Aluminum HX, Condensate and Corrosion

Mech E

Hello all,

I have read some interesting remarks about aluminum hx, condensate and corrosion in past threads but I wanted to give a little input. In my opinion, aluminum metals should never be used with mod/con boilers for multiple reasons. The rate of corrosion for aluminum is extremely high in environments where pH is less than 7, or greater than 8.5, but also with the introduction of sulfates, nitrates, hydroxides, etc. We should all know that condensate is extremely acidic (pH far below 7) and natural gas and propane have impurites like sulfur and nitrogen which will combine with hydrogen and oxygen to form corrosive products as mentioned above. The corrosive products will combine in the presence of aluminum to form Al2SO4 (aluminum sulfate), Al(OH)3 (aluminum hydroxide) and AlNO3 (aluminum nitrate) which are extremely corrosive. So in conclusion, if you have a boiler which will operate below the dewpoint (therefore producing condensate) then an aluminum heat exchanger will fail (it's just a matter of time).

If you need to see "numbers" or research to believe this than you are more than welcome to read the research paper on gas condensing boiler heat exchangers conducted at the University of Leoben. Enjoy.

Xc8p2dC

The good with the bad

While I agree there are potential issues, more from lack of maintence and setup there is also an upside. There was a report a few years ago from SAE or similar type ORG, that looked at the heat transfer properties of different materials. This wasn't just boilers

The direction and findings where the AL and Mag where better at acheiving quicker heat transfer ramp up speeds. The emphasis was on effficiency. the quicker things got up to temp the more efficient the product was. This has been greatly benifical to the automotive/truck industry where efficiency standards are being cracked down on any why most have gone to AL heads and blocks [as well a weight]

I would proabably suspect that is why the well known experianced European company started/chose AL in it's benifits

While I am not disputing the "potential", I would question the dating on the report being from the 60's to early 2000's since technology has changes so much

Mech E

OK, I agree that aluminum has a quicker heat transfer ramp up speed (much in part due to aluminum having one third the density of steel), the question at hand is what material should be used for a gas mod/con boiler. I agree that aluminum has been used in the automotive industry as it should be in certain instances because of it's low density (therefore low mass), but the car engine is not the boiler, and aluminum should not have a place in the condensing boiler industry, the big "IF" here is, if you are operating below dewpoint. For the mod/cons which never condense and only operate above the dew point, aluminum is a great solution. However why would you pay for a high efficiency mod/con boiler if it never condenses?

Also the paper was released in 2005. I don't think aluminum has changed much since then...

Henry

Meanwhile ultra conservative Raypak has just put out a new residential alum xh mod/con!

Bill Clinton_6

Am I the only one

Am I the only one ever to have leaks in a hydronic system?

Like the one where we had a problem with the expansion tank that then became waterlogged, that caused the relief valve to open when the boiler fired, that caused there to be an intermittent stream of oxygenated water to enter the boiler that corroded the bejeezus out of the water side of the boiler.

Or like the job where we changed out the old Weil McLain cast iron boiler for a super duper efficiency Buderus aluminum boiler, little realizing there was a pinhole leak somewhere in the expansive system. Six months later, we were changing that boiler out for a prestige: For free. The Buderus totally plugged up with waterside corrosion.

Install another Aluminum boiler? Not on your life!

Bill

[Deleted User]

i wanna space shuttle tile

the interior of a mod hx. groovy man

Dan H

"For the mod/cons which never condense and only operate above the dew point, aluminum is a great solution."

Not really true in my world. Most of the Al HX I've replaced seem to be making more domestic hot water or only domestic hot water. The temps are very high and not producing much condensate. Am I crazy or should the higher temp systems last longer under your argument?

Mark Eatherton

You're not alone Bill... I saw it once...

no, wait a minute, twice, no thrice, uh four, five, six. Easy to lose track dontcha know... :-)

Then I got smart and quit making a solid make up connection to systems, and put low pressure AND low water cut off's on all systems, and then I knew when there was a leak, regardless of the means of leakage, 'cause the boiler would shut down, and the customer would call and complain...

The older we get, the smarter we get.

