleshooting and even though the heat works well the hot water heat exchanger is developing a slow leak, hopefully just a washer but if not that one little piece may have me spending a couple of thousand bucks for a full replacement. I hate the eggs in one basket concept, I especially hate the possibility of being kept hostage by a device that is way too difficult to repair or get up and running until a perm fix can be performed. My replacement will be a CI boiler when the day comes.

Doug_7

Your list does not include FUEL COSTS.

Mod Con high-efficiency boilers provide substantial FUEL COST SAVINGS which your list of cons does not even include. If you are only looking at the installation and maintenance cost, but not the efficiency and fuel cost benefits, you are only kidding yourself.

We have 3 sister buildings, each about 45,000 sq ft, only one of which was retrofitted 16 years ago with Mod Con Boilers, Indirect DHW Tank, modern Ventilation systems, Driveway Melting and advanced process controls.

Fuel use on the two sister buildings with the 30-year old original natural draft boilers with ON-OFF control is DOUBLE that of the retrofitted building, because they also only think maintenance cost is important. I am quite happy to save about $20,000 / year on the fuel bill for the retrofitted building.

So the answer is - do the full economics - consider total long-term cost of ownership.

Doug

SuperTech

My opinion as a service tech who works on boilers in the northeast every day is that for your situation the cast iron boiler and Indirect is a better option. Most of my customers who have a condensing boiler on high temperature emitters regret the decision to get one when it comes time to replace the expensive parts that are never in stock or when the mod con inevitably fails faster than their original cast iron boiler. I don't have any hard data to back it up but it seems like any gains in efficiency are lost by the high cost of service and repair and early failure.  It's not unheard of for two mod cons to fail in the average lifespan of a cast iron boiler. 

Honestly I think the best thing you can get is a Energy Kinetics EK-1F with the Carlin EZ Gas burner.  Close to 90% AFUE and a bullet proof design. Super reliable and should last 30 years without a problem. 

EBEBRATT-Ed

I agree with @SuperTech & @tim smith above. The number don't favor mod cons unless you can keep them condensing.

If the Homeowner can do his own service that helps.

I am very Leary due parts availability and parts prices. A blower motor assembly can cost 1/4-1/3 the cost of a whole new boiler. After 10-15 years (maybe less) the mfg has moved on to a different design and parts are no longer available


I have seen mod cons work great on the right installation.


We used then to heat a 100,000 gallon tank located outside that stored fire sprinkler water at 50 degrees. They condensed all the time and two 200,000 btu mod cons replaced an oversized 1,500,000 btu gas fired atmospheric boiler.

They save enough in gas costs to pay for the entire job in less than a year. But that is a commercial job.

As @tim smith mentioned residential is different.

Jamie Hall

Actually, @Doug_7 , I did mention fuel costs as being a significant factor, and I believe the OP is considering that. The problem with fuel (or energy costs in general) costs is very simple: they are completely out of your control, and any attempt to project even five years into the future is a fool's game -- never mind using today's costs to project savings or otherwise a three decades into the future. A situation such as @EBEBRATT-Ed mentioned, where the cost recovery can be measured in a matter of a couple of years is vastly different, and projections can be made which are at least reasonably valid. This applies to the overall cost of energy, but even more to relative cost of various energy sources.

hot_rod

Id look at the structure first, get the load as low as possible with reasonable upgrades

Then a heatloss calculation 

Then a radiator assessment 

Only then should you make a fair comparison 

suppose 80% of the year you could run 129f supply? Not unheard if with over radiated homes

At least 15 years, closer to 20 on name  brand
Mod cons

micro zoning can cycle a cast boiler to death, efficiency can plunge

Combustion air requirements need to be addressed also with conventional boilers. Return protection on an ODR cast boiler needs to be addressed

jesmed1

hot_rod said:

suppose 80% of the year you could run 129f supply? Not unheard if with over radiated homes

LOL, this is true. We run <129F supply 99% of the year in our 100-yr-old over-radiated converted gravity system...with cast iron boilers and no bypass. 25+ yr old Weil McLains with no signs of condensation problems.

