High efficiency Or Cast iron boiler

Ainu

Hello, 

House is 4200 sqft in the Northern New Jersey. Built in 1990 with average insulation.

Converting from oil to natural gas for heating boiler. Considering the rebate for high efficiency, I got the same amount of estimate for a Crown Bali2 150k power vent side wall discharge cast iron boiler and Viessmann 150k Btu high efficiency boiler (B1HE-150).

I like the newer technology of high efficiency boilers but I hear these are troublesome and do not last long. 

On the other hand, cast irons are old non efficient but generally trouble free. I also see the new Cast iron boilers are almost 50% lighter than the old ones. Which raise concerns about their quality and longevity. My existing 150k OWB cast iron boiler is 680lb where the Crown is 380lb.

Please share your opinions. 

Thanks. 

Steamhead

What make and model OWB?

Ainu

Williamson OWB-4 from ~1990.

Jamie Hall

The key question is -- is your installed radiation enough that you will be comfortable (that is, warm) at the low temperatures which a high efficiency boiler has to run at to achieve anything close to its advertised efficiency? Anot so minor detail which sometimes gets overlooked.

Or, to put it another way, if you have to run the system at a high temperature -- say anything over 160 -- to stay warm enough, the "high efficiency" boiler will be no more efficient than a conventional boiler -- and a good deal more difficult to maintain.

hot_rod

How long are you planning on living in that home? Maybe that plays into the choice.  

It would take some calculation, but determining 
how often the V could run  in condensing mode would tell about the efficiency gains in $$


I suspect the power vented boiler may be a little bit louder, if that matters.

 Its hard to beat Viessmann quality, that should be a 20 year boiler

If longevity is the biggest decider, the cast may be the better choice.

HVACNUT

Considering a 125K net on either boiler, that's 29.76 BTU per sq ft. Are you sizing based on DHW?
Obviously you get the turndown on the Viessmann, but it doesn't seem like a heat loss calculation was done. 

Ainu

HVACNUT said:

Considering a 125K net on either boiler, that's 29.76 BTU per sq ft. Are you sizing based on DHW?
Obviously you get the turndown on the Viessmann, but it doesn't seem like a heat loss calculation was done. 

I am not a heating expert. Is it over dimensioned or under dimensioned just for heating-only? I have the plan for indirect hot water tank when my electric one dies. Thanks. 

Big Ed_4

A house with low temp radiation , radiant and radiators I recommend a Good condensing boiler . A house with high temperature radiation , Air coils and baseboard . I would recommend a Good standard boiler with a chimney ...

MaxMercy

Ainu said:

Converting from oil to natural gas for heating boiler.

You didn't ask about that point, but I would check what costs are for both to compare.

Where I am (Connecticut), oil has historically been cheaper (sometimes a lot cheaper) than NG and especially propane.

For instance, on my commercial building, I spend $700 a year with Eversource for NG just for "delivery", even during the 6 months my boiler is shut down. That will buy a full tank of oil at current cost.

When I shut my oil boiler down at home during the summer, it costs zip.

HVACNUT

Ainu said:

HVACNUT said:

Considering a 125K net on either boiler, that's 29.76 BTU per sq ft. Are you sizing based on DHW?
Obviously you get the turndown on the Viessmann, but it doesn't seem like a heat loss calculation was done. 

I am not a heating expert. Is it over dimensioned or under dimensioned just for heating-only? I have the plan for indirect hot water tank when my electric one dies. Thanks. 

The sizing seems too big. I'm not real familiar with the Crown but if this is your model, I don't see a 150.A heat loss calculation must be done. And as mentioned, if using a 90%+ boiler, there need to be enough emmiters to help ensure low temperature return water so the boiler can condense, and be in that 90% range. Otherwise all you have is a fancy 85% boiler.

Ainu

HVACNUT said:

Ainu said:

HVACNUT said:

Considering a 125K net on either boiler, that's 29.76 BTU per sq ft. Are you sizing based on DHW?
Obviously you get the turndown on the Viessmann, but it doesn't seem like a heat loss calculation was done. 

I am not a heating expert. Is it over dimensioned or under dimensioned just for heating-only? I have the plan for indirect hot water tank when my electric one dies. Thanks. 

The sizing seems too big. I'm not real familiar with the Crown but if this is your model, I don't see a 150.A heat loss calculation must be done. And as mentioned, if using a 90%+ boiler, there need to be enough emmiters to help ensure low temperature return water so the boiler can condense, and be in that 90% range. Otherwise all you have is a fancy 85% boiler.

These are Crown BWF140BN and Viessmann B1HE150. What input BTU, do you recommend at ballpark ? Thanks. 