I once had a customer who replaced his boiler 3 times in 2 years with another service company. As he was explaining this to me over the phone, I said "You've got a leak somewhere in your system..." to which he responded "Really? Why didn't the OTHER company tell me that? They just kept replacing the boiler, and charging me for it!"

Long story short, he found it and fixed it and I've not heard back from him since. CFT boilers to boot. Ever seen a CFT heat exchanger that was so loaded up with calcium that it melted and fell into the combustion chamber? Now THAT's ugly...

ME

scrook_3

Then...

"For the mod/cons which never condense and only operate above the dew point, aluminum is a great solution."

Then you might as well go to a wet base cast iron boiler w/ a power burner, vs. spending the extra for condensing when you don't, though w/o condensation the aluminum might hold up fine.

D107

it's been said

a number of times on the wall that the 'mod' in modcon is the greater saver than the 'con'. So is it feasible to use a mod con as a modulator only--and protect boiler with a bypass or via a control system that maintains boiler temp at 140 or so? is it feasible that in the shoulder seasons the boiler would be able to modulate to the lower firing rates and still maintain the minimum con-condensing water temperature? So the HX will theoretically not corrode as rapidly.

Thanks,

David

Xc8p2dC

BINGO, David

There is one of the over looked benifits. My orig system had a 140k btu input bangbang and ran 180°+. With a few keystrokes, I can dial down my Modcon to 21-24K btu input and still easily obtain 140+ deg output water

Bill Clinton_6

Hi, Mark: Glad I'm not alone...

I have an argument against what you advise. In my experience, ALL hydronic systems leak. Doing what you advise, it seems to me, especially on a low water volume system, is going to guarantee a nuisance shutdown. It may take a year or two, what with water making it out of the air vent or through rubber gaskets a molecule at a time, but it's going to happen. (Yes, I call a molecule at a time a "leak".) It's a judgement call, but where I am, I come down on the side of having an open feed valve. Whichever side you're on, it still seems aluminum has vulnerabilities not shared by stainless steel, so why install aluminum? Makes no sense to me.

Mark Eatherton

It may take a year, or two...

Bill, if you are supporting the manufacturers warranty, you WILL be on site every one or two years to service the appliance and can recharge the system. Hence, not a "problem", but more a solution.

You are correct that Al HXers are more susceptible to problems than their cousins, but they are ALL subject to lime scale accumulation due to inadvertent leakage. It's your personal preference to not control the make up water to a system. Been there seen that more times than I care to recollect. And yes, you do get the occasional nuisance call due to leakage, but as I said, no leak is a good leak and it needs to be addressed and fixed.

Did you know that in the insurance world, that water claims hold the record for causing the most damage and monetary loss to the insurance companies?

To each his own. I'd rather fall on the side of being cautious.

Good to see your words.

ME

Mech E

As you can see from my prior posts I am not a huge fan of aluminum hx's and would never advise anyone to install one. I should probably keep my sarcasm off the wall, but yea that should be re-worded to say an OK or good solution. But to answer your question, it really depends on your definition of "last". There are also many factors that also should be looked at, for example, the water quality, the run times and the boiler temperatures. With any mod/con boiler there will be times when condensate is produced, even if you have a DHW only system with mostly high temperatures. For this reason I do not recommend aluminum ever.

Unknown

mark's nailed this one on the head.

automatic makeup water is, once the initial charge of air is removed, automatic destruction waiting to happen.

Paul Cooke

Automatic Makeup Water

Mark

Great points about liability and makeup water. How about the idea of installing makeup water with a reduced pressure backflow device like we do here in Oregon, and after the initial fill, leave the valve in the closed position.

That leaves a simple way to add water, as needed, and also protects against catastrophic leaks.

[Deleted User]

That works OK Paul...

so long as it DOES get shut off after replenishment.

People (including our employees) get lazy and forgetful. If they look at a system and see a hose still on it, they know something doesn't look right, hopefully :-)

On our leaky commercial jobs, we use to use what I refered to as an EFE, which stood for Excess Flow ELiminator. I'm on my way out the door for a meeting, but will try and find a picture of it. SImply stated, it is a swing check, installed upside down and backwards at a 45 degree angle. This keeps the flapper check hanging down via gravity, and allows a small (seepage) amount of water to pass freely by, but should a line freeze and break, the water tries to flow though the device, and WHAM, it slams shut and keeps the place from getting completely flooded out. It has saved some serious water damage on numerous of the jobs we had incorporated it on.

