Aluminum, Stainless Steel or Cast Iron what's the better value?

kgk14

For a new gas boiler system, one contractor has proposed a Bosch Greenstar while another has suggested Baxi or HTP. The Greenstar has an aluminum heat exchanger and the Baxi/HTP contractor recommends stainless steel only.
The Bosch contractor has stated that the aluminum block will outlast steel or stainless steel. On the other hand I have read where stainless steel outlasts aluminum in heat exhchangers and that there is a much narrower ph window for AL compared to SS, which increases AL's corrosiveness in a boiler.
I have also been advised to steer clear of the HTP Munchkin/Contender though the Elite would be fine.

Yet another has suggested that if I wanted a durable, reliable boiler go with a Burnham or Weil cast iron, with average efficiency - being cheaper, easier to install and service and lasting.
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I plan to make a decision soon. Any advice would be appreciated?

hot_rod

The key to a long happy life lies with the installation and care of the boiler. All boilers should be cleaned and flushed of oils, flux, assembly lube, etc at installation, in my opinion. This takes time and $$ to do properly.

They should be filled with quality water as per the manufacturers direction. DI or DM water is best if you can purchase or filter at the jobsite.

Keeping the HX surfaces inside and fireside clean is good ongoing preventive maintenance.

Burners need to be adjusted to the spec in the installation manual, a combustion analyzer is a must to assure proper adjustments on mod con boilers.

Proper flow rate assures best heat transfer and promotes efficiency. Again refer to the manufacturers pump spec, and suggested piping methods.

Some installers prefer adding a boiler treatment and most of the aluminum boilers include product recommendations for treatment products they have tested and approved.

There are special glycols for aluminum, if antifreeze will be added.

You should be able to find the I&O manuals online for all the boilers you are considering. Might be a good idea to get an idea of what each requires.

Your warranty will depend on proper installation and operation. Go with the installer that you feel will take all the proper steps to protect your investment.

HydronicComfort

The better value may be the cast-iron boiler. Pay particular attention to performing, or having performed, a heat-loss calculation. You can then size the boiler based upon that calculation.

A conventional boiler may be less expensive as well, depending upon the size required and if your chimney needs re-lining.

Condensing boilers reach higher efficiencies with return water temperatures at 130-degrees and lower. This may necessitate adding additional heat emitters to provide the correct amount of heat utilizing a lower water temperature. Either way, adding additional heat-emitters can help even with a cast-iron boiler. You can utilize a lower supply water temperature. You will need to utilize a control, mixing and sensor strategy to keep return temps above condensing level (~ 130-degrees) in a cast-iron boiler. Doing so will allow you to take full advantage of an outdoor reset. Every 4-degrees you can lower supply temperatures results in a 1% savings

All of the mod-cons will achieve well over 90% efficiencies in condensing mode. They will also modulate to lower fire rates on warmer days.

The rub with mod-cons is basically the service required to keep them operating properly, increased proprietary electronics, lower life expectancy ( expected to be less than a cast-iron boiler). There are a lot of differing designs, some with proprietary controls and heat exchangers and you need to ensure that you find a good installer that will be able to service the unit. Because it will need regular servicing.

When you add the increased servicing costs along with lower life expectancy (presuming you have enough heat-emitters sizing to allow condensing), are you really saving?

I'd ask the installers about the life expectancy and the annual maintenance costs with mod-con vs cast-iron. Also ask if you have enough heat-emitter sizing to allow for boiler condensation. Finally, I'd ask if they have training on the proper installation and servicing of the unit they intend to install. Then you can make a better decision.

Good luck and let us know what you decide.

Gordy

Don't get to hung up on the condensing of mod/cons most of the savings is modulation. condensing adds a few bonus points, but the ability to modulate the burner saves far more.

When it's 35 out would you rather have a burner going full out at 70k 82%, or a burner going 20k at 82% efficiency to satisfy the load.

Odr only goes so far with CI.

There will come a day when the choice will only be high efficiency equipment. Look across the pond.

