Copper vs Cast Iron Heat Exchanger

Mike T., Swampeast MO

Copper fin boilers are OK for some applications.

Fast and hot heat transfer makes them especially suited to fin baseboard. If reset is used, it should be minimal and with low temp protection.

They will overheat with low flow so if this is a zoned system you either have to buffer small zones or lock them out until larger zone(s) call as well. Without buffering ensure that the boiler WILL NOT RUN unless you have at least the minimum recommended flow AND enough emission capability to keep the boiler from RAPIDLY reaching high limit.

They will die prematurely in high mass systems like tube-in-slab.

They [should] be quite suitable for "staple-up" radiant without plates even if that method is only preferred in very specific applications. The "ensure sufficient emitter output ability" warning in a zoned system applies doubly as this form of system is already poor in this regard.

They are very poorly suited to high-volume, mid-mass systems using standing iron radiators.

They [should] be reasonably suitable for mid-volume, mid-mass systems using modern panel radiators. Same warnings and suggestions regarding fin baseboard apply.

Will defer to the field experts when it comes to cleaning. Illustrations and photos I've seen make me think such is a PITA.

Mike in Illinois

Copper vs Cast Iron Heat Exchanger

I am in the process of replacing my residential heating system boiler and am looking at a Lochinvar Solution CBN260M (260,000 BTU) and a Peerless MI-08 (227,500 BTU). The platforms are of course very different and I wondered if anyone had any views and experience based on a heating system built around the copper exchanger versus the cast iron exchanger? In addition, any views on reliability?

Thanks,

Mike

Alan(CaliforniaRadiant)Forbes

Personal Preference

I'm a cast iron man (said in a deep voice with his chest thrust out) only because I feel that cast iron is more forgiving than copper then it comes to heat transfer.

Also, cast iron heat exchangers are much easier to clean than copper ones.



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hr

I'd steer you

towards a modulating condensing type. Lochinvar and Peerless both offer one, among a handful of others.

They adjust to loads, have reset built in, more efficient, quiet, sealed conbustion. Miles ahead of basic atmospheric equipment.

hot rod

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Constantin

I'm with Hot Rod

Once you figure operating costs, etc. into the equation, I expect that the marginal cost of going with a low-mass, modulating, condensing boiler will be made up in record time considering the current trends in gas pricing.

There are plenty of great boilers in that input range, and some of them even have HX's made of the material I prefer for the application, stainless.

Ike Gatlin

Mike,
All the points here valid.
What I think folks are missing... the Solution is standard with a built in by-pass that assists an installer in making just about any existing piping work. The solution also is standard with a 2 stage firing feature. The 2 stage feature fires the boiler at 50% or 100% based on system load.

If you have further questions drop me a line at 615-889-8900.

Ike

Steve Ebels_3

CU vs FE

Copper: fast heat transfer, prone to failure if flow and temperature requirements are not within mfgr specs, about the same efficiency as other types of boilers in the same genre', usually less expensive to buy, will short cycle badly on low flow applications.

Iron: Durable, most models are easy to clean, less prone to short cycling due to higher mass, more tolerant of varying flow rates found on zoned systems.

That being said, allow me to be blunt. Considering anything but a high efficiency condensing and modulating boiler in the face of energy costs we are looking at today and in the future would be a poor choice.

Mike T., Swampeast MO

Ike. Agree that a built-in bypass or primary/secondary will do wonders to keep flow in the allowable range but such does nothing to address a low-load condition. Two-stage firing will be HIGHLY useful in this regard provided that the boiler isn't typically oversized...

However, there could still be a problem if say one bathroom with a few feet of b/b or other small amount of emission capability calls by itself. (A quite probable event if you've zoned a bath individually.) Locking it out until a larger zone calls or buffering would still be highly desired. This plays heqq with efficiency and no boiler really "likes" it, but have heard that this is especially undesirable with copper fin boilers.

Good planning and engineering will maximize the efficiency and life of any boiler, just as poor planning and engineering will reduce efficiency and life.

hr

You didn't mention

what type of emitters you have. copper fin tube baseboard, cast iron radiators, radiant?? And how many zones. i would weigh all these factors to help in a selection.

Two stage burners are a help, but nothing compared to modulating. Especially if it is multi zoned, and varing, sometimes small, loads.

