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Nestor_Kelebay 11-23-2008 12:39 AM

KNOWLEDGABLE condensate advice needed
I recently had a 1960 vintage boiler replaced with two Weil McLain Ultra 310 boilers. These are "condensing" boilers, meaning that the flue gas contains H2O condensate. That condensate is corrosive and has a pH of about 3 or 4. The company that installed the new boilers ran a drain pipe from the boilers to my sump pit.

I don't like the idea of leaving it that way because I'm concerned that the acidity of the condensate will corrode the cast iron drain piping from the sump pump. I can replace the sump pump easily enough, but replacing the drain piping in the crawl space under my building would be a ***** with a price tag to match.

I built a neutralizing filter to run the condensate through before it goes into the sump pit. The filter contains ordinary limestone.

My question is: Would it be better to use calcitic marble in the filter?

There is a quary in Ontario where calcitic marble is mined and used for colouring concrete. The sales rep of the company that mines this marble sent me a sample of that calcitic marble. The problem I'm having with it is that I don't know that calcitic marble is as reactive with the acidic condensate as ordinary limestone. It seems to me that lots of old buildings are made from limestone, and statues are carved from marble, often calcitic marble. When you look at old buildings built of limestone, they look more deteriorated than statues carved from marble, and both have been deteriorated by the same acid rain.

That would suggest to me that the old limestone on old buildings is more reactive with acid rain than the calcitic marble that statues are carved from, and that would suggest that limestone is more reactive with acid than calcitic marble. And, in turn, that would suggest to me that a limestone media would neutralize the condensate better than a calcitic marble media in my pH neutralization filter.

Would the KNOWLEDGEABLE people in here give me their opinions on which filtration media would work best on a condensate pH neutralization filter, limestone with a 95% calcium carbonate content, or calcitic marble with a 99% calcium carbonate content?

I contacted the U of Manitoba and talked to a professor of geology and he suggested that the limestone would be more reactive than the marble, but he couldn't give any explanation as to why he felt that way. My experience with university professors is that they don't always know what they're talking about. Period, full stop. They're like the rest of us in that respect.

I'm hoping to find someone knowledgeable in neutralizing the condensate from high efficiency boilers that will know which filtration media works best.

Maybe don't bother responding if you're just guessing. I can do that myself.

beenthere 11-23-2008 05:24 AM

Neither, the Ph is too low.

You can use a combination mix of calcite and(calcium carbonate) and corsex (magnesium oxide).

Calcite alone, is not great at ph levels below 5.
Although 1 CF would handle the low volume of the boilers.

You must have a Huge house to need 2 Ultra 310s

Nestor_Kelebay 11-23-2008 05:25 PM


Finally I get to talk to someone who knows something about this. Most other people I talked to have never even heard of corsex.

How can you say that calcium carbonate won't work well at pH levels below 5? Right now I'm running my condensate through a 5 foot long 3 inch diameter PVC pipe full of limestone and collecting the condensate that comes out in a plastic bottle. The plastic bottle is situated inside my sump pit, and it it continuously overflows into that sump pit. So, the water collected in the plastic bottle is a "running average" pH of the water coming out of the neutralizing bed. What I do once a month is literally drink some of that water out of the bottle to see if it tastes acidic or not.

I find that it tastes like distilled water. No acidity at all.

What I'm wanting to know is whether I can go for a longer period of time without having to clean my neutralizing media if I were to switch to a calcitic marble, which has a higher calcium carbonate content.

What are your thoughts?

jerryh3 11-23-2008 05:30 PM

Why not just have a seperate condensate pump for the boiler? It could be pumped outside of the house bypassing the sump.

kennzz05 11-23-2008 06:56 PM


Originally Posted by jerryh3 (Post 189161)
Why not just have a seperate condensate pump for the boiler? It could be pumped outside of the house bypassing the sump.

someone that bothers to write 750 words to explain his problem aint going for our low tech redneck solution just cuz it dosent make sense to some dosent mean it dosent make sense

Nestor_Kelebay 11-23-2008 07:06 PM


You must have a Huge house to need 2 Ultra 310s
No, I own a 21 unit apartment block which is a full time job maintaining, managing and renovating.


