Acidic Condendsate from High Efficiency Gas Furnaces

[George Bokros]

Just a head up.

I learned this the hard way. The condensate from the combustion of natural gas in high efficiency gas furnaces is highly acidic. I know because it destroyed my basement sump pump in 2 1/2 years. The pump started spraying water and when I removed the radon cover I found the pump covered in white corrosion. I did some research on line and found out that the condensate is high acidic. From what I read it can completely destroy a cooper drain line in as little as 5 months. I am investigating adding a filter that will reduce the acidity of that condensate to prevent the destruction of my next sump pump.

I am not referring to condensate from air conditioning but from the combustion of natural gas in high efficiency gas furnaces. Some municipalities are requiring these devices to reduce the acidity of the condensate.

Just a head up.

[Brad Adams]

Furnace condensate is acidic, but it is not highly acidic. It is about the same as orange juice. It is usually around a PH of 5.

[Adam Herman]

ours has eaten away at the cast iron drain, i pulled about a cup of rust out that was clogging the p trap. you can use marble chips to reduce the acidity. but you have to make some kind of container that will contain them and the water. we have only been in this house a couple years, i plan on making a larger resivoir at the furnace end where the small plastic trap is now, and fill that up.

[Robert Maloney]

Purchase a condensate neutralizer. It is basically marble or limestone chips in a pvc tube. It is required here in NY to have one installed between your boiler or furnace and your drain. They do suggest that you change the chips annually.

[George Bokros]

Furnace condensate is acidic, but it is not highly acidic. It is about the same as orange juice. It is usually around a PH of 5.

Any PH of 6 or lower is considered to high as I understand it.

[Mike Henderson]

The manufacturers of condensing (high efficiency) tankless water heaters always warn that the condensate is highly acidic. The Rheem that I have has a neutralizer kit in the unit. I checked with Rheem and they say that it needs to be changed about every 3 to 6 years, depending on how much you use it.

The advantage of the condensing units is that you can use PVC for venting because the vent gases are relatively cool. They also recommend that you put a drain in the vent and drain that to a safe place or put a neutralizer kit in the drain line.

If you can install a outdoor tankless water heater, go with a non-condensing and you won't have those problems. You won't get 90+ efficiency but you will get about 80 percent efficiency and natural gas is not that expensive.

In my mind, the only reason to go with a condensing unit is for an inside install and that's so you don't have to use expensive stainless steel venting material - you can use Schedule 40 PVC. Note that you can vent a condensing unit to the side of the house - you don't have to go through the roof. The exhaust is cool so shrubbery is not burned (except for the acidic exhaust gases) and there's not a danger to people and animals. The exhaust cover is not bad looking and people really won't notice it - it's essentially flat with the side of the house.

Mike

[George Bokros]

Update


Furnace condensate is acidic, but it is not highly acidic. It is about the same as orange juice. It is usually around a PH of 5.

Just found info that indicates that the condensate from the combustion process is a Ph of about 3.5 - 4 which is quite acidic. In gardening a Ph of 6 or lower in garden soil is considered acidic soil.

This indicates to me that the condensate is quite acidic, I would say more than orange juice for sure.

[Ole Anderson]

This indicates to me that the condensate is quite acidic, I would say more than orange juice for sure.

FYI: Orange Juice. Orange juice ranges in pH from 3.3 to 4.19. From the internet, so it must be true...

Actually an interesting thread as I installed a 98% efficient furnace last fall and never thought about the effect of the condensate on my floor drain/sump pump. Might have to get a neutralizing filter.

[George Bokros]

FYI: Orange Juice. Orange juice ranges in pH from 3.3 to 4.19. From the internet, so it must be true...

Actually an interesting thread as I installed a 98% efficient furnace last fall and never thought about the effect of the condensate on my floor drain/sump pump. Might have to get a neutralizing filter.

This is interesting, I never looked up how acidic orange juice was. Guess I wonder how it effects my esophagus.

All I know is my sump pump is crusted with white crystals. I will take a picture when I pull it our to replace it Friday or Saturday. New pump is scheduled to be delivered Thursday (tomorrow).

Until I get a neutralizer installed I will drain the combustion condensate into a five gallon bucket and dilute it before dumping it down the drain. Working with my HVAC service company to get it quoted and installed. I do not want to do anything that jeopardizes my furnace warranty.

