At a crossroads -- help with choosing new boiler system

oldvictorian

Hello All:

I am a new homeowner of an old (1870s) Victorian home in the upper midwest (cold winters). The house is about 4000 square feet in total, with about half the square footage coming from an addition added around 25 years ago. The original portion of the house has cast iron radiators on three floors of living (1-3); the addition has radiant heating in the basement and first two floors above grade.

We currently have a Weil-McLain 245k gas-burning water boiler; it is about 25 years old. While it is currently functioning, my wife and I have decided to be proactive and replace it and our gas-fired water heater (100 gallon AO Smith from 20 yrs ago) at the same time as we plan on being in the house for many years to come. We have many zones for heating (8) in the house.

I have spoken with two contractors, both of whom I find trustworthy and honest, but both have given me different recommendations that are rather divergent.

One contractor, whom I used to replace our A/C systems (and has been great to work with), sells Crown Boilers. While he's quoted both cast iron (Aruba) and high efficiency (Phantom) models, he is recommending a cast iron model based on longevity, durability, and ease of management/care. He would preserve all eight zones of heating, using each separate thermostat for controlling temperature (and variations throughout the home). I have four pumps that would be replaced. An additional bonus, which I find compelling, is that as long as they provide regular annual service to the boiler ($100), they will cover 100% parts and labor for any problem that I have for 10 years.

The other contractor (whom I chose because he installs Viessmann, after the strong praise Viessmann garners on this board), recommends reducing and simplifying the number of zones to just a few, but relying on the furnace (either Vitodens 200 or Vitocrossal 300) to provide steady output and managing output at the furnace level (excuse my poor understanding of the technology and misuse of words) to balance heating, basically no longer relying on thermostats. I am told the high efficiency furnace would allow us to get rid of the four pumps we currently have.

While I am sensitive to increased efficiency and environmental considerations, I don't want this to come at the expense of longevity and reliability. I like the idea of simplifying the setup (reducing zones, getting rid of the need for pumps and expansion tanks), but it's not a big deal to me to keep things status quo.

I don't have definite pricing yet, but at the end of the day, I want to take the long view and choose what is the best option -- for comfort, dependability, longevity -- rather than the cheaper up-front option.

Does it make sense to keep the many zones I have, or is it better to simplify?

Can I expect longevity on the order or 20-25yrs with a regularly-serviced high efficiency furnace?

This is all new to me -- any insight or recommendations would be greatly appreciated.

Thanks in advance to all and best!

Jamie Hall

Well... you'll get different opinions, and what follows is mine.

While a heating system is just that, a system, and all the bits need to work together, in some ways individual aspects can be treated individually

So On the boiler. My preference would be for the cast iron boiler, as longevity is better (perhaps much better) and maintenance costs are lower. Yes, the modern mod/cons are more efficient -- perhaps 5% better, all else being equal, over a season. But they need more maintenance and a are somewhat more "finicky" and the controls particularly, can be difficult to work with except for really skilled techs.

On the zoning, that's really a somewhat different matter. Multiple smaller zones do create some problems -- with any boiler -- in that very often the boiler is putting out a lot more heat than the one or two zones calling can absorb. To some extent this is managed better with a mod/con, as it can throttle down (up to a point). However, any boiler can be (and should be) piped "primary/secondary" so that the circulating water temperature is somewhat independent of what the boiler is doing, and the boiler only needs to give the system a shot of heat now and then. But how many zones you have is very much a matter of how fine a control over the temperature in your various spaces you want. If you do not have the separate thermostats for the various zones, you don't have control over them. What your Viessman man is thinking of is using outdoor reset for the boiler -- which is the only way to get the advertised efficiency from it -- and setting that so that the water which it makes is just hot enough to heat the spaces, but no more. Sometimes that works. In your house, as I envision it, I'd not be so sure -- I have a feeling that the heating load of the various spaces is probably not all that constant, and that there will be some that need a lot more heat under certain conditions than others under the same conditions.

