Impact of High Efficiency Gas

Furnace Condensate on Septic Systems

We are all aware that the combustion products (CO2, H2O, NOX) of

low efficiency furnaces go up the chimney to the atmosphere. These older furnaces put more pollutants in the atmosphere but do

not damage your plumbing or septic system.

Such is not the case when gas (either natural gas or propane) burns

in a high efficiency furnace as a fluid or condensate is formed.

(C3H8) OR (CH4) + O2 > H2O + CO2

PROPANE OR METHANE + OXYGEN > WATER+ CARBON DIXOIDE

The flame in the fire is hot enough to cause a reaction between the

nitrogen (from the air) and oxygen in the combustion chamber to produce nitrogen dioxide and nitrous oxide which dissolves in the

water vapor to form nitric acid.

N2 + O2 > NO2 AND NO + H2O > HNO3.H20

The amount of condensate produced by a high efficiency furnace

is approximately 4L (1Gal) per 100,000 BTU per hour.

As an example a 150,000 BTU furnace or boiler running

approximately 8 hours a day in the winter months would produce roughly 50L or 11IG of condensate.

150,000BTU/HR * 8hr = 48L (10.5IG)/day

That is over two five gallon buckets per day of this solution going into

your septic system. This condensate is corrosive and has a low pH.

A pH of 4 can damage drainage pipes, septic tanks, treatment

plants and other materials handling waste water. The pH scale is not linear. Each whole number step below 7 is 10 times more acidic than

the previous higher number.

Some tests have found the pH of the condensate to be as low as 1.8 or 2.0 which

is in part due to the odorant that is added to natural gas. Propane can contain

low concentrations of sulfur dioxide which would help increase the acidity of the

condensate.

The picture below shows what happens when the untreated

condensate is mixed with house water that has iron bacteria.

There is a solution and it is quite simple.

A neutralizer needs to be installed before the

condensate is discharged. A neutralizer consists

of a container filled with either limestone or

marble chips that dissolve as the condensate is

filtered through it, thereby raising the pH of the

condensate before it enters the septic system.

They are relatively inexpensive and are readily available at such

suppliers as Home Depot or other wholesale plumbing suppliers (Emco, Corix etc)

The neutralizer is self regulating as the limestone or marble will not

dissolve if the condensate is not acidic.

In closing, it is critical that you find out if the homeowner already has

a high efficiency furnace or plans to install one in the future so that

you can take the necessary precaution to add a neutralizer to the

design of the project.

In closing, it is critical that you find out if the homeowner already has

a high efficiency furnace or plans to install one in the future so that you can take the necessary precaution to add a neutralizer to the

design of the project.

Questions