Not saying that's ideal, just musing about the weird combinations of equipment that can sometimes work even when they shouldn't.

flat_twin

In eight years our WM modcon has required nothing but routine cleaning. I am a retired telco tech and took an interest in how this boiler works and why it works so well with the cast iron rads in our old house. The boiler is programmed to run between 88 and 140 degree supply water which is good to minus 20 degrees outside. It is pretty much condensing all the time in heating mode.
Do a heat loss survey, add up your radiator EDR and see if you stand a chance of running in the condensing range most of the time. Off the top of my head our heat loss is 62k btu and the radiators are capable of putting out 102k btu at 180 degree supply water. This is a 1740 sq ft house built in the 1830's. Modern windows, doors, insulation allow for lower supply water temps. We have ten radiators.
I bought a basic gas analyzer and do my own maintenance. Over the last few years I've picked up some spare parts, a blower, gas valve, circulator, spare maintenance kits. I haven't needed anything but the maintenance kits so far. The main board is quite expensive and would blow a lot of the fuel savings if that ever had to be replaced. Fingers crossed.
The modcon replaced a fuel oil cast iron boiler. Our local HVAC company installed it. The following year I installed an indirect WH to replace a very old electric WH.
Taking heating degree days into account and trying to make as fair a comparison as possible, we spent 38% less on home heating the first year with the modcon.
I'm hoping to get 20 years or more out of this modcon by keeping an eye on water quality and keeping it clean. When the time comes to replace this modcon, maybe air to water heat pumps will be something to consider?

The Steam Whisperer

I'd look very carefully at circumstances for the fuel savings that are being presented. It is very likely that most if not all of the existing boilers were grossly oversized for the heat load and probably well past thier prime. This causes a very large reduction in efficiency.... especially when looking at atmospheric gas boilers. I have found that simply going from a 2x oversized atmospheric boiler to a properly sized atmospheric (in residential) is about a 12% reduction in fuel use. Tales of 36% saving are probably true, but how much savings would there be by just properly sizing the equipment? I have done many commercial projects where we replaced existing boilers with 2 or 3 staged atmospheric boilers and saw typical savings from 35 to 40%.
I just replaced my 60% oversized stack damper equipped atmospheric boiler in my home's high mass conerted gravity system( which I combustion tested and it was running about 30% excess air and about 84% efficient) and replaced it with an about 60% oversized tiny power burner gas boiler with stack damper ( firing about 30% excess air and 84% efficient) and it looks like I have reduced fuel usage about 20%.
A simple on/off cast iron boiler connected to a single zone high mass system is a very efficient combination. There is no need for outdoor reset, as the mass of the system automatically resets the water temperature, and the boiler will have very long on cycles with very long off cycles for very high operating efficiency. About the only gains you will have with a condensing boiler is due to the condensing, which is probably worth about 12% reduction in fuel use. These mod con fuel savings will also be offset in part due to higher electrical usage of a typical modcon ( 2 pumps, blower motor and onboard electronics running nearly 24 hours a day all winter long.

Also, Mod cons have been around a lot longer that 15 years or so. They have been in use in Europe for more like 30 to 35 years ( the Triangle Tube models are one example) and the typical life is in the 12 to 15 year range.

In my book mod cons are simply not cost effective. Focusing investment on reducing heat loss of a structure is likely much more cost effective, because it has a 4 fold impact....Lower heat loss at a given outdoor temperature, a reduction in the length of the heating season ( a building is self heating due to internal gains) , cooling loads are probably reduced, and you are more comfortable year round.

EBEBRATT-Ed

@flat_twin

I think that is great that your learned your boiler and system and bought the equipment to clean and service it.

Most customers are not going to be able to do that. Which will last longer a neglected CI boiler or a neglected Mod Con?

Granted neither situation is any good. Either one could fail, either one could make CO.

But the neglected CI boiler unless the sections crack and leak will be able to be kept running for 30 years or more. If the boiler doesn't leak anything on that boiler can be fixed with standard parts even if the boiler mfg goes out of business with 1 exception.......the burners.

A Mod Con can't do that.

And I am not against Mod Cons. They are great on the right job, there great when maintained and they are great when the MFG still has parts and parts availability is an issue. And it shouldn't be after 20+ years of Mod Cons.

JMWHVAC

I love reading old school vs mod-con discussions. Just did a replacement of a CI. We came up with an 80% higher price for a mod-con due to many job specific factors. One of my biggest peeves with CI/Indirect setup is the fact the boiler sits there ALL summer at an average of 130-140 degrees even with a proper postpurge. Most heavy boilers have very little insulation and so it sits there putting off heat all summer while the AC runs to remove it. The only properly insulated heavy weight boiler I've seen is some Viessmann boilers. With a mod-con/Indirect setup at least the boiler doesn't have much mass to hold heat for long.

