aluminum vs stainless steel heat wxchage
gilbo41
| Posted in Energy, Heating & Insulation on
Can anyone offer some insight regarding the durability of a stainless steel heat exchanger and it’s huge cost compared to an aluminum unit when used in a gas fired boiler.Is it worth it?
Replies
AL's specific heat is higher so it will bend (expand and contract in a heater) more than stainless over repeated cycles. This will lead to a AL unit cracking sooner and a shorter life span. Not sure on timelines, lifespans or cost benefit. Just my two cents.
Nothing to do with specific heat. Aluminum's coefficient of thermal expansion is 50% greater than that of stainless steel. That means the stresses will be higher if it is not free to grow when hot. Al is also not as strong as stainless, but you can engineer around that. The only plus to Al is it has a greater heat conductivity than SS.
I'd go with the SS in most cases. I'd use Al in a radiator application and SS in a boiler application. If both are warranteed and designed right then maybe it's not a big deal.
More to the point, in condensing furnaces: Aluminum is more subject to corrosion. The AL used in heat exchangers is generally coated or treated somehow to minimize corrosion -- hard to say how much good it does.My general impression, when furnace-hunting several years back, was that you get pretty much what you pay for, regardless of brand or price point. There are exceptions, no doubt, but generally the more expensive unit is better, and roughly in proportion to the price difference.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Just inspected my mother's furnace, built in 1953 with stainless heat exchanger - still in great shape!
If you are going to keep your house for a long time, go stainless.
Either one works well when installed properly and maintained.
Both do not tolerate poor water chemistry. Actually, bad water will kill any boiler, including cast iron.
Al and SS are not your grandfathers boiler, you have to follow instructions for installation and maintainence.
I don't know jack about hot water boilers.
Can you give a brief explanation of the "water chemistry" involved? ( I am very faminliar with low and high pressure steam boilers)
I have never heard anyone hear talk about chemical treatment for hot water boilers.
With AL boilers, the biggest issue is pH and type of glycol. Propelyne only that is rated for AL. Saw one "dissolve" in less than a year. The wrong glycol was packaged in the right container. Big oops for the manufacturer. Lots of sludge being formed with all these pretty little silver flecks on the side stream filter.
Stainless, especially the giannoni heat exchangers need low mineral water. IIRC they like less than 7 grains hardness. Scaling can be a big issue.
But it can be the same problem with a CI hx that has lots of makeup water. Amazing to see a section totally plugged.
And low operating temps leading to the flue gases condensing can rot a CI hx.
Chemical treatment of hot water heating systems is an area that I try to stay out of. I can test for the basics but I like sending the sample to someone I trust. A good chemical guy is worth lots, and a bad one is worth whatever a new system costs.
Other than glycol, most resi systems don't need any chemical, but they should still be tested once in a while.
BTW, happy birthday.
Edited 4/1/2009 2:08 am ET by rich1
If you contact the manufacturer they will usually provide the warranty on exchangers, so you can compare the differences. Frankly, a cracked heat exchanger will result in a "red tagging" of your system and likely its entire (read entire furnace) replacement rather than just that part. That's the recomendation you will likely receive from the mechanic.
Therefore to avoid the hassle, I'd upgrade to the stainless steel. Ammortized over the typical 20 year guarantee, I think its a simple decidion. Then again... I could be all wrong :P
No offense, but you are wrong. The op was talking about boilers. A cracked hx in a boiler doesn't usually get redtagged, cause you ain't got no heat anyway.
:)
Oops, I have furnace on the brain these days....
Spend your money wisely, go stainless. Otherwise you'll be part of some huge class action suits down the road
Ever seen a SS HX leak? How about CI? AL? Steel? I've seen them all. And they ALL go back to installation and water quality.
gas with sulfer content will eventually ruin an aluminum exchanger...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
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Forget the primal scream, just ROAR!!!
and what restoration said...
Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming
WOW!!! What a Ride!
Forget the primal scream, just ROAR!!!