Working on radiant snowmelt geothermal or air to water heat pump systems Be aware of bacteria!

Working on a radiant, snow-melt, or heat pump systems? Be aware of bacteria!

Bacteria are one-celled organisms that can be found everywhere, including soil, water, plants, and animals. They play an essential role in certain environments, but not so much in a hydronic heating system.
Bacteria multiply rapidly when in temperatures between 40F/4.5C and 140F/60C, making a low temperature hydronic system the perfect breeding ground for it.

Types of bacteria
Bacteria can be classified into two main groups, anaerobic and aerobic, based on their need for oxygen to survive.

Aerobic bacteria require oxygen to survive and thrive. They are commonly found in soil, water, and in the human body.

Unlike aerobic bacteria, anaerobic bacteria do not require oxygen to survive. These bacteria use other sources such as nitrates or sulfates, to carry out their metabolic processes.

Why do I need to worry about the types of bacteria in a hydronic system?
Because both of these types of bacteria can grow in an untreated low temperature hydronic system. The bacteria then forms into biofilms; a slime-like texture, causing huge heat transfer losses and therefore, reduced efficiencies and system performance.
Combine the low temperatures with oxygen in a system and you have aerobic bacteria growth. Wondering how oxygen gets into a closed loop system? Don’t worry; we’ve got you covered in another one of our blogs – “How does oxygen get into a closed-loop system”.
Some inhibitors on the market also contain nitrates, so this is something to be very wary of when dosing a system with inhibitor. Always check inhibitor ingredients!
What effects does bacteria have on low temperature hydronic systems?
As bacteria builds up, the biofilms attach to system surfaces. This layering on the system surfaces causes heat transfer issues and therefore reduced efficiencies. ALVIM1, a company that innovates high-tech solutions for biofilm monitoring actually found that, less than 1mm of biofilm in a heat exchanger can result in up to a 30% loss in heat transfer, which is a huge loss for a system considered to be highly efficient
Bacteria also causes microbial influenced corrosion, with copper, iron, nickel, aluminum, and steel being the most vulnerable to this type of corrosion. Yes, you’ve guessed it! No hydronic system is safe from bacteria.

Final Thoughts
In conclusion, both anaerobic and aerobic bacteria have unique characteristics that allow them to thrive in low temperature hydronic systems, causing heat transfer issues and corrosion, which has an overall effect on the systems’ performance and efficiencies. This biofilm forming bacteria and corrosion can also lead to blockages and reduce the life of the system and its components.


  1. ALVIM:  Biofilm & Energy efficiency (