clammy

Get your chimney lined and stick to cast iron ,longer life less yearly maintenance and a a huge amount of specific parts on any mod con . Unless some one is going to do a heat lose and then figure at what low temp you can heat your home with it all heresy and speculation . I have a mod con but I changed out all my baseboard to modern panel rads and sized my panels to my lose and to the highest temp I want to operate on about 135 at 10 outdoor temp.yeah I had to buy larger panel and it cost a bit more but my return temps are never above about 120 at design day. It seems that a lot of guys install them but it seems a lot do not own a combustion analyzer and those who do ,don’t test the unit upon intinal start up I **** at them and lecture them and say If you don’t test you don’t know and you don’t have any bench market for the future if and when a issue happen why cause you never tested . I know this because I get called about what should I do and I ask do you have any combustion number from when you did the start up and I always hear the same poop . No test no clue .
As other stated are you going to stay ? And even if you do will it be worth it when you have to replace in 10 years I doubt it . Yearly maintenance is a **** and never cheap . I only install mod con s where they make sense ,where they can operate at or below condensation point for most of the season but I tend to shy away when it comes to hi temp systems ,yeah modulation saves short cycling but correct sizing and possible buffer tank for micro zones off a cast iron boiler also works just fine . Either way you look at it when’s having a heating system replaced makes sure your contractor proposal is a Apple to Apple comparison not just a cut and slide in . Make sure your getting what you paid for not re use all the old stuff pressure reducing valve backflow Andy expansion tank .Be sure you get a micro air elimator ,pump on supply pumping always isolation valves on all circulator and boiler supply and returns ,also don’t forget water chemistry ie hard water possibly filll w demoneralized water and make up water filter and acorrision inhibitor to protect your boiler heat exchanger and all the new ecm circ of the future.
Not all installation contractors approach jobs the same and not all contractors do the same job ,not all are up on the newest approaches to proper installation and some have never read a installation and operation manual for what they install ,this is true w mod cons at least from a lot of the installs I see .
The biggest favor you can do yourself is be educated and ask question and if a contractor cannot answer your question and is doing a talk about in circles find another contractor . Install a mod con properly is never cheap and to do a beautiful wall hung on a panel ,painted and piped w a hydro separator and all the right stuff like polypropylene vent pipe over pvc no gas flex and properly supported and easy to service comes far and few between and never comes cheap .usually in my book about 50 % more for a mod con over cast and that’s not including a stainless steel chimney liner . I wish you the best of luck but be wise and stay away from low ballers that have no real answers and remember to ask about yearly service costs ,gotta factor all the stuff in . Those who do the Gucci work are never in a huge rush because ya cant do the Gucci work quickly it takes a little time to make it perfect and perfection does not happen when your in a rush to get done . That happen on a slip in and slide cause there’s zero money just a days pay .
The sweeten of a cheaper price is often forgotten after the bitterness of poor quality
. Peace and good luck clammy

hot_rod

jesmed1 said:

hot_rod said:

suppose 80% of the year you could run 129f supply? Not unheard if with over radiated homes

LOL, this is true. We run

jesmed1 said:

hot_rod said:

suppose 80% of the year you could run 129f supply? Not unheard if with over radiated homes

LOL, this is true. We run

Have you measured the flue gas temperature? Especially at the top of the termination? Condensation can be happening in the flue that you don’t observe in the firebox. Is it brick chimney or B vent?

clammy

Brick ceramic lined on outside needs a liner always in my book unless the home owners wants to pay a mansory contractor to re point and repair ,Andy then line it .b vent usually is not a issue usually if ran inside the house in a chase but when installed In a framed out box outdoors there can be issue w the roll out switch and spill switch due to the b vent cold temp ,it happens .. as stated before most if not all masonry chimneys on outside needs to be lined or pay some big bucks to repair and not line only to suffer the same damages in a few years . My adage is repairs and line it and be done ,no liner mansonary repairs are in the crystal ball of the future . Any contractor who shrugs off talking about the chimney are not the educated contractor you want ,they just want the sale ,they offer nothing for your benefit . My mantra is yeah I include a lots of stuff that most would not do or think about ,the reason is different concerns there’s is there pocket book mine is both of yours. But a lot don’t see it that way and I’m really good w that that’s why we live in the free est country in the world and any adult can make a decission weather informed or uninformed . Gotta love this country home of the free thanks to the brave .
Peace and good luck clammy

jesmed1

hot_rod said:

jesmed1 said:

hot_rod said:

suppose 80% of the year you could run 129f supply? Not unheard if with over radiated homes

LOL, this is true. We run

jesmed1 said:

hot_rod said:

suppose 80% of the year you could run 129f supply? Not unheard if with over radiated homes

LOL, this is true. We run

Have you measured the flue gas temperature? Especially at the top of the termination? Condensation can be happening in the flue that you don’t observe in the firebox. Is it brick chimney or B vent?