Jamie Hall

Do you have a heat loss calculation? Do you have the capacity and size of the emitters (radiators or baseboards or whatever)? Without that information, it is not possible to either a size or a type.

EricPeterson

I had a similar question when I replaced my boiler in 2011.
I went with a traditional design - cast iron boiler - rather than a more efficient model.
One reason was that I wanted a simpler, proven design that would probably outlast more complicated designs.
The other was that based on the chart below, the efficiency of a condensing boiler is lost as the water temperature increases. At 130F the efficiency drops to 87% according to this chart, and my Burnham ES2 is rated at 85%. So the efficiency gain did not seem worth pursuing for my application, as the return temperature is 130F and higher for most of the heating season.
I don't know if this chart is still accurate in 2023, it is copied from Siegenthaler's 1995 version of "Modern Hydronic Heating".

Eric Peterson

hot_rod

Keeping in mind even a properly sized cast iron boiler is over-sized 80% of the year

It is right sized the few at design days. In many areas design day never happens anymore🤨

so that steady  state efficiency number posted on a boiler, rarely is it ever realistic

If you were to data log run time, convert it to cycle efficiency, low 80% would be my guess on actual fixed output boiler efficiency. The more it is zoned the less efficient it runs also with frequent on off cycles.

Oversized and microzoned may  drag you into the 70 or even 60% efficiencies 

The modulating part of mod con doesn’t get enough attention. Or efficiency  credit.

So the argument really boils down to perceived longevity between mod cons and fixed output cast, steel, or copper style boilers.

fentonc

The "oversized" thing really shouldn't be ignored - my cast iron boiler is about 4x oversized vs the design temp, and the effective efficiency is pretty terrible. This is for a nominally 83% efficient boiler:



I've also got so much baseboard I could get away with ~115F water temps on the design temperature.

EricPeterson

I was focused on the lessening efficiency of modcons as indicated in the chart. Perhaps Mr. Sigenthaler should have also included a chart explaining the apparent “efficiency gap” brought up in this discussion for cast iron boilers.

john123

So why didn't someone design a gas valve that would modulate (even manually) for the cast iron boilers?

JohnNY

Ainu said:

Hello, 

I got the same amount of estimate for a Crown Bali2 150k power vent side wall discharge cast iron boiler and Viessmann 150k Btu high efficiency boiler (B1HE-150).

How the heck did that happen? These boilers are around $1,500-$2,000 different in price off the shelf and the piping has to be reconfigured significantly to accommodate a high efficiency installation.

GGross

JohnNY said:

Ainu said:

Hello, 

I got the same amount of estimate for a Crown Bali2 150k power vent side wall discharge cast iron boiler and Viessmann 150k Btu high efficiency boiler (B1HE-150).

How the heck did that happen? These boilers are around $1,500-$2,000 different in price off the shelf and the piping has to be reconfigured significantly to accommodate a high efficiency installation.

Not to get too into pricing, but we sell that vito for about $20 less than the equivalent power-vented cast iron

JohnNY

GGross said:

JohnNY said:

Ainu said:

Hello, 

I got the same amount of estimate for a Crown Bali2 150k power vent side wall discharge cast iron boiler and Viessmann 150k Btu high efficiency boiler (B1HE-150).

How the heck did that happen? These boilers are around $1,500-$2,000 different in price off the shelf and the piping has to be reconfigured significantly to accommodate a high efficiency installation.

Not to get too into pricing, but we sell that vito for about $20 less than the equivalent power-vented cast iron

What is your company?

GGross

JohnNY said:

GGross said:

JohnNY said:

Ainu said:

Hello, 

I got the same amount of estimate for a Crown Bali2 150k power vent side wall discharge cast iron boiler and Viessmann 150k Btu high efficiency boiler (B1HE-150).

How the heck did that happen? These boilers are around $1,500-$2,000 different in price off the shelf and the piping has to be reconfigured significantly to accommodate a high efficiency installation.

Not to get too into pricing, but we sell that vito for about $20 less than the equivalent power-vented cast iron

What is your company?

I'll DM you

HomerJSmith

john123, asks,

So why didn't someone design a gas valve that would modulate (even manually) for the cast iron boilers?

Most Mod/Con boilers have water capacities that are less than 3 gal and many in the 1 gal range. Cast iron boilers have capacities much greater than that. So, condensing is a reason. Venting another reason.
I'm trying to think of a cast boiler that has a return temp less than 130 deg whereas a Mod/Con is designed to operate at colder return temp where condensing flue gasses occur. Cast iron and acidic flue condensate don't mix.
You might want to look at: https://forum.heatinghelp.com/discussion/193158/can-you-modify-a-cast-iron-boiler-so-it-modulates#latest