So... bottom line, if it were mine I'd go with the first guy's ideas -- and the cast iron boiler.

HVACNUT

I would go with the cast iron as well.
But I would go with a cast iron 3 pass boiler and a power gas burner. More efficient  than atmospheric burners. Primary/secondary piping, outdoor reset and probably a buffer tank for the radiant. 
Actually I'd convert to oil. 
I have nothing against mod cons, they keep me busy so I'm happy. 

mattmia2

Both are equally valid approaches if done properly. Getting the balance right for the modulating with outdoor reset option and getting it to perform as well as zone valves would be very tricky.

I don't think I would advocate for replacing a 25 year old CI boiler in good shape with a mod con with the idea that it would improve reliability over the current situation. The 25 year old boiler could go another 30 or 40 years or it could leak tomorrow. The mod con will need more regular maintenance than the CI boiler.

The Steam Whisperer

I also favor the cast iron boiler approach, but with a different twist. A typical atmospheric gas boiler reaches peak efficiency when running at full capacity, so the trick is to keep your boiler running at full capacity. The way to do that is to stage on smaller boilers as needed so that the smaller boilers will reach full capacity quickly. In your case, I would install one small cast iron boiler that is sized to heat the house on typical winter days and warmer ( about 90% of the heating season) and the leave the current boiler in place so it could only be used a few days a year when its really cold. This way, you get measurably improved efficiency, still keep the boilers simple to repair, and have back up should a boiler not work in cold weather. We have seen fuel savings between 15% ( where the current boiler was properly sized to the heating needs....and this is very rare, nearly all boilers are about 60% oversized.... and a more compact modern design) to 50% or more with large boilers running on standby all winter long.
Most of the best boiler people here seem to agree that the greatest amount of savings from a modulating/condensing boiler is from the modulating aspect and outdoor reset. You can get those savings from much simplier boilers with the proper installation.

I am have lived and worked in Northern Illinois my whole life, so I have lots of experience with this type of setup in this climate, for both steam boilers and hot water boilers.

EBEBRATT-Ed

@oldvictorian

As we say many times on this forum the "contractor" is more important than the "boiler"

You already have a good experience with this contractor so trust his judgement and go with him.....as long as he sizes the boiler right and his $$$$are within reason

