Condensing Boilers and Sewage Treatment Issues

Condensing Boilers and Sewage Treatment Plant Problems

One point which is overlooked some times is that the condensate form a condensing boiler cannot be run into the foul drainage system if the house has a septic tank or sewage treatment plant.  It also poses serious problems if it is disposed of into soakaways.

As a result of changes to Building Regulations in 2005, the sales of condensing boilers have rocketed.

They may be energy efficient, but every new technology brings problems that become evident over time.

The problem is that the condensate is very acidic - the pH of condensate from an HE boiler is typically 2.9 to 4.  The average amount of condensate produced is substantial at over 800 litres per year.

This fact was not taken into account and many installations were carried out which could eventually result in serious damage to septic tanks, sewage treatment plants, drains and the structure of the property.

The little known fact is that condensate from gas boilers contains nitric acid and that condensate from oil boilers contains a mixture of nitric and sulphuric acids. These condensates will dissolve lime-based mortar, clay drainage pipes, concrete septic tanks and kill the beneficial bacteria in sewage treatment systems.

Under no circum­stances should boiler condensate be put straight to ground or down the side of buildings as the lime is dissolved from the mortar, resulting in continuous re-pointing of the brickwork.  In serious cases, we have seen the entire foundations of a wall undermined as the acidic condensate found its way to the house wall and ate away the foundations.  Underpinning is NOT inexpensive!

Discharging direct to ground is also not an option as there is likely to be a significant detrimental effect on local groundwaters.

These boilers may be 'GREEN' in energy terms, but their condensate certainly isn't!