HydronicComfort

With mixing valve and control strategy, a cast-iron boiler reset matches mod-cons; they are not limited to 130- to 140-degree return water for the reset water temp.

Oversizing a boiler has always been a problem. An accurate heat-loss calculation will help with proper sizing for design condition.

To minimize short-cycling, you can add a buffer tank.

Gordy

By the time you add buffer, and controls to a CI you are approaching the cost of a MOD/CON with everything on board. Not to say there are not cases where micro zoning, and or low loads requires buffering with a mod/con.

I remember not so long ago when high efficiency was all the rage around here. Now people are second guessing that choice because of cost of ownership, and life expectancy. A good mod/con install should last as long as a CI boiler with proper care. SS firetube is pretty robust if water quality is maintained in the system and intake contaminants are kept clear as HotRod points out in his post.

Again squeezing an extra 10% efficiency out of a boiler by going high efficiency goes a long ways in the big picture when you think about thousands of homes that have oversized inefficient heating plants.

To answer the original question of the better value in HXs Fire tube SS. In the high efficiency.

So the HTP ELite FT, TT, Knight firetube,WM 97, Vitodens 200(not firetube, but SS HX.

Over all a good installer should be able to do either install efficiently, and correctly high efficiency, or standard efficiency.

Better value to your wallet, or to the environment is the question you have to ask yourself.

RobG

Gordy said:

By the time you add buffer, and controls to a CI you are approaching the cost of a MOD/CON with everything on board. Not to say there are not cases where micro zoning, and or low loads requires buffering with a mod/con.

I remember not so long ago when high efficiency was all the rage around here. Now people are second guessing that choice because of cost of ownership, and life expectancy. A good mod/con install should last as long as a CI boiler with proper care. SS firetube is pretty robust if water quality is maintained in the system and intake contaminants are kept clear as HotRod points out in his post.

Again squeezing an extra 10% efficiency out of a boiler by going high efficiency goes a long ways in the big picture when you think about thousands of homes that have oversized inefficient heating plants.

To answer the original question of the better value in HXs Fire tube SS. In the high efficiency.

So the HTP ELite FT, TT, Knight firetube,WM 97, Vitodens 200(not firetube, but SS HX.

Over all a good installer should be able to do either install efficiently, and correctly high efficiency, or standard efficiency.

Better value to your wallet, or to the environment is the question you have to ask yourself.

Let us not forget the cost / time of hauling in the CI boiler, as well as possible assembly.
I don't know about you all, but cast iron seems to get heavier with each passing year.

Thank god for cascading commercial systems.

Rob

Bob Bona_4

I've really been puzzled by the speculations of mod con longevity. Like Gordy said, I see no reason why a 20 year lifespan isn't possible when properly installed and maintained. What also puzzles me is the cry of "extra cost of service". What's so different than the required takedown of a CI boiler to brush and vac, chimney inspection etc.

All in a days work either way.

The life expectancy one really gets me. Based on what? I have Munchkins out there purring away since 2002. Get 20 years out of it and replacement time.

RobG

It doesn't modulate but I have a 1983 pulse combustion boiler that I service annually. It still has the mechanical sequence timer! Except for getting parts (which the owner smartly keeps a stock of) It is the easiest boiler to service that I have encountered. (don't get me wrong, I have taken more out than I have put in) but this one must have been built on a Wednesday.

If a pulse boiler can last over thirty years there is no reason that more modern ones can't.

Rob

SWEI

Let's not forget that the castings in today's CI boilers are much thinner than the pre-1990 ones most of us are hauling out of basements these days. Thinner walls and lower mass are not just for mod/cons.

Gordy

Bob Bona said:

I've really been puzzled by the speculations of mod con longevity. Like Gordy said, I see no reason why a 20 year lifespan isn't possible when properly installed and maintained. What also puzzles me is the cry of "extra cost of service". What's so different than the required takedown of a CI boiler to brush and vac, chimney inspection etc.



All in a days work either way.



The life expectancy one really gets me. Based on what? I have Munchkins out there purring away since 2002. Get 20 years out of it and replacement time.