[jared herbert]

my high efficiency lenox furnace, of course installed in our basement drains into the shower that I use after work, when I am really dirty, also located right next to the furnace. The drain water comes out of a hose and runs across about 18 in of concrete before it gets to the shower drain. Over a period of years it has eroded a track about 1/2 deep and an inch wide.

[Ronald Blue]

As info.

http://altered-states.net/barry/update178/phdiagram.gif

[Wade Lippman]

It is required here in NY to have one installed between your boiler or furnace and your drain. They do suggest that you change the chips annually.

Since when? I've never seen one.

[Mark Bolton]

Furnace condensate is acidic, but it is not highly acidic. It is about the same as orange juice. It is usually around a PH of 5.

Not true for high efficiency condensing furnaces. The flue condensate can be 3.0 or a bit lower. 3.0 mind you is Hydrochloric Acid. There is a reason you are not to use foam core PVC and to be tentative to condensate routing with HE condensing appliances.

[David Helm]

When my high efficiency gas furnace was installed two years ago, the condensate line was installed to pump it outside under the deck where it does no harm.

[Wade Lippman]

Not true for high efficiency condensing furnaces. The flue condensate can be 3.0 or a bit lower. 3.0 mind you is Hydrochloric Acid. There is a reason you are not to use foam core PVC and to be tentative to condensate routing with HE condensing appliances.

pH of HCl depends on the concentration, but it is about the strongest acid; nearly pH 1 when concentrated.
Coke is about 2.5 and vinegar about 3.

[Wade Lippman]

When my high efficiency gas furnace was installed two years ago, the condensate line was installed to pump it outside under the deck where it does no harm.

You might not be cold enough to worry about freezing, but if you are, you had better insulate it.

[John Stankus]

pH of HCl depends on the concentration, but it is about the strongest acid; nearly pH 1 when concentrated.
Coke is about 2.5 and vinegar about 3.

pH will depend on the concentration for all acids.
You have to be careful when talking about strong vs. weak regarding acids.
A strong acid completely dissociates in solution (gives loses an H+ ion (though technically it forms a hydronium ion H3O+ but that is another story))
The common strong acids are things like HCl (hydrochloric acid (also known as muriatic acid)), HNO3 (nitric acid), H2SO4 (sulfuric acid), HBr (Hydrobromic acid), HI, (Hydroiodic acid), HClO4 (perchloric acid) and HClO3 (chloric acid)

pH is a way to characterize the concentration of H+ ions (again technically H3O+ ions)

pH=-log[H+] where [H+] is the concentration of the H+ ions

By changing the concentration I can hit any pH below 7

Weak acids on the other hand do not completely dissociate. An equilibrium is formed where the H+ ions are continually coming off and reattaching to the acid. So the concentration of the H+ ions will be less than the total concentration of the acid. Now don't think that because it is a weak acid it is not as reactive. Hydrofluoric acid is a weak acid, and it will etch glass.

Water (normal tap water) is usually a bit acidic due to the dissolved carbon dioxide forming carbonic acid. The pH of rain after falling through the atmosphere and absorbing CO2 can be around 5.7


John (my day job is teaching chemistry)

[David Helm]

You might not be cold enough to worry about freezing, but if you are, you had better insulate it.

ot a problem here.
N

[Mike Henderson]

John (my day job is teaching chemistry)

Thanks for the information, John. I don't remember much of my college chemistry and it was nice to have an explanation.

Mike

[Jason Roehl]

pH of HCl depends on the concentration, but it is about the strongest acid; nearly pH 1 when concentrated.
Coke is about 2.5 and vinegar about 3.

And the pH of your gastric (stomach) acid can be as low as about 1.5...

[Mark Bolton]

pH of HCl depends on the concentration, but it is about the strongest acid; nearly pH 1 when concentrated.
Coke is about 2.5 and vinegar about 3.


No doubt, Regardless I have been installing HE condensing waterheaters and furnaces in customers homes for nearly 30 years. Its a given with any acid the PH is based on concentration. I can choose to wash a concrete/brick job with straight muriatic or dilute it 50:1. None the less, every boiler, furnace, direct vent water heater, on demand water heater, manufacturer calls out their spec's. You can flout your "coca cola is 2.5" spec all you want. The simple fact is the manufacturer of the appliance calls out the spec for their flue requirements. There is a reason all PVC vented condensing appliances spec no foam core.

We can "jack" around about concentration all we want, or just put the appliance in in a way that we meet the manufacturers spec and cover our butts (but you better still pay your liability).