BigRob

I have two Lochinvar mod cons serving a 12 condo building in SF. I am impressed with Lochinvars. Over 170k ignitions and 35k hours between the two with no breakdowns ever over ~10 years. Installation is key, as stated. The original contractor was a fool and one of the boilers ran 3000 hours with 48k ignitions. Not a typo. The Lochinvars are pretty simple mechanically and fire tubes are elegant, but like all mod-cons, they have relatively complex digital circuit boards. If a pump relay goes out, you have to buy a whole new board. Compare that to a Taco zone controller that uses standard plug in relays. They also have a lot of sensors and stuff with the potential to break. Also keep in mind the stated 95% efficiency for mod cons is a marketing best case. There are assumptions, from memory, that include installing the boiler in a conditioned space that will contribute the boiler waste heat to the structure, in addition to unrealistically low water return temperatures for most applications. Even if your boiler is in conditioned space, it may not contribute to meaningful structure heat depending on its location. If you are in a dry winter climate, condensing is reduced. San Francisco is obviously coastal and our radiant floor boiler will condense all day feeding 10k sqft of thin slab radiant flooring. This is a perfect application for a mod con. Condensate treatment is an issue that I would rather not deal with. Our boiler room is on the roof and the condensate is routed down our roof drain. I have an extra large condensate treatment tank because I cannot have that cast iron roof drain rust away- it would be a massive expense to replace it. I've thought about looking into a liner. Condensate pumps break, too. Condensate treatment is annoying, but not a deal breaker by itself. Cost of service is absurd in SF, so I haven't serviced either boiler, ever, which has saved me enough over 10 years to buy a new boiler. Even so, the exhaust temperatures are much lower than the incoming boiler water, so they are probably fine. With that said, I will have them serviced sooner or later. There is a reason old cast iron boilers last - big **** beefy heat exchangers and analog controls. I will probably go that route on replacement for our hot water heating. Actually, our building originally had a copper fin standard efficiency boiler feeding a reverse indirect water heater. It was probably more efficient than our two high efficiency boilers considering waste heat and power. For some reason the jerks said the HOA needed another gas line to the roof for an additional boiler, even though the building never had heat or hot water issues. You should have seen their install. So many pumps and extreme short cycling. It was a joke. I wish I had been involved, then. A reverse indirect water heater might be an interesting option for you to consider. Lochinvar now makes a reverse indirect with optional connections for heating zones for buffering. Turbomax is another brand. We had an Ergomax brand. The reverse indirect would allow you to have thermal storage for your smaller zones to keep the boiler from cycling too much while also heating water. I think with startup heat loss, electric inrush, etc, each ignition needs to last about 15 minutes to be energy effective, but the others here can advise. With your radiators, a reverse indirect might be a nice setup. You could use a thermostatic mixing valve for the floor zones depending on what water temp they need. I also think it's dumb to have one pump per zone unless you absolutely need to. Each pump has heat loss from water and electrical losses and consumption. Optimally, one Taco VR ECM (or whatever) zone pump and a bunch of ball zone valves is what I would do. The boiler needs a pump, too. So best case, two pumps. Maybe two zone pumps if you need a different temperature for the radiant floors, depending on how you do it. If the radiant is staple up maybe you can use one temperature for all the zones to keep it simple.

I think a power vent cast iron boiler at 90% is what I would do. The ATH KN series looks neat and might offer 10 to 1 turn down in the smaller sizes if you don't like thermal storage for whatever reason. (https://www.knseries.com/products)

The LAARS FT series looks nice from a design perspective and is affordable. The Combi hot water option is ~$200 and can feed a storage tank.

Anyway, some food for thought.

oldvictorian

Thanks to all for your time and insight.

The quote I received from one contractor for a Viessmann system running at constant circulation was prohibitively, eye-wateringly expensive -- literally almost 2.5x the next estimate for a mod-con boiler and almost 3x higher than the CI estimate I received. While I trust his sincerity and ability to do good work, it's just not feasible or justifiable. Besides an unrealistic initial outlay, it would take a century to even start to recoup the ROI.

Where it has now gotten interesting, however, is the other contractor (who has done great work for me in the past) has now supplied quotes for CI vs mod-con that are <$1500 off.

While I was heavily leaning towards a cast iron boiler for durability and longevity, the price differential really is making me second-guess myself. My gas company offers a $350 rebate up front, and the increased efficiency (whatever it might be in a real-world situation) should be recouped in perhaps 5 years (given the likely forecast of increasing NG prices this winter).

I would have both units serviced regularly, so that cost is a wash.

I'm keeping zones as I have them. This makes installation simpler and follows the "if it ain't broke, don't fix it" mantra. Given our home, with a mix of radiant and radiator (cast iron and baseboard) spread over three above-grade floors, I think separate zones with individual thermostats -- while less elegant than a constant circulation system -- while allow us to adjust temperatures to match our needs for rooms we are actually using.

Any last advice on conventional vs mod-con given the price differential?

Again, thanks to all for your help and expertise.

Hot_water_fan

https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new

Calculate your heat loss real quick with this. The amount of money/energy/emissions available to save depends on how much you use now. Recently, someone posted about how pissed they were at their modcon, which was saving them 25-30%! It was because they didn’t calculate their heat loss and their installer definitely didn’t either (well not correctly). Hard to save money if your heat loss is only 25kBtu. But a big old Victorian might be >4x that. 

oldvictorian

To Hot_water_fan:

thanks for this. I calculated the heat load at about 50k, which surprised me at how low it was. That said, it is artificially low, as we were not living in the house (we were renovating) and the thermostat was kept artificially low (I think I had it at 56 for most of the winter). 