I'll get back to you.

ME

[Deleted User]

Question for Mech E

You don't happen to work for Viessmann do you? No problem if you do. I just think people should let people know where they sit before they tell them where they stand. Full disclosure and all dontcha know...

Just curious :-)

ME

Dale

2009 code

One of the changes in the 2009 fuel gas code is now requiring a low water cut off on all new hot water boilers. A little late but good.

S Ebels_2

Valve left open

WELL YAAAAAaaaaahh

Had a service call this winter about 10PM one evening. The customer had another service company over to take care of air in the BB. He purged the air all right and left the fast fill lever on the B&G PRV open. The HO cam home to a basement full of steam and 3" of water on the floor.

I do it the same as Mark. No chance for a flood.

Mech E

I understand what you mean, and yes I do. How'd ya know?

Mark Eatherton

Lets call it...

Browsers intuition.

Did you know that Viessmann had some boilers out there with AL HXers on them?

Fortunately, they learned their lesson early...

ME

Xc8p2dC

Too bad

This topic had validity, until it was learned it was more about putting down the compitition, than actual facts.....

I use the ULTRA with the 15 year P/R warranty on the HX and saves more than $3000, in fact if they do fail too soon, I will replace it with another one and still be under the cost of the V, by then techenology will have changed anyway

Derheatmeister

I guess Mark can tell by your E-mail address.
BTW visiting the Big V in Allendorf was great

And i agree that aluminum shall not have a place in Condensing boilers under certain situation i.e. the Buderus design.

Did you see the Weisshaupt Condensers at the ISH ?

Mark and i talked about a past post and i wanted to Apologize for that,I guess i did not know the whole story, nice to see you here...Richard

Mark Eatherton

I don't think it took away any validity...

this is HIS opinion, not the opinion of Viessmann.

To each, his own.

ME

Mech E

Yea I usually don't like to get involved with these kind of things, but I saw false statement after false statement about corrosion, aluminum hx's and condensate. I started the thread to try and clarify some things.

I have never spoken bad about any other boiler manufacturer and my points raised here are of my own. All I wanted to do was spread awareness of the possible downsides of aluminum hx's.

Anyways I hope everyone had a great easter, talk to you soon.

Herb the poor schmuck homeowner

Buderus condensing boiler

Gentlemen,
I live at 9000 ft where we fall below dew point 7 months of the year. In May of 2006, we had a Buderus GB142 condensing boiler installed (aluminum heat exchanger). On 12/11/2008 we had a catastropic failure of the heat exchanger with it leaking a glycol water mix into the heater closet. The heat exchanger had corroded, with a quantity of white powdery corrosion on the heat exchanger and multiple points of leak.
We paid our plumber for the labor to replace it and he had Buderus provide the heat exchanger under warrenty. We have since had to replace 4 taco heating zone pumps and a pump that circulates the domestic hot water,as well as several manual shut off valves. The Taco and Grundfos domestic circulating pumps were installed when the house was built in 2002. April 12,2009 - the heat exchanger in the Buderus failed again - leaking and with a white powdery corrosion. Also , a manual shut off valve and a pressure relief valve have failed - also corroded. We did check the pH of the water glycol mix in the heating system - it is at 7.0 . Is it possible and if so how likely is it that the corrosion
from the heat exchanger would affect the other components of the system e.g. the taco , the grundfos and the brass shut offs.
thanks
Herb

Dan Foley

Glycol

Are you using a glycol designed for aluminum block boilers? That could be the problem. -DF

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Herb the poor schmuck homeowner

Yes, the plumber refers to it as an aluminum protective glycol
Thanks

Xc8p2dC

I would \"suspect\" your problem lies elsewhere

Faulty installation?, . The glycol and condensate are on two different sides. If the glycol is leaking in the room, it's probably not related to the HX corrosion from condensate as this thread talks about.. Only PICs would help,,, ph 7 is too low [installation]as glycol ph lowers as time goes by

If you do a search, not alot of reports of GB142 failures and can't imagine it happening after 1 year from corrosion, would have to sit in a pool or contaminants or backed up drain<<< Maybe a pressure problem or feed? I would also question AL rated glycol if from that side

Rhomar Mike

Alum safe Glycol

RhoGard Aluminum Safe Multi- Metal Antifreeze.