@hot_rod We have the boilers serviced and cleaned every year, new nozzles installed, and the combustion gases analyzed and the air settings adjusted as needed. Stack temperature is 420 gross/350 net, 12% CO2, with draft set to specs. It's a 3-story brick chimney in the center of the house, so only the attic portion and above the roof is exposed to atmospheric temps. Terra cotta liner. We just had the chimney inspected for possible conversion to gas burners. Very experienced, reputable local sweep inspected the chimney and said it was fine, though we would have to line it for a gas conversion, which we ultimately decided not to do.

Vent pipes are standard single-wall galvanized 7" two-into-one, with larger diameter at/after the tee where the second boiler tees in. They've been there 25+ years with no evidence of deterioration or condensation.

With both boilers running 45-minute cold start cycles with supply water temps mostly under 130 and never exceeding 140, everyone keeps warning me these things should be condensing somewhere, but no one can find any condensation and everything is in good condition after 25+ years. It's a mystery.

flat_twin

EBEBRATT-Ed said:

@flat_twin

I think that is great that your learned your boiler and system and bought the equipment to clean and service it.

Most customers are not going to be able to do that. Which will last longer a neglected CI boiler or a neglected Mod Con?

Granted neither situation is any good. Either one could fail, either one could make CO.

But the neglected CI boiler unless the sections crack and leak will be able to be kept running for 30 years or more. If the boiler doesn't leak anything on that boiler can be fixed with standard parts even if the boiler mfg goes out of business with 1 exception.......the burners.

A Mod Con can't do that.

And I am not against Mod Cons. They are great on the right job, there great when maintained and they are great when the MFG still has parts and parts availability is an issue. And it shouldn't be after 20+ years of Mod Cons.

I have to agree. I suppose the death of a firetube modcon would be the HX developing a hole or obsolete parts. I don't know what the HX costs but it's probably enough to make you think hard about investing more into a boiler whose parts support is waning. And if the longevity doesn't work out with our current boiler, I would certainly have to consider replacing with a simpler on/off boiler. I'll also have to get my chimney repaired and lined. Not having to repair the chimney was a small part of the justification for the modcon. All I can do is give it my best shot.

hot_rod

Well we know some of the early mod con running are over 20 years old. A fluke? Better installation? Better quality?
Usually with few exceptions we only hear about problem boilers here in HH, not the 100 of thousands of happy, healthy, problem-free ones

tim smith

This is a good discussion, we still put in mostly mod cons but the #s don't lie. Service vs lifespan and savings. Although as one poster mentioned, large users save a lot of fuel, (expense). This offsets the service and lifespan expense.

craigs2023

Although I don’t want to admit it, my situation is probably a good fit for mod cons.

The radiators are probably hugely oversized vs heat demand compared with when the house was built 100 years ago - before insulation, double pane windows etc. So, the radiators could be supplied with lower temp water, keep condensing etc 


I need to calculate the radiator output and heating use/demand - will come back with those numbers 

hot_rod

Yes, if you want to make an informed decision base on the numbers, the radiator sizes are the next good step.

What would you need to discover to make you go with a mod con?

jesmed1

craigs2023 said:

Can’t really use the chimney to vent in the future given the planned layout. So, if I want to use a traditional CI, I would need to use a power vent?- and they seem to be somewhat problematic and noisy? Am I off base in this?.

Another option is the Energy Kinetics Resolute, which is a compact, non-condensing boiler that can sidewall vent, and uses "air dilution" venting instead of a powered blower. That would allow you to locate the boiler away from the chimney and sidewall vent, while giving you the reliability of an EK without the added complications of a mod-con.

https://energykinetics.com/90-resolute_multi-fuel_boiler/

sixplex

I'm thinking about the same thing as the OP, have a bunch of CI baseboard radiators which are oversized so low supply is in the cards.

I think a mod con makes no sense in residential unless gas prices are extremely high or service costs are extremely low, neither of which i think is true in most places in north america, europe has high gas prices which where mod cons originated from what i understand.

where a mod con does make sense is commercial, if the property is extremely large the savings will outweigh the cost of maintenance

hot_rod

So you  will run a conventional boiler at 150-160 to get low 120 swt to the cast iron? A cast iron boiler will never get above 85%, much lower if it short cycles under partial loads

Basically foot to the floor and use the brake to control speed. That is how a fixed output high temperature boiler operates in zoned, low temperature systems

if a home can be heated with 180 on design day, 80% or more of the year it can run at lower supply temperature 

My experience shows that modcons makes sense in any application where modulation and low temperature supply is acceptable

sealed combustion with outside air ducted to the burner is another benefit 

Less complicated machine is really the benefit of cast iron boiler, possibly a longer life.

Gilmorrie

You already posed this exact question on DIY heating, and received extensive, thoughtful replies.