Regardless, this is “load” and not “loss”. While helpful in determining the size of boiler, it is less helpful for the choice between CI vs mod-con. 

The critical issue I think is the actual real-world efficiency difference — 84% for cast iron vs XX% for high-efficiency. Even though it’s published as 95%, there is quite a lot of thought (and data) that would suggest in real world situations the difference is much less than the 11% I’ve been led to believe. 

at this point, the initial investment delta is small enough that it’s not that important — but if the longevity and temperamental/finicky nature of a mod-con is inferior, any energy savings would be more than offset by greater headaches, repairs, and a shorter lifespan. 

And again, thanks for taking the time to share your expertise and thoughts 

EBEBRATT-Ed

Just my opinion.

Efficiency aside, mod cons don't gain much efficiency unless used on low temperature system. The fact that they modulate does increase their efficiency and is a big advantage.

My biggest concerns with mod cons is:

Longevity: we need more years of run time to evaluate this but 15 years seems to be the best if well maintained. All boilers need regular service but it can't be skipped on mod cons.

Parts availability and parts prices:
I have seen where the supply houses do not have the parts in stock, you may have to wait several days. Parts are propriatary and don't fit anything else which doesn't allow service techs to keep parts on hand.

A blower motor and fan assembly can be $$$$.$$ installed (watch the decimal point)

Their is no right or wrong answer to this, it's your choice but to me a cast iron boiler if sized correctly installed properly is the best choice

Hot_water_fan

thanks for this. I calculated the heat load at about 50k, which surprised me at how low it was. That said, it is artificially low, as we were not living in the house (we were renovating) and the thermostat was kept artificially low (I think I had it at 56 for most of the winter).

Boilers are often 3x oversized, this is not surprising at all! A 10:1 turndown boiler of 80-125 Btu seems well sized.

The critical issue I think is the actual real-world efficiency difference — 84% for cast iron vs XX% for high-efficiency. Even though it’s published as 95%, there is quite a lot of thought (and data) that would suggest in real world situations the difference is much less than the 11% I’ve been led to believe.

You might be surprised about this! Oversized cast-iron boilers can underperform their AFUE significantly too. AFUE isn't a law of nature, it's a test result. The testing includes a small oversize factor (I think it's 1.4x load). If you're 3x oversized, AFUE does not apply.

https://forum.heatinghelp.com/discussion/185035/one-year-ng-utilization#latest

Here's a case where an oversized boiler was replaced (with another oversized mod con - don't do that) with savings probably north of 30% if you subtract out the non-heating gas usage, 27% if you don't. And that's with baseboard heat, which generally uses higher temperatures than your cast iron radiators (and much higher temps than a radiant floor).

mattmia2

A modcon has the advantage to run outdoor reset natively which may increase comfort a lot by making the heat more even but you could also set up a CI boiler primary-secondary with an outdoor reset control.

Steamhead

mattmia2 said:

A modcon has the advantage to run outdoor reset natively which may increase comfort a lot by making the heat more even but you could also set up a CI boiler primary-secondary with an outdoor reset control.

Most CI boilers now come with AquaSmart, HydroStat or similar controls, which have outdoor reset built in- all you need is to add a sensor.

My advice? Cast-iron, for all the reasons @EBEBRATT-Ed mentioned.

PC7060

I selected modcon when I replaced my 2x oversized iron boiler last year. I followed @hot_rod advice and set the system up with outdoor reset and SWT of 120F max.  This works well because of the insulation and air sealing upgrades along with many large CI radiators. 

My boiler is a Fire Tube type set up with one primary loop that circulates at 4GPM with cold return (30F delta T) and increases to 7-8GPM as system warms up (20F deltaT). 

Heating cycles average 45-60 minutes throughout the season.