Endorsed by Buderus, Crown, Slant/Fin, Weil-McLain, Burnham, Aerco, Utica, Dunkirk, Patterson-Kelly and others. Environmentally friendly,Non-Hazardous. Add the correct fluid and quit worrying about the water-side of your system.

www.rhomarwater.com

Xc8p2dC

MIke

Is there still a better benifit to that than PT 922, if your not in a dire freeze situation

Unknown

Boilers

Seems like more of a reason to fill/treat water/pressurize and disconnect the city or well water feed. No PRV no back flow prevention. Just make sure you have a low water cut-off. Been doing it for years, just makes the inspectors nervous but it works.

Mech E

Sorry Herb

I am very sorry to hear about your heating system issues.

A hydronic heating system is a closed loop system, meaning no liquid should enter or exit the system. However, if you have a leak in your system, especially in your heat exchanger then there is a real possibility of cross contamination here. The heat exchanger is the heart of the boiler and one of its purposes is to separate the harmful toxins of the combustion side from the water side. If the condensate and exhaust gases penetrated through the aluminum hx then it is very possible that they may have found their way into your heating system. The leakage of glycol/water from your heating system means "something else" took its place in your heating system, it could have been exhaust gases or condensate or just plain air (perhaps a mixture of all three...) but we may never know.

This is just another reason why I would never put an aluminum hx boiler in my house.... sorry again for your troubles.

eluv8

Something to consider

I have always been concerned myself about aluminum heat exchangers but after seeing Patterson Kelley and the Mach I think it can be done in the right applications with a quality glycol, or inhibitor. Cryotek and a couple other glycols had an issue with their Aluminum safe glycols that were reported to cause premature failure in Aluminum boilers. I have always recommended Rhomar and been good thus far. If aluminum was truly an uncontrollable problem I find it odd that after trying other materials so many commercial manufactures are coming out with their version of an aluminum alloy boiler. As for condensing boilers many have been miss applied and the end users will never see a return on their investment, where a high efficiency cast iron boiler or copper fin would have been better suited, or a combination hybrid non-condensing and condensing multiple boiler scenario for the shoulder season efficiency and peak load requirements and load matching with greater turndown and redundancy. Its amazing how many commercial projects I run into that are designed at 140-150 return water and it is spec'd with condensing boilers, not to mention residential projects also and the control packages are not designed or setup to address outdoor reset. I think so often we get mixed up with the products and the hype and miss the writing on the wall when it comes to actual system efficiency, performance, return on investment and reliability. As an observation It seems like when the aluminum boiler fails its always the aluminum and PH or glycol, stainless steel was the chlorine or flow rate, copper was flow or condensation, cast iron was flow, condensation or thermal shock. Every boiler material and design that I know of is going to have its benefits and weaknesses. While some products are more forgiving than others and some manufactures have proven to be better at assembly and engineering a reliable product,I believe in our quest for the perfect heat exchanger material we are doing ourselves a disservice as we constantly seem to be tearing down each boiler design and material after a product failure when often times those failures were the result of incorrect installation, maintenance or defective products used within the system and yet it seems its often conveyed as the boilers fault, or a materials weakness. What is Mr homeowner to believe who is reading our posts on the Wall, has a stainless steel boiler or Aluminum boiler and has had no problems for 7-8 years and the igniter or flame rod goes out? Are some boilers better than others, of course. Is Lexus better than Toyota? Yet both companies are successful.(for now anyways) You get my point. I think it is an invaluable tool to have access to the opinions and experience of the amazing people who frequent the wall forums. I think we just need to be careful at times on the image we give the materials and products we install, sell and maintain. Radiant and hydronic heat and cooling is already viewed as being complicated, expensive, and problematic or troublesome to own. I feel better now thanks...

