Condensing water heaters achieve higher energy efficiency than standard boilers by condensing the water vapour in the flue gasses and using the latent energy recovered through this process to heat the return water going into the water heater.
The condensing process is achieved by passing the piped hot flue gases through the cooler return water flowing back into the boiler. Flue gas starts to condense when it drops below its dew point of 55°C. This is why condensing boilers are designed to accommodate a return water temperature of 54°C or less.
It is this resulting condensate liquid that is acidic and requires treatment to avoid damage to piping systems, sewerage systems and other items it may come in contact with.
The condensate expelled from a condensing water heater is acidic with a pH of between 2 and 4, so it is critical that the appropriate materials are used in all piping where this liquid is present.
In high temperature areas, like the flue, stainless steel must be used to prevent corrosion.
The low temperature piping, such as that which drains the condensate from the heat exchanger condensate draining system, should be PVC or ABS to also mitigate corrosion. This system normally consists of a short length of PVC or ABS pipe with a water trap to prevent exhaust gases from being expelled into the drain and building.
How to Treat Condensate
Treated condensate should be as close to 7 (neutral) as possible with 5 being the minimum. Most national and state codes prohibit anyone from allowing acidic liquid into a drainage system without treating it to raise its pH.
To increase the pH to acceptable levels, whereby it no longer has the potential to damage the sewer system or environment, a Condensate Neutraliser should be installed. Condensate Neutralisers are designed specifically for this task, and consist of a tank or module containing alkaline limestone aggregate or chips.
Automatic Heating offers several models that accommodate water flow rates from 6.05l/hr to 155l/hr depending on the size of the condensing water heater system.
The acid is converted to water, carbon dioxide and mineral salts when exposed to the media. The carbon dioxide will generally stay diluted in the water and pass out of the neutralizer. The mineral salts generally settle at the bottom of the neutralizer. Over time the media dissolves and must be replenished.
If applied properly and maintained regularly, damage associated with acidic condensate in the drain piping can be avoided.
For more information, please visit our Managing Condensate for Condensing Boilers page.