All in all that Lochinvar Knight looks to be an excellent choice that would work very well regardless of the system.

Over and over again we hear how the burner modulation is key to lower operating costs.

hot rod

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Mike in Illinois

My emitters are traditional upright cast iron radiators (perhaps 1920s vintage?) and there are no subdivided zones. Windows have storms, but are not thermal. House was built around 1926 and is brick exterior, about 3600sf plus basement. Current boiler is pilot light, atmospheric vented into chimney and 26 years old. I am not sure if it has a damper. Input BTUs are 240,000. There is a B&G dry pump capable of putting up to 70 GPM through the pipes. Fuel bills running about $2500/yr and peak in Jan/Feb at about $500/mo.

Modulated/condensing sounds interesting, but I am concerned that sophisticated electronics are a potential weak link in reliability. In addition, I understand heat exchanger is often copper, which based on posts above seems to be somewhat more temperamental if it falls outside of temperature or flow rate ranges. Since I've got the chimney, this would also probably be my preferred venting option versus punching a hole through foundation or brickwork in a visible area of the house.

Area contractors seem to have limited exposure to the modulated condensing boilers, perhaps because there is not a lot of new construction.

hr

If I were you

Do a heatloss calc first. There is a free calculator available right at this site. That sounds like a lot of boiler for 3600 square feet? Even at a high "guesstimate" of 35 BTU/ square foot that is a boiler of 126,000 output.

A grossly oversized boiler can lead to inefficient short cycles. Bad for fuel consumption and wear on the boiler.

The condensing boilers, including that Lochinvar Knight are stainless steel heat exchangers. As good, perhaps much better than copper in many cases. Some use aluminum Weil, Buderus, and MZ.

As for electronics... seems every high efficiency appliance these days will be driven by a microprocessor. You car is, as we speak we are microprocessing. They have come a long ways! Most manufactures offer extended warranties that cover parts and labor on heating appliances.

Plenty of guys, including Mike Swampeast, on this list have done conversions on systems like yours. Condensors are an excellent match, thermostatic valves may be added for more room by room control.

Contact someone to do a heatload for you if you want to get this important first step done. Don't buy anything until you get a handle on the size needed, would be my advise

hot rod

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Mike T., Swampeast MO

While there are no guarantees, you can consider 40% - 60% as a reasonable fuel reduction if you change to a properly sized condensing/modulating boiler. The more greatly oversized your current boiler, the higher the reduction you can expect.

If gas goes as high as some suspect and stays there for any length of time, paybacks get shorter and shorter--particularly in a fairly large home. Unfortunately, even the smallest condensing/modulating boilers available in the US are suited to fairly large homes in any but the coldest climates.

The electronics are probably the least concern as far as reliability. As you likely know, when electronics fail, it's usually quite rapidly--usually a manufacturing flaw that causes thermal failure. Once they're "burned in", electronics outlive mechanics in most devices.

There will be more maintenance with a condensing/modulating boiler. Routine (annual or perhaps semi-annual) cleaning seems a requirement. Some are much easier (less expensive) to clean. Those using an aluminum heat exchanger are expected to be sensitive to water chemistry and you are well advised to have your system water "adjusted" (if necessary) after installation and monitored. Stainless steel is considered more forgiving with regards to water chemistry and water treatment/maintenance is likely not required. Soft, quite acid water is (I believe) the worst for stainless.



Your chimney may or may not be able to be used with a condensing/modulating boiler. All such boilers have specific venting requirements (some require proprietary components) and none can be directly vented into an existing masonary flue.

Mike in Illinois

I must admit I am drawn to the technology, of the high efficiency solution, but it seems that reliability is not yet up to snuff. For example, the manufacturer's don't yet have the confidence in the modulating/condensing boilers to go beyond a 12 year warranty (with pro-ration beginning after year 7).