That's because you installed them Bob.

"Competent installer" is the key constant with any type of boiler.

Bob Bona_4

I'm also a big fan of the SS firetube. AL is too high maintainence for me. Gianonni too much pressure drop.

SWEI

The fire tube design pioneered by Triangle Tube really changed the game here in North America. Just look at how fast and how many manufacturers have jumped ship during the 3 years that design has been available to them...

hot_rod

lots of welds in that fire tube design, however. I've heard rumors that may have been the reason TT changed manufacturer, after a bunch of leakers. That opened the channel for other brands to get access to that fire tube design HX.

The Giannoni style HX up to 120K or more, pumps with a small wet rotor circs, 15-58, 007, etc.

If you use one of the brands or models like the HTP MC series, Lochinvar Cadet, among others, I don't think there are any welds if the composite NORYL headers and case were used to gather the loops of the Giannoni.

What should the life expectancy of a residential boiler be? Most appliances in the home are engineered to a 15- 20 life cycle.

SWEI

TT moved to a polypropylene bottom pan for the second generation HX design (TriMax series.) Far less welds in those, and they should be less susceptible to leaching chlorides. Time will tell.

Gordy

Ha had a GE profile dishwasher literally melt the innards because the heating element stuck on in 3 years. The profile fridge blew the mother board in same time frame.

Electrolux dryer 2 heating elements in 6 years. The same washer front load bladder gasket to the drum tore.

Gordy

Oh yeah there is my 09 acadia with recalls like junk mail.

Jean-David Beyer

"What should the life expectancy of a residential boiler be? Most appliances in the home are engineered to a 15- 20 life cycle. "

In my experience, they used to be much better than they are now. When I bought this house in 1976, it had a still-working electric refrigerator by Kelvinator, that was obviously original equipment in this house built in 1950. It would not be cold enough to keep ice cream in it, so I got rid of it about 1980. It also had an electric stove from that era It was still working when I replaced it in 2006. My GE oil burner boiler from 1950 was still working when I bought the house, but I replaced the original burner with a Beckett because they could no longer get parts from the original burner. I diddled the temperatures because the floor got too hot, and it cycled too fast. As a result, I ran about 140F supply and G.O.K. what return temperatures. It used up metal exhaust pipes, but the boiler never leaked. I got rid of that when I switched to gas in 2009; it was still working OK.

I have gone through at least three refrigerators since then. All GE. So they last around 10 years each, but the first one lasted the longest, and the most recent the least. If I remember correctly, Consumer Reports says refrigerators are now averaging about 9 years.

An electric dryer quit after 5 or 6 years because the design of the connector where the 240 volt and neutral came in cracked and shorted 240 into the controls that expected 120. Melted the insulation of the wiring harness and zapped the controls. The repair technician came in (he does not sell appliances) and recommended I get a new one because he would charge almost as much for repairing it as a new one would cost. I was prepared to do that, but I had to replace the matching washing machine (that was working fine) because only that brand and model would fit the space available (they were stacked). And the new dryer could not be stacked on top of the old washer. Grrr.

Now I hear one should expect only 15 or 20 years from a boiler. I really resent that. If I can buy 40 year shingles for my roof, why can I not buy 40 year appliances? I would pay more; I am interested in total cost of ownership, not just initial cost.

kgk14

At this time I have competitive offers from four contractors for the following natural gas boilers:
Bosch Greenstar, TT Prestige Excellence, Veissman Vitodens 100, HTP Elite, and Baxi Luna. All contractors appear to be able to take the proper steps to install correctly. Based on conversations in this thread I am leaning toward the SS HX. Heat loss is about 80000 btu. Domestic hot water needs is to fill a 30 gallon tub, run a shower and dishwasher at the same time. The house is in central NH. While the knowledge and skill of the install is a significant factor for trouble-free performance, and assuming that is a constant, what would be the number one natural gas boiler choice if you were in my shoes?

Gordy

HTP Elite FT will get you closest to your heat loss. Tell that contractor you want the FT (fire tube model HX).