Is Furnace Condensate Toxic?

If you have a high-efficiency furnace, then the exhaust gases don’t get pushed out of the system right away – they get a chance to cool down and, consequently, produce condensate. 

Furnace condensate is not a toxic liquid; however, it is an acidic solution that consists of water, carbon dioxide, nitric acid, and, in some cases, traces of metal, mold, and mildew. This condensate is corrosive and has to be neutralized before getting drained into the wastewater system.

Where Does Condensate Come From?

There are two main types of gas furnaces – conventional and condensing. The latter incorporates newer technology and is, in general, more efficient (condensing furnaces have the highest AFUE ratings).

Just like a conventional furnace, a condensing unit has a gas burner that heats the air that has been drawn in from the house. However, the main difference is how the unit handles the combustion gases.

In a conventional furnace, the gases are sent directly to the flue from the combustion chamber. In a condensing model, the exhaust gases get to pass through a second heat exchanger.

The hot gases get a chance to cool down within the system so that no heat goes to waste. When the temperature of the combustion gases drops, they condense and form water and CO2.

This water is called ‘the condensate’. It drips out through a special drain pipe and the remaining gases get vented to the outdoors.

Read: Why Furnace Blower Motor Is Making Noise When Starting?

Is Furnace Condensate Toxic?

Furnace condensate can’t really be labeled as ‘toxic’, but it has plenty of chemicals in it.

Let’s take a closer look at the chemistry of gas combustion.

Your gas furnace is able to heat the air thanks to a reaction between gas and oxygen – that is usually either methane (CH4) or propane (C3H8) and oxygen (O2). 

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As a result, water (H2O) and carbon dioxide (CO2) are produced.

Water and carbon dioxide are not toxic, but what makes condensate unsafe is nitrogen. The hot flame in a gas furnace ‘sucks in’ the atmospheric nitrogen, and this element ends up reacting with the oxygen.

That’s why we should add nitrogen dioxide (NO2) and nitrous oxide (NO) to the formula above. These things dissolve into the vapor and form nitric acid.

Read: Is It Worth Getting A High Efficiency Furnace? And Why?

Is Condensate from a Furnace Acidic?

Due to the fact that nitrogen products come along with the water vapor, the system ends up getting rid of a dilute solution of nitric acid.

In general, furnace condensate has a pH between 3.0 and 5.0 which means that the solution is acidic. However, in some cases, the condensate can reach 1.8 (that is even closer to the acidic end of the pH scale).

Is Condensate Water Corrosive?

As the condensate is acidic, it will damage pretty much any metal that it is able to come in contact with. If you live in an older home and your condensate drains into the building’s plumbing, the solution can damage the pipes.

By the way, the longer the fluid sits in the trap or a pipe, the more it evaporates and, consequently, the more concentrated it becomes. In such a case, the condensate will most certainly corrode cast-iron pipes.

Acid can’t really harm PVC plastic. But do bear in mind that even if your older pipes have already been replaced in the house, that does not mean that the contractors didn’t leave the cast-iron pipes in the basement.

Moreover, the majority of the pipes that run under the ground are made out of metal. So, your condensate might end up damaging those.

Read: Why Furnace Is Making A Clicking Noise – Troubleshooting Guide

Is Condensate Flammable?

Condensate is acidic and is, basically, a corrosive substance, but it doesn’t have enough nitric acid that can serve as an oxidizing agent, so it’s not flammable.

Can You Drink Condensation Water from a Furnace?

You might be thinking that if this water forms during condensation, then it can be considered distilled and, therefore, is relatively safe to drink.

But even though, technically, condensate is distilled water, it is not safe to drink

First of all, the liquid is very acidic. Even though some beverages have a pH level of 4.5 (or even less), drinking such liquids can damage your health.

For example, acidic water can be bad for bone health and your teeth.

Secondly, and most importantly, condensate can contain traces of metals and mold and mildew that are present in your HVAC system. As the water isn’t actually boiled, it can also have plenty of microorganisms in it.

It has been scientifically proven that acidic water is more likely to leach heavy metals from the surroundings. Exposure to such water can potentially lead to heavy metal poisoning

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Is Furnace Condensate Safe for Plants?

If you dump the condensate outside or collect it to water your plants, the solution will kill the grass and flowers, basically, everything that it comes in contact with.

This will happen simply because the solution is acidic.

However, if you have a condensate neutralizer, the water might be close to neutral (pH-7). In such a case, you can try using the fluid on your plants (do bear in mind that some might not like it).

Do I Need to Neutralize Condensate?

If you have a gas-fired condensing appliance, you are going to need to neutralize the condensate. 

If you allow the acidic water to drain directly into the pipes or even the local wastewater system, the equipment can get seriously damaged.

In fact, a lot of plumbing codes state that any condensate from fuel-burning appliances has to be neutralized to at least a pH of 6 before being disposed to a sanitary system. Moreover, the condensate piping has to be made out of approved corrosion-resistant material.

How Do You Neutralize Condensate?

Condensate neutralizers are special filtration devices. They contain a media that interacts with the acidic condensate and raises its alkalinity.

Neutralizers are built right into the system so that the condensate cannot leave the furnace without going through the neutralizer. Once the condensate passes the media, it becomes 100% safe to be released into the wastewater system.

Fact: a neutralizer raises the pH level of the condensate to 5.0-9.5.

Some heating systems already come equipped with a condensate neutralizer. If your system doesn’t have one, then you should install a neutralizer before firing the unit up.

For maximum efficiency, the neutralizer has to be installed between the furnace and the drain (before the condensate pump).

Read: How To Clean Gas Furnace?

Why Should You Install a Condensate Neutralizer?

  1. Acidic condensate can deteriorate septic systems. When the liquid moves into the sewers, it comes in contact with human waste and kills all the good bacteria that are responsible for breaking the waste down. 
  2. Untreated condensate can literally eat through a lot of building materials. Concrete foundations, cast-iron pipes – these things can get damaged by the acidic fluid; a neutralizer will help avoid costly repairs.
  3. It is against national plumbing codes to release untreated condensate into the system. In fact, the contractors and engineers who have failed to install a treatment solution for the acidic condensate can get fined or even fired.
  4. Untreated condensate can kill vegetation and pollute the groundwater if it gets pumped into the ground. The groundwater often flows into lakes and rivers, so the consequences can be devastating.