eluv8

Something to consider

I have always been concerned myself about aluminum heat exchangers but after seeing Patterson Kelley and the Mach I think it can be done in the right applications with a quality glycol, or inhibitor. Cryotek and a couple other glycols had an issue with their Aluminum safe glycols that were reported to cause premature failure in Aluminum boilers. I have always recommended Rhomar and been good thus far. If aluminum was truly an uncontrollable problem I find it odd that after trying other materials so many commercial manufactures are coming out with their version of an aluminum alloy boiler. As for condensing boilers many have been miss applied and the end users will never see a return on their investment, where a high efficiency cast iron boiler or copper fin would have been better suited, or a combination hybrid non-condensing and condensing multiple boiler scenario for the shoulder season efficiency and peak load requirements and load matching with greater turndown and redundancy. Its amazing how many commercial projects I run into that are designed at 140-150 return water and it is spec'd with condensing boilers, not to mention residential projects also and the control packages are not designed or setup to address outdoor reset. I think so often we get mixed up with the products and the hype and miss the writing on the wall when it comes to actual system efficiency, performance, return on investment and reliability. As an observation It seems like when the aluminum boiler fails its always the aluminum and PH or glycol, stainless steel was the chlorine or flow rate, copper was flow or condensation, cast iron was flow, condensation or thermal shock. Every boiler material and design that I know of is going to have its benefits and weaknesses. While some products are more forgiving than others and some manufactures have proven to be better at assembling and engineering a reliable product,I believe in our quest for the perfect heat exchanger material we are doing ourselves a disservice as we constantly seem to be tearing down each boiler design and material after a product failure when often times those failures were the result of incorrect installation, maintenance or defective products used within the system and yet it seems its often conveyed as the boilers fault, or a materials weakness. What is Mr homeowner to believe who is reading our posts on the Wall, has a stainless steel boiler or Aluminum boiler and has had no problems for 7-8 years and the igniter or flame rod goes out? Are some boilers better than others, of course. Is Lexus better than Toyota? Yet both companies are successful.(for now anyways) You get my point. I think it is an invaluable tool to have access to the opinions and experience of the amazing people who frequent the wall forums. I think we just need to be careful at times on the image we give the materials and products we install, sell and maintain. Radiant and hydronic heat and cooling is already viewed as being complicated, expensive, and problematic or troublesome to own. I feel better now thanks...

Derheatmeister

Erik,Yes i have also mixed options about the usage of Aluminum , I myself have serviced some large commercial 1.700.000 PKs' and was very pleased to find very clean none deteriorating heat exchangers! These boilers are made in PA USA and are a very nice!

It is very strange that most of my calls are due to someone not following installation Instructions or does not play "Match maker" (Like you mentioned certain boiler for each situation!)

I myself was raised in Germany not to far form Buderus!
I went to Trade school as a Heat tech in Bad Homburg near Frankfurt and all we installed were Buderus, i was on the "Blue Team" and the boilers back then were nice work horses',In fact my parents still have a woodboiler made by Buderus which is great!

I do not what really to "bad mouth" Buderus but i have got this bad taste in my mouth!

When Buderus first introduced the GB series in the USA i had some concerns about the glycol! Buderus back then was NOT supporting the Usage of Rhomar! In fact i was told to use Hercules AL or i would Void the Warranty! Due to my Concern i only installed 4 boilers!

After about 5 months Buderus GB series were seeing some serious Premature deterioration of the heat exchangers due to improper fluid quality !Buderus did not pay for any Labor to flush install Rhomar 9100 and wait; flush again and then install the 922 on these boilers,in fact i was told by a Buderus tech on the east coast to install the 922 to clean the system and use the 9100 as a treatment which is exactly the reversed way! I had to argue with that tech and go above his head to have his supervisor correct him!...VERY BAD!

AS per the combustion side of the heatexchanger: Not on any of my installs but of others which no longer help the customers i have removed Bags of Aluminum Oxide! these boilers were adjusted with a combustion analyzer by the Dutch connection!

In my opinion they were very disorganized and did not do enough Field testing or R&D before they lanced this boiler into the US market!These are just my opinions !