Why not just have a seperate condensate pump for the boiler? It could be pumped outside of the house bypassing the sump.
Because I live in Manitoba, Canada. The only exterior wall in my boiler room is just wide enough to accomodate the air intake (goose neck) for the old boiler, and it's only about 2 feet wide. That wall opens onto my parking lot. If I pumped that condensate onto my parking lot, it would create a skating rink in the parking lot and expose me to the liklihood that tenants would be slipping and falling and cracking their skulls and suing me for creating the hazard. If I pumped the water to the end of the parking lot, it would spill onto the sidewalk and create the same hazard there until the water in the pipe froze solid and prevented the condensate pipe from working until spring thaw.

I'm far better off to neutralize the condensate, and then dispose of it through the existing drain piping.

As it stands now, my limestone filter will neutralize the water to a pH of 7, so it's fine for the regular drain piping. The problem is that the limestone I'm using is about 95% calcium carbonate, which is the reactive chemical. As that limestone dissolves in the condensate, the remaining 5 percent that doesn't dissolve in the condensate forms a "fuzzy" film over the limestone stones that impedes contact between the limestone and the condensate. Basically, that 5 percent forms an "insulating blanket" of stagnant water around each stone as it dissolves that prevents good contact between the condensate and the calcium carbonate. As that stagnant water blanket around each stone grows in thickness, not only does the filtration media become less effective, the drag on the water flowing through the filter increases and eventually the condensate will spill out at the boilers instead of flowing through the filter.

What I'm doing now, or roughly about every 1000 hours of boiler operation, is emptying out the limestone in my filter into a bucket and cleaning my limestone by rubbing the stones together so that each one scrapes the fuzzy stuff off it's neighbors.

Obviously, I should be able to go for longer without cleaning the stones if I had a lower percentage of insolubles in my limestone.

There is a quarry in Perth, Ontario where a company called Omya obtains almost pure calcitic marble. It's supposed to be 99.5 percent pure calcium carbonate. Theoretically, I should be able to go 10 times as long between cleanings because the percent of insolubles is only 1/10 of what it is in my limestone.

The problems I'm facing are:

A. It's marble and not limestone. Marble is either dolomite or limestone that has been squashed under the weight of land or water until it takes on a more dense form. And, apparantly according to my local geology professor is not as readily soluble in acid as limestone. And, I can see that with my own eyes when I look at the limestone facades of old banks and marble statues. The marble stands up better to acid rain than limestone. This would mean that I'd have to have a larger pH neutralizing filter (for greater retention time) or a finer stone size (for more surface area between the condensate and the marble) in order to get the same effect on the pH of the condensate as I'm getting now with limestone.

B. Right now I'm getting limestone almost free from my local cement plant. I pull up in my car and ask if I can have a 5 gallon pail of their smallest clean limestone, and the guy just says "Help yourself, we throw out more than that every day from our concrete testing lab". And to me, a 5 gallon pail of 1/2 inch clean limestone is like a 5 year supply.

The calcitic marble is a different story. Since it's used to colour concrete, it's normally sold by the truckload at Perth, Ontario. They don't sell the stuff by the 5 gallon pail, but they will for me (cuz I've talked to them about shipping it out to me in pails). The problem is that it's going to cost me about $45 dollars just for shipping from Perth to Winnipeg, and the cost of the pail and the marble is on top of that. I'm willing to pay that amount if I can only clean my filter once a year or so. I just don't know if that $45 is going to just buy me a problem because my existing filter won't be big enough.

What I need is someone knowledgeable enough about condensing boilers or furnaces to know the best strategy for me, primarily from a labour perspective, but also keeping the cost in mind.

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