cast iron vs stainless for replacement boiler

newvermonter

My heat is hot water through baseboards. I am converting from an oil-fired boiler to propane. One installer has proposed a Weil-McClain cast iron boiler, and the other has proposed a Burnham Alpine stainless steel (model ALP105). From what I gather, the cast iron is a bit more expensive but has a longer life expectancy and requires less maintenance. But someone from the propane company mentioned to me that I might have an issue with rust during the months that the heat is not on. (Hot water is coming from a separate source -- this would just be for heat.) I am new to all of this and would love thoughts on the pros and cons of each.

Hot_water_fan

Almost every cast iron boiler in America spends months off every summer. Not sure why rust is a concern from that company.

GroundUp

If the water is properly treated, rust will never be a concern regardless of operational status. Is the person who told you this the same person proposing the Alpine, by any chance? Don't get me wrong, I love a mod-con boiler but if the system is all high temp emitters I really don't think they're a cost effective option. You may save 10% on fuel, but will spend all of that and then some on maintenance/replacement over the lifespan of the system. Very seldom does a mod-con save anything in the long run over a CI boiler in my experience. Proper piping to allow ODR on the emitters while keeping the CI boiler above 140* is pretty tough to beat, in my opinion.

newvermonter

Thanks for the comments so far. The person who mentioned the rust was the guy from the propane company who was just there to figure out where the tank will go, so he's got no stake in it. But I've talked to 4 or 5 different people at this point and most seem quick to recommend one of the stainless boilers and I'm trying to figure out why that is.

Jamie Hall

These days efficiency is a big selling point -- and the Burnham (and some, but not all, other stainless steel boilers are, indeed, capable of very high efficiency -- as much as 10% more than a typical cast iron boiler.

But. That assumes that they can, in fact, operate in condensing mode -- and that depends on how much baseboard you have. The more baseboard length you have, the lower the temperature at which you can run the boiler, and thus the more likely that it will be in condensing mode. The only way to determine that is to measure the length of the baseboards, and determine the heat loss of the house (technically what we call "Manual J" -- Slant/Fin has a very nice and remarkably easy to use calculator for that) and then figure out what temperature water is needed to heat the house.

You may -- or may not -- be able to use the condensing feature, but it is at least one reason why people these days seem to promote them.

There is another factor, too: maintenance and parts. The fancier boilers, such as the Burnham do take more maintenance, and take more experience on the part of the installer and the service folks to keep them running as well as they can.

hot_rod

as @jam do as @Jamie Hallmentioned first, the load calc
Do a heat emitter survey, what type, how many

Is the system zoned? If so how many
Modern cast boilers are much smaller, less water content, less cast mass. They do not like to be short cycled on multi zoned systems. The modulating feature of a mod con stainless boiler can be a game changer

newvermonter

Thanks for the additional comments/advice! The house is 2500 square feet, with four zones. It's in Vermont -- cold winters! It's a second home. We'll be using it ourselves and also renting it out, so it will be on full blast for quite a bit of the winter, but some of the time it will just be on high enough to keep the pipes from freezing.

GroundUp

For part-time winter use with just above freezing temps indoors, a condensing boiler wouln't even be a consideration in my book. No way I would install a system like that for any of my customers unless there was a redundant heat source. As someone who owns several rentals and rents his fair share of STRs as well, I can say with absolute certainty that peace of mind is worth bookoo bucks in this racket. Unless you plan to visit the home daily during the cold stuff, you're skating on thin ice with a mod-con. Smart thermostats help, but they don't solve the potential issues.

EBEBRATT-Ed

We can't talk $$$ here but a mod con is usually more $$$ than CI.

I would go CI for many reasons but that's just me

pecmsg

EBEBRATT-Ed said:

We can't talk $$$ here but a mod con is usually more $$$ than CI. I would go CI for many reasons but that's just me

More $’s up front and when it breaks even if parts are available!

hot_rod

GroundUp said:

For part-time winter use with just above freezing temps indoors, a condensing boiler wouln't even be a consideration in my book. No way I would install a system like that for any of my customers unless there was a redundant heat source. As someone who owns several rentals and rents his fair share of STRs as well, I can say with absolute certainty that peace of mind is worth bookoo bucks in this racket. Unless you plan to visit the home daily during the cold stuff, you're skating on thin ice with a mod-con. Smart thermostats help, but they don't solve the potential issues.

What about the millions of condensing furnaces?  All the same parts and technology, no water😙

newvermonter

Thank you, everybody! I appreciate your input.

GroundUp

What about the millions of condensing furnaces?  All the same parts and technology, no water😙

What about them? A HE furnace has an inducer, HX, ignitor, flame sensor, and not much else that can go bad. Plus, most parts are available nearby as very little is proprietary. That is not even close to the case with mod-con boilers. There are millions of 20 year old HE furnaces out there that have never been touched. How many HE boilers can say the same?

Tom_133

I live in VT and if the manufacturer hadn't given me a wall hung I would have gone Weil McLain GV90 +.
I assume you are in the lower part of the state, because no wholesalers up north stock Burnham Alpine parts and most guys dont use those boilers. I will also mention that many service guys struggle with mod cons, but the ole cast irons are a bit simpler and pretty well known around here so repairs are typically straight foward.

Skyline

GroundUp said:

If the water is properly treated, rust will never be a concern regardless of operational status. Is the person who told you this the same person proposing the Alpine, by any chance? Don't get me wrong, I love a mod-con boiler but if the system is all high temp emitters I really don't think they're a cost effective option. You may save 10% on fuel, but will spend all of that and then some on maintenance/replacement over the lifespan of the system. Very seldom does a mod-con save anything in the long run over a CI boiler in my experience. Proper piping to allow ODR on the emitters while keeping the CI boiler above 140* is pretty tough to beat, in my opinion.

While I mostly agree, especially with the TCO for mod-con vs CI boiler...

My my old house has high temp heat emitters, CI radiators and baseboard in two zones, the fuel savings in the first year had been much higher, than 10%:



One can change the heating curve on the mod-con boiler, based on the weather forecast, to keep the unit condensing. I've done that during the first heating season and worked out just fine.

With that said, the savings isn't much as far as monetary value is concerned. On the other hand the resulting environmental impact, around 30% less CO2 exhaust, is something to consider as well.