At the ISH this year i was talking to Weishaupt germany www.weishaupt.de and years ago they apparently had some "Growing pains" with the aluminum wallhung condensers as well! After some R&D they since changed the design and have a pretty nice boiler!
(Not for the US yet!)

Let me close with something positive and back to the SS boilers: I have got a VIESSMANN Vitodens 200 at 11.200 feet,and yes it is on Propane! i service it every year and i am always happy to see a Heat exchanger that looks like new! No harm intended just my Opinions... Richard

eluv8

Perfect example, thanks

Perfect example, thanks. Its sad to see a manufacture as large and influential as Buderus making these kind of mistakes in the US. The GB was a very popular boiler in Colorado for some time until they started dumping the heat exchanger by the pallet. Sad day (year) for aluminum and Hercules Cryotek AL glycols and the contractors and homeowners who installed them. While Weil Mclain has had a pretty good run with the aluminum, and I have heard good things about just about every PK Aluminum boiler(If you haven't seen the block its worth a look of a cutaway section)they claim to use a unique aluminum alloy that does not pit, its been in the US about 6-7 years and Europe for close to 30. I believe Mclain and PK use the same supplier for their heat exchangers, although use different designs. I have not seen to many others in my area to trend a success or not for the manufacture, but I hope there are many more successes than failures as every success helps bring the comfort and benefits of Radiant and Hydronic heat to another convert over scorched air and makes our jobs that much easier.

eluv8

Austrian Aluminum Study

While a good study, be sure to note that this boiler was used with an OIL burner and low mass aluminum and fins which evidently does not work well together. There are also several grades and alloys of aluminum of which some are more resistant than others to corrosion of certain chemicals, similar to the grades of stainless steel(300, 400, etc..)with their own advantages and disadvantages. This particular setup hopefully is not being repeated by a manufacture in the United States.

Mech E

Eric G, I have to correct you, the paper was analyzed with GAS not oil. If you read the title of the paper, it explains it all, "Material Requirements for Heat Exchangers in Gas Condensing Boilers" (the confusion probably came in the translation of the paper from Austrian to English because they used the word oil in a few instances, but it should read gas)....I agree that aluminum has different grades and alloys just like steel, but the heat exchanger mentioned in this paper is a combination of AlSi7Mg (body), AlMg0.5 (fins) and Al99.5 (plates) which are all common materials for aluminum heat exchangers (as a matter of fact do you recognize the heat exchanger in the picture?)....

So unfortunately this is being repeated in the US.

eluv8

Austrian Study

Thank you for the clarification on that, I reread that study, it was late last night. I see where I missed the gas at the beginning and pretty much the middle also. I was thinking it was an oil boiler but the gases referred to the steam within the combustion chamber and condensation. I would like to see a similar study done on a high mass cast block aluminum design from a couple of the more well known manufactures. I think we would see a different result. The fins appear to be nearly pure aluminum and low mass, leaving room for condensate to pool, corrosion of the coil, and resultant spotty temperature extremes across the coil I presume accelerating the process of self destruction. I like to associate it to a paper cup with water in it. Paper cups can boil water, take the water out and it burns up. The thickness and quality of the paper determines how long you can boil that water. If you have exposed edges increasing surface area and they cause weakness in the main vessel you will fail sooner. Who would have thought a cast iron boiler with an aluminum pan would be marketed as a condensing product? Yet they are doing it today rather successfully. I anxiously am awaiting the verdict on this one myself, that's one heavy boiler. Why not aluminum alloy blocks designed for the application? Ever looked at a cast iron drainage system that has had condensate pumped into it for a couple of months that has not been neutralized. Its not good. Warning Soapbox coming..... All condensing boilers in a condensing application should be sold with or have condensate neutralizers installed. Thankfully we have access to the wall and have the ability to watch out for these design weaknesses manufactures beta test on us as they do their research projects. I just hope we don't get carried away and group a product or certain material as bad because of the learning experiences of another simply because they have something in common. Nearly every great success has been preceded by numerous failures. I have my share of flops, and duh moments. Post above included. Good and Bad we are better today because of the mistakes of yesterday.