Assume a Peerless atmospheric 82.7% AFUE costs me $5,000 installed and has a useful life of 25 years (has a non-pro-rated lifetime warranty on exchanger). It appears that a modulating condensing 92% AFUE will run about $7,000 installed, but it only has a 12 year warranty and begins pro-rating after 7. Assuming a 12.5 year useful life I have to buy another one in year 12.5 for another $7,000 to match the 25 year lifespan of the Peerless. I will generously assume that the modulating/condensing will save me 15% in heating costs (even though AFUE is only 10% different) under actual operating conditions. At an estimated $2000 per year for the atmospheric would be $300 per year in savings for the modulating condensing or $7,500 over 25 years. However, my purchase costs for the modulating condensing are $9,000 higher, so this option produces a net loss versus the atmopheric.

I also remain concerned about the electronics on the high efficiency, since the manufacturers have no more than a 1 year warranty on these components. The same is unfortunatly true of the atmospheric, but the electronics are that much simpler. While cars certainly have complex electronics, I believe that many, including BMW and Mercedes, had many issues when stepping up the complexity of their electronics. If the manufacturers belive in their product they should reflect it in their warranties.

Constantin

Step away from AFUE....

.... it is not a credible measure to reflect on the seasonal efficiency of a boiler system. For example, Mike T. in Swampeast MO tested it for himself in his own home with a mix of low-temp emitters. Even though the old boiler had an AFUE of 80% and the new Vitodens "only" has an AFUE of 94%, his heating-degree-day-adjusted fuel reduction was 43%, way beyond the 14% that the AFUE difference would suggest.

Plus, the math above seems convoluted. According to your numbers, the peerless is only $2000 cheaper to install. The annual savings are likely to be 20% or more, for an annual savings of $400. Within 5 years, the new boiler would have paid for the difference, the rest is gravy. And, just because the manufacturers don't give super-long warranties, I have no reason to believe that a properly-maintained stainless HX won't outlast a cast iron one.

Whenever someone is waving 25-year warranties around, I say consider the source. A lot of heating equipment manufacturers have been in and out of the market over the last 25 years. For that matter, I am only aware of one company that has had significant issues with their electronics, a teething issue. The electronics in cars make those found in high-tech condensing boilers are not comparable, the former are far more complicated and capable than the latter.

Tony_23

Amen

There is simply NO COMPARISON between 80% CI boilers and condensing, modulating boilers.

Standard CI boilers haven't changed for 50 years. All my Ultra customers (on bbd or iron) are saving well over 30%. One of them had a 15 yr old CI boiler with an 83% sticker on it. Oh, the ones who only save 30% aren't using outdoor reset. Their choice, they want to setback at night, and reset won't recover quick enough. If they'd only listen

Mike T., Swampeast MO

Mike, you said, "I will generously assume that the modulating/condensing will save me 15% in heating costs (even though AFUE is only 10% different) under actual operating conditions."

It's those actual operating conditions that make AFUE comparisons between conventional and condensing/modulating boilers nearly meaningless.

AFUE ratings come from a steady-state test (load = net boiler output at full fire) at quite specific, and quite high, temperatures. This is when conventional boilers perform their best. AFUE does give a reasonable comparison basis for boilers of the same class even if manufacturers do engage in a bit of "designing for the test" to boost the rating.

Real-world conditions are NOTHING like that laboratory test! Any time that a conventional boiler is supplying more heat than is being lost by the structure (excepting deep setback recovery this is 100% of the time by the way) it looses efficiency. The warmer the outdoors and the less heat being lost, the more the boiler looses efficiency. Combine this with the fact that nearly every boiler on a system like yours is significantly oversized to begin with and the inefficiencies become extreme.

With my own system (similar size house, similar size boiler, a bit warmer climate, cast iron radiators) I measured and tested for years. I found that the boiler AVERAGED a bit less than 50% of its' rated OUTPUT actually being delivered to the system as usable heat! And this was after outdoor reset, warm-weather shutdown, TRVs, and constant circulation had already improved efficiency!

Modulating boilers effectively re-size themselves to the constantly changing load. They strive to maintain steady-state between output and load. By doing this they maintain their input vs. output efficiency in nearly all circumstances.

In addition to the modulation, nearly all such boilers further increase efficiency by reducing the supply and return temperatures with decreasing load. This is "reset". Some do this via outdoor temperature feedback, some do it with indoor temperature feedback. Both have the same result. Transmission loss decreases with lowered temperatures. Flue loss decreases with lowered flue temperatures.

All of the condensing/modulating boilers achieve a very high degree of heat transfer between the flame and the heat exchanger. Most seem to maintain this quite well regardless of the state of modulation or the supply/return temperatures involved. Some maintain this efficiency with near perfection.

I hooked up my new condensing/modulating boiler (Viessmann Vitodens) to a number a data-logging sensors and monitored throughout the entire last heating season. The maximum FLUE temperature recorded was 127.9°F!! This with the outdoor temp at about 0°F!!! The sensing bulb for the flue gas is only about 3" away from the heat exchanger!!! Hours of flue temps right around 110°F were recorded during periods of continuous boiler operation during moderate weather. During times when the boiler was forced to fire for a few hours at minimum modulation and then stop for a long periods flue temps are typically below 100°F! During extremely moderate weather when the boiler is forced to cycle fairly rapidly, flue temp was around 80°F!!!

I do not own a measuring device capable of reading the flue gas temp of the old boiler. One word for the "hand test", HOT!!! Very capable of burning the skin in a SHORT time! As the outdoor reset control lowered the supply temperature with rising outdoor temp, the "hand test" told me that the flue gas was even hotter!

All of the modulating boilers are also condensing boilers capable of recovering some heat from the oxidation of hydrogen. While not an extreme amount, such is significant. In general, the lower the supply/return temperatures the more of this heat can be recovered. A system such as yours is very likely capable of using very low temperatures while providing nearly perfect comfort.

Search this site for threads with the subject "Vitodens Operation". I posted many graphs of actual operation in .pdf format. Study them a bit and I think you'll understand why I can quite confidently make that 40% - 60% fuel reduction claim.

I'm mainly a homeowner like you. I have no ties to ANY manufacturer of heating-related equipment. I chose a Vitodens because it is expected to be the longest-lived condensing/modulating boiler currently available AND because it utterly THRIVES when driving cast iron radiators with Thermostatic Radiator Valves (TRVs). Those valves are required by law in Germany so it only makes sense that it is designed with TRVs in mind. The built-in variable-speed circulator (2 smaller models) is a great clue...

Alan(CaliforniaRadiant)Forbes

I like the way

Mike thinks:

Atmospheric - simple bang-bang; no bells or whistles; no expensive repair costs; easy to fix if something goes wrong; higher fuel bills, but it works out in the long run since he will have lower maintenance costs.

Trust your instincts.

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Mike T., Swampeast MO

This Mike Used to Think the Same Way

Replace a still working boiler that will probably last another 20 years with almost no maintenance just to save a little bit of fuel. Even the finest replacement not expected to have a lifespan similar to the old plus requiring more maintenance. Stupid!

Used insulation, weatherization and controls to maximize the efficiency of the current boiler, but rapid increase of fuel cost made the bills climb steadily despite reduced consumption.

Then I realized that non-traditional uses of natural gas were GREATLY increasing demand for a limited resource. Fuel price was almost certain to stay high and continue to climb.

Only way I know to slow the increased price is for MANY, MANY people to significantly reduce demand. I did my part and will have achieved payback in just a few years. Considering the current speculation regarding natural gas, payback may well be much sooner than originally anticipated.

Alan(CaliforniaRadiant)Forbes

Not fair

You bought a Vitodens, but even they have their problems. I just replaced a pressure switch on one installed less than a year ago. Some might argue that you could have the same problem on an atmospheric boiler.

My previous comment was fueld by the frustrations of just having worked on a Baxi Luna for 5 hours, spending hundreds of dollars in parts and in the end not being able to fix.

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Ron Schroeder_3

did we just read the same post?

?????

Mike T., Swampeast MO

Everything Can and Does Have Problems

I suspect that the Vitodens told you exactly what component was defective and that it took very little time to replace. Even with my huge hands, everything inside that boiler is easily accessible.

My Vitodens arrived with a defective "brain" (Comfortrol™ Unit), although I do suspect that the problem was mechanical in nature—the adjustment dial—rather than electronic. Viessmann immediately replaced and even sent an additional control board in the event that it too might be defective (it wasn't).

Alan(CaliforniaRadiant)Forbes

Nope

Sorry to say that it didn't tell me. It just sat there and I had to jumper out the limit string to tell where it was.

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Mike T., Swampeast MO

Oh well, I guess nothing's perfect!